SONOCATALYTIC FENTON OXIDATION PROCESS USING
NATURAL MARTITE FOR TREATMENT OF COLOR IN WATER
THESIS SUBMITTED TO
THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES
OF
MIDDLE EAST TECHNICAL UNIVERSITY
BY
MAHSA DINDARSAFA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR
THE DEGREE OF MASTER OF SCIENCE
IN
ENVIRONMENTAL ENGINEERING
FEBRUARY 2017
Approval of the thesis:
SONOCATALYTIC FENTON OXIDATION PROCESS USING NATURAL
MARTITE FOR TREATMENT OF COLOR IN WATER
Submitted by Mahsa Dindarsafa in partial fulfillment of the requirements for the
degree of Master of Science in Environmental Engineering Department, Middle
East Technical University by,
Prof. Dr. Gülbin Dural Ünver
Dean, Graduate School of Natural and Applied Sciences
Prof. Dr. Kahraman Ünlü
Head of Department, Environmental Engineering
Prof. Dr. İpek İmamoğlu
Supervisor, Environmental Engineering Dept., METU
Prof. Dr. Alireza Khataee
Co-Supervisor, Applied Chemistry Dept., University of Tabriz
Examining Committee Members:
Prof. Dr. F. Dilek Sanin
Environmental Engineering Dept., METU
Prof. Dr. İpek İmamoğlu
Environmental Engineering Dept., METU
Prof. Dr. Ayşegül Aksoy
Environmental Engineering Dept., METU
Assoc. Prof Dr. Selim Sanin
Environmental Engineering Dept., Hacettepe University
Assoc. Prof. Dr. Emre Alp
Environmental Engineering Dept., METU
Date:
iv
I hereby declare that all information in this document has been obtained and
presented in accordance with academic rules and ethical conduct. I also declare
that, as required by these rules and conduct, I have fully cited and referenced all
material and results that are not original to this work.
Name, Last name: Mahsa Dindarsafa
Signature:
v
ABSTRACT
SONOCATALYTIC FENTON OXIDATION PROCESS USING
NATURAL MARTITE FOR TREATMENT OF COLOR IN WATER
Dindarsafa, Mahsa
M.S., Department of Environmental Engineering
Supervisor: Prof. Dr. İpek İmamoğlu
Co-Supervisor: Prof. Dr. Alireza Khataee
February 2017, 88 pages
This study aims to investigate the removal efficiency of an organic dye, Acid
Blue 92 (AB92), using heterogeneous sono-Fenton-like process and compare
it with its homogeneous counterpart. High energy planetary ball milling was
applied to prepare sono-Fenton nanocatalyst from natural martite. The
unmilled and ball milled samples were characterized by XRD, FT-IR, SEM,
EDX and BET analyses. The catalytic performance of the 6h ball milled martite
was the best for removal of AB92 in heterogeneous sono-Fenton-like process.
The particle size distribution of the 6 h-milled martite was in the range of 10
nm to 90 nm, which had the highest surface area compared to the other samples.
Then, the impact of main operational parameters such as initial pH, catalyst
dosage and dye concentration on the AB92 degradation were investigated on
both the heterogeneous and homogeneous sono-Fenton-like processes
vi
comparatively. The effect of ultrasonic power and different scavengers were
just considered on heterogeneous sono-Fenton-like process. The degradation
efficiency of AB92 in heterogeneous system was much higher than that of the
homogeneous one. The treatment process followed pseudo-first order kinetic.
Environmentally-friendly modification of the unmilled martite, low leached
iron amount and repeated application at milder pH were the significant benefits
of using 6 h ball milled martite in heterogeneous sono-Fenton-like process.
Intermediates generated during removal were identified.
Keywords: Nanoparticles; Martite; Heterogeneous and homogeneous sono-
Fenton-like process; Ball milling.
vii
ÖZ
DOĞAL MARTİT KULLANARAK SONOKATALİTİK FENTON
OKSİTLEME IŞLEMİ İLE SUDA RENK GİDERİMİ
Dindarsafa, Mahsa
Yüksek Lisans, Çevre Mühendisliği Bölümü
Tez Yöneticisi: Prof. Dr. İpek İmamoğlu
Ortak Tez Yöneticisi: Prof. Dr. Alireza Khataee
Şubat 2017, 88 sayfa
Bu çalışmanın amacı, Acid Blue 92 (AB92) organik boyar maddesinin heterojen sono-
Fenton-benzeri süreçle giderimini incelemeyi ve sürecin homojen eşleniği ile
karşılaştırılmasını hedeflemektedir. Doğal martit parçacıklarına yüksek enerjili
gezegensel öğütücü uygulanarak sono-Fenton nanokatalisti hazırlanmıştır. Doğal ve
öğütülmüş martit parçacıklarının karakterizasyonu XRD, FT-IR, SEM, EDX ve BET
analizleri ile gerçekleştirilmiştir. Altı saat öğütülmüş martit, AB92 gideriminde en
yüksek katalitik performansı sergilemiştir. Altı saat öğütülmüş martitin paçacık boyut
dağılımı 10 nm ila 90 nm arasında olduğu ve diğer öğütülmüş martitlere nazaran en
yüksek yüzey alanına sahip olduğu belirlenmiştir. AB92 giderimine pH, katalizör
dozu ve başlangıç boyar madde derişiminin etkisi heterojen ve homojen süreçler için
viii
kaşılaştırmalı olarak incelenmiştir. Ultrasonik güç ve çeşitli tutucuların etkisi yalnızca
heterojen sono-Fenton-benzeri süreç için incelenmiştir. AB92'nin giderim veriminin
heterojen sistemde, homojen sistemde olduğundan çok daha yüksek olduğu tespit
edilmiştir. Arıtma sürecinin sözde-birinci derece kinetiği takip ettiği belirlenmiştir.
Doğal martitin çevreyle nano parçacığa dönüştürülmesi, makul pH seviyelerinde
yeniden kullanılabilirliği ve suya düşük oranda demir salması, altı saat öğütülmüş
martit nanokatalizörünün heterojen sono-Fenton-benzeri süreçte kullanımında önemli
avantajlar oluşturmaktadır. Heterojen süreçte oluşan çeşitli bozunma ürünleri
tanımlanmıştır.
Anahtar Kelimeler: Nanoparçacık; Martit; Heterojen ve homojen sono-Fenton-
benzeri süreç; gezegensel öğütücü.
ix
AKNOWLEDGMENTS
Experimental work presented in this thesis was carried out partly in Department of
Applied Chemistry, University of Tabriz, Iran (under Prof. Dr. Alireza Khataee’s co-
supervision) and partly in the Department of Environmental Engineering, METU,
Turkey. The supervisor at METU was Assist. Prof. Dr. Barış Kaymak until the time
he left METU in October, 2016. Following that, Prof. Dr. İpek İmamoğlu became the
supervisor and oversaw the finalization of experimental work and write-up of thesis,
with continuing help from Assist. Prof. Dr. Barış Kaymak.
I would like to express my deepest gratitude to Prof. Dr. İpek İmamoğlu for the
motivation, support and encouragement she provided me throughout the study. She
has always been optimistic about my progress and made me believe that I can proceed
further.
I also would also like to thank Assist. Prof. Dr. Barış Kaymak for his help and
contributions throughout the study.
I would like to express my appreciation to my co-supervisor Prof. Dr. Alireza Khataee
for his support, trips and advice he has organized that gave me a clear view of the study
area.
I would like to thank to my thesis committee members Prof. Dr. Kahraman Ünlü, Prof.
Dr. Ayşegül Aksoy, Assoc. Prof. Dr. Selim Sanin and Assoc. Prof. Dr. Emre Alp for
their contribution.
I am, and always will be, grateful to my parents Prof. Dr. Kazem Dindarsafa and
Mahnaz Mirfakhraei and my sister Roya Dindarsafa, for their continuous and
unconditional love, encouragement, and support at all stages of my life.
Last but not least, to my beloved husband, Amir Rahmani, who always with me and
makes me feel happy and confident, especially at the hectic times, and believing in me
at all times; thank you for your endless love and support.
x
TABLE OF CONTENTS
ABSTRACT ................................................................................................................. v
ÖZ ............................................................................................................................... vii
AKNOWLEDGMENTS ............................................................................................. ix
LIST OF TABLES .................................................................................................... xiii
LIST OF FIGURES ................................................................................................... xiv
LIST OF ABBREVIATIONS ................................................................................. xviii
CHAPTERS
1. INTRODUCTION .................................................................................................... 1
2. LITERATURE REVIEW ......................................................................................... 5
2.1 Water pollution .......................................................................................... 5
2.1.1 Organic dyes and their removal .......................................................... 5
2.1.2 Classes of organic dyes....................................................................... 6
2.1.3 The characteristics of organic dye used in the present study ............. 7
2.2 Sonochemistry ............................................................................................ 8
2.2.1 General information ............................................................................ 8
2.2.2 Sono-catalytic process ........................................................................... 11
2.3 Iron minerals ............................................................................................ 12
2.3.1 General information .............................................................................. 12
2.3.2 Iron oxide nanoparticles ........................................................................ 13
2.4 Fenton process as an AOP ............................................................................ 14
2.4.1 Advanced Oxidation Processes (AOPs) ................................................ 14
2.4.2 Fenton versus Fenton-like reaction ....................................................... 16
2.4.3 Heterogeneous and homogeneous sono-Fenton-like processes ............ 17
2.4.4 Sono-catalytic homogeneous and heterogeneous reaction ............... 18
2.5 Kinetic reaction ........................................................................................ 19
xi
3. MATERIAL AND METHODS ............................................................................. 21
3.1 Experimental Solutions ............................................................................ 21
3.2 Preparation of catalyst ............................................................................. 23
3.3 Characterization of martite catalyst ......................................................... 26
3.3.1 SEM analysis .................................................................................... 27
3.3.2 EDX analysis .................................................................................... 27
3.3.3 Particle size distribution ................................................................... 27
3.3.4 BET analysis ..................................................................................... 27
3.3.5 XRD analysis .................................................................................... 28
3.3.6 FT-IR analysis .................................................................................. 29
3.4 Experimental set-up ................................................................................. 29
3.4.1 Measurement of dye concentration .................................................. 34
3.4.2 Measurement of soluble Iron Concentration .................................... 36
3.4.3 Identification of intermediates during degradation of AB92 ........... 37
4. RESULTS AND DISCUSSION ............................................................................ 39
4.1 Characterization of the unmilled and milled martite ............................... 39
4.1.1 SEM analysis .................................................................................... 39
4.1.2 EDX analysis .................................................................................... 40
4.1.3 Particle size distribution ................................................................... 41
4.1.4 BET analysis ..................................................................................... 43
4.1.5 X-ray Diffractıon (XRD) .................................................................. 44
4.1.6 FT-IR analysis .................................................................................. 45
4.2 Removal of AB92 with sono-Fenton-like process ................................... 47
4.2.1 Comparing of unmilled and ballmilled martite samples .................. 47
4.2.2 The effect of catalyst concentration ................................................. 50
4.2.3 The influence of initial pH ............................................................... 54
4.2.4 The effect of initial dye concentration.............................................. 59
4.2.5 Reaction time .................................................................................... 63
4.2.6 The effect of ultrasonic power .......................................................... 65
4.2.7 Evaluation of reusability and stability of the martite ....................... 67
4.2.8 The effect of organic and inorganic salts ......................................... 68
4.2.9 Intermediates generated in heterogeneous sono-Fenton-like system .... 72
xii
5. CONCLUSION ...................................................................................................... 75
5.1 Conclusions .............................................................................................. 75
5.2 Recommendations for Future Studies ...................................................... 76
REFERENCES ........................................................................................................... 79
xiii
LIST OF TABLES
TABLES
Table 2.1 Characteristics of the dye stuff used in this study. ....................................... 7
Table 2.2 Oxidation potential of some oxidants in the water (Pignatello et al., 2006).
.................................................................................................................................... 15
Table 3.1 Summary of experimental conditions in heterogeneous and homogeneous
sono-Fenton-like systems ........................................................................................... 32
Table 4.1 Surface area and pore volume characteristics of unmilled (primary), 2 h, 4 h
and 6 h ball milled martite samples. .......................................................................... 44
Table 4.2 Plot of apparent pseudo-first and second order reaction rates of different
catalysts for degradation of AB92.............................................................................. 50
Table 4.3 Apparent pseudo-first order reaction rate of catalyst dosage for removal of
AB92. ......................................................................................................................... 54
Table 4.4 Impact of the different pH values on the apparent pseudo-first and second
order reaction rates for AB92 degradation. ................................................................ 59
Table 4.5 Apparent pseudo-first order reaction rates of various dye concentration for
degradation of AB92. ................................................................................................. 63
Table 4.6 Operational conditions that resulted in the best AB92 removal efficiency.
