Photocatalytic degradation of nonylphenol by immobilized TiO2 in dual layer hollow fibre membranes

Chemical Engineering Journal 269 (2015) 255–261

Contents lists available at ScienceDirect

Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej

Photocatalytic degradation of nonylphenol by immobilized TiO2 in dual layer hollow fibre membranes Hazlini Dzinun a, Mohd Hafiz Dzarfan Othman a,⇑, Ahmad Fauzi Ismail a, Mohd Hafiz Puteh b, Mukhlis A. Rahman a, Juhana Jaafar a a b

Advanced Membrane Technology Research Centre (AMTEC), Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia Department of Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The work aims to fabricate dual layer

hollow fibre membrane via single step process.  The membrane comprised of dual layers, which inner is PVDF while outer is PVDF/TiO2.  The NP degradation of dual layer membrane was compared with single layer one.  The dispersion of TiO2 nanoparticles was improved in the dual layer structure.  Dual layer membrane exhibited superior degradation compared to the control sample.

a r t i c l e

i n f o

Article history: Received 10 November 2014 Received in revised form 29 January 2015 Accepted 31 January 2015 Available online 7 February 2015 Keywords: Dual layer hollow fibre membranes Immobilized titanium dioxide Photocatalytic degradation Nonylphenol Co-spinning

a b s t r a c t Nonylphenol (NP) is one of refractory degradation intermediates of nonylphenol ethoxylates (NPEO) surfactant and among the most toxic and prevalent endocrine disrupting compounds (EDCs) found in the environment. This paper reports an effort in removing nonylphenol in water using novel photocatalytic dual layer hollow fibre membrane, where the outer layer comprised of polyvinylidene fluoride (PVDF)/titanium dioxide (TiO2) while the inner layer was 100% PVDF. Single layer hollow fibre membrane which consists of PVDF/TiO2 was also fabricated as the control sample. The presence of TiO2 on the outer surface of both dual and single layer hollow fibres was confirmed by scanning electron microscopy (SEM), energy dispersion of X-ray (EDAX) and contact angles analysis. The removal of 85% in NP concentration was achieved for dual layer hollow fibre after 4 h UVA irradiation in submerged membrane photoreactor, compared to 70% for the single layer one. The kinetic rate of dual layer membranes was calculated to be 0.0092 min1 against 0.0062 min1 for the single layer counterpart. In general, dual layer hollow fibre membranes exhibited superior photocatalytic performance in comparison to single layer hollow fibre membranes due to the better dispersion of TiO2 on the outer membrane surface. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction ⇑ Corresponding author at: Advanced Membrane Technology Research Centre (AMTEC), Faculty of Petroleum and Renewable Energy Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia. Tel.: +60 75536373; fax: +60 75535925 http://dx.doi.org/10.1016/j.cej.2015.01.114 1385-8947/Ó 2015 Elsevier B.V. All rights reserved.

The treatment of organic pollutants is a serious problem that attracts the attention of many researchers during last decades. Among the methods for organic pollutants reduction from

