Studies on the behaviour of reactive dyes onto the …...Studies on the behaviour of reactive dyes...

INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 3, 2013

© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article ISSN 0976 – 4402

Received on September 2013 Published on November 2013 323

Studies on the behaviour of reactive dyes onto the cross-linked chitosan

using adsorption isotherms Deepika R, Venkateshprabhu. M, Pandimdevi. M

Department of Biotechnology, School of Bioengineering, SRM University, Kattankulathur

[email protected]

doi: 10.6088/ijes.2013040300010

ABSTRACT

The removal of textile reactive dyes in an aqueous media was studied by chitosan beads and

cross-linked chitosan beads. The chitosan beads were formed by dissolving in 0.3N acetic

acid and were cross-linked with 0.05M glutaraldehyde and 40% glyoxal. Their adsorption

capacity was evaluated by the removal of acid orange-10 and direct black-22 in the textile

wastewater. The effect of the parameters like biosorbent concentration, initial dye

concentration, contact time, temperature and pH were evaluated. The data for adsorption

isotherm was interpreted by the Langmuir equation and Langmuir constants was determined

for chitosan beads and cross- linked chitosan beads .The experimental data obtained for the

adsorption equilibrium from the chitosan beads and cross-linked chitosan beads were

correlated well with the Langmuir isotherm equation.

Keywords: Chitosan beads; cross-linked chitosan beads; glutaraldehyde; glyoxal; acid

orange-10; direct black-22; adsorption isotherm; Langmuir Isotherm.

1. Introduction

Water pollution is a common problem in worldwide due to economic and technological

development. Water pollution has become more and more serious especially regarding dyes.

Dyes mainly from dyeing industries, paper and pulp industries, textile industries, and many

other industries, have become serious threats to human beings and the aquatic ecosystem, due

to their toxicity and persistence after being released into the natural water. It was reported

that the textile wastewater contained a large variety of dyes and chemicals additions that

make the environmental challenge for textile industry not only as liquid waste but also in its

chemical composition (Venceslau et al., 1994). The main pollution in textile wastewater is

normally from dyeing and finishing processes. Large input of a wide range of chemicals and

dyestuffs, which generally are organic compounds of complex structure are used in these

processes. The textile materials does not adsorb all of them and the effluents caused disposal

problems. The major pollutants in textile wastewaters are high suspended solids, chemical

oxygen demand, heat, colour, acidity, and other soluble substances (Dae-Hee et al.,

1999).The removal of colour from textile industry and dyestuff manufacturing industry

wastewaters represents a major environmental concern. In addition, only 47% of 87 of

dyestuffs are biodegradable (Pagga and Brown, 1986).

1.1 Commonly used dyes

Dyes are divided into classes according to the types of fibers they are most compatible with.

The most notable are: acid dyes, premetalized acid dyes, chrome dyes (mordant dyes),

cationic dyes (basic dyes), direct dyes (substantive dyes), direct developed dyes, disperse

dyes, naphthol dyes, reactive dyes, sulfur dyes, and vat dyes (Price, Cohen, & Johnson, 2005).

Studies on the behaviour of reactive dyes onto the cross-linked chitosan using adsorption isotherms

Deepika R, Venkateshprabhu. M, Pandimdevi. M

International Journal of Environmental Sciences Volume 4 No.3, 2013 324

1.2 Acid Dyes

Acid dyes produce bright colors that have excellent fastness, or the ability of the dye to stay

on the fabric and not rub off or fade, to dry cleaning, but not necessarily to washing or light

and perspiration and have ionic interactions. Acid orange-10 is used in our studies.

Figure 1: Structure of Acid Orange – 10

1.3 Direct dyes

Direct dyes are used on cellulosic fibers and have excellent fastness to perspiration and dry

cleaning, but poor fastness to washing and varied light fastness and have intermolecular

forces. Direct black-22 is used in our studies.

Figure 2: Structure of Direct Black - 22

Some of the dyes are toxic and carcinogenic, use of these dye contaminated water without

any treatment may cause adverse effect on human health, domestic animals, wildlife and on

the environment. So it is necessary to treat or remove color from the wastewater before

discharge. Various treatment methods for removal of colour and dye are coagulation,

oxidation, flocculation, ozonation, biological treatment, adsorption and membrane processes.