.................................................................................................................................... 64
Table 4.7 Impact of the ultrasonic power on the apparent pseudo-first order reaction
rates for removal of AB92.......................................................................................... 66
Table 4.8 Impact of the scavengers on the apparent pseudo-first order reaction
constants toward removal of AB92. ........................................................................... 71
Table 4.9 Identified intermediates during removal of the AB92 in sono-Fenton-like
system. ........................................................................................................................ 73
xiv
LIST OF FIGURES
FIGURES
Figure 2.1 Growth and explosion of bubbles in aqueous solution with ultrasonic
process. ....................................................................................................................... 10
Figure 2.2 Classification of Fenton processes (Nidheesh, 2015). .............................. 16
Figure 3.1 martite before crushing. ............................................................................ 23
Figure 3.2 jaw crusher (IndiaMART, 1996). ............................................................. 24
Figure 3.3 Schematic shape of the Cone crusher (Lipu, 2016). ................................. 25
Figure 3.4 (a) planetary ball mill with four containers; (b) stainless steel container with
balls (Retsch, 2017). ................................................................................................... 26
Figure 3.5 SIEMENS D5000 X-Ray diffractometer. ................................................. 28
Figure 3.6 (a) The FT-IR apparatus (Brucker TENSOR 27) connected to the computer;
(b) The Hydraulic press 15-25 ton load. .................................................................... 29
Figure 3.7 Set-up of (a) heterogeneous and (b) homogeneous sono-Fenton-like
reactors. ...................................................................................................................... 31
Figure 3.8 Absorption spectrum of AB92 (10 mg/L). ................................................ 34
Figure 3.9 Calibration of AB92 at various dye concentration in (a) heterogeneous and
(b) homogeneous sono-Fenton-like system. ............................................................... 35
Figure 3.10 Atomic absorption spectrometer. ............................................................ 36
Figure 4.1 SEM micrographs of (a) martite sample before ball milling, (b) 2 h ball
milled martite nanoparticles, (c) 4 h ball milled martite nanoparticles and (d) 6 h ball
milled martite nanoparticles. ...................................................................................... 40
Figure 4.2 6 h ball milled martite EDX spectrum. ..................................................... 41
Figure 4.3 Size distribution of (a) before ball milling martite, (b) after ball milling
martite samples. .......................................................................................................... 42
Figure 4.4 N2 adsorption-desorption isotherm of (a) unmilled martite, (b) martite
nanoparticles after 2 h, (c) 4 h and (d) 6 h mechanical milling samples obtained from
the BET test. ............................................................................................................... 43
xv
Figure 4.5 XRD spectra of (a) unmilled martite, (b) martite nanoparticles after 2 h ball
milling, (c) 4 h ball milling and (d) 6 h ball milling. ................................................. 45
Figure 4.6 FT-IR spectra of (a) unmilled martite, (b) ballmilled martite after 2 h, (c) 4
h and (d) 6 h milling time. .......................................................................................... 46
Figure 4.7 Comparing the removal efficiency of AB92 under the effect of different
processes (a) catalyst only (b) sonolysis alone, (c) unmilled (d) 2 h, (e) 4 h, (f) 6 h ball
milled martite catalysts in sonocatalysis process. Experimental conditions: [AB92]0 =
10 mg/L, catalyst dosage = 2.5 g/L, ultrasonic power = 150 W, and pH = 7. ........... 47
Figure 4.8 Plot of apparent pseudo- first order reaction rate constants. .................... 49
Figure 4.9 Impact of the catalyst dosage on the sonocatalytic degradation of AB92 in
(a) heterogeneous (6 h ball milled martite) and (b) homogeneous (FeCl3) sono-Fenton-
like processes. Initial dye concentration = 10 mg/L, 6 h milled martite, ultrasonic
power = 150 W, and pH = 7 for the heterogeneous system. Initial dye concentration =
10 mg/L, ultrasonic power = 150 W, and pH = 3 for the homogeneous system. ...... 51
Figure 4.10 Plot of apparent pseudo-first order reaction rate constants for degradation
of AB92 in (a) heterogeneous and (b) homogeneous sono-Fenton-like processes. ... 53
Figure 4.11 The effect of suspension pH on the degradation efficiency of AB92 by (a)
2.5 g/L 6 hr ball milled martite (b) 20 mg/L FeCl3, [AB92]0 = 10 mg/L, ultrasonic
power = 150 W. .......................................................................................................... 56
Figure 4.12 Dissolved iron concentration in solution phase after 60 min; [Martite] =
2.5 g/L. ....................................................................................................................... 57
Figure 4.13 Plot of apparent pseudo-first order reaction kinetic for AB92 degradation
at different pHs for (a) heterogeneous and (b) homogeneous Fenton process. .......... 58
Figure 4.14 The impact of initial dye concentration on AB92 degradation in (a)
heterogeneous and (b) homogeneous sono-Fenton-like system and removal of AB92
in the (c) heterogeneous and (d) homogeneous sono-Fenton-like systems................ 61
Figure 4.15 Plot of pseudo-first order reaction rate constants for AB92 degradation for
various initial dye concentration (a) heterogeneous and (b) homogeneous sono-Fenton-
like processes. ............................................................................................................ 62
Figure 4.16 The efficiency of AB92 removal at optimum conditions in both
homogeneous and heterogeneous sono-Fenton-like systems. .................................... 64
xvi
Figure 4.17 Impact of ultrasonic power on the degradation of AB92. [AB92]0 = 10
mg/L, and dose of catalyst = 2.5 g/L, and pH = 7. ..................................................... 66
Figure 4.18 The plot of pseudo-first order kinetic reaction rate constants for ultrasonic
powers at heterogeneous sono-Fenton-like system. ................................................... 67
Figure 4.19 AB92 removal efficiency with martite nanoparticles used in five
consecutive experimental runs. Catalyst dosage = 2.5g/L, [AB92]0 = 10 mg/L,
ultrasonic power = 150 W, and pH = 7. ..................................................................... 68
Figure 4.20 Impact of scavengers on removal of AB92 in sono-catalytic process.
Operational conditions: [AB92]0 = 10 mg/L, [Martite] = 2.5 g/L, ultrasonic power =
150 W, pH = 7 and [Scavenger]0 = 10 mg/L. ............................................................ 70
Figure 4.21 Plot of pseudo-first order kinetic reaction rate constants for different
scavengers in heterogeneous sono-Fenton-like process. ............................................ 71
xvii
LIST OF ABBREVIATIONS
AAS: Atomic Absorption Spectroscopy
AB92: Acid Blue 92
AOP: Advanced Oxidation Process
BET: Brunauer, Emmett and Teller
BJH: Barrett-Joyner-Halenda
BOD: Biochemical Oxygen Demand
COD: Chemical Oxygen Demand
EDX: Energy-Dispersive X-ray
FT-IR: Fourier Transform Infrared
GC-MS: Gas Chromatography-Mass Spectrometry
IUPAC: International Union of Pure and Applied Chemistry
JCPDS: Joint Committee on Powder Diffraction Standards
METU: Middle East Technical University
SEM: Scanning Electron Microscopy
TOC: Total Organic Carbon
XRD: X-Ray Diffraction
1
1. CHAPTER 1
INTRODUCTION
Synthetic dyes are manufactured in large amounts and applied in textile, food,
cosmetic, paper and leather industries. Azo dyes such as AB92 are greatly applied dyes
that is used in the textile industry, where up to 10-15% of generated dyes all over the
world gets discharged into the environment during their production or dying process
(Khataee and Zarei, 2011; Orge et al., 2012; Petre et al., 2013; Sheydaei et al., 2013).
Most of these dyes are generally resistant to biodegradation and are persistent in the
environment, possessing a negative influence on ecosystems as well as human health
(Khataee and Zarei, 2011). Hence, utilization of the treatment methods like advanced
oxidation processes (AOPs) is essential from an environmental point of view. AOPs
remove these dyes by mineralizing them without producing secondary wastes (Orge et
al., 2012). Among AOPs, ultrasonic and Fenton processes are favorable and effective
methods for treatment that are extensively utilized for the removal of different
contaminants in wastewaters (Poyatos et al., 2009). Hydroxyl radicals (•OH) has the
highest oxidation potential and it unselectively attacks organic pollutants and
eventually mineralizes them without producing secondary wastes (Petre et al., 2013).
Hydroxyl radicals can be produced through the heterogeneous Fenton-like process in
which Fe3+ ions act as catalyst and react with hydrogen peroxide for formation of
hydroxyl radical (Eqs. (1-1) and (1-2)). Hydroxyl radicals also would be formed as a
result of water dissociation under the effect of ultrasonic waves (Eq. (1-3)) through
cavitation approach (Khataee et al., 2015b). It is proven that the hydrogen peroxide
can be generated in the solution under ultrasonic irradiation (Eq. (1-4)) (Juan A.
Melero, 2011).
2
Fe3+ + H2O2 → Fe2+ + •OOH + H+ (1-1)
Fe2+ + H2O2 → Fe3+ + •OH + OH- (1-2)
)))
2H O OH H (1-3)
•OH +
•OH → H2O2 (1-4)
Ultrasonic radiations into a aqueous medium makes the cavitation phenomenon results
into the growth, production and eventually implode of microbubbles creating high
concentrated temperatures and pressures described by hot spot method (Weng et al.,
2013). Nevertheless, ultrasonic process requires high time and energy because of its
low removal rate. Therefore, combination of ultrasonic process with different
processes like Fenton process is important for enhancing its efficiency (Khataee et al.,
2015a).
The main challenge of homogeneous Fenton process are the catalyst segregation from
the treated water and requirement of acidic condition (pH 3) to hinder precipitation of
iron hydroxide producing considerable amounts of sludge. Thus, application of
heterogeneous Fenton process, which is applicable at milder pHs and has low iron
release to the solution, becomes a practical way to reduce the mentioned drawbacks
(Sheydaei et al., 2014).
Hematite (Araujo et al., 2011), magnetite (Liang et al., 2012), goethite (Lin et al.,
2015) and pyrite (Wang et al., 2012) as heterogeneous catalysts has been applied in
Fenton process. In fact more hydroxyl radicals would be generated as a result of Fe
ions on the surface of catalyst. Martite (Fe2O3) is a mineral, which yielded as a result
of magnetite (Fe3O4) oxidation under the earth depth and hematite generation (Fe2O3)
exhibiting the physical characteristics of the hematite (Mücke and Raphael Cabral,
2005). Therefore, usage of martite in the heterogeneous Fenton process is important.
Mass transfer limitation and limited active sites are two main problems of this process
when comparing with the homogeneous Fenton process. The efficient ways to solve
these problems are application of catalysts in nano scale and ultrasonic irradiation
3
(Sheydaei and Khataee, 2015). However, production of nano-sized compounds
through chemical synthesis methods require use of toxic reactants and high cost (Jung
et al., 2008).
One of the most efficient and cost effective ways for production of nanoparticles is
applying mechanical ball milling process (Khataee et al., 2016a; Tu, 1996; Weiwei et
al., 2008). Moreover, nanoparticles are able to be formed at ambient temperature in
large quantities in a short processing time. Hence, this method is can be very
appropriate for large scale industrial productions from an economical viewpoint (Aber
et al., 2009; Morris et al., 1981). There are a number of studies that have used diverse
nanomaterials such as LiF (Donohue and Aranovich, 1998), ZnS (Reddy et al., 2009),
Cu2O (Taseidifar et al., 2015) and FePt (Babuponnusami and Muthukumar, 2014) that
were formed using the high energy mechanical ball milling process. Meanwhile, there
is no report on production of martite nanoparticles by mechanical ball milling.
Removal of AB92 as an organic dye and production of martite nanoparticles by
employing mechanical ball milling process in sono-Fenton-like process are the most
important purpose of this research. The main goals are:
Generation of martite nanoparticles by applying planetary ball milling process
and fully characterize them.
Evaluation of martite as a catalyst in heterogeneous sono-Fenton-like system.
Comparing the martite nanoparticles performance as a catalyst with the
homogeneous system.
To determine the impact of milling process time, medium pH, ultrasonic
power, initial dye dosage, and presence of organic and inorganic salts the AB92
removal efficiency.
To calculate reaction rates of heterogeneous and homogeneous sono-Fenton-
like processes for removal of AB92.
In Chapter 2 the characteristics organic dyes and their effects on pollution of
environment is described. Also, the beneficial effect of ultrasound as AOP on removal
4
of these kinds of pollutant is demonstrated. In addition, martite as catalyst that is used
for acceleration of removal efficiency are presented.
In Chapter 3, the materials and methods used in the research is described. A general
explanation of martite used as catalyst is given in this chapter. Some information about
the instrument and methods for preparing martite nanoparticles and characterization
of martite are presented as well. Lastly, used reactor, method of measuring the
concentration of dye and iron concentration, and identification of by-products are
mentioned.
In Chapter 4, characterization of unmilled martite and martite nanoparticles using
Scanning Electron Microscopy (SEM), size distribution, X-ray Diffraction (XRD),
Fourier Transform Infrared spectroscopy (FT-IR), Energy Dispersive X-ray
spectroscopy (EDX), and Brunauer, Emmett and Teller (BET) analyses are discussed.
Influence of experimental parameters including impact of catalyst concentration,
effect of pH, impact of ultrasonic power, influence of initial dye concentration, effect
of organic and inorganic salts, and assessing the stability and reusability of catalyst on
the removal efficiency of AB92 are investigated as experimental parameters in
heterogeneous and homogeneous sono-Fenton-like processes. Furthermore,
byproducts result from degradation of AB92 are discussed.
In a final manner in Chapter 5, summary of findings as a conclusion is presented
together with some suggestions for future study.
5
2. CHAPTER 2
LITERATURE REVIEW
2.1 Water pollution
Environment plays a important role in people life and neglecting the significance of it
causes undesirable effects on inhabitants of the earth especially for future generations.
Hence, they would have to live in an environment that previous generations have
destructed with their negligence. Human beings play an important role on
environment. This is an inevitable reality. Whether they are playing an important role
or not, there are many approaches which each person can perform their role to preserve
the environment. When people protect the environment, they are protecting themselves
and their future as well.
Water is a vital element with its notable and unique features. It is the most abundant
and act as a solvent in nature, it also facilitates physico-chemical reactions of
metabolism in the living organisms body. Furthermore, it provides a good environment
for transferring materials in the living organisms’ body.
The availability of safe and clean water is one of the most significant issues facing
humanity. Pollutants can be introduced into the water resources in various ways. Water
is extensively needed by industry and discharged after use. Constituents used in
industry hence find its way into the natural environment.
2.1.1 Organic dyes and their removal
Due to mass production and widespread use, organic dyes constitute an important part
of industrial effluents. Organic dyes are employed in different industries such as
6
leather, pulp and paper, textiles, cosmetics and agriculture. In compare with high
percent of various kinds of dyes that are produced yearly, only low present of them
released into the aquatic system (Xu et al., 2013a). Wastewater originating from the
dying process in textile industries generally include remaining color pigments and
intermediates such as aromatic amines and inorganic sodium salts. Several wastes with
various combinations are produced at different stages of production process. Color
contaminants are toxic because of presence of different aromatic structures which are
resistant to biodegradation. They can also reduce the amount of oxygen dissolved in
the solution and correspondingly cause increase in anaerobic bacteria activity in the
water (Han et al., 2009; Matilainen and Sillanpää, 2010).
On the other hand, dye removal from wastewater is more important compared to non-
colored organic materials because dyes can be visible through the naked eye even at
low concentrations (below 1 ppm) (Daneshvar et al., 2004). Therefore, applying a
reliable method for removal of dye pollutants prior to discharge into the environment
is essential. Different chemical, physical and biological approaches are applied to
eliminate organic dyes from the wastewater to meet environmental regulations.
Different physico-chemical methods such as electrocoagulation and removal by
adsorption on activated carbon are recently used especially in Iran. The main problem
with these methods is transferring pollution from one phase to another. Hence, a new
type of contaminant would be generated needing to be refined. In recent decades,
increase in industrial activities and the need to protect the environment have induced
scientists to find new water and wastewater treatment methods (Forgacs et al., 2004;
Martínez-Huitle and Brillas, 2009).
