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Membrane fouling during the filtration process is a perennial issue and could lead to reduced separation efficiency. In this work, poly(citric acid)-grafted graphene oxide (PGO) was incorporated into a matrix of single-layer hollow fibre (SLHF) and dual-layer hollow fibrr (DLHF) membranes, respectively, aiming to improve membrane antifouling properties during water treatment. Different loadings of PGO ranging from 0 to 1 wt% were first introduced into the SLHF to identify the best PGO loading for the DLHF preparation with its outer layer modified by nanomaterials. The findings showed that at the optimized PGO loading of 0.7 wt%, the resultant SLHF membrane could achieve higher water permeability and bovine serum albumin rejection compared to the neat SLHF membrane. This is due to the improved surface hydrophilicity and increased structural porosity upon incorporation of optimized PGO loading. When 0.7 wt% PGO was introduced only to the outer layer of DLHF, the cross-sectional matrix of the membrane was altered, forming microvoids and spongy-like structures (more porous). Nevertheless, the BSA rejection of the membrane was improved to 97.7% owing to an inner selectivity layer produced from a different dope solution (without the PGO). The DLHF membrane also demonstrated significantly higher antifouling properties than the neat SLHF membrane. Its flux recovery rate is 85%, i.e. 37% better than that of a neat membrane. By incorporating hydrophilic PGO into the membrane, the interaction of the hydrophobic foulants with the membrane surface is greatly reduced.

In this study, two types of hydrophobic polyvinylidene fluoride hollow fibre membranes were fabricated by the wet/dry phase inversion method with N,N-dimethylacetamide and N-1-methyl- 2-pyrrolidone as solvents, respectively. The effects of solvent on the membrane characteristics were investigated based on the results of gravitational method and scanning electron microscope. The gravitational test revealed that the membrane porosity and pore size could be improved with the use of N-1-methyl-2-pyrrolidone solvent. The scanning electron microscope images of membrane cross-section demonstrated a similar finger-like layer structure in both membranes, extending from inner to outer surface. Lastly, the performance test of sodium chloride removal by direct contact membrane distillation indicated that the polyvinylidene fluoride membrane with N-1-methyl-2-pyrrolidone solvent had a better performance in relative to that with N,N-dimethylacetamide solvent. This finding implied that the polyvinylidene fluorid...

Due to the rapid expansion of nanotechnology and the increasing range of nanomaterials under production and development, a significant amount of research interest has been dedicated to the innovative exploitations of various inorganic nanomaterials in environmental applications. The incorporation of inorganic nanomaterials as fillers within a polymeric matrix has expanded opportunities to produce a multifunctional nanocomposite membrane that is capable of performing tasks beyond separation alone. The architectures and performances of these nanocomposite membranes have triumphed over polymeric membranes to overcome the underlying conspicuous drawbacks. This review aims to shed more light on the roles of inorganic nanomaterials in advancing the characteristics and separation performance of polymeric ultrafiltration membranes. Inorganic nanofillers such as metal oxides, metals and carbon-based materials are incorporated into polymeric membranes to render the desired properties for ultrafiltration separations...

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 b...

In this work, the properties of pristine polyvinylidene fluoride (PVDF) hollow fiber membranes were altered by incorporating different types of additives, that is, ethylene glycol (EG) and polyvinylpyrrolidone (PVP) into dope solution. Prior to the separation process, the resulting membranes were first characterized with respect to structural morphology, hydrophobicity, overall porosity, gas permeability, wetting pressure, mechanical, and thermal stability. It is found that PVP has major impact on the membrane structural properties due to the PVP residue in the membrane matrix. The PVP has transformed the PVDF membrane into hydrophilic ones, while EG did not negatively affect the hydrophobicity of the PVDF membrane. During direct contact membrane distillation process, it is reported that both membranes were able to achieve at least 99% rejection of reactive black 5 when tested under counter-current flow condition. Compared to the PVDF–PVP membrane, the experimental results showed that the PVDF–EG ...

Membrane distillation (MD) is a thermal-driven membrane separation process which recently garners interest from academic and industry due to its low energy requirements and the ability to integrate with renewable energy. In this work, two different additives, i.e. polyethersulfone (PES) and ethylene glycol (EG), were added into dope solutions consisting of polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) to prepare membranes for MD applications. The membranes were characterized with respect to thickness, pore size, porosity, and water contact angle using scanning electron microscope and water contact goniometer. Compared with the membranes made from pure PVDF and PVDF–EG system, it is found that PVDF–EG–PES membrane displayed improved characteristics i.e. having optimum porosity, large pore size, and thin membrane thickness coupled with finger-like structure extended from both inner and outer layers of the membrane. In addition to this, the permeate flux of PVDF–EG–PES membrane duri...

A series of polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes made of different titanium dioxide (TiO2) concentrations with the presence of polyvinylpyrrolidone as additive was prepared. The membrane performances were characterized in terms of pure water flux, permeate flux, and oil rejection, while the membrane morphologies were analyzed using scanning electron microscope and atomic force microscope. The experimental results showed that when 2 wt.% TiO2 was incorporated into PVDF membranes, optimized permeate flux and oil rejection of 70.48 L/m2 h (±1.41) and 99.7% (±0.3), respectively, could be obtained when tested using 250 ppm synthesized oily solution under vacuum condition. Compared to the PVDF membrane without TiO2 addition, all the composite membranes showed relatively higher permeate flux and oil rejection. Based on the results obtained, it is reported that the composite PVDF membrane incorporated with 2 wt.% TiO2 exhibited the best separation performance in which comp...

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...