Among these methods, adsorption method appears to offer the best prospect for overall

treatment of colour removal. Many adsorbents have been tested on the possibility to lower

dye concentrations from aqueous solutions, such as activated carbon(Mc Kay G, 1983, Allen

SJ, 1993), peat (Ramakrishna KR, Viraraghavan T,1997,Ho YS, McKay G, 1998), chitin

(McKay G, Blair HS, Gardner JR., 1983,Juang RS, Tseng RL, Wu FC, Lee SH. 1997), silica

(McKay G,1984), activated carbon (Tsai WT, Chang CY, Lin MC, Chien SF, Sun HF, Hsieh

MF., 2001).




Recently, chitosan which is the second largest biopolymer next to cellulose has been

observed for the high potentials of the adsorption of dyes (Yoshida H, Okamoto A, Kataoka

T., 1993, Wu FC, Tseng RL, Juang RS., 2000), metal ions (Guibal E, Milot C, Tobin

JM.,1998,Liu XD, Tokura S, Haruki M, Nishi N, Sakairi N.2002,Oshita K, Oshima M, Gao

Y, Lee K-H, Motomizu S.,2003), proteins (Zeng XF, Ruckenstein E.,1998, Benesch J,

Tengvall P.,2002) and others (Matsumoto M, Shimizu T, Kondo K.,2004,Strand SP, Varum

KM.,2003). The adsorption of reactive dyes in neutral solutions using chitosan showed large

adsorption capacities of 1000–1100 g/kg (Wu FC, Tseng RL, Juang RS., 2000).

Chitosan is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-

glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). Chitosan is

produced by deacetylation of chitin, which is the structural element in the exoskeleton of

crustaceans (such as crabs and shrimp) and cell walls of fungi.

Figure 3: Structure of Chitin

Figure 4: Structure of Chitosan

Shrimp shell waste materials were collected and shrimp shells were scraped free of loose

tissue, washed with cold water and dried in sun for 2 days, and then Chitin was extracted

from shrimp shell by the following steps: Demineralizations of shells, was done using 4%

HCl and suspended at room temperature in the ratio of 1:14(w/v). After 36 hours, the shells

were quite squashy and were rinsed with water to remove acid and calcium chloride. The

demineralized shells were then treated with 5% NaOH at 90°C for 24 hours with a solvent to

solid ratio of 12:1(v/w). The residue was then collected and washed to neutrality in running

tap water. Then it was dried in sun and the product is chitin. The preparation of Chitosan is

simply deacetylation of chitin. Removal of acetyl groups from the chitin was achieved by

using 70% NaOH solution with a solid to solvent ratio of 1:14 (w/v) at room temperature for

72 hours. The mixture was stirred after some times for homogenous reaction. The resulting

chitosan were washed to neutrality in running tap water and rinsed with distilled water. Then

filtered and dried in sun.

Several Methods have been used to modify raw chitosan flake either physical (McKay G,

1984, Aksu Z., 2001) or chemical modifications (Namasivayam C, Kavitha D.,2002). These




modifications were proposed in order to improve pore size, mechanical strength, and

chemical stability. Acid environments produce the partial dissolution of the polymer and to

make the polymer insoluble in acidic medium, modification by using cross- linking agents

used. Although cross-linking reduces the adsorption capacity but it enhance the resistance of

chitosan against acid, alkali and chemical (Robinson T, Chandran P, Nigam P.,2002). The

cross-linked chitosan also are very stable and maintain their strength even in acidic and basic

solutions (Namasivayam C, Kavitha D.,2002).These characteristics are very important for a

adsorbent so that it can be used in a lower pH environment. Cross-linking also can change the

crystalline nature of chitosan and enhance adsorption abilities (Annadurai G, Juang RS, Lee

DJ., 2002).

2. Materials and methods

Chitosan powder and reactive dyes, acid orange-10 and direct black-22 were commercially

purchased and the reagent namely sodium tri poly phosphate (TPP), glutaraldehyde, glyoxal,

hydrochloric acid, sodium hydroxide were purchased from Southern Indian Chemical

industries.