2.1.2 Classes of organic dyes
Synthetic dyes are greatly applied in many industries such as leather, textile, food,
paper and cosmetic industries. There are different classifications for synthetic dyes.
They are often classified based on their structure such as azo dyes, anthraquinone,
derivatives of sulfur, indigo, zantn, phenyl methyl (Trytyl) and phthalocyanine
7
(Martínez-Huitle and Brillas, 2009). However, most of dyes used in the industrial
applications are azo derivatives. The majority of the textile effluents contain
significant amount of organic dyes.
2.1.3 The characteristics of organic dye used in the present study
AB92 is an azo dye. Azo dyes are the most significant group of synthetic dyes which
are resistant against biodegradation (Stolz, 2001). Removal of these pollutants are
important because many products like aromatic amines that are produced during
degradation process have been reported to be carcinogenic (Shaul et al., 1991).
Table 2-1 illustrates structural formula and properties of organic dye used in the
present study.
Table 2.1 Characteristics of the dye stuff used in this study.
Molecular
configuration
Chemical
formula
Color index
number
λmax
(nm)
MW
(g/mol)
N
N
OH
NaO3S
SO3Na
N
HNaO3S
C26H16N3Na3O10S2
13390
570
695.58
AB92 can be applied in dyeing wool, silk, leather and paper (World dye variety, 2012).
It is water-soluble and somewhat soluble in ethanol and is not soluble in other organic
solvents. AB92 is a sulfonate salt. In fact the degradation rate of the AB92 are effected
by sulfonate and groups of substances that are on the selected dye. In other word,
sulfonate salt typically decrease the degradation of Acid dyes (Tehrani-Bagha and
Holmberg, 2013).
8
2.2 Sonochemistry
2.2.1 General information
Sonochemistry is a branch of chemistry that studies the effects of ultrasonic waves on
chemical reactions (Balcioglu and Arslan, 1999). In other words, sonochemistry is
attributed to the impact of ultrasound in generation of acoustic cavitation in aqueous
solutions leading to the enhancement or initiation of the chemical activity within the
solution. In a liquid solution, longitudinal sound waves make water molecules vibrated
to back and forth. This movement is look like a spring stretched and then released.
Under the influence of this vibration, periodic phases of compression and rarefaction
(expansion) would be created without the movement of water molecular layers. As a
result, at the point where molecular layers of water are compressed the pressure would
be higher than normal pressure.
On the other hand, compression of the liquid is followed through rarefaction in which
a sudden pressure drop generates oscillating and small bubbles. In the expanded points
the water molecules get away from each other and at that points the microbubbles
would be produced (Wang et al., 2008). Cavitation is the generation, growth and
collapse of bubbles in an aqueous medium. The residence time of these high energy
points are in the scale of ns (nanosecond) where the pressure and temperature reaches
about 1800 atm and 5000 K, respectively. Under these conditions called hot spots
many chemical reactions could occur. High temperature around the bubbles brings
about the water molecule dissociation and form hydroxyl radicals, and as a result,
oxidation of organic dye adsorbed at the bubble interface would occur (Neppolian et
al., 2012). The radius of the bubble is estimated to be micrometer in size before
collapsed. The time required for the bubble collapse is less than 100 ns (Berberidou et
al., 2007). These hot spots lead to pyrolysis of water molecule into the OH and H
radicals according to the reaction (Eq. (2-1)) (Nam et al., 2003).
H2O + Ultrasonic irradiation → OH● + H● (2-1)
In addition, number of continuous chain reactions can take place as stated in Eqs. (2-2)
to (2-7) (Kubo et al., 2005; Nam et al., 2003; Wang et al., 2005).
9
OH● + H● → H2O (2-2)
OH● + OH● → H2O2 (2-3)
H2O2 + H● → H2O + OH● (2-4)
2OH● → H2O + O● (2-5)
H● + O2 → HO2● (2-6)
HO2● + HO2
● → H2O2 + O2 (2-7)
According to Eqs. (2-3) and (2-7), hydrogen peroxide would be produced as a result
of reaction between hydroxyl radicals on the surface of bubble or in aqueous solution
result in production. Also, hydroxyl radicals are reproduced during the reaction of
hydrogen radicals with hydrogen peroxide. Studies show that oxidation potential of
ultrasonic waves increase when the heterogeneous catalysts was used in ultrasonic
system. In the presence of heterogeneous catalysts, the created hydrogen peroxide
reacts with ferric ions on the catalyst surface and produces new oxidizing species
improving removal of organic dyes (Salavati et al., 2012; Tuziuti et al., 2005).
The main mechanism of microbubble generation is not totally understood, but there
are recently some theories. Among them, cavitation theory is the most popular. When
the liquid phase is exposed with waves of ultrasonic, microbubbles referring to as
cavities are formed through the hydraulic vibration. Cavities are successively
contracted and expanded through the ultrasonic energy, and finally exploded. Fine
droplets are ejected from the liquid surface by the shock waves produced through
cavity collapse (Figure 2.1).
10
Figure 2.1 Growth and explosion of bubbles in aqueous solution with
ultrasonic process.
Ultrasonic waves are waves with frequencies higher than 20 kHz which cannot be
heard by human. Even though there is a wide range of ultrasound frequencies, these
waves are arranged into three major groups. The first group is sonochemistry
ultrasound waves. It is used in chemical processes which has frequencies in the
range of 20-100 KHz. The second group is power ultrasound wave. This group is
employed in various industries such as food processing. The ultrasonic frequency of
this group is in the range of 100 KHz to 2 MHz. The third group is used for medical
diagnostic tests where the frequency range is between 5 to 10 MHz (O'Sullivan et al.,
2014).
Ultrasonic bath is an accessible and relatively cheap laboratory equipment for
generating ultrasonic waves. The bath often is in the form of a stainless steel tank and
ultrasonic transducer are located in the floor of the bath. In the large bathes array of
transducers may be used. Frequency and sound intensity in the bath, depends on the
number and type of these transducers.
Sonochemistry has some advantages given as follows (Yang et al., 2003):
Increase in the reaction rate
Use at lower pressure condition
Economic
11
Improvement in catalyst efficiency
In recent years ultrasound has been applied in AOPs because of its high performance
and ease of use in water treatment and purification systems. The usage of ultrasound
waves are one of the effective method to remove organic contaminants. Energy saving,
safety and lack of secondary pollutant are of the advantages of ultrasound when
compared to other AOPs (Chowdhury and Viraraghavan, 2009).
2.2.2 Sono-catalytic process
In recent years, use of ultrasound for the treatment of wastewater has attracted more
attention because of its effectiveness and ease of use. Ultrasonic irradiations have been
applied for removal of various organic dyestuffs in water (Adewuyi, 2001). In this
process, microbubbles produced as a result of ultrasonic waves, are contained vapors
from the solvent (Pang and Abdullah, 2012).
Recently, applying ultrasound for degradation of dye has been popular (Vajnhandl and
Majcen Le Marechal, 2005). The breaking down of bubbles results in high pressure
and temperature during ultrasonic irradiation allowing the generation of oxidizing
species including hydroperoxyl radicals (HO2●), hydroxyl radicals (●OH), hydrogen
peroxide (H2O2) and hydrogen radicals (H●) (Melero et al., 2008).
Accordingly, depending upon the nature of the organic contaminants, they can be
removed at the interface between bubble and solution, or in the solution (Drijvers et
al., 1999). Discoloration of azo dyes as hydrophilic compounds would occur during
the oxidation process in the bulk liquid. Even though according to the number of
studies removal of different kinds of dyes was done with ultrasonic irradiation alone,
the total degradation of the azo dye compounds is hard to achieved (Vajnhandl and
Majcen Le Marechal, 2005).
Moreover, in terms of economic analysis, the cost of incineration is comparable to
sonochemical oxidation. Hence, the useful method for total mineralization of textile
dyes is combining AOPs with ultrasound (Muruganandham et al., 2007). The favorable
12
results have been obtained as a result of applying ultrasonic irradiation with Fenton’s
reagent for the dissociation of endocrine disruptors (Ben Abderrazik et al., 2005; Ioan
et al., 2007), anionic surfactants (Manousaki et al., 2004), chlorinated aromatic
hydrocarbons (Liang et al., 2007b), 2,4-dinitrophenol (Guo et al., 2005) and dyes (Sun
et al., 2007; Zhang et al., 2007).
Some studies were even conducted without addition of H2O2. Torres et al. (2007)
reported that when Fe2+ added into the solution, the reduction of bisphenol A increased
from 45-80% under effect of ultrasonic. Ai et al. (2007) performed several studies over
Fe2O3 which removed 40% of the pentachlorophenol and all Rhodamine B within 60
min of reaction time under ultrasonic. In those studies, hydrogen peroxide was
produced in situ through sono-chemical reactions of oxygen and water molecules.
Therefore, sono Fenton reaction is considered as a potential method in terms of
decrease in cost resulting from the consumption of hydrogen peroxide.
2.3 Iron minerals
2.3.1 General information
Iron is blocked in ferromagnesian silicate in rocks at the surface of earth highly as
black or green ferrous-ferric iron. In terms of mass, iron is the fourth most plentiful
element in the earth’s crust. The red ferric oxide is hematite, the black ferrous-ferric
form is magnetite and the yellow-brass ferrous sulfides are generally cubic pyrite. Iron
also appears as green iron silicate, white to dark brown ferrous carbonate (siderite) and
glauconite (Ghows and Entezari, 2013). To improve or increase the rate of reaction in
chemical processes, iron catalysts are utilized. Iron (hydro) oxides can be found
everywhere possessing high degradation ability towards organic pollutants. Owing to
their natural abundance, enhanced stability, low cost, easy separation and
environment-friendly properties. The capacity of natural iron oxides or hydroxides for
degrading contaminants depends upon the structure, property and composition of the
minerals. Different iron minerals are applied as heterogeneous Fenton catalysts to
mineralize diverse recalcitrant organic contaminants. The use of iron minerals as a
13
catalyst has some benefits: (i) no change in pH of solution; (ii) reusability and long
lifetime of catalyst; (iii) catalyst separation is straightforward compared to
homogeneous catalyst after treatment process (Nidheesh, 2015). Unlike other iron
hydroxides, martite exceptionally contains both Fe2+ and Fe3+ within its structure (He
et al., 2015). This property would have positive effect on the AB92 removal.
Martite. Martite (psuedomorph of hematite after magnetite) is a natural ore with
chemical formula Fe2O3. It was supplied from Sangan mine (Mashhad, Iran).
Martite forms during the oxidation of magnetite in the high temperature and pressure.
Martite ores are high-grade iron ones. Martite is mineral form of iron(III) oxide
(Fe2O3). It belongs to family of hematite and exhibit the same physical characteristics.
It is formed during the oxidation of magnetite at the earth depth in that oxidation
potential of hydrothermal solutions surrounding the previously formed magnetite is
high (Swanson-Hysell et al., 2011). Martite has attracted more attention as a
heterogeneous catalyst owing to the fact that martite is a cheap abundant mineral. Also,
it can be employed as a feed material for pig iron production in a blast furnace after
losing its reactivity (Cao et al., 2015).
2.3.2 Iron oxide nanoparticles
Iron oxides can be found in different forms in the nature. Martite (Fe2O3) is one of the
common form. Recently, the application and synthesis of iron oxide nanomaterials
with new functions and properties have been greatly studied owing to their high
surface area (Hu et al., 2010).
Selection of appropriate material and method for treatment of wastewater is an intricate
work. It requires a number of factors that should be considered such as the cost,
efficiency and quality standards. Iron oxide nanomaterials are favorable for the
treatment of wastewaters in industrial scale owing to ease of separation, enhanced
stability and low cost (Fan et al., 2012).
14
Recent usages of iron oxide nanoparticles in polluted water treatment can be divided
into two approaches: (1) those which employ iron oxide nanoparticles as
photocatalysts to convert or dissociate pollutants into less toxic compounds; (2) usage
of iron oxide nanoparticles in the form of immobilization carrier or nanosorbent for
enhanced degradation efficiency. However, it should keep in mind that a lot of
technologies may apply both processes (Xu et al., 2012).
2.4 Fenton process as an AOP
2.4.1 Advanced Oxidation Processes (AOPs)
Chemical, biological and physical methods are used for organic dyes degradation from
wastewater to meet environmental regulations. In recent decades, a lot of researchers
have focused on dominant role of a class of oxidation method known as AOPs. They
generally operate at or near ambient pressure and temperature. AOP is based upon the
production of non-selective and very active species including hydroxyl radical (•OH),
hydrogen peroxide (H2O2) and superoxide anion radical (O2•-) which are strong
oxidants. In Table 2-2 oxidation potential of the different oxidants are listed. Owing
to the high oxidizing power of hydroxyl radical (2.8 eV), It is becoming more popular
(Brillas et al., 1998; Sun and Pignatello, 1993). Only oxidation potential of fluorine
gas is higher than the oxidation potential of hydroxyl radicals. The reaction rate
constant of the majority of organic compounds with hydroxyl radical is about 106-109
M-1 s-1 (Kajitvichyanukul et al., 2006; Malato et al., 2002).
15
Table 2.2 Oxidation potential of some oxidants in the water (Pignatello et al., 2006).
Oxidizing species Oxidation potential (eV) Fluorine gas (F2) 3.06
Hydroxyl radical (•OH) 2.80
Atomic oxygen (O) 2.42
ozone (O3) 2.07
Hydrogen Peroxide (H2O2) 1.77
Hydroperoxide radical (HO•2) 1.70
Permanganate 1.67
Chlorine Dioxide 1.50
Chlorine gas 1.36
Oxygen 1.23
AOPs use different systems including Fenton, photo-Fenton, O3/ H2O2/UV, H2O2/UV,
O3, O3/UV and O3/H2O2. Indeed, O3 and H2O2 act as precursor of oxidation reactions.
Ultraviolet (UV) radiation or ultrasound (US) are also applied in these processes
(Brillas et al., 2000). In fact, AOPs like other ones have their own benefits and
drawbacks.
The main benefits of AOPs are listed as follows (Nidheesh, 2015):
The high rate of degradation and oxidation of pollutants
Flexibility in different water conditions
Less amount of equipment is required
Disadvantages of AOPs are:
High cost
The danger of using highly reactive chemicals such as O3, H2O2
Generation of hazardous byproducts when reaction is not completed
Among different kinds of AOPs, Fenton process has attracted attention. Fenton process
uses ferrous/ferric ions and hydrogen peroxide for the generation of hydroxyl radicals
16
as the second strongest oxidant in aqueous solution. Generally, classification of Fenton
processes can be shown in Figure 2.2.