256

H. Dzinun et al. / Chemical Engineering Journal 269 (2015) 255–261

wastewater, the total degradation process using membrane photoreactor (MPR) systems appears to be highly attractive due to their promising function in treating organic pollutants and filtering clean water. Generally, there are two main configurations of MPR systems, namely as separated and hybrid systems. Separated system comprised of two different chambers for degradation and filtration processes, while in hybrid system, both processes are occurred in a single chamber [1]. Suspended nanoparticles photocatalyst in hybrid MPR system always encounters with a number of problems [2]. In this type of configuration, membrane fouling together with the loss of nanoparticles from the photoreactor are inevitable, thus significantly affects the photocatalytic degradation efficiency of pollutants. Many efforts have been done to minimize these problems, which one of them is by immobilizing nanoparticles in the membrane support. Anatase-type TiO2 is the most often used photocatalyst due to its good photocatalytic activity, high stability, low-environment impact and low cost, ability as well as its potential antifouling abilities [3]. A suspension of catalyst has a higher degradation efficiency but the catalyst particles need to be separated from the treated water after the detoxification and the small size of TiO2 nanoparticles makes its recovery from the reactor difficult. Hydrophilic TiO2 nanoparticles were incorporated in filtration membrane to improve membrane permeability and fouling resistant of by imparting hydrophilicity to their surface [4]. So far, few works were reported on the photodegradation by membrane loaded anatase. Tahiri et al. [5] studied photocatalytic membrane reactors with entrapped of TiO2 within polymer membranes. However, the loading of TiO2 nanoparticles within membrane only 7.5 wt% for the best photocatalytic membrane. The lower amount of TiO2 nanoparticles showed little photoactivity. Moreover, the flat sheet membrane has lower surface areas compared to hollow fibre membrane. The lack of interest in anatase-loaded membranes is probably due to such a risk of anatase-catalyzed degradation of the membrane matrix under lights. For this purpose, the selection of support material is one of the aspects that need to be considered carefully as it determines the dispersion of the TiO2 nanoparticles in the membrane matrix [6]. Among polymeric materials available in the market, polyvinylidene fluoride (PVDF) membrane is of great interest because of its open structure, thermal stability, mechanical strength, relative chemical inertness and insolubility in most organic solvents [7]. The large amount of available pore sites (100–500 nm) provided by the PVDF support membrane are essential for preparation of nanoparticles inside the membrane matrix [8]. To date, many researchers have attracted to fabricate dual layer hollow fibre membrane due to its advantages such as (1) low material cost; (2) elimination of complex post treatment process; (3) optimized membrane performance by using a functional material of high performance as the selective layer. Various studies clearly reveal the applicability of dual layer fibre spinning technology for various gas [9–13] and liquid separations applications [14–17]. Most of the researchers have focused on morphological studies and application of dual layer hollow fibre membranes as a separation medium. There is a very limited publication reported on the dual layer hollow fibre membrane structure for simultaneous reaction and separation. As mentioned by Bhandari [18], the morphology of inner and outer layer of hollow fibre membrane are formed based on the required properties in each layer by manipulating of spinning parameters. Therefore, the objective of this study is to develop a novel dual layer hollow fibre membrane for photocatalytic degradation of organic pollutants. In this membrane design, the outer layer comprised of polyvinylidene fluoride (PVDF)/titanium dioxide (TiO2) while the inner layer was 100% PVDF. The catalytic efficiency of