2.1 Preparation of chitosan Beads

3 grams of chitosan were dissolved 100ml of 0.3N acetic acid solution. Using a magnetic

stirrer it was stirred till a highly viscous solution was obtained. Chitosan solution was

dropped using syringe from a height of 20cm3 into the 1% TPP aqueous solution and the

beads were formed (Tapan Kumar Saha, Nikhil Chandra Bhoumik, Subarna Karmaker,

Mahmooda Ghani Ahmed, Hideki Ichikawa, Yoshinobu Fukumori, 2010), and the stability of

the beads were checked.

2.2 Preparation of cross-linked chitosan beads

The chitosan beads prepared were washed with deionized water and two different cross-

linking agents were used to modify chitosan at a ratio of 1 : 1 (chitosan: cross-linking agent),

they were suspended in 0.05 M glutaraldehyde and 40% glyoxal and were left standing for 24

hours and then the cross-linked chitosan beads were washed with distilled water and filtered

(W.S . WanNgah, C.S. Endud, R. Mayanar, 2002).

1.3 Effect of biosorbent concentration

10mg/L of the dye concentration at pH 7 and temperature 32oC were standardized. Varying

biosorbent concentration from 1g/L to 5g/L was prepared and 100mL of the cross-linkers was

taken for each biosorbent concentration, then they were kept in a shaker at 200 rpm. Finally

O.D at 477nm for acid orange-10 and at 484nm for direct black-22 was measured using UV-

Vis spectrophotometer for 0th time and different time interval.

1.4 Effect of dye concentration

1g/L of the biosorbent concentration at pH 7 and temperature 32oC were standardized. Dye

concentration from 10mg/L to 50mg/L was prepared and 100mL of the cross-linkers was

taken for each initial dye concentration. They were kept in a shaker at 200 rpm, and the

optical density at 477nm for acid orange-10 and at 484nm for direct black-22 was measured

using UV-Vis spectrophotometer for 0th time and different time interval.




1.5 Effect of temperature

1g/L of the biosorbent concentration and 10mg/l of dye concentration at pH 7 and

temperature 32oC were standardized. Temperature was varied from 30oC to 70oC. 100mL of

the cross-linkers was taken and was standardized. They were kept in a shaker at 200 rpm. The

O.D at 477nm for acid orange-10 and at 484nm for direct black-22 was measured using UV-

Vis spectrophotometer for 0th time and different time interval.

1.6 Effect of pH

1g/l of the biosorbent concentration and 10mg/l of dye concentration at temperature 32oC

were standardized. pH was adjusted using 1N HCl and 1N NaOH and then was varied from 2

to 9. 100mL of the cross-linkers was taken and was standardized. They were kept in a shaker

at 200 rpm. The O.D at 477nm for acid orange-10 and at 484nm for direct black-22 was

measured using UV-Vis spectrophotometer for 0th time and different time interval.

3. Results and discussions

Parameters like biosorbent concentration, dye concentration, temperature, pH were selected

at constant agitation speed to conduct experiment on the reduction of acid orange-10 and

direct dye-22 dye in textile waste water.

3.1 % Removal

a) The % Removal of the reactive dye was calculated using the formula:

% Removal = Co – Cr *100

Co

Where, Co = Initial concentration

Cr = Residual concentration

b) Using the above formula % removal was found and was tabulated.

c) A graph was drawn between time and % removal.

3.2 Effect of biosorbent concentration

Table 1 and Table 2 indicates that the optimum biosorbent concentration is attained at 1 g/L

for both acid orange-10 and direct black-22 of chitosan which can also be inferred from

Figure 6 and Figure 7.

Table 1: Effect of acid orange -10 on chitosan biosorbent

Conc.

(g/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

1440

(mins)

2880

(mins)

1 48.67 56.45 58.31 59.97 63.29 63.46

2 51.01 63.30 63.64 66.66 68.69 68.86

3 58.60 68.95 69.12 70.95 77.63 77.96

4 56.11 66.02 66.19 67.79 71.68 71.86

5 62.95 76.12 76.43 77.21 78.76 79.06




Figure 6: Effect of biosorbent concentration on the removal of acid orange - 10

Table 2: Effect of direct black -22 on chitosan biosorbent

Conc.