Figure 2.2 Classification of Fenton processes (Nidheesh, 2015).
2.4.2 Fenton versus Fenton-like reaction
The difference between Fenton and Fenton-like processes is that Fe2+ and H2O2 are
initiators of Fenton reaction whereas in Fenton like reaction Fe3+ and H2O2 initiate the
reaction. However, the results of these two process are the same since Fe2+ and Fe3+
are involved in the reactions as a catalyst and these reactions take place as a cycle (Eqs.
(2-8) to (2-14)) (Deng and Englehardt, 2006).
Fe2+ + H2O2 → Fe3+ + •OH + OH- k1 = 76 M-1 s-1 (2-8)
Fe3+ + H2O2 → Fe2+ + HO•2 + H+ k2 = 0.001-0.01 M-1 s-1 (2-9)
•OH + H2O2 → HO•2 + H2O (2-10)
•OH + Fe2+ → Fe3+ + OH- (2-11)
Fe3+ + HO•2 → Fe2+ + O2H
+ (2-12)
17
Fe2+ + HO•2+ H+ → Fe3+ + H2O2 (2-13)
2HO•2→ H2O2 + O2 (2-14)
Indeed, differentiation between Fenton and Fenton-like is quite difficult because
ferrous and ferric ions are in the successive Fenton reactions (Pignatello et al., 2006).
Another main difference between Fenton and Fenton-like processes is the acceleration
of hydroxyl radicals generation. The rate of hydroxyl radical formation at the
beginning of Fenton oxidation Eq. (2-8) is higher than that of in Fenton-like oxidation
Eq. (2-9).
2.4.3 Heterogeneous and homogeneous sono-Fenton-like processes
In the case of heterogeneous sono Fenton process catalyst is solid in which ferrous or
ferric ions are in the surface of the catalyst. The heterogeneous process is in contrast
with homogeneous process because iron ions are solved in to the solution in the case
of homogeneous system. There is not pH limitation when Heterogeneous catalysts are
applied (Caudo et al., 2007). This is because in such catalysts the Fe3+ species are
“immobilized” within the interlayer space or pore of the catalyst. Consequently, the
catalyst can sustain its capability to produce hydroxyl radicals from hydrogen peroxide
formed through the sonication process. Precipitation of iron hydroxide is hindered
Since iron is already in solid form within the catalyst iron hydroxide (Chen and Zhu,
2006). Furthermore, heterogeneous sono Fenton process shows low iron ion release,
and the catalysts remain active over successive operations. Also, it is easier to reuse
heterogeneous catalyst compared to homogeneous catalyst (Sum et al., 2005).
New studies have developed new catalysts applying nanosized particles possessing a
high surface area which can increase the speed of the Fenton/Fenton-like reaction.
Nanotechnology is applied in different fields especially in production of catalyst in
nanoscale (<100 nm) (Lines, 2008; Mamalis, 2007).
On the other hand, in homogeneous process the pH 3 is the optimum pH when the iron
exists as Fe3+ and partially as Fe(OH)3 within the solution. At low pH (< 3), the
18
hydroxyl radicals are scavenged through protons and the concentration of Fe(OH)3
decreases whereas at high pH (> 3), Fe3+ precipitates as an iron hydroxide (Bobu et al.,
2008). Great amount of acid (generally sulfuric acid) is needed to adjust the pH of the
solution in 3 value (Valdés-Solís et al., 2007). Therefore, employing homogeneous
sono-Fenton system for treatment process in the environment is not practical way
because without the pH adjustment Fe(OH)3 would be precipitated, creating high
amount of sludge that need to be disposed (Sum et al., 2005).
2.4.4 Sono-catalytic homogeneous and heterogeneous reaction
Homogeneous sono Fenton reaction is capable of degrading and oxidizing the organic
contaminants in acceptable efficiencies. Hence, this reaction is very often applied in
treatment of various wastewaters. However, some main drawbacks including pH value
limitation, separation of iron ions from the treated aqueous solution and high cost of
consuming hydrogen peroxide prevent the homogeneous Fenton reaction from being
employed greatly in practical applications. Also, employing the homogeneous catalyst
lead to disposal of sludge because of the precipitation of ferric hydroxide during the
neutralization step (Melero et al., 2008). To overcome this drawback heterogeneous
catalysts were employed instead of homogeneous ones (Pignatello et al., 2006).
During the combination of ultrasound with heterogeneous Fenton process, the surface
area of the catalyst and micro bubble generation would be increased respectively (Kim
et al., 2007). In some studies, ultrasound has been combined with heterogeneous
Fenton-like process proposed where Cu/Al2O3 (Kim et al., 2007), a mixed (Al-Fe)
pillared clay (FAZA) (Nikolopoulos et al., 2006), CuO.ZnO/Al2O3 (Kim et al., 2007),
CuO (Drijvers et al., 1999), Fe2O3/SBA-15 (Molina et al., 2006), iron powder (Liang
et al., 2007a; Zhang et al., 2009) goethite (Melero et al., 2008; Neppolian et al., 2004)
were used as heterogeneous catalysts. Martite is an iron oxide that is found in the
nature abundantly (Lin and Gurol, 1998), and also the most especial properties of the
martite catalyst is its reusability in that the catalyst applied in different runs without
missing its activity (Neppolian et al., 2004).
19
Studies show that heterogeneous catalysts can increase the oxidation power of
ultrasound. In the presence of heterogeneous catalysts, hydrogen peroxide produced
with ultrasound (Eqs. (2-15) and (2-16)) reacts with the catalyst surface and produce
more oxidizing species that can improve the degradation of dye (Ghows and Entezari,
2013; Zhou et al., 2009). Produced Hydrogen peroxide (H2O2) reacts with ferric ions
Fe (III) to initiate Fenton-like reactions.
Fe3+ + H2O2 → Fe2+ + HO2• + H+ (2-15)
Fe2+ + H2O2 → Fe3+ + •OH + HO- (2-16)
Even though a detailed mechanism is still under question, heterogeneous substances,
particularly porous substances such as martite, have been revealed importantly
promoting the cavitation bubbles appearance under the ultrasonic. The presence of
heterogeneous substances brings about trapped vapor gas nuclei in the pores and
crevices resulting in formation of more cavitation bubble (Kim et al., 2007).
2.5 Kinetic reaction
To obtain a high efficiency, understanding the sonochemical kinetic reaction is
significant. The kinetic of different sonocatalytic degradation and sonochemical
reactions have formerly been indicated and the mechanism of the especial cases
including sonodegradation of dye (Okitsu et al., 2005), sonication of water (Kubo et
al., 2005; Nam et al., 2003; Tezcanli-Güyer and Ince, 2004), reactions using
ultrasound/TiO2 (Priya and Madras, 2006), reactions using UV/TiO2 (Sivalingam et
al., 2003) (Hoffmann et al., 1995) are well-studied. The literature reports represents
that sonocatalytic and sonochemical dye removal in liquid media can be shown
through the first-order reaction (as a function of irradiation time) (Lin et al., 2008;
Rehorek et al., 2004; Siddique et al., 2011). Hence, in this study, the reactions were
modeled as first-order reaction (Eq. (2-17)):
dC
KCdt
(2-17)
20
Generally, in sonochemical degradation of organic dyes in the presence of catalyst, the
rate-determining step is the reaction between OH● radicals and dye. The kinetics of
sonocatalytic degradation follows pseudo-first order kinetics. The kinetic expression
is given in Eq. (2-18).
r = k[OH●][AB92] = kapp[AB92] (2-18)
Where rate of the reaction is shown with r and apparent-first order rate constant is
indicated with kapp = k [OH●] with unit of (time-1) and [AB92] depicts the concentration
of AB92 (mass/volume).
In this study, the residence time of OH● radical is about 10 ns and measurement of its
concentration is impossible. Therefore, pseudo first order reaction was used in all
experiments.
The pseudo-second order reaction kinetic for the AB92 degradation is also given as
follows:
app
2d[AB92]k [AB92]
dt
app
t 0
1 1k t
[AB92] [AB92]
(2-19)
21
3 CHAPTER 3
MATERIAL AND METHODS
This study was done for AB92 removal by employing the martite nanoparticles as
catalyst in sonocatalystic process. The mechanical ball milling process was applied for
production of nanoparticles. Also, comparing of the results of AB92 degradation in
heterogeneous process with homogeneous one is the other part of this research. The
most important parts of this study in the case of operation were summarized as follow;
firstly, materials and solutions that was used during the heterogeneous and
homogeneous Fenton like process was prepared, secondly, four main processes was
done on natural martite to generation of martite nanoparticles, thirdly, some analysis
was done for characterization of unmilled and ball milled martite, finally, effect of
main operational parameters was evaluated over removal efficiency of AB92.
first part was preparation of chemicals and solutions used during the heterogeneous
and homogeneous sono-Fenton-like processes, second part was preparation of martite
nanoparticles through different processes, third part was characterization of unmilled
and milled martite samples via various analyses and fourth part was consideration of
influence of operational parameters over the removal efficiency of AB92.
3.1 Experimental Solutions
Laboratory distilled water. Distilled water was used where needed for preparation
chemical solution.
Stock dye solution. AB92 dye was obtained from Shimi Boyakhsaz Co. (> 98%
Purity) for heterogeneous and homogeneous sono-Fenton-like experiment. 0.1 g of
22
powdered AB92 was weighted and poured in distilled water. Then, the solution was
brought to volume at 1000 ml with distilled water in a volumetric flask. A solution
with 100 mg/L of concentration was obtained.
Iron(III) chloride hexahydrate solution (FeCl3.6H2O). 2.02 g of powdered iron(III)
chloride (Merck, Catalogue No: 1039431000, > 99 % purity) was weighted and poured
in to the distilled water. Then, the solution with concentration of 20 g/L was obtained
with distilled water in a 100 ml volumetric flask.
Sulfuric acid solution (H2SO4). For the preparation of sulfuric acid solution at a
concentration of 0.1 M, 0.55 mL of concentrated sulfuric acid (98 %) (Merck,
Catalogue No: 1120802500) was brought to volume with distilled water in a 100 ml
flask.
Sodium hydroxide solution (NaOH). 0.4 g of solid sodium hydroxide (Merck,
Catalogue No: 1064625000, ≥ 99 % purity) was poured in distilled water. Then, the
volume was brought to 100 ml in a flask with distilled water to provide a 0.1 M sodium
hydroxide.
Sodium chloride solution (NaCl). To prepare NaCl solution with 5 mM
concentration, 0.146 g of sodium chloride (Merck, Catalogue No: 1064041000, ≥ 99.5
% purity) was poured in distilled water. A solution with the 500 ml volume was
obtained with distilled water in a flask.
Sodium sulfate solution (Na2SO4). To prepare 5 mM solution, 0.355 g of sodium
sulfate (Merck, Catalogue No: 1066491000, ≥ 99 % purity) was poured in distilled
water. The solution with the volume of 500 ml was obtained with distilled water in a
flask.
Ethanol solution (CH3CH2OH). 6.576 ml of ethanol (Merck, Catalogue No:
1009834000, ≥ 96 % purity) was poured in distilled water. The solution with 500 ml
volume was obtained with distilled water in a flask. 5 mM CH3CH2OH solution was
prepared.
23
Chloroform solution (CHCl3). To prepare 0.07 M CHCl3 solution, 0.0521 ml of
chloroform (Merck, Catalogue No: 1024452500) was dissolved in distilled water and
obtained solution was brought to volume of a 250 ml in a flask with distilled water.
Diethyl ether and O-Bis (trimethylsilyl) acetamide. Diethyl ether (Merck,
Catalogue No: 1009215000, ≥ 99.7 % purity) and N,O-Bis(trimethylsilyl)acetamide
(Merck, Catalogue No: 1096490025) were used as solvent without any alteration in
GC-MS analysis of byproducts generated in heterogeneous sono-Fenton-like process.
Alconox. Alconox (Sigma Aldrich) was used as the detergent to clean tubes and other
glasswares after each experiment in this study.
3.2 Preparation of catalyst
Martite is applied in sono-Fenton-like system as heterogeneous catalyst (Figure 3.1).
Martite sample was provided by Sangan mine (mashhad, Iran) and processed in a series
of crushing and sieving process prior to ball milling to reduce the particle size to be
suitable for ball milling. The samples were first passed through jaw crusher and then
cone crusher to obtain particles with the size of 0.5-2 cm. Next, the martite sample was
crushed further through tumbler rod mill to form micro-grained martite particles with
size between 30-50 µm. Finally, interrupted high energy planetary ball mill was
performed for various time (2 h, 4 h and 6 h) to gain the nano-sized martite powders.
Figure 3.1 martite before crushing.
24
Jaw crusher. In this study martite sample were crushed with jaw crusher (Kian Madan
Pars Mining and Industrial Company, Iran) present at Geological Survey of Iran-
Northwestern Regional Office-Tabriz Center. The jaw crusher uses compressive force
for breaking of particles to achieve centimeter-scale particles. Figure 3.2 shows a
schematic shape of a jaw crusher.
Figure 3.2 jaw crusher (IndiaMART, 1996).
Cone Crusher. The cone crusher is greatly applied for fine and secondary crushing in
the fields of chemical industry, metallurgy, mining, building materials. Cone crusher
(Kian Madan Pars Mining and Industrial Company, Iran) present at Geological Survey
of Iran-Northwestern Regional Office-Tabriz Center was applied after jaw crusher to
produce 0.5 to 2 cm in size martite. Figure 3.3 presents the structure of a cone crusher.
25
Figure 3.3 Schematic shape of the Cone crusher (Lipu, 2016).
Tumbler rod mill. Before processing martite sample with planetary ball mill, the cone
crushed sample were milled with tumbler rod (Kian Madan Pars Mining and Industrial
Company, Iran) present at Geological Survey of Iran-Northwestern Regional Office-
Tabriz Center to form micro-grained martite particles with size between 30-50 µm.
Then, martite particle were collected to further process with planetary ball mill.
Planetary ball mill. In the final step, crushed martite particles with a diameter
between 30 and 50 µm were milled with a planetary ball mill ((Retsch, Model PM 400,
Germany) at the Institute of Material and Energy, (Kraj, Iran). The planetary ball mill
was operated at 320 rpm and mass ratio of ball to martite sample was 10:1. In the
milling process 10 hardened steal balls with 10 mm diameter and 5 hardened steel ball
with 20 mm diameter were used to investigate the influence of milling duration on
characteristic of martite nanoparticles and performance as a catalyst in sono-Fenton-
like reactions. Tree sets of nanoparticles were formed with 2 h, 4 h, and 6 h milling
period. Figure 3.4 present schematically planetary ball mill applied in this research.