immobilized TiO2 in dual layer hollow fibre membranes was evaluated using submerged membrane photoreactor. For comparison, single layer hollow fibre that comprised the same formulation as the outer dope of dual layer hollow fibre was also fabricated and characterized. In this study, nonylphenol (NP) was chosen as the target pollutant due to greater tendency to bioaccumulate their toxicity in aquatic life [19]. As NP is toxic to the biota, detailed studies on the fate of NP in the environments are lacking. The precise measurement of NP degradation rates in the environments is considered important. 2. Materials and experimental methods 2.1. Materials Polyvinylidene fluoride (PVDF Solef 6000 Series – powder, Solvay Specialty Polymers France) was used as polymer base. Titanium dioxide (TiO2) (Anatase, average particle size 16 nm) was supplied from Johnson Matthey, UK. Dimethylacetamide (DMAc) (Merck, >99%) was used as received and to dissolve the PVDF. Nonylphenol (CAS 84852-15-3), acetonitrile (HPLC grade, >99%) and ethanol (absolute) were supplied by Sigma–Aldrich and used without further purification. 2.2. Preparation of dual layer and single layer hollow fibre membranes PVDF and TiO2 were dried in a 50 °C vacuum oven for 24 h to remove moisture prior to dope preparation. The TiO2 and DMAc at desired amount were added in Scott bottle with an overhead stirrer. After the TiO2 mixture became a homogeneous solution, the desired amounts of polymer was added to the solution. Then, the dope solution was cooled down to room temperature. The detailed compositions of the polymer dope solutions are shown in Table 1. The solution was degassed by using ultrasonic bath system (Ultrasonic Cleaner DC-150H) at ambient temperature over night prior to spinning. The viscosity of the polymer dope solutions was measured using viscometer 20–2 million centiPoise (Cole Parmer, Model: EM-98965-40). Then, the spinning dope mixture was extruded using a triple orifice spinneret [20] to form dual layer hollow fibre membranes. The spinning conditions and different pairs of the outer and inner dope solutions were used to make PVDF/TiO2 hollow fibre membranes as described in Table 1. The as-spun hollow fibres were immersed into water bath for 1 day to remove residual solvent. Prior to air drying, the fibres were post-treated using (ethanol:water, 50:50 wt%) for 1 h, then 100% of ethanol for 1 h in order to improve the membrane wettability and pore collapse [5]. Finally, the hollow fibre membranes were dried at room temperature for 3 days before membrane characterization and module fabrication. 2.3. Characterization methods The inner and outer layer morphology were explored qualitatively using Scanning Electron Microscopy (SEM) and Energy Dispersion of X-ray (EDX, S250, EDAX) analysis and quantitatively by permeation analysis. The morphology of the cross section and surface of the membranes were inspected by SEM (Model: TM 3000, Hitachi). The line scan of spectrum of EDX was used to investigate the nanoparticle distribution on top surface of the tested composite membrane. The hollow fibres were immersed in liquid nitrogen for 10 min and then fractured into short samples, for the purpose of maintaining the original cross sectional of the membranes. The samples were then positioned on a metal holder and sputter coated with gold under vacuum for 3 min. The micrographs of the cross section and surface of the hollow fibre membranes

H. Dzinun et al. / Chemical Engineering Journal 269 (2015) 255–261 Table 1 Spinning conditions of the hollow fibre membranes.

Outer dope composition (wt%) Outer dope flowrate (ml/min) Inner dope composition (wt%) Inner dope flowrate (ml/min) Bore fluid Bore fluid flow rate (ml/min) Air gap (cm) Take up speed (m/s) Spinneret dimension (mm)

Dual layer (DL)

Single layer (SL)

PVDF/TiO2/DMAc (15/7.5/77.5) 1

–

PVDF/DMAc (18/82) 8

PVDF/TiO2/DMAc (15/7.5/77.5) 8

Distilled water 8

Distilled water 8

10 0.18 0.8/1.2/2.6/3.0/3.5

10 0.18 0.8/1.2/2.6

–

were taken at various magnifications. The images of membranes before and after UV irradiation were also captured for comparison purposes. Contact angle measurements on the hollow fibre membranes were conducted using the contact angle goniometer (Model: OCA 15EC, Dataphysics) with deionized water as contact liquid. The water droplets of 2 lL were dropped on the fibre surfaces. An average and standard deviation of at least 10 independent measurements was obtained at different points of one sample. Pure water flux experiments were conducted in a U-like membrane module filtration apparatus. For each module, fifteen fibres with 30 cm length were assembled into the filtration module and pure water flux measurements were performed in a cross flow mode through outside-in configuration. Each membrane sample was tested at different pressure in order to get the permeability of membranes. Tensile strength and elongation at break of the hollow fibres were measured by LRX, LLYOD test machine with a load cell of 2.5 kN, at a constant elongation velocity of 10 mm/m at room temperature. At least six fibres with 50 mm length were tested and the average data were taken for each sample. The deviation between the sample values and the average value was less than 5%. Tensile strength was calculated by using the following Eq. (1) [21]:

