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Preparation of electrospinning polystyrene nanofibrous membrame and
nanofiltration for simulated dyeing wastewater
Zuoyi Yang 1, a, Xunan Ning 1, b, Han Wang 1, c Jingyong Liu 1, d 1Faculty of Environmental Science and Engineering, Guangdong University of Technology,
Guangzhou, Guangdong, 510006
[email protected] ,
b Corresponding author: [email protected] ,
[email protected]
[email protected]
Key words: electrospinning, polystyrene, nanofiltration, simulated dyeing wastewater
Abstract. In this thesis, polystyrene nanomembranes made by electrospinning technique were
utilized to deal with Cu2+
(5mg/l), Cr6+
(5mg/l) and methylene blue (10mg/l) contained in simulated
dyeing wastewater. Polystyrene liquor (8% (m/m), dissolved in chloroform) was electrospun and
processed nanofibrous membrane; the nanofiber diameter was 250nm~15µm; the detected pore size
was 3nm~0.5µm and the membrane thickness was 170µm. A plate membrane system was used to test
nanofiltration characteristics of pollutants (Cu2+
, Cr6+
and methylene blue). The experiment showed
that the interception rates were above 91%, and the water flux was about 5.8-15.4ml/ (cm2⋅ h).
Introduction
Nanofiltration (NF) was introduced in the late 1980s, it was defined as “a process intermediate
between reverse osmosis (RO) and ultrafiltration (UF) that rejects molecules which have a size in the
order of one nanometer”[1]. Excellent organic nanofiltration membrane and cheap inorganic
membrane were popular in the treatment of dyeing effluents. Traditional fabricating procedure of
nanofiltration membrane included confecting and strickling liquors, vaporizing, waterlogging and
heat-treating etc. These techniques are not only grievously polluting and difficult to control hole size,
but also prolix, complex and material-consuming. Nowadays, nanofiltration membrane of different
apertues can be gotten by controlling the electrospun techniques, which can get ultrafine fibres thin to
1 nm diameter.
In 2003, Zheng-Ming Huang summarized 44 polymers electrospun in solvent solution and 6
polymers electrospun in melt form [2]. Polystyrene (PS) fibers of different molecular weights have
been reported by electrospinning, mostly in solvent solution of tetrahydrofuran or dimethylformamide.
For example, Minsung Kang compared superhydrophobic characters of polystyrene membranes made
by electrospinning in the solvent of N, N-dimethylformamide (DMF) (non-volatile solvent) with PS
membrane of tetrahydrofuran (volatile solvent) [3]. However, few dyeing wastewater have been
reported to be treated by ultrafiltration or nanofiltration of PS membrane.
During these years, nanofiltration (NF) has emerged in wastewater treatment, sometimes
cooperated with reverse osmosis (RO) and ultrafiltration (UF). In 1988, Erswell began to deal with
reactive dye liquors by nanofiltration membrane, but the membrane permeate efficiency was just
30 l/m2·h in the pressure of 4 MPa [4]. Chen used ATF50 nanofiltration membrane to deal with two
brown colored wastewaters of chemical oxygen demand (COD) 14200mg/L, pH 10.2, and pH 5.5,
COD 5430mg/L, the results showed that COD 14200mg/L decreased 95%, and COD 5430mg/L
reduced 80-85%, the quality of the permeate was all above the discharge standard for foul sewer in
Hong Kong [5]. Wang separated Fe2+
, Mn2+
, Zn2+
, Al3+
contained in sulfuric acid waste liquid by
2540 nonomembrane experimental equipment. When the operation pressure was 2 MPa, the ratio of
thin liquid to dope was 2, the mass fractions of sulfuric acid was 10%, all the retention rates of the four
metallic ions achieved above 96% [6].
Water scarcity and more stringent legislation make water reuse in dye related industries become
more important. There are different deleterious materials in the dye ing wastewater, such as dyes,
clear reagents, antibiotics, grease, sulfide, heavy mentals and inorganical salts, nanofiltration can be
Applied Mechanics and Materials Vols. 55-57 (2011) pp 1554-1559Online available since 2011/May/03 at www.scientific.net© (2011) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.55-57.1554
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used to deal with the deleterious materials. Low molecular weight organic compounds
(200~1000g/mol), divalent ions and large monovalent ions such as hydrolyzed reactive dyes can be
effectively rejected by nanofiltration process, which shows great potential for the direct reuse of such
wastewaters. In this study, Polystyrene of 100, 000g/mol was dissolved with chloroform and
nanofiltration membranes were made by electrospinning, and simulated dyeing waste water was
treated with the PS membranes to check its availability in the resue of dyeing waste water.
