W.J. Lau

Synthesis and characterization of novel thin film nanocomposite reverse osmosis membranes with improved organic fouling properties for water desalination

In this study, a new type of thin film nanocomposite (TFN) reverse osmosis (RO) membranes was prepared by incorporating different amounts of halloysite nanotubes (HNTs) into the polyamide (PA) selective layer via in situ interfacial polymerization. The effect of HNTs incorporation into the PA selective layer on the surface morphology, separation performance and antifouling properties of the membranes were thoroughly investigated and discussed. The presence of HNTs in PA layer was verified using EDX, XRD and FTIR analysis. The “leaf-like” outgrowth morphology of PA layer was observed using FESEM. Upon addition of HNTs, the hydrophilicity, surface roughness and water flux of TFN membranes have all increased. The water flux enhancement can be ascribed to higher hydrophilicity and additional water pathways through porous HNTs in TFN membranes. It is noteworthy that the TFN membrane that was embedded with 0.05 wt/v% HNTs (labeled as TFN0.05) could exhibit water flux as high as 36 L m−2 h−1 (at 15 bar gauge) with NaCl rejection maintained at 95.6%. In comparison to the control thin film composite (TFC) membrane, the water flux of TFN0.05 membrane was 90% higher. Although further increase in HNTs loading to 0.1 wt/v% could result in greater water flux, its RO performance was compromised by a significant decrease in NaCl rejection. Besides offering greater water flux, the TFN0.05 membrane also showed better antifouling affinity than HNTs-free TFC membrane. It is most probably due to the increase in hydrophilicity as well as surface negative charge upon addition of HNTs. Based on the results obtained in this work, it can be concluded that incorporating an appropriate amount of HNTs into PA rejection layer could potentially improve the performance of TFC membrane during RO applications.

Treatment of dyeing solution by NF membrane for decolorization and salt reduction

Abstract A synthesized dyeing solution consisted of reactive dye, salts, and polyvinyl alcohol was prepared and treated by two different types of commercial nanofiltration (NF) membranes, i.e. NF90 and NF270 under various process conditions. These NF membranes were evaluated for permeate flux, salt, and color rejection as well as fouling propensity for a certain period of operation. Results revealed that NF90 suffered significant flux decline compared to NF270 after four operation cycles of treatment process, indicating its high sensitivity to foulant attachment. With respect to color removal, it is found that NF270 demonstrated greater stability in maintaining its separation efficiency (between 94 and 98% rejection) regardless of the feed properties and number of operation cycles. Though the salt rejection of NF270 was not as high as NF90, its consistent separation performance throughout the study period proved its reliability in long run. Recommended chemical cleaning process was also conducted in an ef...

Effect of PVP Molecular Weights on the Properties of PVDF-TiO2 Composite Membrane for Oily Wastewater Treatment Process

Polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes consisted of TiO2 and different molecular weight (Mw) of polyvinylpyrrolidone (PVP) (i.e., 10, 24, 40, and 360 kDa) were prepared to treat synthesized oily wastewater. The membrane performances were characterized in terms of pure water flux, permeate flux, and oil rejection while their morphological properties were studied using SEM, AFM, and tensile tester. Results show that the PVDF-TiO2 composite membrane prepared from PVP40k was the best performing membrane owing to its promising water flux (72.2 L/m2.h) coupled with good rejection of oil (94%) when tested with 250 ppm oily solution under submerged condition. It is also found that with increasing PVP Mw, the membrane tended to exhibit higher PVP and protein rejection, greater mechanical strength, smaller porosity, and a smoother surface layer. Regarding the effect of pH, the permeate flux of the PVDF-PVP40k membrane was reported to increase with increasing pH from 4 to 7, followed by decrease when the pH was further increased to 10. Increasing oil concentration in the feed solution was reported to negatively affect the water flux of PVDF-PVP40k membrane, owing to the formation of thicker oil layer on the membrane surface which increased water transport resistance. A simple backflushing process on the other hand could retrieve approximately 60% of the membrane original flux without affecting the oil separation efficiency. Based on the findings, the PVDF-TiO2 membrane prepared from PVP40k can be potentially considered for oily wastewater treatment process due to its good combination of permeability and selectivity and reasonably high water recovery rate.