(g/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

1440

(mins)

2880

(mins)

1 28.24 41.18 49.41 54.12 62.35 62.35

2 26.83 36.59 40.24 45.12 85.37 85.37

3 24.68 31.17 49.35 53.25 84.42 84.42

4 23.96 60.00 60.42 60.50 80.21 81.25

5 27.78 45.56 60.00 65.56 74.44 74.44

Figure 7: Effect of biosorbent concentration on the removal of direct black-22

It also shows that equilibrium is attained at 4 g/L for Acid orange and 5 g/L for Direct black

of chitosan-glutaraldehyde from Table 3 and Table 4 which is also observed from the Figure

8 and Figure 9.




Table 3: Effect of acid orange -10 on cross-linked chitosan-glutaraldehyde biosorbent

Conc.

(g/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

1 9.74 12.82 12.31 12.56

2 4.26 7.02 7.27 7.52

3 1.91 4.09 4.91 4.91

4 4.24 4.78 5.37 5.37

5 4.12 5.93 6.44 6.96

Figure 8: Effect of % removal of acid orange-10 by cross-linked chitosan glutaraldehyde

Table 4: Effect of direct black -22 on the cross-linked chitosan-glutaraldehyde biosorbent

Conc.

(g/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

1 15.63 25 27.08 28.13

2 10.31 14.43 16.50 17.53

3 13.33 16.67 17.78 17.78

4 37.37 40.40 44.44 45.46

5 44.57 48.91 52.17 52.17

Figure 9: Effect of % removal of direct black-22 by cross-linked chitosan-glutaraldehyde




It is seen from Table 5 and Table 6 that acid orange-10 and direct black-22 attains

equilibrium at 3 g/L of chitosan-glyoxal which can also be compared in Figure 10 and Figure

11.

Table 5: Effect of acid orange-10 on cross-linked chitosan-glyoxal biosorbent

Conc.

(g/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

1 6.00 6.87 7.97 8.51

2 3.97 5.46 5.71 5.71

3 3.73 4.52 4.79 5.05

4 6.03 7.54 8.04 8.04

5 6.94 8.74 9.25 9.51

Figure 10: Effect of % removal of acid orange-10 by cross-linked chitosan-glyoxal

Table 6: Effect of direct black-22 dye on the cross-linked chitosan-glyoxal biosorbent

Conc.

(g/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

1 7.96 12.50 14.77 14.77

2 4.60 6.90 9.20 10.35

3 9.41 11.77 14.12 14.12

4 6.38 12.77 15.96 15.96

5 9.38 15.39 17.58 18.68




Figure 11: Effect of % removal of direct black-22 by cross-linked chitosan-glyoxal

3.3 Effect of dye concentration

Table 7 and Table 8 data shows that the optimum initial dye concentration of chitosan is 30

mg/L for acid orange-10 and 20 mg/L for direct black-22 which can also be concluded from

the Figure 12 and Figure 13.

Table 7: Effect of acid orange-10 dye on chitosan

Conc.

(mg/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

10 31.54 43.15 43.57 43.98

20 38.61 46.69 47.01 47.17

30 43.96 50.55 50.77 50.99

40 9.62 12.41 12.76 13.11

50 45.33 49.69 50.00 50.16

Figure 12: Effect of dye concentration on the removal of acid orange-10 by chitosan




Table 8: Effect of direct black-22 dye on chitosan

Conc.

(mg/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

10 4.76 6.35 7.41 7.94

20 1.80 5.76 6.47 6.47

30 2.84 6.03 6.38 6.74

40 5.30 12.88 13.64 14.39

50 6.42 9.17 10.09 10.09

Figure 13: Effect of dye concentration on the removal of direct black-22 by chitosan

From Table 9 and Table 10 equilibrium is attained at 20 mg/L for acid orange-10 and direct

black-22 of chitosan-glutaraldehyde which is observed from the Figure 14 and Figure 15.

Table 9: Effect of acid orange-10 dye on the cross-linked chitosan-glutaraldehyde

Conc.