Experiment
Membrane preparation
Polystyrene (Shanghai, Jing Chun Chemical Reagent Co., 100, 000g/mol) was mixed with
chloroform and its concentration was 8~16 wt%. After sufficiently dissolved at rest for 24h, the
solution was stirred at room temperature for 30 minutes and was preserved hermetically to prevent
chloroform from volatilization. Fig. 1 shows such process and related machines. A syringe pump was
utilized to supply a constant flow of 100µl/h polymer solution during electrospinning. The distance
between needle and collector was 15cm. The voltage of 10 kV was applied to draw the nanofibers
with the prepared solution [7].
Wastewater filtration Test
The simulated dyeing waste water was confected with CuSO4 (5mg/l), K2Cr2O7 (5mg/l) and
methylene blue (Molecular Weight 352, 10mg/l), pH 7.1. The waste water was treated at cross-flow
velocity by a wiggly pump (BT-100E/153Y) in a plate module configuration, The diameters of the
membrane and frame module were 10cm, and the ambient temperature was 35℃. Cu2+
and Cr6+
were
detected by inductively-coupled plasma atomic emission spectrometry (AAS, Z-2000, Hitachi) , the
instrumental condition of AAS(WFX210) was listed in Table 1. Methylene blue were detected by
colorimetry. All the data were the average of two detections.
Flux and intercepting rate
The intercepting rate (R) was defined as: %R= 1-CP/CR, where CP, CR are the concentrations of
permeating effluent and retentate (mg/L), respectively. Flux (J) is volume of permeate (V) collected
per unit membrane area (A) per unit time (t); flux is related directly to driving force and total
resistance offered by the membrane as well as the interfacial region adjacent to it, which is calculated
as: J =V/(At) [8].
Fig. 1 Schematic diagram of electrospinning and related machines.
Fig. 2 Flow chart of wastewater by nanofiltration process..
Table 1 Instrument condition of AAS(WFX210)
Ele-
ment
Wavelengh
/nm
Slit
/nm
Lamp
Current
/mA
Burner
height
/mm
Air
pressure
/mPa
Acetylene
pressure
/mPa
Air
flow
/L·min-1
Acetylene
flow rate
/L·min-1
Cu 357.9 0.4 3.0 8 0.3 0.09 7.0 2.5
Cr 324.7 0.4 3.0 6 0.3 0.09 7.0 1.0
Applied Mechanics and Materials Vols. 55-57 1555
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Results and discussions
Electrospinning conditions and configuration of polystyrene nanofibrous membrane
In the electrospinning process, the fiber diameters change with the voltage. When the liquid droplet
is affected by larger voltage, the field force will become larger. The surface tension of the liquid
droplet can be easily overcome and divided into smaller droplets, and the corresponding smaller fiber
diameter was processed. The accepted distance of the fiber and the solvent concentration both affect
the fiber’s diameter. The small accepted distance can bring high field force and get thin fibres if the
voltage is fixed. To get thinner fiber, polystyrene concentration should be small, and the
electrospinning fluidity can be enhanced with the decreasing of the viscosity.
Electrospinning nanofibers and membrane can be generally characterized by scanning electron
micrographs (SEMS). Fig. 3 shows the configuration of PS nanofibrous membrane. At the same time,
we can get some important information of PS nanofibrous membrane from Table 2. The fiber
diameter of PS nanofibrous membrane is 250nm~15µm, and picture statistic calculation shows the
detected pore size is 3nm~0.5µm. The membrane thickness is 170 µm, thinner than 400 µm of
Polyvinyl Alcohol (PVA) membrane which was made in our initial experiment [7].
Table 2 Process conditions and polystyrene membrane properties
Conditions Membrane properties
Polymer concentration 8-16 wt% Fiber diameter 250nm~15µm
Spinneret inside
diameter
230 µm Detected pore size 3nm~0.5µm
Tip-collector distance 15 cm Membrane thickness 170 µm
Air pressure 101.3 kPa
Flow-rate 100 µl/h
Humidity 75%
4000× 6000×
8000× 10000×
Fig. 3 Configuration of membrane electrospun by 8% PS solution
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Experiment of the PS solution concentration
In this study, polystyrene was dissolved in chloroform and confected to 8%~16%. 250nm~15µm
polystyrene nano-fibres were made by electrospinning because of the excellent electrical and
michanica characteristics of PS. Electrospinning fiber diameter was added with the PS concentration
of the solution. As the PS concentration increased, larger electric field strength was needed to
overcome the surface tension of droplets. Because the droplets became more difficult to split into
thiner trickle, the diameter of the fibers increased. At the same time, the viscosity of the polymer
solution also increased with polystyrene concentration and increased the electrospinning nozzle
because of the decreasing mobility.