26
Figure 3.4 (a) planetary ball mill with four containers; (b) stainless steel
container with balls (Retsch, 2017).
3.3 Characterization of martite catalyst
Characterization of ball milled and unmilled martite particles was conducted with
SEM, EDX, particle size distribution, BET, XRD, and FT-IR analyses. To prepare the
samples for above mentioned analysis and prior to each experiment, the following
procedures were followed:
To remove any possible organic material from the catalyst surface, ethanol which is
an organic solvent was used. This is performed in order not to introduce any organic
pollutant to the solution where martite is added. 50 ml ethanol and 0.2 to 0.5 gram
catalyst were added in an erlenmeyer flask. For dispersing the solution, the Erlenmeyer
flask was fixed by a clamp within ultrasonic bath for 30 to 45 min. After that, the
solution was transferred from erlenmeyer flask to a beaker. A syringe was used for
removing the ethanol from the beaker and the remaining ethanol was evaporated in the
oven at 110ºc. The dried catalysts were poured into the plastic container used for
characterization analysis.
27
3.3.1 SEM analysis
The SEM utilizes a focused beam of high-energy electrons to produce a variety of
signals on the solid surface. The signals driving from electron-sample
interactions exhibit information regarding the sample involving external morphology
of materials. In this study the SEM images represent the morphology of unmilled (the
sample before ball milling), 2 h, 4 h and 6 h ball milled martite (MIRA3 FEG-SEM,
Tescan, Czech Republic). This analysis was conducted in the laboratory of the Tabriz
University.
3.3.2 EDX analysis
EDX is an X-ray technique applied to identify the elemental composition
of substances. The amount of iron and other elements in the martite sample was
determined with (EDX) MIRA3 FEG-SEM (Tescan, Czech Republic) analysis that
was conducted in the laboratory of the Tabriz University.
3.3.3 Particle size distribution
Particle size is an important parameter that provides information on physical properties
of the particle. The micro and nanoparticles size distribution were measured employing
micro/nanostructure distance measurement software. Micro-structural Image
Processing (MIP) (Nahamin Pardazan Asia Company, Iran) is a software of image
analysis for calculating the quantitative parameters of microscopy images of SEM.
3.3.4 BET analysis
Specific surface area of materials was determined by BET analysis via physical
adsorption of molecules of gas on the surface of solid. Assessment of specific surface
area of materials identifies not only their external surface area and pore area but also
pore volume.
28
N2 physisorption analysis of the martite nanoparticles were conducted by Quantachrome
Autosorb-6 apparatus in the central laboratory of METU. Martite catalysts were degassed
at 250°C for 3 hours before the analysis. It was performed at a relative pressure (P/P0)
ranging from 0.05 to 1.00 at liquid nitrogen temperature of 77 K.
3.3.5 XRD analysis
The aim of the XRD analysis is to characterize crystalline materials. Since the most
crystalline materials possess unique X-ray diffraction, XRD is applied to distinguish
materials through characterizing and identifying their compounds. XRD analysis were
performed for unmilled martite and ball milled martite nanoparticles.
Each sample was bombarded with X-rays with 1/10 to100 Angstrom wavelength. The
SIEMENS D5000 X-Ray diffractometer present in Geological Survey and Mineral
Exploration of Iran was employed for this analysis (Figure 3.5).
Figure 3.5 SIEMENS D5000 X-Ray diffractometer.
29
3.3.6 FT-IR analysis
FT-IR (Brucker TENSOR 27, Germany) analysis was performed to identify chemical
bonds and functional groups over the surface of the martite catalyst in the laboratory
of the Tabriz University. The potassium bromide KBr pellet technique was applied in
this analysis according to the following procedure (Figure 3.6):
The potassium bromide (KBr) powder was transformed into clear pellet
through crushing the particle size within an agate mortar.
Calibration of the FT-IR apparatus was conducted by the KBr pellet.
The KBr powder along with martite sample were mixed.
The achieved mixture was transformed into pellet.
The pellet was taken into the FTIR apparatus.
Figure 3.6 (a) The FT-IR apparatus (Brucker TENSOR 27) connected to the
computer; (b) The Hydraulic press 15-25 ton load.
3.4 Experimental set-up
In this study, homogeneous and heterogeneous sono-Fenton-like experiments were
conducted in batch reactors. Ultrasonic bath and 250 ml volumetric erlenmeyer flask
were used during the experiment. The volumetric erlenmeyer flask was fixed one
centimeter above the bottom of the ultrasonic bath using a clamp (Figure 3.7). All
30
experiments were performed using 100 ml dye solution at a predetermined
concentration. Unmilled and milled martite are used as the catalyst in heterogeneous
process where FeCl3.6H2O is used as the catalyst in homogeneous process. To measure
the amount of dye removal at specific time intervals, 3 ml samples were taken from
the reactor employing pipette and transferred to a test tube. A super magnet was
dropped into the each test tubes in order to absorb the nanoparticles onto the super
magnate surface to avoid interference of martite with spectrophotometer reading.
Before measuring the samples absorbance through UV-Vis spectrophotometer
apparatuses samples were centrifuged to precipitate the possible suspended
nanoparticles.
Experimental procedure for heterogeneous sono-Fenton-like process set-up:
1- specific amount of dye was poured into 100 mL volumetric flask;
2- the volumetric flask was brought to the volume with distilled water;
3- the obtained solution was poured into an Erlenmeyer flask;
4- a given amount of catalyst was added into the solution;
5- pH of solution was adjusted;
6- 3 mL of solution was withdrawn at t = 0;
7- The Erlenmeyer flask was kept 1 cm above the bottom of ultrasonic bath
through a clamp;
8- 3 mL sample was taken at specific time interval and transferred into test tube;
9- A super magnet was dropped in each test tube to precipitate suspended
nanoparticles;
10- UV-Vis spectrometer was used to measurement of dye absorbance.
Experimental procedure for homogeneous sono-Fenton-like process set-up:
1- specific amount of dye was poured into volumetric flask with the volume of
100 mL;
2- the volumetric flask was brought to the volume with distilled water;
3- the obtained solution was poured into an Erlenmeyer flask;
4- a given amount of FeCl3 was added into the solution;
31
5- pH of solution was adjusted;
6- 3 mL of solution was withdrawn at t = 0;
7- The Erlenmeyer flask was kept 1 cm above the bottom of ultrasonic bath
through a clamp;
8- 3 mL sample was taken at specific time interval and transferred into test tube;
9- UV-Vis spectrometer was used to measurement of dye absorbance.
In this study, different set of trials were employed to investigate the impact of initial
dye concentration, catalyst dosage, pH, inhibitors, reusability of the catalyst and
ultrasonic power. Each test was performed triplicate in both homogeneous and
heterogeneous processes. Table 3.1 shows the summary of experiments done in both
heterogeneous and homogeneous sono-Fenton-like systems. It should be noted that
experiments with various ultrasonic power could only be carried out for heterogeneous
sono-Fenton-like experiments due to the limitation of the ultrasonic bath used at
METU laboratory during homogeneous sono-Fenton-like experiments. Also, effect of
scavengers was not tested for homogeneous system owing to the already low efficiency
observed in homogeneous sono-Fenton-like system for AB92 removal.
Figure 3.7 Set-up of (a) heterogeneous and (b) homogeneous sono-Fenton-
like reactors.
32
R
eact
or
vo
lum
e
(ml)
Dy
e
con
cen
tra
tio
n
(mg
/L)
Ult
raso
nic
po
wer
(W)
Het
ero
gen
eou
s so
no
-
Fen
ton
Ho
mo
gen
eou
s
son
o-F
ento
n
Sca
ven
ger
Sca
ven
ger
con
cen
tra
tio
n
(mg
/L)
Rea
ctio
n
tim
e
(min
) p
H
Ba
ll
mil
led
cata
lyst
Ca
taly
st
do
sag
e
(g/L
)
pH
Ca
taly
st
do
sag
e
(mg
/L)
Comparison of
milling
10
0
10
- 7
6
h
2.5
-
- -
- 6
0
10
0
10
15
0
7
- -
- -
- -
60
10
0
10
15
0
7
Pri
mar
y
2.5
-
- -
- 6
0
10
0
10
15
0
7
2 h
2
.5
- -
- -
60
10
0
10
15
0
7
4 h
2
.5
- -
- -
60
10
0
10
15
0
7
6 h
2
.5
- -
- -
60
Effect of catalyst
dosage
10
0
10
15
0
7
- 0
3
0
- -
60
10
0
10
15
0
7
6 h
1
.0
3
5
- -
60
10
0
10
15
0
7
6 h
1
.5
3
8
- -
60
10
0
10
15
0
7
6 h
2
.5
3
10
- -
60
10
0
10
15
0
7
6 h
3
.0
3
15
- -
60
10
0
10
15
0
7
6 h
4
.0
3
18
- -
60
Effect of pH
10
0
10
15
0
3
6 h
2
.5
2
10
- -
60
10
0
10
15
0
5
6 h
2
.5
3
10
- -
60
10
0
10
15
0
7
6 h
2
.5
4
10
- -
60
10
0
10
15
0
9
6 h
2
.5
5
10
- -
60
Tab
le 3
.1 S
um
mar
y o
f ex
per
imen
tal
condit
ions
in h
eter
ogen
eous
and h
om
ogen
eous
sono
-Fen
ton
-lik
e sy
stem
s
33
Tab
le 3
.1 (
Cont’
d).
Rea
cto
r
vo
lum
e
(ml)
Dy
e
con
cen
tra
tio
n
(mg
/L)
Ult
raso
nic
po
wer
(W)
Het
ero
gen
eou
s so
no
Fen
ton
Ho
mo
gen
eou
s
son
o F
ento
n
Sca
ven
ger
Sca
ven
ger
con
cen
tra
tio
n
(mg
/L)
Rea
ctio
n
tim
e
(min
) p
H
Ba
ll
mil
led
cata
lyst
Ca
taly
st
do
sag
e
(g/L
)
pH
Ca
taly
st
do
sag
e
(mg
/L)
Effect of dye
concentration
10
0
10
15
0
7
6 h
2
.5
3
10
- -
60
10
0
20
15
0
7
6 h
2
.5
3
20
- -
60
10
0
30
15
0
7
6 h
2
.5
3
30
- -
60
10
0
40
15
0
7
6 h
2
.5
3
40
- -
60
Effect of
ultrasonic
power
10
0
10
15
0
7
6 h
2
.5
- -
- -
60
10
0
10
30
0
7
6 h
2
.5
- -
- -
60
10
0
10
40
0
7
6 h
2
.5
- -
- -
60
Effect of
scavengers
10
0
10
15
0
7
6 h
2
.5
- -
- -
60
10
0
10
15
0
7
6 h
2
.5
- -
NaC
l 1
0
60
10
0
10
15
0
7
6 h
2
.5
- -
Na 2
SO
4
10
60
10
0
10
15
0
7
6 h
2
.5
- -
CH
3C
H2O
H
10
60
10
0
10
15
0
7
6 h
2
.5
- -
CH
3C
l 1
0
60
34
3.4.1 Measurement of dye concentration
To determine the concentrations of AB92 used in this study, the absorbance profile of
AB92 was developed over ultraviolet-visible spectroscopy. Absorbance spectrum of
10 mg/L AB92 solution measured by spectrophotometer (WPA lightwave S2000,
Germany) in the wavelength range of 200-800 for heterogeneous sono-Fenton-like
system in Tabriz University shown in Figure 3.8. Also, in homogeneous sono-Fenton-
like system, a UV-Visible spectrophotometer (HACH, DR2800, Germany) in METU
was used to scan AB92 absorbance. As it is seen in the figure, the maximum
absorbance of the selected dye was observed at 570 nm. To develop the correlation of
AB92 concentration with absorbance at 570 nm, absorbance of AB92 solution with
various known concentration were measured. The relevant calibration curves are
separately plotted are shown in Figure 3.9(a) and (b) in heterogeneous and
homogeneous sono-Fenton-like processes, respectively. As can be seen from
Figure 3.9(b), pH 7 indicates no FeCl3 solution and pH 3 is in the presence of FeCl3
solution (10 mg/L). Calibration at pH 7 and 3 for homogeneous sono-Fenton-like
system presents that the points form a straight line showing that absorbance and
concentration are in accordance with each other.
Figure 3.8 Absorption spectrum of AB92 (10 mg/L).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
200 300 400 500 600 700 800
Ab
sorb
an
ce
Wavelength (nm)
λmax
35
Figure 3.9 Calibration of AB92 at various dye concentration in (a) heterogeneous and
(b) homogeneous sono-Fenton-like system.
The color removal efficiency (CR%) was mesuared through the ratio of absorbance of
the sample to the original wastewater at the maximum absorbance wavelength (570
nm). In fact, CR% represents rate of the removal of the materials. The relevant formula
is as follows:
y = 0.0201x
R² = 0.9695
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15 20 25
Ab
sorb
an
ce
[AB92] (mg/L)
(a)
y = 0.0188x
R² = 0.9967
y = 0.0135x
R² = 0.994
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15 20 25
Ab
sorb
an
ce
[AB92] (mg/L)
(b)
pH = 7 without FeCl3
pH = 3 and FeCl3
36
0
0
A ACR% 100
A
(3-1)
where A0 represents the initial absorbance of the substance, A is the absorbance at any
time and CR% is the removal efficiency percentage at a given time.
3.4.2 Measurement of soluble Iron Concentration
To determine the amount of dissolved iron from martite into the solution at different
pH, 2.5 g/L martite (6 h-milled) was solved into 100 ml distilled water and placed
within the ultrasound bath for 60 min. This test was repeated at pH 3, 5, 7, and 9. Then,
25 ml sample was taken and transferred into a test tube. Amount of iron that was
leached into the solution was determined through atomic absorption spectrometry
(Analytik jena, nova 400P, Germany) at laboratory of the Tabriz University for each
pH values. Figure 3.10 shows the atomic absorption apparatus.
Figure 3.10 Atomic absorption spectrometer.