Tensile strength ðPaÞ ¼

Load at break ðNÞ Cross sectional area ðm2 Þ

257

photocatalytic degradation, the temperature of NP solution gradually increased from room temperature (27 °C) to about 45 °C. To avoid the evaporation of solution, photocatalytic reactor was covered by glass mirror. In addition, Mozia [24] showed that solution temperature ranging from 20 to 80 °C does not have apparent impact on photocatalytic degradation of organic pollutants. The reaction solution was moderately stirred using magnetic stirrer in order to prevent pollutant deposition at the bottom of the reactor. It would also be possible to reduce cake build up by vigorous stirring and bubbling at some energy penalty [25], but it was not applied in this work. The external beaker surface was covered with aluminium foil whose reflecting surface was directed in the inner side. The diameter of the beaker is 18.5 cm and the volume of the solution is 3 L. A Philips lamps (UVA radiation) emitting radiation in the 365 nm of wavelength was used to irradiate the immobilized TiO2 in membrane sample. The lamp was placed in the middle of the beaker as shown in Fig. 1. The light intensity was measured using UVP UV Radiometer at the distance positioned the membrane module is 4.5 cm. During the photodegradation process, 10 mL of aliquots were taken from the reactor at every 30 min for 4 h by means of 10 mL syringe and examined using high performance liquid chromatography (HPLC, Agilent Technologies 1260 Affinity) coupled with programmable fluorescence detector. HPLC separations were performed using a Zorbax Poroshell 120 EC-C18 column (4.6 mm  50 mm, 2.7 lm) thermostatted at 40 °C, injection volumes of 20 lL, flow rate of 2 mL min1 and isocratic elution with 40% water and 60% acetonitrile during 25 min. Analytes were monitored by fluorescence detection (kex: 222 nm, kem: 305 nm) and quantified by external calibration using peak area measurements. 2.5. Adsorption kinetics measurement Adsorption kinetics were measured by exposing membrane to solutions with different concentrations (10 and 30 ppm) of NP solution at 298 K for 2 h in the dark. The kinetic reaction was evaluated by the decrease of NP concentration. The NP concentration

ð1Þ

The membrane surface roughness and mean pore size of the membranes were investigated by Atomic Force Microscopy (AFM) (Model: SPA-300HV, Seiko). The procedure for measurement of surface roughness, mean pore size and overall porosity are described elsewhere [22]. 2.4. Submerged membrane photoreactor and experimental procedure Experimental works using a batch submerged membrane photoreactor were conducted to evaluate the NP degradation efficiency of the membranes. A bundle of 20 hollow fibres with approximate length of 23.5 cm (total effective membrane area: 248 cm2) was potted into PVC tube using epoxy resin (E-30CL LoctiteÒ Corporation, USA). The module was then left at room temperature for hardening before its protruding parts were cut and fixed into a PVC adaptor to complete the module preparation. The prepared module was then fitted in the ultraviolet A (UVA) photoreactor system. A 10 ppm of feed solution was prepared by dissolving 3 g nonylphenol (NP) in H2O:acetonitrile (9:1) [23] for 3 L of volume. The solution was stirred at 298 K in the dark for 65 min (adsorption equilibrium) prior to UVA photocatalytic degradation. The initial pH of NP solution was about 6.8. During the

Fig. 1. Schematic diagram of photodegradation apparatus: (1) UVA lamp, (2) PVC, (3) beaker, (4) dual layer hollow fibre membranes and (5) magnetic agitator.

258

H. Dzinun et al. / Chemical Engineering Journal 269 (2015) 255–261

dC ¼ kKC dt   Co ¼ kKt ¼ kapp t ln C r¼

ð3Þ

ð4Þ

where: kapp is the apparent rate constant (min1) and Co is the concentration of pollutants after adsorption in the dark (mg/L). 3. Results and discussion 3.1. Characterization of the morphology and physico-chemical properties of PVDF/TiO2 hollow fibre membranes Fig. 2. UV absorbance of NP standard.