The intercepting effects of different electrospinning membranes made by PS concentration(8%,
10%, 12%, 16%) were compared to obtain appropriate concentration. Fig. 4 shows the intercepting
rate of different membrane to the simulated dyeing waste water (Cu 5 mg/l, Cr 5 mg/l, Methylene
blue10 mg/l) after filtrating for 120min. It shows that membrane made by 8% PS can effectly interrupt
98.6% Cu, 98.0% Cr and 97.3% methylene blue. As the PS concentration increased from 8% to 16%,
the interrupting rate of Cu, Cr and methylene blue decreased but remained above 91%. Considering
that the membrane should have enough intension, thickness and water flux, 8% PS was chosen to
research the properties in the resue of the dyeing waste water.
0.9
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
6% 8% 10% 12% 14% 16% 18%
Polystyrene concentration
Interceptting rate(%)
Cu(5mg/L) Cr(5mg/L) Methylene blue （10mg/L)
Fig.4 Intercepting ratio of Cu
2+, Cr
6+ and methylene blue at different PS concentrations
Water flux and intercepting ratio of PS nanomembrane
The permeate separation efficiency was monitored by measuring the intercepting efficiency of Cu2+
,
Cr6+
and Methylene blue. The detected membrane pore size was 3nm~0.5µm, the thickness was
170µm and the wiggly pump speed was 20rpm. Table 3 showed that the water flux of PS
nanomembrane was 5.8~15.4ml/(cm2⋅ h). the water flux were decreasing in 4h. The PS
nonomembrane can effectively intercepte methylene blue, methylene blue( MW 352) can be
interrupted because of the pore size range, the intercepting rate increased from 92.1% to 99.9%. At
the same time, the water flux decreased gradually because of the jam of the dye molecules.
It is electronegative in the polystyrene nanofibrous membrame surface, and heavy metal ions such
as Cu2+
and Cr6+
are positive charges. Table 3 showed the intercepting ratio of Cu2+
changed between
92.7% and 100%, the ratio of Cr6+
increased from 91.3% to 99.9% in 4h. Because the PS nanofibrous
membrame can adsorb heavy metal ions tightly in the surface, and the pores were jamed by the dye
molecules or metal ions, membrane pores gradually reduced and more and more ions can be
interrupted with the time change.
Compared with the other researcher’s work, the water flux of the PS nanomembrane was excellent ,
but the intercepting rate was a little weak. The water flux and the intercepting rate can be affected by
Applied Mechanics and Materials Vols. 55-57 1557
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the operating pressure and the thickness of the membranes [6, 8]. The characters of the PS membrane
could be enhanced by the optimizition of the electrospinning techniques, and complex membranes of
PS and inorganic membrane having more excellent capability could be developed in the dyeing waste
water treating.
Table 3 Water flux and intercepting ratio of PS nanomembrane to the simulate dyeing waste
water
Time(h) Filtrate
Volume(ml)
Water flux
(ml/cm2⋅h)
*Methylene blue
(mg/l)/interceptin
g ratio
*Cu
2+(mg/l)/
intercepting
ratio
*Cr
6+(mg/l)/
intercepting
ratio
0.5 603 15.4 0.825/92.1% 0.385/92.7% 0.475/91.3%
1.0 539 13.7 0.645/94.2% 0.355/93.3% 0.360/93.1%
1.5 478 12.2 0.475/95.3% 0.210/96.2% 0.285/95.7%
2.0 404 10.3 0.275/97.3% 0.115/98.6% 0.150/98.0%
2.5 334 8.5 0.107/99.1% 0.045/99.1% 0.028/98.5%
3.0 286 7.3 0.054/99.5% 0.012/99.8% 0.014/99.7%
3.5 255 6.5 0.005/99.9% 0.002/100.0% 0.004/99.9%
4.0 227 5.8 0.007/99.9% 0.004/99.9% 0.005/99.9%
* means the concentration in the permeating effluents.
Summary
Nanofiltration can improve the manufacturing process of dye and help to realize cleaner production,
which has significant economic and environmental benefits. In this work, we studied the technique of
fabrication and configuration of PS nanofibrous membrane. PS electrospun nanofiber membrane
showed good filtration capability to the simulated dyeing wastewater; it expressed a potential value to
the resue of emitted dyeing waste water as a cheap and efficient organic nanomembrane.
Nanofiltration was vital for the treatment of dye wastewater but the major limitation is fouling.
Zahrim reviewed that coagulation/flocculation can be effective to enhance nanofiltration performance
towards water reuse and minimisation of fouling [9]. In the same way, it is worth for us to make
further research on the membrane fouling control and reuse of fouled polystyrene membrane in the
treatment of saline dye wastewater with low concentration.
Acknowledgements
This research is supported by the Project of Enterprise Special Plan of Guangdong Province,
Ministry of Education and Science and Technology (No. 2009B090600016).
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