(mg/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

10 3.35 4.64 5.16 5.41

20 1.79 2.55 3.06 3.06

30 3.69 4.42 4.67 4.91

40 2.15 3.34 3.82 4.06

50 1.14 2.35 2.82 2.82




Figure 14: Effect of dye concentration on the removal of acid orange-10 by cross-linked

chitosan-glutaraldehyde

Table 10: Effect of direct black-22 dye on the cross-linked chitosan-glutaraldehyde

Conc.

(mg/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

10 4.35 13.04 15.22 16.30

20 8.08 14.14 17.17 19.19

30 6.42 12.84 15.60 17.43

40 6.78 11.02 15.25 15.25

50 4.80 10.40 12.00 12.80

Figure 15: Effect of dye concentration on the removal of direct black-22 by cross-linked

chitosan-glutaraldehyde.




Table 11 and Table 12 indicate equilibrium is attained at 30mg/L for acid orange-10 and

direct black-22 of chitosan-glyoxal which can also be seen from the Figure 16 and Figure 17.

Table 11: Effect of acid orange-10 dye on the cross-linked chitosan-glyoxal

Conc.

(mg/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

10 3.90 5.29 6.69 6.96

20 1.37 2.74 3.84 4.11

30 2.11 2.64 2.90 3.17

40 1.56 3.38 3.90 3.90

50 1.79 3.32 4.34 4.59

Figure 16: Effect of dye concentration on the removal of acid orange-10 by cross-linked

chitosan-glyoxal

Table 12: Effect of direct black-22 dye on cross-linked chitosan-glyoxal

Conc.

(mg/L)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

10 16.47 23.53 27.06 29.41

20 14.74 16.84 20.00 21.05

30 8.26 11.00 13.76 13.76

40 6.78 11.02 14.41 15.25

50 5.60 12.00 12.80 12.80




Figure 17: Effect of dye concentration on the removal of Direct Black-22 by cross-linked

Chitosan–Glyoxal

3.4 Effect of temperature

Table 13 and Table 14 shows the optimum temperature of chitosan was 40°C for acid orange-

10 and 50°C for direct black-22 which is confirmed from the Figure 18 and Figure 19.

Table 13: Effect of temperature on the adsorption of acid orange-10 on chitosan

Temperature

(°C)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

30 27.36 29.85 30.35 30.35

40 25.41 27.03 27.57 28.11

50 3.19 6.91 8.51 8.51

60 3.87 4.97 6.08 6.63

70 9.52 11.91 12.86 13.33

Figure 18: Effect of temperature on the removal of acid orange-10 by chitosan




Table 14: Effect of temperature on the adsorption of direct black-22 on chitosan

Temperature

(°C)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

30 12.20 14.63 15.85 17.07

40 9.38 15.63 18.75 18.75

50 19.44 30.56 38.89 38.89

60 15.52 27.59 32.76 34.48

70 15.00 30.00 37.50 37.50

Figure 19: Effect of temperature on the removal of direct black-22 by chitosan

Table 15 and Table 16 presents results that the equilibrium is attained at 70°C for acid

orange-10 and direct black-22 of chitosan-glutaraldehyde which is also confirmed from the

Figure 20 and Figure 21.

Table 15: Effect of temperature on the adsorption of acid orange-10 on cross-linked

chitosan-glutaraldehyde

Temperature

(°C)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

30 1.65 4.96 8.68 8.68

40 5.70 47.80 51.75 51.75

50 3.81 46.67 48.57 49.05

60 43.00 46.00 49.50 49.50

70 6.78 14.41 19.49 20.34




0

10

20

30

40

50

60

30 60 120 180% D

ye

Rem

ova

l 30°C

40°C

50°C

60°C

70°C

Time (mins)

Figure 20: Effect of temperature on the removal of acid orange-10 by cross-linked chitosan-

glutaraldehyde

Table 16: Effect of temperature on the adsorption of direct black-22 on chitosan-glyoxal

Temperature

(°C)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

30 3.68 8.09 11.77 11.77

40 4.17 9.72 11.11 11.81

50 1.65 7.44 9.92 10.74

60 5.00 19.00 22.00 22.00

70 6.59 12.09 13.19 14.29

0

5

10

15

20

25

30 60 120 180

% D

ye

Rem

oval

30°C

40°C

50°C

60°C

70°C

Time (mins)

Figure 21: Effect of temperature on the removal of direct black-22 by cross-linked chitosan-

glutaraldehyde

Table 17 and Table 18 shows equilibrium is at70°C, 60°C for acid orange-10 and direct

black-22 respectively of chitosan-glyoxal which can also be inferred from the Figure 22 and

Figure 23.