Surface modification of thin film composite membrane by nanoporous titanate nanoparticles for improving combined organic and inorganic antifouling properties

In this study, nanoporous titanate (NT) nanoparticle synthesized by the solvothermal method was used to modify polyamide layer of thin film composite membranes with the aim of improving membrane resistances against organic and inorganic fouling. Thin film nanocomposite membranes (NMs) were synthesized by adding mNTs (modified nanoparticles) into polyamide selective layer followed by characterization using different analytical instruments. The results of XPS and XRD confirmed the presence of mNTs in the polyamide layer of NMs, while FESEM, AFM, zeta potential and contact angle measurement further supported the changes in physical and chemical properties of the membrane surface upon mNTs incorporation. Results of fouling showed that NM1 (the membrane incorporated with 0.01w/v% mNTs) always demonstrated lower degree of flux decline compared to the control membrane when membranes were tested with organic, inorganic and multicomponent synthesized water, brackish water or seawater. Besides showing greater antifouling resistance, the NM also displayed significantly higher water flux compared to the control M membrane. The findings of this work confirmed the positive impact of mNTs in improving the properties of NM with respect to fouling mitigation and flux improvement.

A facile modification approach for polyacrylonitrile-based UF hollow fiber membrane utilizing polyacrylonitrile-g-poly(vinyl alcohol) graft copolymer

Facile blending approach utilizing amphiphilic copolymers has received enormous attention from researchers owing to their unique self-organizing behaviour that can improve membrane structure and separation properties. This paper discusses the effect of the amount of acrylonitrile (AN) monomer added during polyacrylonitrile-g-polyvinyl alcohol (PAN-g-PVA) copolymer synthesis and its relationship to the properties and performance of PAN-based ultrafiltration (UF) hollow fiber membrane. The hollow fiber membranes were characterized using atomic force microscope, scanning electron microscope, X-ray photoelectron spectroscope and contact angle goniometer, in addition to performance evaluation with respect to protein rejection and antifouling resistance. As for the UF experiments, the membrane incorporated with copolymer of highest monomer composition achieved the highest pure water flux (178.76xa0L/m2.hr) coupled with good rejection of bovine serum albumin (BSA) and albumin from chicken egg (at least 83xa0%) when tested at 1xa0bar. The promising results are mainly due to the changes in the membrane morphological properties, surface roughness, surface chemical composition and hydrophilicity upon the addition of the copolymer. In terms of anti-fouling performance, generally, blend membrane prepared from copolymer of lowest amount of monomer produced good flux recovery for all proteins (74xa0%, 67xa0% and 62xa0% during BSA, albumin from chicken egg and trypsin) filtration due to the enrichment of PVA on membrane surface and its low surface roughness. The experimental results offer an important insight into the relationship between amount of monomer added during graft copolymer synthesis and membrane properties and performance, providing valuable information for high performance UF membrane for fouling mitigation especially in the area involving proteinaceous solution.

Solvothermal synthesis of nanoporous TiO2: the impact on thin-film composite membranes for engineered osmosis application

In the current study, the impact of self-synthesized nanoporous titanium oxide (NT) on the morphology, performance and fouling of a polyamide (PA) thin-film composite (TFC) membrane was investigated when the membrane was applied for engineering osmosis (EO). The nanoporous structure and the spindle-like shape of NT were revealed through transmission electron microscopy (TEM), while the AATPS modification of NT was verified by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results of x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) confirmed the presence of modified NT (mNT) in the PA dense active layer of the TFC membrane. The outgrowth of the leaf-like structure, upon mNT loading, at the surface of the PA layer was observed by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The TFC membrane prepared with 0.05 wt% mNT loading in the organic phase showed the water flux of 26.4 l m(-2) h(-1) when tested in the forward osmosis (FO) mode using 0.5M and 10 mM NaCl solution as the draw and feed solution, respectively. Moreover, the TFC-mNT membrane also demonstrated an intensified antifouling property against organic foulant during FO application and it was possible to retrieve the initial water flux almost completely with a simple water-rinsing process.

