B. C. Ng

Inorganic Nanomaterials in Polymeric Ultrafiltration Membranes for Water Treatment

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. Novel strategies using a wide range of these inorganic nanomaterials have been well explored and established for the manufacturing of membrane with significantly enhanced properties that are highly desired to heighten the separation performances. With the renaissance of this emerging innovative technology, many possible solutions and valuable options can be offered to serve as the primary driver in excelling ultrafiltration membrane technology.

Effects of shear rate and forced convection residence time on asymmetric polysulfone membranes structure and gas separation performance

The objectives of this study are to illustrate the effects of shear rate and forced convection residence time on asymmetric polysulfone membrane structure and gas separation performance. The membranes were produced by a simple dry/wet phase inversion technique using a pneumatically-controlled flat sheet membrane casting system. Varying the casting speed varied shear rate. Rheologically induced molecular orientation in membranes during casting was measured directly using plane polarized reflectance infrared spectroscopy technique. The highly sheared asymmetric membranes tend to exhibit greater molecular orientation in the skin layer. Thus, a high pressure-normalized flux and selectivity were obtained. The mean pressure-normalized fluxes of O2 and CO2 were about 5.05 and 11.41 GPU, respectively. The selectivity of O2/N2 and CO2/CH4 were approximately 6.72 and 32.63, respectively, at shear rate of 367 s−1. However, increasing forced convection residence time in the dry phase inversion step resulted in lower pressure-normalized flux but higher selectivity membrane. The best membrane performance obtained based on the trade-off between pressure-normalized flux and selectivity was observed at forced convection residence time of 20 s and at 367 s−1 shear rate.

Pre-treatment of multi-walled carbon nanotubes for polyetherimide mixed matrix hollow fiber membranes.

Mixed matrix hollow fibers composed of multi-walled carbon nanotubes (MWCNTs) and polyetherimide (PEI) were fabricated. Pre-treatment of MWCNTs was carried out prior to the incorporation into the polymer matrix using a simple and feasible two stages approach that involved dry air oxidation and surfactant dispersion. The characterizations of the surface treated MWCNTs using TEM and Raman spectroscopy have evidenced the effectiveness of dry air oxidation in eliminating undesired amorphous carbon and metal catalyst while surfactant dispersion using Triton X100 has suppressed the agglomeration of MWCNTs. The resultant mixed matrix hollow fibers were applied for O(2)/N(2) pure gas separation. Interestingly, it was found that removal of disordered amorphous carbons and metal particles has allowed the hollow structures to be more accessible for the fast and smooth transport of gas molecules, hence resulted in noticeable improvement in the gas separation properties. The composite hollow fibers embedded with the surface modified MWCNTs showed increase in permeability as much as 60% while maintaining the selectivity of the O(2)/N(2) gas pair. This study highlights the necessity to establish an appropriate pre-treatment approach for MWCNTs in order to fully utilize the beneficial transport properties of this material in mixed matrix polymer nanocomposite for gas separation.

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.

Physicochemical study of polyvinylidene fluoride–Cloisite15A® composite membranes for membrane distillation application

In this work, polyvinylidene fluoride–Cloisite15A® (PVDF–C15A) hollow fiber membranes were prepared, characterized and evaluated. The membranes were applied to treat a dye solution via a direct contact membrane distillation (DCMD) system. The concentration of the C15A incorporated into the PVDF membrane was varied (3, 5 and 10 wt%) and the corresponding effects were investigated in terms of structural properties and performances. The PVDF–C15A membranes were prepared using a dry-jet wet spinning method and characterized with respect to their morphology, porosity, wetting pressure, contact angle, surface roughness, mechanical strength and thermal stability. The presence of the C15A particles was confirmed by Fourier-transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy with an energy dispersive X-ray spectroscopy (SEM-EDX) analysis. Highly porous membranes with large finger-like structures were shown by the SEM images. The characterization results indicated that the incorporation of C15A particles has shown a significant influence on the physicochemical properties of the membranes. The DCMD experiments revealed that the PVDF membrane incorporated with 3 wt% C15A (PVDF–3% C15A) exhibited the best MD performance in which complete dye rejection was able to be achieved with consistent permeate flux. The promising results obtained by the PVDF–3% C15A membrane are mainly attributed to its improved structural properties resulting from the good distribution of C15A particles in the membrane matrix. This study shows that the PVDF membranes incorporated with C15A particles have potential to further improve the performances of pristine PVDF membranes in DCMD of dyeing wastewater.