37
3.4.3 Identification of intermediates during degradation of AB92
By-products generated during the sono-catalytic degradation process was identified by
GC-MS analysis. The test was conducted with the solution of 20 mg/L of the AB92
along with 2.5 g/L 6 h-milled martite for 5 minutes within the ultrasonic bath. Before
transferring the solution containing byproducts, the martite nanoparticles was
precipitated by a super magnet. The produced aromatic and aliphatic intermediates
were extracted from aqueous phase to the organic using 40 mL of diethyl ether (Merck,
Catalogue No:1009265000,≥99.7% purity) in each time. Each time the separating
funnel containing AB92 solution and diethyl ether was agitated. This procedure was
conducted three times. The resulting organic phase within separating funnel was
poured into a small container concentrated to 1 ml for GC-MS analysis. Then,
derivatization was performed. During this process, obtained intermediates were mixed
with 100 µL N,O-Bis(trimethylsilyl)acetamide (Merck, Catalogue No: 1096490025)
and heated over a magnetic stirrer within the water bath at 60 C° for 15 minutes.
Finally, Sylyl products introduced into the GC-MS system (Agilent 6890 gas
chromatography and 5973 mass spectrometer, PaloAlto, Canada). This test was
conducted in the chemical laboratory of Tabriz University.
38
39
4 CHAPTER 4
RESULTS AND DISCUSSION
4.1 Characterization of the unmilled and milled martite
4.1.1 SEM analysis
SEM images of microsized unmilled martite (before planetary ball milling) and
nanosized martite (after planetary ball milling) are shown in Figure 4.1. Based on the
SEM images, before the ball milling process, martite microparticles are made up of
nonuniform particles with different sizes (Figure 4.1(a)). Figures 4.1(b) to (d) show
SEM images of martite nanoparticles processed in planetary ball mill for 2 h, 4 h and
6 h, respectively. These figures show that after applying planetary ball milling process,
martite microparticles efficiently converted into nanoparticles with fairly uniform in
size. This increases the catalytic activity of nanoparticles in heterogeneous sono-
Fenton-like process because the catalytic activity is strongly affected through particle
size. In other words, the nanostructured particles have high surface area compared to
microstructure particles.
40
Figure 4.1 SEM micrographs of (a) martite sample before ball milling, (b) 2 h
ball milled martite nanoparticles, (c) 4 h ball milled martite nanoparticles and
(d) 6 h ball milled martite nanoparticles.
4.1.2 EDX analysis
To identify the presence of main elements in martite sample (6 h-ball milled),
EDX analysis was carried out. Figure 4.2 shows the EDX graph and inset table
indicates main elements together with their weight and atomic percentage in
the sample. In the EDX spectrum, the peak between 2 and 2.25 KeV of energy
is ascribed to the gold container used during the specimen preparation step. As
41
can be observed in Figure 4.2, oxygen, iron, silicon and carbon are the main
elements in the martite structure. Also, oxygen and iron have the higher weight
percentage compared to other elements. Since the presence of iron and oxygen
can be attributed to iron oxide, it can be stated that it is martite (Fe2O3).
Figure 4.2 6 h ball milled martite EDX spectrum.
4.1.3 Particle size distribution
Measurement of particle size distributions was performed via MIP software. This
software is employed to determine the martite nanoparticles size achieved by ball
milling technique. Figure 4.3 presents the particles diameter of unmilled and milled
martite samples. As can be seen in the figures, the average diameter of ball milled
42
martite is in the range of 10-90 nm. Also, it shows that the 53.3% of size distribution
of the 6 h ball milled martite nanoparticles are in the range of 30-50 nm.
Figure 4.3 Size distribution of (a) before ball milling martite, (b) after ball
milling martite samples.
0
10
20
30
40
50
60
10-30 30-50 50-70 70-90
Fre
qu
ency
(%
)
Nanoparticles size distribution (nm)
(b) 2 h ball milled
4 h ball milled
6 h ball milled
0
10
20
30
40
50
60
30-50 50-70 70 -90 90-140
Fre
qu
ency
(%
)
Microparticles size distribution ( m)
unmilled martite
43
4.1.4 BET analysis
Specific surface area of unmilled and milled martite samples produced by the ball
milling process was measured and their BET isotherm models (N2 adsorption-
desorption) were provided. Results of BET analysis of the samples are presented in
Figure 4.4 . These plots are in terms of volume of nitrogen absorbed per gram of
martite sample versus relative pressure. These plots can be determined the type of
adsorption isotherm. According to the IUPAC classification, the martite samples
demonstrated a combination of isotherms of type IV and V, which is typical of
mesoporous materials. Type IV and V isotherms characterize presence of mesopores
in martite structure. The mesopre range for particle pore diameter is defined as 2-50
nm.
Figure 4.4 N2 adsorption-desorption isotherm of (a) unmilled martite, (b)
martite nanoparticles after 2 h, (c) 4 h and (d) 6 h mechanical milling samples
obtained from the BET test.
According to Figure 4.4, the hysteresis shape starts from nearly relative pressure (P/P0)
of 0.50 to 1.00 for all the unmilled and milled martite samples. It represents their large
porosity. Hysteresis type was determined to be type H3 (according to IUPAC types of
44
hysteresis loops) for all martite samples in relative pressures (P/P0) higher than 0.5
owing to the capillary condensation of N2 in the mesopores of the samples. Besides,
steep and well-defined hysteresis loops and parallel adsorption-desorption branches
are the characteristics of mesopores formation (Mistura et al., 2013).
BET surface area for the primary, 2 h, 4 h and 6 h ball milled martite were calculated.
Corresponding pore volume of the samples were also computed by means of Barrett-
Joyner-Halenda (BJH) method. Average adsorption pore diameter were 172, 234.7,
282.5 and 357.8 nm for unmilled, and ball milled samples after 2h, 4 h and 6 h,
respectively. This result revealed that pore diameter of samples enhance by increasing
the mechanical milling time.
Table 4.1 show the specific surface area, pore volume of unmilled martite and ball
milled martite. As is seen in the table, surface area increased from 5.675 to 21.01 m2/g
and the pore volume increased from 7.961 × 10-3 to 3.386 × 10-2 cm3/g after 6 h of
mechanical ball milling process compared to the unmilled sample. The large surface
area would lead to higher performance of a heterogeneous catalyst. Fenton-like process
would occur over interphase between the solid surface and aqueous phase, and the
more catalyst surface area, the more iron(III) would be available for Fenton-like
reactions.
Table 4.1 Surface area and pore volume characteristics of unmilled (primary),
2 h, 4 h and 6 h ball milled martite samples.
Martite sample unmilled 2 h-milled 4 h-milled 6 h-milled
Specific surface area
(m2/g) 5.675 16.36 17.81 21.01
Pore volume (cm3/g) 7.961 × 10-3 1.638 × 10-2 2.963 × 10-2 3.386 × 10-2
4.1.5 X-ray Diffractıon (XRD)
Figure 4.5 presents XRD patterns of the unmilled martite (a) and ball milled martite
samples (b-d). The observed peaks at 2θ values of 24.22, 33, 35.72, 41, 49.52, 53.9,
45
57.58, 62.56, and 64.06o were attributed to the characteristic (0 1 2), (1 0 4), (1 1 0), (1
1 3), (1 2 4), (1 1 6), (1 2 2), (2 1 4), and (3 0 0) planes. The obtained XRD pattern was
very close to hematite (JCPDS No.33-664), which is a reasonable finding since martite
is a hematite pseudomorphs after magnetite and its physical properties are similar to
hematite (Morris et al., 1981; Weiwei et al., 2008). Moreover, the same peaks in the
XRD spectra showed that the ball milling procedure was not effect on structure of
martite samples. The decline of XRD peak intensity after the ball milling process can
be related to the crystallinity decrease nano-sized martite is obtained (Fathinia et al.,
2015).
Figure 4.5 XRD spectra of (a) unmilled martite, (b) martite nanoparticles
after 2 h ball milling, (c) 4 h ball milling and (d) 6 h ball milling.
4.1.6 FT-IR analysis
For investigation of chemical bonds and functional groups in martite samples the FT-
IR analysis was carried out. The results of FT-IR analyses for unmilled and milled
46
martite are presented in Figure 4.6. In FT-IR spectra (Figure 4.6), the peaks at 2854.8
and 2923.7 cm−1 were shown the asymmetric and symmetric C–H bonds, respectively
(Aber et al., 2009). In addition, the O–H vibration peak at 3450.5 cm-1 indicated the
presence of O-H group. Finally, the peaks of the –COO– vibration (1386.3 and
1599.0cm-1), the Si–O vibration (1094.9 cm-1), the Fe–O vibration (467.6 and 552.7
cm-1) were also observed in all of the samples. The functional groups on the ball milled
martites were similar to the ones in unmilled martite sample. It should be mentioned
that, the intensity of the peaks increased especially at 467.63 and 552.75. It has been
reported that the intensity of peaks is related to size of the particle in FT-IR analysis.
The intensity of peaks increases, by decreasing the size of particle (Zhang et al., 2002).
Figure 4.6 FT-IR spectra of (a) unmilled martite, (b) ballmilled martite after 2
h, (c) 4 h and (d) 6 h milling time.
47
4.2 Removal of AB92 with sono-Fenton-like process
4.2.1 Comparing of unmilled and ballmilled martite samples
The treatment of AB92 was conducted with heterogeneous sono-Fenton-like process
applying the unmilled martite and different ball milled martite samples. The removal
efficiencies for the sonication in this process during 60 min are shown in Figure 4.7.
Figure 4.7 Comparing the removal efficiency of AB92 under the effect of different
processes (a) catalyst only (b) sonolysis alone, (c) unmilled (d) 2 h, (e) 4 h, (f) 6 h
ball milled martite catalysts in sonocatalysis process. Experimental conditions:
[AB92]0 = 10 mg/L, catalyst dosage = 2.5 g/L, ultrasonic power = 150 W, and pH =
7.
As can be seen from the figure, when sonication is not applied, the sorption of AB92
on 6 h ball milled martite is insignificant (Figure 4.7a). It represented that sorption
process is negligible in the presence of martite samples. Also, influence of sonolysis
power without addition of the catalyst was found to be less than 40% for the dye
removal (Figure 4.7b). After 30 min reaction time highest AB92 removal (100%) was
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
(f)
(b)
(c)
(d)
(e)
(a)
48
observed when 6 h ball milled martite was used as catalyst. By considering costs
during the process the optimum reaction time was limited to 60 minutes. The longer
the ball milling process, higher the AB92 removal efficiency. Unmilled martite
catalyst demonstrated lower AB92 removal efficiency than ball milled martite catalyst.
Higher removal efficiency observed with the ball milled martite catalyst can be
attributed to higher surface area and available sites per gram of the catalyst.
The application of ultrasonic irradiation was the practical way for segregation of water
molecules (Eq. (4-1)) and extra production of Fe2+ by forming of •OH (Eq. (4-2)); lead
to the generation of more radicals species (Sheydaei and Khataee, 2015):
HOHOH2
))) (4-1)
HOHFeOHFe 2
2
3 ))) (4-2)
Also, according to Eqs. (2-15) and (2-16), excess •OH would be produced.
Furthermore, aggitation of the solution and mass transfer between solid and liquid is
expected to increase under sonication (Reddy et al., 2009). Disaggregation of the
nanoparticles enhances the available sites on the surface of the catalyst. Furthermore,
more cavitation microbubbles are formed owing to the low tensile strength between
solid and liquid and cavitation nuclei in the cracks of the solid (Taseidifar et al., 2015).
Figure 4.8 and Table 4.2 demonstrate that heterogeneous sono-Fenton-like process
with martite as catalyst follow pseudo-first order kinetic, which is agreement with
previous studies (Khataee et al., 2016b). The apparent pseudo-first order rate constants
(kapp) for the degradation of AB92 were estimated from ln (A0/At) versus time (t) plots
and indicated in Table 4.2. The A0 and A stand for the absorbance of AB92 at the
beginning and at process time, respectively (Khataee et al., 2016c). The linear
regression lines with coefficient of determination (R2), higher than 0.99, show the
validity of first order reaction kinetics. As is observed from the table, the reaction rate
of 6 h ball milled martite is higher than others. Consequently, the 6 h ball milled martite
was selected as the desired nanocatalyst for remaining experiments in the treatment
process.
49
Pseudo-second order reaction kinetic model is also tested on the experimental data
(Table 4.2). By comparing the coefficient of determination (R2) for both pseudo-first
order reaction model and pseudo-second order reaction model, the first one was
selected as the best reaction model. In fact (R2) is higher for pseudo-first order reaction
model.
Figure 4.8 Plot of apparent pseudo- first order reaction rate constants.
0
5
10
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
Adsorption
Sonication only
Unmilled
2 h-milled
4 h-milled
6 h-milled
50
Table 4.2 Plot of apparent pseudo-first and second order reaction rates of
different catalysts for degradation of AB92.
Catalyst
Pseudo-first order Pseudo-second order
kapp
(min-1) R2
kapp
(mg-1 L.min-1) R2
Catalyst only 0.0014 0.9870 0.0048 0.9895
Sonication only 0.0090 0.9957 0.0542 0.9872
Unmilled martite 0.0138 0.9923 0.0870 0.9890
2 h ball mill martite 0.0281 0.9964 0.3516 0.9476
4 h ball mill martite 0.0584 0.9974 1.606 0.7801
6 h ball mill martite 0.2100 0.9983 0.9321 0.1870
4.2.2 The effect of catalyst concentration
The catalyst amount is one of the significant parameters that effect the removal
efficiency of dye pollutant. Figure 4.9(a) demonstrates the removal efficiency over
time for various 6 h ball milled dosages catalyst. As is seen in the Figure 4.9(a) the
removal efficiency enhanced as the initial catalyst dosage increased in the range of 0
to 2.5 g/L. This was owing to the more available sites for Fenton-like reaction and
increase in radical formation and AB92 degradation (Zhang et al., 2014). Kuang et al.
(2013a) found that active sites on the surface of the catalyst increase by increasing the
amount of the catalyst dosage in the sono-catalystic Fenton-like process. Also,
according to Eq. (2-9), more ferric ions react with hydrogen peroxide resulting in
generation of more hydroxyl radicals. As a result, more hydroxyl radicals would
destroy AB 92. Afterwards, an opposite trend was observed through increasing the
catalyst dosage more than 2.5 g/L, and the removal efficiency of AB92 declined. This
observation was possibly owing to the reaction between iron ions with hydroxyl
radicals (Eq. (4-3)) (Kuang et al., 2013b; Sun and Lemley, 2011). In addition,
screening effect of the extra catalyst particles on the ultrasonic waves might have
inhibited the dissipation of energy (Vahid et al., 2014).