Adsorption and photocatalytic degradation of methylene blue using high surface area titanate nanotubes (TNT) synthesized via hydrothermal method

Removal of methylene blue (MB) via adsorption and photocatalysis using titanate nanotubes (TNTs) with different surface areas were investigated and compared to commercial titanium dioxide (TiO2) P25 Degussa nanoparticles. The TNTs with surface area ranging from 20xa0m2/g to 200xa0m2/g were synthesized via hydrothermal method with different reaction times. TEM imaging confirmed the tubular structure of TNT while XRD spectra indicated all TNTs exhibited anatase crystallinity. Batch adsorption rate showed linearity with surface properties of TNTs, where materials with higher surface area showed higher adsorption rate. The highest MB adsorption (70%) was achieved by TNT24 in 60xa0min whereas commercial TiO2 exhibited the lowest adsorption of only 10% after 240xa0min. Adsorption isotherm studies indicated that adsorption using TNT is better fitted into Langmuir adsorption isotherm than Freundlich isotherm model. Furthermore, TNT24 was able to perform up to 90% removal of MB within 120xa0min, demonstrating performance that is 2-fold better compared to commercial TiO2. The high surface area and surface Bronsted acidity are the main reasons for the improvement in MB removal performance exhibited by TNT24. The improvement in surface acidity enhanced the adsorption properties of all the nanotubes prepared in this study.

Preparation of polysulfone-based PANI–TiO2 nanocomposite hollow fiber membranes for industrial dye rejection applications

Polysulfone-based polyaniline–TiO2 containing hollow fiber membranes were prepared via a dry wet spinning method. Polyaniline (PANI) coated TiO2 nanotubes were prepared via chemical oxidative polymerisation and were incorporated into the hollow fiber membranes at different compositions. The hollow fibers were fabricated by varying the air gap distance during the spinning process. The effects of the addition of PANI coated TiO2 and the variation in the air gap distance on membrane performance, such as morphology and the permeability of the membranes, were analysed. The addition of the PANI–TiO2 nanocomposite enhanced the hydrophilicity and antifouling ability of the prepared membranes. The polysulfone hollow fiber membranes were examined for their dye rejection of Reactive Black 5 and Reactive Orange 16. The results indicated that the polysulfone hollow fibers containing 1.0 wt% of PANI–TiO2 fabricated using a 5 cm air gap can be used as a potential candidate for industrial dye rejection and showed a maximum rejection of 81.5% and 96.5% for Reactive Black 5 and Reactive Orange 16, respectively.

Control of Membrane Surface Roughness and Pattern Wave Length by Changing the Nonsolvent (Water) Influx Rate

The control of surface roughness of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS) and cellulose (CE) membranes was attempted by changing the rate of nonsolvent influx in the phase inversion process. PVDF and CE were chosen to represent membranes of high hydrophobicity and hydrophilicity, respectively, while PES and PS were chosen to represent membranes of intermediate hydrophobicity/-philicity. The concentration of sodium chloride (NaCl) in the aqueous coagulation medium was increased from 0 to 1.9 mol/L to decrease the rate of nonsolvent (water) influx in the solvent/nonsolvent exchange process. As well, the effect of polymer concentration and solvent on the surface roughness was investigated with respect to PVDF and PES. It was observed that the membrane surface roughness increased and decreased, respectively, for the hydrophobic PVDF and hydrophilic CE membrane as the rate of nonsolvent influx was decreased. For the PES and PS membranes of intermediate hydrophilic/-philicity, no significant roughness change was observed. The surface roughness tended to increase as the solution viscosity decreased. It was also observed that the pattern wave length of the hydrophobic membrane did not change significantly while that of the hydrophilic membrane increased significantly as the solvent influx rate was reduced. This trend is predictable by considering the shrinking or swelling of the cast polymer solution during the solvent/nonsolvent exchange process.

A study of Computational Fluid Dynamics on membrane module in membrane distillation

Membrane distillation is one of the recently interest rising membrane separation processes used for the separation of seawater and saline wastewater, and etc. Membrane distillation has the advantage of adopting the low grade waste energy and/or renewable energy such as solar and geothermal energy due to the nature of thermal driven process and low temperature range. Computational Fluid Dynamics (CFD) is a numerical simulation tool that is able to perform the calculation in order to investigate and simulate the performance of the processes that involve fluid, heat and mass transfer. In this study, a direct contact membrane distillation (DCMD) experiment will be studied using hollow fiber membrane module. A three dimensional (3D) CFD simulation will be examined for its viability in the investigation of the DCMD. Furthermore, various CFD multiphase models will be studied for its suitability in predicting heat and mass behavior within the membrane.