Preparation and characterization of PVDF membranes incorporated with different additives for dyeing solution treatment using membrane distillation

AbstractIn 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 ...

Effect of Dispersed Multi-Walled Carbon Nanotubes on Mixed Matrix Membrane for O2/N2 Separation

Mixed matrix membranes (MMMs) consisting of multiwalled carbon nanotubes (MWCNTs) embedded within polyetherimide were prepared. Surfactants of different charges were utilized to disperse the nanotubes through a simple non-covalent approach. The characterization results suggest that proper selection of the dispersing agent contributed to better dispersion of nanotubes. The MMMs exhibited improved thermal stability and mechanical strength, which indicate the improvement of dispersion and compatibility within the polymer matrix. The resulting membrane exhibited permeance improvement of O2 and N2 as much as 87.7% and 120% respectively compared to that of neat polyetherimide. The results implied that Triton-X100 treated MWCNTs is a promising filler to enhance gas permeability.

Thin film nanocomposite embedded with polymethyl methacrylate modified multi-walled carbon nanotubes for CO2 removal

Over the past decades, carbon nanotubes (CNTs) have gained tremendous attention as nanofillers in nanocomposite membranes owing to their potential to improve the physical properties and gas separation performance. In this work, polyamide–ethylene oxide (PA–EO) thin film nanocomposite (TFN) membranes embedded with polymethyl methacrylate (PMMA) grafted multi-walled carbon nanotubes (MWNTs) were successfully fabricated. The TFNs were fabricated via an interfacial polymerization (IP) technique to allow the formation of a very thin selective skin. The effects of the incorporation of nanofiller within the coating and selective thin film layers on the membrane morphologies and gas separation performance have been highlighted. The TFN incorporating milled PMMA-MWNTs within its coating layer showed a 29% increment in CO2 permeance (70.5 gas permeation units (GPU)) with 47% and 9% enhancement in CO2/N2 and CO2/CH4 selectivity respectively compared to its thin film composite counterpart. While the improvement in gas separation performance can be primarily attributed to the presence of highly diffusive channels rendered by the CNTs, PMMA grafting is also believed to play an important role to ensure good nanofiller dispersion and good filler–polymer compatibility. Uncovering the construction of membrane fabrication could pave facile yet versatile ways for the development of effective membranes for greenhouse gas removal.

Carbon nanotubes for desalination - an innovative material with enormous potential

This article aims to provide an insight into the use of carbon nanotubes to enhance the performance of available sea-water and brackish water desalination systems in a holistic manner. It looks at current hurdles and future challenges that relate to the use of this material.

A REVIEW OF ASSEMBLED POLYACRYLONITRILE-BASED CARBON NANOFIBER PREPARED ELECTROSPINNING PROCESS

Electrospinning is a very simple and versatile process by which polymer nanofibers with diameters ranging from a few nanometers to several micrometers can be produced using an electrostatically driven jet of polymer solution (or polymer melt). Significant progress has been made in this process throughout the last decade and the resultant nanostructures have been exploited to a wide range of applications. An important feature of the electrospinning process is that electrospinning nanofibers are produced in atmospheric air and at room temperature. This paper reviews the assembled polyacrylonitrile (PAN)-based carbon nanofibers with various processing parameters such as electrical potential, distance between capillary and collector drum, solution flow rate (dope extrusion rate), and concentration of polymer solution. The average fiber diameter would increase with increasing concentration of the polymer solution and the flow rate. Therefore, the screen distance could also increase but the average electrical potential of the fibers diameter decreases. Electrospinning process can be conducted at higher electrical potentials, lower flow rate, nearer screen distance, and higher concentrations of dope.