Table 17: Effect of temperature on the adsorption of acid orange-10 on chitosan-glyoxal

Temperature

(°C)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

30 6.86 11.77 13.73 14.71

40 5.56 11.11 16.67 17.78

50 3.66 9.76 14.63 14.63

60 8.45 15.49 19.72 21.13

70 7.69 15.39 16.72 16.72

0

5

10

15

20

25

30 60 120 180

% D

ye

Rem

ova

l

30°C

40°C

50°C

60°C

70°C

Time (mins)

Figure 22: Effect of temperature on the removal of acid orange-10 by cross-linked chitosan-

glyoxal

Table 18: Effect of temperature on the adsorption of direct black-22 on cross-linked

chitosan-glyoxal

Temperature

(°C)

30

(mins)

60

(mins)

120

(mins)

180

(mins)

30 9.43 22.64 24.53 24.53

40 14.58 20.83 27.08 31.25

50 11.29 17.74 20.97 20.97

60 18.42 26.32 31.58 34.21

70 47.62 57.14 76.19 80.95




0102030405060708090

30 60 120 180

% D

ye

Rem

oval

30°C

40°C

Time (mins)

Figure 23: Effect of temperature on the removal of direct black-22 by cross-linked chitosan-

glyoxal

3.5 Effect of pH

Table 19 and Table 20 depicts that the optimum pH value is 3pH and 4pH for acid orange-10

and direct black-22 respectively of chitosan which can also be inferred from the Figure 24

and Figure 25.

Table 19: Effect of pH on the adsorption of acid orange-10 on Chitosan

pH 30

(mins)

60

(mins)

120

(mins)

180

(mins)

2 6.25 16.35 18.27 18.75

3 7.41 13.23 14.81 14.81

4 8.57 13.88 18.78 19.18

5 2.97 11.44 15.25 15.25

6 5.20 13.60 19.60 20.00

7 8.91 16.19 21.05 21.46

8 10.97 13.08 18.99 18.99

9 7.19 19.42 21.22 21.58

Figure 24: Effect of pH on the removal of acid orange-10 by chitosan




Table 20: Effect of pH on the adsorption of direct black-22 on chitosan

pH 30

(mins)

60

(mins)

120

(mins)

180

(mins)

2 4.46 15.29 17.83 18.47

3 3.43 11.43 17.71 18.29

4 5.00 12.00 19.00 19.00

5 2.61 12.00 21.57 22.22

6 6.02 15.04 24.81 24.81

7 4.55 14.55 24.55 25.46

8 5.36 11.90 20.24 20.83

9 5.35 11.23 17.65 17.65

Figure 25: Effect of pH on the removal of direct black-22 by chitosan

Table 21 and Table 22 data confirms that equilibrium is attained at 8pH for acid orange-10

and 6pH for direct black-22 of chitosan-glutaraldehyde which is also seen from the Figure 26

and Figure 27.

Table 21: Effect of pH on the adsorption of acid orange-10 on chitosan-glutaraldehyde

pH 30

(mins)

60

(mins)

120

(mins)

180

(mins)

2 1.25 4.15 5.81 5.81

3 1.67 3.77 4.60 5.02

4 1.79 4.02 5.36 5.36

5 3.23 5.53 7.37 7.83

6 2.04 4.08 5.31 5.31

7 2.16 3.88 5.17 5.60

8 3.83 5.74 6.70 6.70

9 1.49 5.47 6.97 7.46




Figure 26: Effect of pH on the removal of acid orange-10 by cross-linked chitosan-

glutaraldehyde

Table 22: Effect of pH on the adsorption of direct black-22 on chitosan-glutaraldehyde

pH 30

(mins)