•OH + Fe2+→ OH− + Fe3+ (4-3)
51
Figure 4.9 Impact of the catalyst dosage on the sonocatalytic degradation of AB92 in
(a) heterogeneous (6 h ball milled martite) and (b) homogeneous (FeCl3) sono-
Fenton-like processes. Initial dye concentration = 10 mg/L, 6 h milled martite,
ultrasonic power = 150 W, and pH = 7 for the heterogeneous system. Initial dye
concentration = 10 mg/L, ultrasonic power = 150 W, and pH = 3 for the
homogeneous system.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
(a)
0 g/L
1 g/L
1.5 g/L
2.5 g/L
3 g/L
4 g/L
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
(b)
0 mg/L
5 mg/L
8 mg/L
10 mg/L
15 mg/L
18 mg/L
52
To investigate the impact of catalyst dose (Fe3+) in homogeneous sono-Fenton-like
system, initial dosage of Fe3+ ranging from 0 to 18 mg/L were tested. The results of
homogenous sono-Fenton-like experiments are presented in Figure 4.9(b). The
removal efficiency was less than 50% in each of the experiment after 60 min of
reaction time. Generally, by increasing the (Fe3+) from 0 mg/L to 10 mg/L, the dye
removal enhanced. However, the removal rate of AB92 decreased as iron dose addition
was higher than 10 mg/L.
The ultrasonic bath used in the homogeneous sono-Fenton-like experiments has
limited power and specifications. Therefore, the dye removal efficiencies obtained in
the homogeneous counterpart of this study may not be representative of the actual
efficiencies that can be obtained with homogeneous sono-Fenton-like process. The
usage of the ultrasonic probe can possibly be a solution to increase the dye removal
efficiency in homogeneous sono-Fenton-like system. This system was not tested
because it was out of scope of this study.
Plots of ln(A0/At) versus time for all dosages of catalyst for heterogeneous and
homogeneous are presented in Figure 4.10(a) and (b), respectively. These figures
present the AB92 removal in the presence of the martite nanocatalysts and FeCl3
solution following pseudo-first order kinetic. By increasing the 6 h ball milled martite
and FeCl3 dosage up to threshold value, kapp increases. But, reaction rate decreases
beyond 2.5 g/L and 10 mg/L dosage of the 6 hr ball milled martite and FeCl3 catalysts.
The amount of kapp were achieved from the linear regression of natural logarithmic
transformed removal efficiency versus time. The rate constant is obtained as 0.21 min-
1 at heterogeneous martite catalyst of 2.5 g/L, whereas it is 0.0123 min-1 at
homogeneous iron solution of 10 mg/L. The values corresponding to initial AB92
concentration and the determination coefficients are given in Table 4.3. According to
this table, the reaction rates of heterogeneous sono-Fenton-like system are much higher
than its homogeneous counterpart.
53
Figure 4.10 Plot of apparent pseudo-first order reaction rate constants for
degradation of AB92 in (a) heterogeneous and (b) homogeneous sono-
Fenton-like processes.
0
5
10
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
(a)sonication
1 g/L
1.5 g/L
2.5 g/L
3 g/L
4 g/L
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
(b)Sonication
5 mg/L
8 mg/L
10 mg/L
15 mg/L
18 mg/L
54
Table 4.3 Apparent pseudo-first order reaction rate of catalyst dosage for
removal of AB92.
Heterogeneous sono-Fenton-like
process
Homogeneous sono-Fenton-like
process
Catalyst dosage
(g/L)
kapp
(min-1) R2
Catalyst dosage
(mg/L)
kapp
(min-1) R2
Sonication only 0.0090 0.9957 Sonication only 0.0012 0.9639
1 0.0257 0.9942 5 0.0063 0.9555
1.5 0.0847 0.9975 8 0.0087 0.9679
2.5 0.2100 0.9983 10 0.0123 0.9808
3 0.0608 0.9990 15 0.0054 0.9809
4 0.0458 0.9959 18 0.0044 0.9813
4.2.3 The influence of initial pH
Effect of pH is another important experimental parameters in the heterogeneous sono-
Fenton-like process. Therefore, the impact of different pHs on the AB92 removal
solution was investigated for both heterogeneous and homogeneous sono-Fenton-like
system. AB92 removal efficiencies obtained from these experiments are shown in
Figure 4.11. In heterogeneous system, higher removal efficiency was achieved at lower
pH values, and the removal efficiency declined at higher pH values. This is because
the higher oxidation potential of the •OH radicals in acidic medium (Babuponnusami
and Muthukumar, 2014).
Also in acidic environment, the surface charge of martite is positive and since AB92
is an anionic dye, the molecules of dye come close to the surface of martite and
oxidation process would be done more efficiently (Xu and Wang, 2012). Besides,
Figure 4.12 illustrates that at lower pH, the amount of leached iron ions from the
surface of martite was higher. In heterogeneous process, when the pH was in the range
of 3 to 7, after 30 min the AB92 concentration reached below detection levels. The
removal process at neutral pH is more straightforward and cost-effective than acidic
condition. Thus, pH 7 was the optimum value for the rest of the experiments. It is to
be noted that, the amount of leached iron concentration was negligible and lower than
55
1 mg/L in the presence of 6 h ball milled martite under pH range of 3 to 9. Therefore,
generation of •OH radicals would be mostly owing to the heterogeneous process for
the AB92 removal (Khataee et al., 2016b; Xu et al., 2013b).
In homogenous sono-Fenton-like process the maximum removal of AB92 was
achieved (49%) at pH 3 (Figure 4.11(b)). The removal efficiency of AB92 decrease
both at pHs lower and higher than pH 3. The obtained data depicted that the
decolorization efficiencies were significantly greater in neutral condition (pH 7) in the
heterogeneous system compared to acidic solutions in the homogeneous sono-Fenton
system. According to the Figure 4.11(b), the removal efficiency diminishes at pH 2. It
can be attributed to the surplus H+ ions as hydroxyl radical scavenger present in the
solution according to Eq. (4-4) (Lucas and Peres, 2006). Also, the backward reaction
would occur by surplus H+ ions as presented in Eq. (4-5) causes an enhancement in
Fe3+ ions (Karthikeyan et al., 2011). Furthermore, according to Figure 4.11(b), the
removal efficiency at higher pH values more than pH 3 was decreased. In fact, Fe3+
ions react with hydroxyl ions and precipitated as Fe (OH)3 . Therefore, regeneration
of Fe2+ as a result of reaction between Fe3+ and H2O2 would not occur.(Nieto et al.,
2011).
H+ + ●OH + e- → H2O (4-4)
Fe3+ + H2O2 → Fe-OOH2+ + H+ (4-5)
56
Figure 4.11 The effect of suspension pH on the degradation efficiency of AB92 by
(a) 2.5 g/L 6 hr ball milled martite (b) 20 mg/L FeCl3, [AB92]0 = 10 mg/L, ultrasonic
power = 150 W.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
pH = 3
pH = 5
pH = 7
pH = 9
(a)
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
(b)pH = 2
pH = 3
pH = 4
pH = 5
57
Figure 4.12 Dissolved iron concentration in solution phase after 60 min;
[Martite] = 2.5 g/L.
Figure 4.13(a) and (b) show ln(A0/At) versus reaction time (min) plots for different
pHs for the AB92 removal process in heterogeneous and homogenous systems,
respectively. The kapp and R2 values for heterogeneous and homogeneous processes
calculated with linear regression of data are presented in Table 4.4. As can be observed
from Table 4.4, all the pseudo-first order reaction rate constants for heterogeneous
system are greater than those for homogeneous system even for the optimum pH of 3.
Also, R2 values in pseudo-first order reaction for homogeneous sono-Fenton-like
process are higher than R2 values for pseudo-second order reaction. This verifies the
selection of pseudo-first order reaction as reaction rate constant.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3 5 7 9
Iro
n c
on
cen
tra
tion
(m
g/L
)
pH
58
Figure 4.13 Plot of apparent pseudo-first order reaction kinetic for AB92 degradation
at different pHs for (a) heterogeneous and (b) homogeneous Fenton process.
0
5
10
15
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
(a)pH = 3
pH = 5
pH = 7
pH = 9
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
(b)pH = 2
pH = 3
pH = 4
pH = 5
59
Table 4.4 Impact of the different pH values on the apparent pseudo-first and second
order reaction rates for AB92 degradation.
Pseudo-first order Pseudo-second order
Heterogeneous sono-
Fenton-like process
Homogeneous sono-
Fenton-like process
Homogeneous sono-
Fenton-like process
pH
kapp
(min-1)
(R2) pH
kapp
(min-1)
(R2)
kapp
(mg-1L.min-1)
(R2)
3 0.2852 0.9944 2 0.0067 0.9686 0.0718 0.9440
5 0.2316 0.9979 3 0.0123 0.9808 0.1707 0.9516
7 0.2100 0.9983 4 0.0013 0.9055 0.0085 0.8978
9 0.0528 0.9935 5 0.0008 0.9527 0.0042 0.9500
4.2.4 The effect of initial dye concentration
Figure 4.14 shows AB92 removal efficiency graph for various initial dye
concentrations. According to the Figure 4.14(a), by increasing the AB92 concentration
from 10 to 40 mg/L, the removal efficiency after 60 min contact time declines from
100% to 70%. At the same experimental conditions, the surface area of the 6 h ball
milled martite that is available to react with the molecules of dye were constant. Also,
the same amount of hydroxyl radicals would be produced even with increasing of the
AB92 molecules and their degradation byproducts (Kwon et al., 1999; Neam u et al.,
2004; Sun and Lemley, 2011). Indeed, when the initial dye concentration increase the
amount of AB92 molecules that react with hydroxyl radicals increase, while the
generation of the hydroxyl radicals remain constant (Liu et al., 2006; Petitpas et al.,
2007). Also, with increasing the initial dye concentration, intermediates created during
the decomposition process would be increased. It is possible that the molecules of
pollutants and intermediates produced during degradation process compete with each
other to react with hydroxyl radicals. So, the removal efficiency decrease and amount
of dye concentration remained within the solution increase (Li et al., 2002; Neamu et
al., 2004). Furthermore, previous studies have shown that increasing the initial
concentration of anionic and nonvolatile dye reduces the generation of cavitation by
60
ultrasonic waves (He et al., 2007). Similar results was reported by Wang et al. (2009)
for removing Acid Red B by sonocatalystic process.
In homogeneous sono-Fenton-like system the effect of initial dye concentration was
evaluated by changing the AB92 concentration in the range of 10 to 40 mg/L and the
achieved results are presented in Figure 4.14(b). The highest removal efficiency was
achieved when the initial dye concentration was 10 mg/L.
Amount of dye mass that was removed both in heterogeneous and homogeneous
process was demonstrated in Figure 4.14(c) and (d). In the case of heterogeneous
process, by increasing the initial dye concentration the mass removal increase too.
According to the figures, higher mass removal was observed at high AB92 dosage in
which the amount of mass that was removed increase from 1.00 to 2.00 mg after 30
min contact time when the concentration of dye change in the range of 10 to 40
mg/L.There is no such parallel increase for homogeneous system. The increase in mass
of AB92 removal is observed from 10 mg/L to 20 mg/L, however, mass removal
decreased at 30 and 40 mg/L Figure 4.14(d). Also, according to Figure 4.14(c) and (d),
the amount of AB92 mass removed in the heterogeneous sono-Fenton-like system was
more than those of in the homogeneous sono-Fenton-like system. In addition, for
removal of AB92 the contact time should be enhanced when the concentration of dye
is more than 10 mg/L in homogeneous system. Moreover, at higher dye concentration
more than 10 mg/L, the contact between Fe3+ ions and dye molecules is increased
resulting in high mass of dye removal.
61
Figure 4.14 The impact of initial dye concentration on AB92 degradation in (a)
heterogeneous and (b) homogeneous sono-Fenton-like system and removal of AB92
in the (c) heterogeneous and (d) homogeneous sono-Fenton-like systems.
Figure 4.15(a) and (b) show ln(A0/At) versus time plots for heterogeneous and
homogeneous sono-Fenton-like systems, respectively. The amounts of kapp and R2
calculated from Figure 4.15(a) and (b) with linear regression are given in Table 4.5.
According to the results, amounts of R2 are higher than 0.99 in heterogeneous sono-
Fenton process and 0.97 in homogeneous sono Fenton process verifying that the
pseudo-first order kinetic reactions took place during the AB92 degradation process.
In addition, by changing the concentration of AB92 in the range of 10 to 40 mg/L, the
values of kapp are decreased from 0.21 to 0.02 min-1 in heterogeneous process and from
0.0111 to 0.0027 min-1 in homogeneous system. Generally speaking, the reaction rates
of heterogeneous sono-Fenton-like process is higher than its homogeneous
counterpart.
62
Figure 4.15 Plot of pseudo-first order reaction rate constants for AB92 degradation
for various initial dye concentration (a) heterogeneous and (b) homogeneous sono-
Fenton-like processes.
0
5
10
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
(a)10 mg/L
20 mg/L
30 mg/L
40 mg/L
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
(b)10 mg/L
20 mg/L
30 mg/L
40 mg/L
63
Table 4.5 Apparent pseudo-first order reaction rates of various dye concentration for
degradation of AB92.
Pseudo-first order
Heterogeneous sono-
Fenton-like process
Homogeneous sono-
Fenton-like process
AB92
concentration
(mg/L)
kapp
(min-1)
(R2)
kapp
(min-1)
(R2)
10 0.2100 0.9983 0.0123 0.9808
20 0.0525 0.9987 0.0067 0.9822
30 0.0363 0.9994 0.0028 0.9844
40 0.0200 0.9986 0.0027 0.9839
4.2.5 Reaction time
The percentage removal of AB92 varied with time both in the homogeneous and
heterogeneous systems as shown in Figure 4.16. In heterogeneous system, the
percentage removal of AB92 with time followed a rapid increase until 20 min and
levels off after that. However, the percentage removal of AB92 followed a slower
steady increase and reached 68% in 130 min of reaction time in homogeneous sono-
Fenton-like system. All in all, the heterogeneous sono Fenton oxidation removed
AB92 by 100%, but homogeneous sono Fenton oxidation degraded AB92 by 68%.
The optimum experimental results are listed in Table 4.6. In this study, reaction time
for homogeneous sono-Fenton-like experiments was determined to be 60 min instead
of 130 min. It is evident that when the reaction time in homogeneous system continues
until 120 min, the removal efficiency results are not comparable with heterogeneous
system. Hence, it was not economical to wait 120 min. Also, there is not a great
difference between the removal efficiency of 47% at 60 min and 68% at 130 min. The
experimental results for the homogeneous sono-Fenton-like system may not be
representative due to the limitations of the sonic bath used in this study. Hence, it may
be expected to achieve higher removal efficiencies with greater rates of reaction,
perhaps, by using a different and more powerful equipment.