was monitored from NP absorbance at a wavelength of 250– 300 nm by using HACH DR5000 UV–Vis spectrophotometer as shown in Fig. 2. From this figure, it is found that the absorbance peak is at 285 nm. 2.6. Photocatalytic degradation kinetics In order to describe the photocatalytic degradation kinetics of pollutants in the aqueous phase, Langmuir–Hinshelwood model has been widely applied [26]:

r¼

dC kKC ¼ dt 1 þ KC

ð2Þ

where: r is the reaction rate (mg/L min), C is the concentration of the pollutant (mg/L), t is the reaction time (min), k is the Langmuir–Hinshelwood reaction rate constant (mg/L min) and K is the Langmuir adsorption equilibrium constant (L/mg). At the dilute concentration of the pollutant (i.e., KC  1), pseudofirst-order kinetics model can be assumed as follows:

(a1)

(a2)

Fig. 3 shows representative SEM images of the PVDF/TiO2 hollow fibre membranes with different configurations. The dispersion of immobilized TiO2 particles is one of the most important factors in the fabrication of the hollow fibre membranes as it impacts directly on adsorption capacity and photocatalytic activity. As shown in Fig. 3(a2), the finger like structure developed at the outer and inner layer, whereas the sponge like structure developed at the intermediate layer. No interlayer was developed in the dual layer hollow fibre membranes fabrication. As reported by Teoh [27], both layers are compatible with each other and there are no delamination and interfacial resistance when PVDF was used for both inner and outer layer dopes. It is expected that the mutual diffusion of polymers was established between the inner and outer layers, thus two distinct layers cannot be observed (seamless interface). The estimation of outer layer thickness of dual layer hollow fibre membranes was performed based on the TiO2 particles are distributed homogeneously in the outer dope as shown as dotted colour in Fig. 3(a3). For dual layer hollow fibre membranes, no diffusion of TiO2 particles into the inner layer was observed from EDX analysis as shown in Fig. 4. The outer layer thickness of the membranes was influenced by the outer dope flow rates [11], where the higher the extrusion rate the thicker the thickness. The outer layer thickness of approximately 8.7 lm (measured from Fig. 3(a3)) was produced when flow rate of 1 ml/min was used in this work. This is

(a3) 8.74μm

(b1)

(b2)

(b3)

186μm

Fig. 3. Overall and partial cross section SEM and EDX images of PVDF/TiO2 hollow fibre for (a) dual layer and (b) single layer hollow fibre membranes.

H. Dzinun et al. / Chemical Engineering Journal 269 (2015) 255–261

Outer surface a1

259

Inner surface a2

Dual layer hollow fibre membranes

b1

b2

Single layer hollow fibre membranes

Fig. 4. EDX spectrum of (a) dual layer and (b) single layer hollow fibre membranes.

Fig. 5. Surface roughness result at outer surface of (a) dual layer and (b) single layer of PVDF/TiO2 hollow fibre membranes.

one of the advantages of co-spinning, where the thickness of the layer can be simply controlled by manipulating the outer dope flow rate. In the dual layer hollow fibre membranes, the amount of TiO2 particles distribution in the outer layer was found to be lower (Fig. 3(a3)) than in the single layer hollow fibre membranes. It is believed that the particles might have spread properly over the outer membrane surface. In contrast, the single layer PVDF/TiO2 hollow fibre membranes (Fig. 3(b3)), showed higher TiO2 loading led to particle aggregation phenomenon and it became less hydrophilic. As mentioned by Damodar [28], the hydrophilicity depends on how TiO2 particles spread over the membrane surface. The surface of TiO2 particles entrapped membrane matrix can be more hydrophilic due to higher affinity of metal oxide to water [29]. Dual layer hollow fibre is more hydrophilic than single layer. The presence of hydrophilic nature of TiO2 particle at the outer layer of the dual layer hollow fibre membranes has successfully improved the hydrophilicity of the membrane as proved by EDX analysis in Fig. 4. The wetting improvement could be explained by an effective of TiO2 particles on the outer surface. The external