60

(mins)

120

(mins)

180

(mins)

2 2.30 5.17 8.05 8.05

3 3.73 6.83 8.70 9.32

4 3.25 5.84 7.79 8.44

5 3.82 6.37 7.64 7.64

6 3.45 5.00 6.21 6.21

7 5.30 9.09 11.36 12.12

8 4.96 9.09 10.74 10.74

9 7.56 10.08 14.29 15.13

Figure 27: Effect of pH on the removal of direct black-22 by cross-linked chitosan-

glutaraldehyde

Table 23 and Table 24 indicate equilibrium is attained at 4pH, 3pH for acid orange-10 and

direct black-22 respectively of chitosan-glyoxal which can also be seen from the Figure 28

and Figure 29.




Table 23: Effect of pH on the adsorption of acid orange-10 on chitosan-glyoxal

pH 30

(mins)

60

(mins)

120

(mins)

180

(mins)

2 2.10 5.59 7.69 8.39

3 2.17 5.80 7.97 7.97

4 2.07 4.83 6.90 6.90

5 5.30 9.09 12.12 12.88

6 3.97 6.35 11.11 11.11

7 1.64 4.10 6.56 7.38

8 1.74 4.35 6.09 6.09

9 2.73 6.36 8.18 8.18

Figure 28: Effect of pH on the removal of acid orange-10 by cross-linked chitosan-glyoxal

Table 24: Effect of pH on the adsorption of direct black-22 on cross-linked chitosan-glyoxal

pH 30

(mins)

60

(mins)

120

(mins)

180

(mins)

2 2.06 7.23 11.34 11.34

3 2.17 5.44 10.87 10.87

4 4.94 8.64 13.58 14.82

5 5.33 9.33 13.33 14.67

6 6.25 9.38 14.06 14.06

7 2.78 9.72 15.28 16.67

8 5.17 12.07 17.24 17.24

9 9.09 18.18 29.55 29.55




Figure 29: Effect of pH on the removal of direct black-22 by cross-linked chitosan-glyoxal

3.6 Langmuir isotherm

a) It is represented as:

Where, Ce = Equilibrium concentration of dye solution

qe= Metal ion adsorbed (mg/g)

b, qmax = Langmuir constants

The adsorption of the reactive dyes onto the chitosan beads and cross-linked chitosan beads

showed a contact time of 60 minutes. Figure 30 and Figure 31 shows adsorption equilibrium

data fitted much better to Langmuir isotherm, where in both acid orange-10 and direct black-

22 reactive dyes, the chitosan-glyoxal cross-linked beads showed better adsorption of the

reactive dyes when compared to the chitosan and chitosan-glutaraldehyde cross-linked beads,

though cross-linked chitosan beads have the advantage that they can be used in a low pH

(acidic) solution, where chitosan beads dissolve.

Table 25: Langmuir isotherm of acid orange-10-Chitosan

Initial dye concⁿ

(Co) mg/l

Final dye concⁿ

(Ce) mg/l

qe=(Co-Ce) V ̸ W

(mg/g) Ce/qe

5 2 3 0.7

10 7.1 2.9 2.45

15 11.5 3.5 3.29

20 17.9 2.1 8.5

25 22.6 2.4 9.4

30 27.7 2.3 12.04

35 32.7 2.3 14.2

40 37.6 2.4 15.67

45 42.1 2.9 14.52

50 47.8 2.2 21.73

Ce= 1 * Ce + 1

qe qmax b.qmax




R2 = 0.959

Figure 30: Adsorption isotherm of acid orange-10 by chitosan

Table 26: Langmuir isotherm of direct black-22-Chitosan

Initial dye concⁿ

(Co) mg/l

Final dye concⁿ

(Ce) mg/l

qe=(Co-Ce) V / W

(mg/g) Ce/qe

5 2.8 2.2 1.27

10 8.4 1.6 5.25

15 13.4 1.6 8.38

20 18.68 1.52 15.67

25 23.9 1.1 21.7

30 28.7 1.3 22.07

35 33.5 1.5 22.33

40 38.7 1.3 22.76

45 43.9 1.1 39.9

50 48.9 1.1 44.46

R2= 0.9169

Figure 31: Langmuir isotherm of direct black-22 by chitosan




Table 27: Langmuir isotherm of acid orange-10-cross-linked chitosan-glutaraldehyde