64
Figure 4.16 The efficiency of AB92 removal at optimum conditions in both
homogeneous and heterogeneous sono-Fenton-like systems.
Table 4.6 Operational conditions that resulted in the best AB92 removal
efficiency.
Operational conditions Heterogeneous
sono Fenton
Homogeneous
sono Fenton
Initial AB92 concentration (mg/L) 10 10
Catalyst dosage (mg/L) 2500 10
Initial pH 7 3
Ultrasonic power (W) 150 150
Reaction time (min) 60 130
Reaction rate (min-1) 0.2100 0.0101
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140
Rem
ov
al
effi
cien
cy (
%)
Time (min)
Heterogeneous sono-Fenton process
Homogeneous sono-Fenton process
65
4.2.6 The effect of ultrasonic power
Ultrasonic power could only be tested in heterogeneous system due to the limitation
of the ultrasonic bath equipment used at METU laboratories. A positive impact of
ultrasound intensity on the AB92 removal by sono-catalytic process in the presence of
nanomartite was indicated in Figure 4.17. According to Figure 4.17, with increase of
the ultrasonic power the removal efficiency also increased at earlier stages of the
experiment, but eventually all ultrasonic powers led to the same removal efficiency.
The removal efficiency of AB92 in the absence of ultrasonic waves, on the other hand,
decreased significantly as was precisely shown in section 4.2.1 and Figure 4.7.
According to this test, the adsorption of AB92 by 6 h ball milled martite catalyst was
lower than 7% after 60 min. Production of bubbles depends on the pressure exerted by
ultrasound. Cavitation occurs when the pressure exerted by the ultrasound waves is
more than the liquid that keep water molecules interconnected. When the intensity of
the sound waves applied to fluid increases, high amount of energy is scattered to the
process increasing the generation of the bubbles (Gogate et al., 2003). Consequently,
the removal efficiency as a result of enhancing the amount of hydroxyl radicals
increase (Zhang et al., 2011). According to the observations, the removal efficiency
after 30 min contact time using the ultrasonic power of 150 and 400 W was not change
considerably; hence, all experiments were carried out under the ultrasonic power of
150 W because it was cost-effective in terms of the energy consumption.
The results in Figure 4.18 and Table 4.7 show that pseudo-first order was selected as
reaction rate. According to this table, when ultrasonic power increases, the reaction
rate of the AB92 removal increases as well.
66
Figure 4.17 Impact of ultrasonic power on the degradation of AB92. [AB92]0 = 10
mg/L, and dose of catalyst = 2.5 g/L, and pH = 7.
Table 4.7 Impact of the ultrasonic power on the apparent pseudo-first order reaction
rates for removal of AB92.
Heterogeneous sono-Fenton-like process
Ultrasonic power
(W) kapp (min-1) R2
150 0.2100 0.9983
300 0.2487 0.9990
400 0.2848 0.9957
Reaction time 60 min
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
400 W
300 W
150 W
67
Figure 4.18 The plot of pseudo-first order kinetic reaction rate constants for
ultrasonic powers at heterogeneous sono-Fenton-like system.
4.2.7 Evaluation of reusability and stability of the martite
Reusability is one the important advantages of a catalyst from operational and
economical point of view. The 6 h ball milled martite was used in five consecutive
experiments during the 60 min of contact time in the sono-catalytic Fenton-like process
when the catalyst dosage was 2.5 g/L and also initial dye concentration was10 mg/L.
The same nanoparticles were used in each run without changing the operational
conditions. The average recovery of 6 h ball milled martite was 97% after each cycle.
The removal efficiency for these five repeated applications is demonstrated in
Figure 4.19. The data revealed that significant changes was not observed in removal
efficiency with each cycle. These results prove that, separating the catalyst from
treated water and reusing it several times for treating the wastewater would be possible.
Moreover, according to the Figure 4.11 the amounts of dissolved iron that leached to
the solution was negligible about 0.5 mg/L at pH 7. 2.5 g/L 6 h ball milled catalyst
0
5
10
15
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
150 W
300 W
400 W
68
was used in each experiment. Hence, martite is an appropriate and stable catalyst to be
used in consecutive tests in sono-catalytic Fenton-like process.
Figure 4.19 AB92 removal efficiency with martite nanoparticles used in five
consecutive experimental runs. Catalyst dosage = 2.5g/L, [AB92]0 = 10
mg/L, ultrasonic power = 150 W, and pH = 7.
4.2.8 The effect of organic and inorganic salts
Most of the industrial wastewaters contain a variety of organic compounds and
inorganic salts. Inorganic salts include anions such as chlorides and sulfates. Most of
these ions is applied to adjust the pH of dye-bath and also improve the color stability.
As a result, wastewater from textile industry contains significant amounts of these ions
(Moumeni and Hamdaoui, 2012). These mineral ions that are derived from the
dissolution of salts in wastewater can reduce the dye removal because of two reasons.
On one hand, mineral ions occupy the catalyst surface and prevent the reaction
between catalyst surface and contaminant and reduce the performance of the catalyst.
On the other hand, they act as hydroxyl radicals scavenger. Accordingly, the removal
0
20
40
60
80
100
1 2 3 4 5
Rem
ov
al
effi
cien
cy (
%)
Number of cycles
69
efficiency of dye decreases (Khataee et al., 2015c). Experiments were done to
investigate the impact of scavengers on AB92 removal efficiency in heterogeneous
sono-Fenton-like systems only, since homogeneous sono-Fenton-like system already
exhibit much lower removal. For this purpose, NaCl and Na2SO4 were used as
inorganic scavengers and chloroform and ethanol were used as organic ones.
Sulfate and chloride are anions that is used in textile wastewaters functioning as the
hydroxyl radical scavengers produced radical species that have lower potential for
oxidizing the pollutants (Eqs. (4-6) and (4-7)). In addition, surface of the catalyst
would be occupied by the mentioned anions presented in the solution. In that case the
Fenton reaction would not occur. Therefore, as can be observed in Figure 4.20, the
removal efficiency decreased in the presence of these kinds of scavengers.
Cl− + •OH → •ClOH− (4-6)
SO42 − + •OH → SO4
• − + OH− (4-7)
Organic compounds including chloroform and ethanol had the same effect on AB92
removal (Figure 4.20) as a result of their scavenging effect on hydroxyl radicals (Eqs.
((4-8) and ((4-9)). Chloride ions and ethanol presented the least and greatest inhibition
influence on the AB92 removal efficiency, respectively (Figure 4.18).
•OH + CH3CH2OH → CH3•CHOH + H2O (4-8)
•OH + CHCl3 →•CCl3 + H2O (4-9)
70
Figure 4.20 Impact of scavengers on removal of AB92 in sono-catalytic process.
Operational conditions: [AB92]0 = 10 mg/L, [Martite] = 2.5 g/L, ultrasonic power =
150 W, pH = 7 and [Scavenger]0 = 10 mg/L.
Figure 4.21 shows that time in the presence of various scavengers, not only the removal
efficiency but also the rate of reaction is affected. The removal rate follows the pseudo-
first order kinetic. Also, coefficient of determination and kapp are calculated from the
plots in Figure 4.21 and given in Table 4.8. As can be observed, in the presence of
ethanol kapp reduced more than the other scavengers. Sodium chloride had the least
effect on kapp. Very low rates are observed by introducing Cl ̶ and SO4 2 ̶ ions to the
reaction medium containing the solution of AB92. The reduction in AB92 removal is
owing to the rapid reaction of the aforementioned anions with ●OH radicals and
production of other anions radicals with lower oxidation potential.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Rem
ov
al
effi
cien
cy (
%)
Time (min)
without scavenger
Sodium chloride
Chloroform
Sodium sulfate
Ethanol
71
Figure 4.21 Plot of pseudo-first order kinetic reaction rate constants for different
scavengers in heterogeneous sono-Fenton-like process.
Table 4.8 Impact of the scavengers on the apparent pseudo-first order reaction
constants toward removal of AB92.
Heterogeneous sono-Fenton-like process
Scavengers kapp (min-1) R2
Without scavenger 0.2048 0.9967
Sodium sulfate 0.0369 0.9697
Sodium chloride 0.1135 0.9352
Chloroform 0.0946 0.9143
Ethanol 0.0303 0.9598
0
5
10
0 10 20 30 40 50 60
ln (
A0/A
t)
Time (min)
Without scavenger
Na2SO3
Ethanol
NaCl
Chloroform
72
4.2.9 Intermediates generated in heterogeneous sono-Fenton-like system
Intermediates generated during the AB92 removal via heterogeneous sono-Fenton-like
process is studied by analyzing aqueous solution after 5 min reaction time. By-
products detected in the GC-MS apparatus were obtained under the operational
conditions of 20 mg/L initial concentration of dye, catalyst dosage of 2.5 g/L 6 hr
milled martite and ultrasonic power of 150W at reaction time of 5 min. Spectrum data
of the apparatus stored in NIST 98 Library was used to compare the spectra of mass
fragmentation presented by the GC-MS. Among diverse intermediates shown by the
apparatus, seven compounds were selected to be good match with peaks resulted from
the sample chromatogram. They are tabulated in Table 4.9. As explained earlier, sono-
catalytic process generates active radicals in the solution. Produced radicals bring
about oxidation and breaking dye molecule structure and then generation of different
by-products. In this study, it was not possible to propose a mechanism for the AB92
degradation. Initially, AB92 was dissociated through reactive ●OH with breakage in
azo bond resulting in the generation of aromatic compounds which are more oxidized
on the catalyst surface. Then, according to Table 4.9, main intermediates can be
perhaps related to loss of ̶ CHO groups, ̶ OH groups or C ̶ C bond connecting two
phenyl rings. It should be noted that GC-MS analysis cannot identify all by-products
generated during the AB92 removal because the AB92 is oxidized and different
aromatic and aliphatic compounds are generated. Compounds listed in Table 4.9
should be taken as samples of possible by-products during complete mineralization of
AB92.
73
Table 4.9 Identified intermediates during removal of the AB92 in sono-
Fenton-like system.
No. Compound Structure tr (min)
Main
fragments
(m/z)
1a Urea, N,N'-
bis(trimethylsilyl)-
O
NH2H2N
10.75 147(100%),
189 (63.56%),
73 (18.04%),
148 (15.23%),
190 (10.73%)
2 1,2-
Benzenedicarboxylic
acid, bis(2-
methylpropyl) ester
OO
O
O
23.72 149 (100%),
57 (14.92%),
150 (9.48%),
223 (9.01%)
3b 1,2-Benzenediol, 3,5-bis(1,1-
dimethylethyl)-
OHOH
21.93 207.10
(100%), 221.1
(58.7%), 193
(18.15%), 73
(18.14%),
4b Butylated hydroxytoluene
OH
18.02 251.1 (100%)
5b 5-Methyl-2-trimethylsilyloxy-
acetophenone
OHO
22.59 207.1 (100%),
208.1
(17.77%), 73
(11%),
6b Malonic acid
O O
OHHO
14 147 (100%),
73 (50.63%),
75 (32.04%)
7 5,6-dihydro-3-(methylthio)-4H-
cylopent[c]isothiazole
SN
S
5.60 171 (100%),
172 (17.15%)
a Value corresponding to the bis-trimethylsilyl derivative
b Value corresponding to the trimethylsilyl derivative
74
75
CHAPTER 5
CONCLUSION
5.1 Conclusions
In this research, martite nanoparticles was produced by applying high energy planetary
ball milling method. Physical and chemical characteristics of the nanoparticle was
investigated through XRD, FT-IR, SEM, EDX and BET analyses. Improvement in
catalytic activity was observed for the removal of AB92 at heterogeneous sono-
Fenton-like system using this ball milled nanocatalyst.
The specific results obtained in this study are:
The most efficient catalyst was martite samples mechanically ball milled for 6
h, which also had the highest surface area and active sites confirmed by BET
and SEM analyses, respectively.
The optimal operational conditions for removal of AB92 in heterogeneous
sono-Fenton-like process were found to be pH 7, catalyst dosage of 2.5 g/L,
concentration of AB92 10 mg/L, and ultrasonic power of 150 W during 30 min
of contact time. AB92 degradation efficiency of 100 % was seen under the
effect of these operational conditions.
In homogeneous sono-Fenton-like system optimum operational conditions was
10 mg/L of FeCl3.6H2O as catalyst, 10 mg/L of AB92 concentration, initial pH
of 3 and contact time of 60 min. A maximum of 53% AB92 removal could be
obtained under these conditions.
In both heterogeneous and homogeneous sono-Fenton-like processes, the
treatment process followed pseudo-first order kinetic.
76
The dye removal decreased in the presence of hydroxyl radical scavengers,
which in turn proved that the hydroxyl radicals had a negative role in the
treatment process during heterogeneous sono-Fenton-like process.
Seven byproducts could be identified by GC-MS analysis during
heterogeneous sono-Fenton-like process.
Significant advantages of using 6 h ball milled martite when compared to
homogeneous sono-Fenton-like processes are: (i) the catalyst can be reused in
repeated cycles; (ii) very low level of Fe is leached into the solution and it does
not necessitate secondary treatment; (iii) process is efficient at neutral pH.
The ultrasonic bath used in the homogeneous sono-Fenton-like experiments has
limited power and specifications. Therefore, the dye removal efficiencies obtained in
the homogeneous counterpart of this study may not be representative of the actual
efficiencies that can be obtained with homogeneous sono-Fenton-like process.
5.2 Recommendations for Future Studies
Since scavengers had a significant impact on removal efficiency, the
combination of the impact of anions such as Cl-, CH3COO-, HCO3-, SO3
2, SO42-
and NO3- on degradation of AB92 should further be investigated.
The color removal efficiency of this proposed sono-Fenton-like system for
wastewaters containing different kinds of organic dyes can be tested and
compared for heterogeneous and homogeneous system.
Impact of sonication power on homogeneous sono-Fenton-like process can be
investigated as it could not be performed in this study due to instrumental
limitations.
Testing of dye removal under optimum conditions with real textile wastewater
should be tested.
Usage of ultrasonic probe instead of ultrasonic bath can be investigated.
To scale-up the capacity of sono-Fenton treatment from a lab-scale to pilot or
full-scale can be investigated.
77
An overall evaluation of cost analysis and energy requirement together with
potential limitations of this system would be useful.
78
79
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