coagulants highly wets to the membrane surface, it would able to come into contact with the TiO2 particles in the internal structure, thus wetting improvement was observed. Besides, it proved that the hydrophilic TiO2 particles in the membrane pores were not covered by PVDF and thus could be easily wetted by water. Fig. 5 presents three dimensional AFM images and surface roughness (Ra) of the PVDF/TiO2 membranes prepared. The AFM images clearly show that the membrane surface roughness of both configurations have no significant difference because the TiO2 particles loading in the dope solution are equal. The membrane surface roughness was strongly dependent on the TiO2 loading [22]. The Ra value of dual and single layer hollow fibre membranes are 42.03 and 43.42 nm, respectively. Table 2 summarize the results of the outer mean pore size diameter, tensile strength and contact angle. Larger pore size was observed and it makes the tensile strength of single layer hollow fibre membranes weaker. As can also be seen in Table 2, the tensile strength and elongation at break of the dual layer hollow fibre membranes was higher

260

H. Dzinun et al. / Chemical Engineering Journal 269 (2015) 255–261

Table 2 Performance of hollow fibre membranes with different configuration. Configuration

Outer mean pore diameter (nm)

Tensile Strength (MPa)

Elongation at break (%)

Pure water flux at 1 bar (L/m2 h)

Contact angle (°)

Dual layer hollow fibre Single layer hollow fibre

163.95

2.50

247.0

55.5

77.6

207.77

1.82

137.9

67.9

84.0

agreement with the hydrophilicity. It may due to the mass transfer resistances in the inner layer of dual layer hollow fibre. The high diffusion of water is expected at the outer layer but it become slower through the inner layer (which only comprised hydrophobic PVDF). 3.2. NP sorption equilibrium The decreasing of NP concentration is shown in Fig. 6. Both kinetic reactions for different initial NP concentrations have reached the steady state of adsorption within 65 min. Therefore, 65 min was selected for the pre-equilibrium period in the dark before UVA irradiation to make sure the degradation was initiated after adsorption equilibrium [5]. 3.3. Photocatalytic degradation of nonylphenol in the batch system

Fig. 6. Absorption onto PVDF/TiO2 dual layer hollow fibre membranes in darkness.

Fig. 7. Degradation kinetics parameters of NP.

than single layer hollow fibre membranes. This is mainly because of the outer layer of dual layer hollow fibre membranes makes the structure stronger than single layer. Even though the dual layer hollow fibre is more hydrophilicity than the single layer, the pure water flux results were not in good

TiO2/UVA photocatalyst exhibits excellent photocatalytic property due to the production of strong hydroxyl radical which can degrade most of the complex organic compounds [28]. The photocatalytic properties of different configuration of hollow fibre membranes were tested using nonylphenol (NP) degradation system. The apparent rate constant, k, was calculated using the Langmuir–Hinshelwood model as shown in Fig. 7. The value of k for single layer was lower than dual layer hollow fibre membranes. Higher k value was obtained by using dual layer hollow fibre membranes, which could be attributed to the deposition of TiO2 in the outer surface (see Fig. 3(a3)). As reported by Tahiri [5], the increase of catalyst loading might enlarge the active site for adsorption and degradation of pollutant. However, too much catalysts led to the light scattering of UV light and catalyst agglomeration (particle– particle interactions). In general, hydrophilicity determines the interaction between the membrane and the foulants (e.g. hydrogen bonding, dipole interaction, electrostatic effect and Van Der Waals interaction) [30]. The dual layer hollow fibre membranes exhibited high surface tension and ability to form hydrogen bonds with water and thus a water layer exists between the membrane and the bulk solution. This phenomenon helps to reduce the adhesion of foulants. Thus, the use of dual layer hollow fibre membranes inhibits high accumulation of particles at the membrane boundary. Therefore, the oxidation by hydroxyl radicals occurs on the external surface and within the pores of the membrane while reactants are permeating in a one-pass flow. The forced of reactants by convection inside the pores may increased the reaction rate by using dual layer hollow fibre membranes. 3.4. Comparison of nonylphenol degradation with literature Table 3 shows the comparison between some of earlier works reported on the organic pollutant degradation, either by using immobilized or suspended photocatalyst configuration. As can be seen, the degradation results that obtained in this work is comparable to other works that also done on the immobilized support [30–32]. The slight variation in the data between these studies