Initial dye concⁿ

(Co) mg/l

Final dye concⁿ

(Ce) mg/l

qe=(Co-Ce) V / W

(mg/g) Ce/qe

5 3 2 1.5

10 7.5 2.5 3

15 12 3 4

20 18 2 9

25 22.8 2.2 10.4

30 28 2 19

35 33 2 16.5

40 37.6 2.4 15.7

45 42 3 14

50 48 2 24

R2= 0.8461

Figure 32: Langmuir isotherm of acid orange-10 by cross-linked chitosan-glutaraldehyde

Table 28: Langmuir isotherm of direct black-22-cross-linked chitosan-glutaraldehyde

Initial dye concⁿ

(Co) mg/l

Final dye concⁿ

(Ce) mg/l

qe=(Co-Ce) V / W

(mg/g) Ce/qe

5 3 2 1.5

10 8.7 1.3 6.7

15 13.5 1.5 9

20 18 2 9

25 23.8 1.2 19.8

30 28 2 19

35 33 2 16.5

40 38.8 1.2 32.3

45 43.5 1.5 29

50 48.5 1.5 32.3




R2= 0.9132

Figure 33: Langmuir isotherm of direct black-22 by cross-linked chitosan-glutaraldehyde

Table 29: Langmuir isotherm of acid orange-10-cross-linked chitosan-glyoxal

Initial dye concⁿ

(Co) mg/l

Final dye concⁿ

(Ce) mg/l

qe=(Co-Ce) V / W

(mg/g) Ce/qe

5 3.5 1 2.3

10 8 1.5 4

15 12.5 2 5

20 18.2 1 10.1

25 23 1.5 11.5

30 28.3 1 16.7

35 33.5 1 22.3

40 38 1.5 19

45 43 1.5 21.5

50 48.5 1 32.3

R2= 0.937

Figure 34: Langmuir isotherm of acid orange-10 by cross-linked chitosan-glyoxal




Table 30: Langmuir isotherm of direct black-22-cross-linked chitosan-glyoxal

Initial dye concⁿ

(Co) mg/l

Final dye concⁿ

(Ce) mg/l

qe=(Co-Ce) V / W

(mg/g) Ce/qe

5 4 1 4

10 8.5 1.5 5.7

15 13 2 6.5

20 19 1 19

25 23.5 1.5 15.7

30 29 1 29

35 34 1 34

40 38.5 1.5 25.7

45 43.5 1.5 29

50 49 1 49

R2= 0.8618

Figure 35: Langmuir isotherm of direct black – 22 by cross-linked chitosan-glyoxal

3.7 Comparative Studies

Figure 36: Comparison of Langmuir isotherm: Acid orange-10




Figure 37: Comparison of Langmuir isotherm: Direct black – 22

5. Conclusion

The percentage removal of dyes, acid orange-10 and direct black-22 were controlled by

factors affecting adsorption capacity such as biosorbent concentration, dye concentration,

contact time, pH, temperature. From this study it was concluded using Langmuir isotherm

that the cross-linked chitosan with glyoxal showed good adsorption capacity of dyes when

compared to the cross-linked chitosan with glutaraldehyde and non-cross-linked chitosan, and

the cross-linked chitosan have the advantage that they can be used in low pH (acidic) solution

where-in non-cross-linked chitosan beads dissolve. The highest percentage removal of Acid

orange-10 was achieved at pH 4, in contact time of 60 minutes, by biosorbent dose of 3g/L of

30mg/L dye concentration, whereas the highest percentage removal of Direct black-22 was

achieved at pH 3 in contact time of 60 minutes by biosorbent dose of 3g/L of 30mg/L dye

concentration, thus the decrease in efficiency was not due to deactivation of binding sites but

due to loss of adsorbent mass during desorption process.

Acknowledgment

The authors would like to thank SRM University, Kattankulathur for providing experimental

facilities and also take the immense pleasure to thank the staff and technicians for their

guidance for the completion of this study.

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