Table 3 Comparison of organic pollutants degradation with literature. Pollutants

Catalyst

Initial concentration

Light source

Reactor type

Time (h)

Degradation (%)

Refs.

Bisphenol A Bisphenol A Methyl red Nonylphenol Nonylphenol Nonylphenol

TiO2 TiO2 TiO2 Au/TiO2 and BiVO4 TiO2 and BiVO4 TiO2

300 ppb 10 ppm 4 ppm 11 ppm 44 ppm 10 ppm

Xenon lamp (150 W) BLB lamp (6 W) Low pressure mercury lamp (17 W) Xenon lamp (300 W) Visible light UV light (24 mW/cm2) UVA (8 W)

Immobilized Immobilized Suspended and immobilized Suspended Suspended Immobilized

3 6 10 2 0.5 4

85 100 100 100 100 85

[31] [32] [33] [23] [34] Our work

H. Dzinun et al. / Chemical Engineering Journal 269 (2015) 255–261

261

can be due to the types of light source and organic pollutant. From this table, it can also be seen that most of the previous studies for NP photocatalytic degradation only focused on the suspended catalyst. Thus, to the best of our knowledge, the present work might be considered as the first report based on hybrid systems for the NP degradation and the membrane processes.

Number: Q.J130000.2509.05H53), Exploratory Research Grant Scheme (Project Number: R.J130000.7842.4L104) and technical supports from both Aquakimia Sdn. Bhd. and Research Management Centre, Universiti Teknologi Malaysia. The authors also acknowledge Solvay Specialty Polymers Italy and Johnson Matthey PLC UK for providing materials used in this work.

4. Conclusions

References

This work has focused on nonylphenol degradation using two types of membrane configuration, i.e. dual layer and single layer hollow fibre membranes. The experimental results showed that NP was degraded around 85% and 70% under UVA illumination by using dual layer and single layer hollow fibre membranes, respectively. It revealed that photocatalytic degradation of NP is more efficient in the dual layer configuration. Using co-spinning process, the dispersion of TiO2 nanoparticles can be optimized in the outer surface, hence it more contact with UV light. Besides, it minimized the agglomeration problem in TiO2 photocatalyst. Moreover, it will reduce the material cost due to the amount of TiO2 used in outer layer of dual layer hollow fibre membranes is much lesser than the single layer one. The performance of dual layer hollow fibre membranes will be maximized by using a functional material of high performance as the selective layer. However, the only limitation of dual layer hollow fibre membranes is the requirement of more advance extrusion facilities and special spinneret for the fabrication. The hybrid systems with immobilized TiO2 within membranes will be the most promising set-up for application because it possesses the advantages of both the degradation and the membrane processes (separation at molecular level). Further research on the filtration processes in photocatalytic reactors could make dual layer hollow fibre membranes more feasible for future applications in water treatment. Membrane photoreactors appear to be a promising alternative to conventional photoreactors and more research in this area can assist overcome some of the problems faced with the use of conventional reactors. Acknowledgements The authors gratefully acknowledge financial support from the European Commission FP7 – LIMPID (Project number: NMP3-SL2012-310177), Research University Grant Scheme (Project

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]

M.N. Chong, B. Jin, C.W.K. Chow, C. Saint, Water Res. 44 (2010) 2997–3027. K.H. Choo, R. Tao, M.J. Kim, J. Membr. Sci. 322 (2008) 368–374. A. Razmjou, J. Mansouri, V. Chen, J. Membr. Sci. 378 (1–2) (2011) 73–84. E. Yuliwati, A.F. Ismail, Desalination 273 (1) (2011) 226–234. O. Tahiri, Q. Trong, C. Mbareck, T. Rhlalou, Appl. Catal. A 358 (2009) 13–20. X. Wang, J. Yang, M. Zhu, F. Li, J. Taiwan Inst. Chem Eng. (2013). N. Peng, N. Widjojo, P. Sukitpaneenit, M.M. Teoh, G.G. Lipscomb, T.S. Chung, J.Y. Lai, Prog. Polym. Sci. 37 (2012) 1401–1424. A. Bottino, G. Capannelli, O. Monticelli, P. Piaggio, J. Membr. Sci. 166 (2000) 23– 29. S. Husain, Georgio Institute of Technology, (2006). N. Widjojo, T. Chung, S. Kulprathipanja, J. Membr. Sci. 325 (2008) 326–335. L. Jiang, T. Chung, D. Fei, C. Cao, S. Kulprathipanja, J. Membr. Sci. 240 (2004) 91–103. D. Fei, T. Chung, R. Wang, Y. Liu, J. Membr. Sci. 198 (2002) 211–223. A.L. Ahmad, W.K.W. Ramli, Sep. Purif. Technol. 103 (2013) 230–240. S.P. Sun, T.A. Hatton, S.Y. Chan, T.S. Chung, J. Membr. Sci. 401–402 (2012) 152– 162. P. Wang, M.M. Teoh, T. Chung, Water Res. 45 (2011) 5489–5500. S. Bonyadi, T.S. Chung, J. Membr. Sci. 306 (2007) 134–146. Y.K. Ong, T. Chung, J. Membr. Sci. 421–422 (2012) 271–282. D. Bhandari, K.O. Olanrewaju, N. Bessho, V. Breedveld, W.J. Koros, Sep. Purif. Technol. 104 (2013) 68–80. M. Ahel, F.E. Scully, J. Hoign, W. Giger, Chemosphere 28 (1994) 1361–1368. M.H.D. Othman, Z. Wu, N. Droushiotis, U. Doraswami, G. Kelsall, K. Li, J. Membr. Sci. 351 (1–2) (2010) 196–204. P.E. Circuits, O.T. Group, Ipc-tm-650 test methods manual 1.0 (2) 4–6. C.S. Ong, W.J. Lau, P.S. Goh, B.C. Ng, Desalin. Water Treat. (2013) 37–41. S. Naya, T. Nikawa, K. Kimura, H. Tada, ACS Catal. 3 (2013) 903–907. S. Mozia, Sep. Purif. Technol. 73 (2010) 71–91. P. Wang, A.G. Fane, T. Lim, Chem. Eng. J. 215–216 (2013) 240–251. P. Wang, T.T. Lim, Water Res. 46 (2012) 1825–1837. M.M. Teoh, T. Chung, Y.S. Yeo, Chem. Eng. J. 171 (2011) 684–691. R.A. Damodar, S.J. You, H.H. Chou, J. Hazard. Mater. 172 (2009) 1321–1328. T.H. Bae, T.M. Tak, J. Membr. Sci. 249 (2005) 1–8. J. Mendret, M. Hatat-fraile, M. Rivallin, S. Brosillon, Sep. Purif. Technol. 111 (2013) 9–19. V.M. Daskalaki, Z. Frontistis, D. Mantzavinos, A. Katsaounis, Catal. Today 161 (1) (2011) 110–114. J.-M. Lee, M.S. Kim, B.W. Kim, Water Res. 38 (16) (2004) 3605–3613. G. Mascolo, R. Comparelli, M.L. Curri, G. Lovecchio, A. Lopez, A. Agostiano, J. Hazard. Mater. 142 (1–2) (2007) 130–137. S. Kohtani, Ã.S. Makino, A. Kudo, K. Tokumura, Y. Ishigaki, Chem. Lett. (2002) 660–661.