Aneela Sabir

Fabrication of tethered carbon nanotubes in cellulose acetate/polyethylene glycol-400 composite membranes for reverse osmosis.

In this study pristine multi-walled carbon nanotubes (MWCNTs) were surface engineered (SE) in strong acidic medium by oxidation purification method to form SE-MWCNT. Five different amount of SE-MWCNT ranging from 0.1 to 0.5 wt% were thoroughly and uniformly dispersed in cellulose acetate/polyethylene glycol (CA/PEG400) polymer matrix during synthesis of membrane by dissolution casting method. The structural analysis, surface morphology and roughness was carried out by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively, which showed that the dispersed SE-MWCNT was substantially tethered in CA/PEG400 polymer matrix membrane. The thermogravimetric analysis (TGA) of membranes also suggested some improvement in thermal properties with the addition of SE-MWCNT. Finally, the performance of these membranes was assessed for suitability in drinking water treatment. The permeation flux and salt rejection were determined by using indigenously fabricated reverse osmosis pilot plant with 1000 ppm NaCl feed solution. The results showed that the tethered SE-MWCNT/CA/PEG400 polymer matrix membrane, with strong SE-MWCNTs/polymer matrix interaction, improved the salt rejection performance of the membrane with the salt rejection of 99.8% for the highest content of SE-MWCNT.

Novel green nano composites films fabricated by indigenously synthesized graphene oxide and chitosan.

Graphene oxide (GO) was indigenously synthesized from graphite using standard Hummers method. Chitosan-graphene oxide green composite films were fabricated by mixing aqueous solution of chitosan and GO using dilute acetic acid as a solvent for chitosan. Chitosan of different viscosity and calculated molecular weight was used keeping amount of GO constant in each composite film. The structural properties, thermal stability and mechanical properties of the composite films were investigated using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and tensile test. FTIR studies revealed the successful synthesis of GO from graphite powder and it was confirmed that homogenous blending of chitosan and GO was promising due to oxygenated functional groups on the surface of GO. XRD indicated effective conversion of graphite to GO as its strong peak observed at 11.06° as compared to pristine graphite which appeared at 26°. Moreover, mechanical analysis confirmed the effect of molecular weight on the mechanical properties of chitosan-GO composites showing that higher molecular weight chitosan composite (GOCC-1000) showed best strength (higher than 3GPa) compared to other composite films. Thermal stability of GOCC-1000 was enhanced for which residual content increased up to 56% as compared to the thermal stability of GOCC-200 whose residue was restricted to only 24%. The morphological analysis of the composites sheets by SEM was smooth having dense structure and showed excellent interaction, miscibility, compatibility and dispersion of GO with chitosan. The prepared composite films find their applications as biomaterials in different biomedical fields.

Conjugation of silica nanoparticles with cellulose acetate/polyethylene glycol 300 membrane for reverse osmosis using MgSO4 solution.

Thermally-induced phase separation (TIPS) method was used to synthesize polymer matrix (PM) membranes for reverse osmosis from cellulose acetate/polyethylene glycol (CA/PEG300) conjugated with silica nanoparticles (SNPs). Experimental data showed that the conjugation of SNPs changed the surface properties as dense and asymmetric composite structure. The results were explicitly determined by the permeability flux and salt rejection efficiency of the PM-SNPs membranes. The effect of SNPs conjugation on MgSO4 salt rejection was more significant in magnitude than on permeation flux i.e. 2.38 L/m(2)h. FTIR verified that SNPs were successfully conjugated on the surface of PM membrane. DSC of PM-SNPs shows an improved Tg from 76.2 to 101.8 °C for PM and PM-S4 respectively. Thermal stability of the PM-SNPs membranes was observed by TGA which was significantly enhanced with the conjugation of SNPs. The micrographs of SEM and AFM showed the morphological changes and increase in the valley and ridges on membrane surface. Experimental data showed that the PM-S4 (0.4 wt% SNPs) membrane has maximum salt rejection capacity and was selected as an optimal membrane.

Novel reverse osmosis membranes composed of modified PVA/Gum Arabic conjugates: Biofouling mitigation and chlorine resistance enhancement

A novel crosslinked Poly (vinyl alcohol) (PVA) reverse osmosis (RO) thin film membrane conjugated with Gum Arabic (GA) with superb performance and features was synthesized for water desalination. RO membrane desalination parameters, such as hydrophilicity, surface roughness, water permeability, salt rejection, Chlorine resistance and biofouling resistance were evaluated using a dead end RO filtration unit. The incorporation of Pluronic F127 and the conjugation of Gum Arabic improved the overall RO performance of the membranes. This study has shown that the membrane PVA-GA-5 that contains 0.9wt% Gum Arabic provided excellent permeation, salt rejection, Chlorine and biofouling resistance and mechanical strength. The most remarkable result to arise from this research is that the overall RO performance enhancement has been achieved while utilizing PVA/Gum Arabic as a separation layer without the use of a substrate, which eliminates negative effects associated with the use of a substrate like internal concentration polarization.

Self-sterilized composite membranes of cellulose acetate/polyethylene glycol for water desalination.

Cellulose acetate/Polyethylene glycol-600 composite membranes were fabricated by two step phase inversion procedure and modified by in-situ reduction of silver nitrate. FTIR spectra demonstrated the existence of functional groups for bonding of silver with oxygen at 370cm(-1), 535cm(-1). The XRD diffractogram indicates characteristic peaks at 2θ values of 38.10°, 44.30°, 64.40°, and 77.30° which confirm the successful incorporation of silver within matrix of composite membranes. The morphology of composite membranes with appearances of spongy voids was exemplified from the scanning electron microscope. The atomic force microscopy was used to determine the increase in the surface roughness of the membranes. The increase in hydrophilicity, measured through contact angle, is rendered to the embedment of silver. The modification of membranes increased the flux from 0.80 to 0.95L/hr.m(2). The resulting membranes have outstanding ability to fight against gram negative Escherichia Coli and Bacillus Sabtilus. The novel cellulose acetate/polyethylene glycol membranes customized with silver have paved the path for evolution of axenic membranes.

An Investigation of Ac Impedance and Dielectric Spectroscopic Properties of Conducting Chitosan-silane Crosslinked-poly (Vinyl Alcohol) Blended Films

The films of chitosan (CS)-silane crosslinked-poly(vinyl alcohol) (PVA) with different weight % were prepared. The effect on conductivity of CS/PVA blended films due to change in the concentration of PVA and temperature was investigated by impedance spectroscopy and showed good conductance properties. The complex impedance plots revealed single semicircular arcs indicating the bulk contribution to overall electrical behavior of all synthesized samples. The ac conductivity obeyed the Jonschers power law for all samples in the frequency range of 2 kHz to 2 MHz. The ionic conductivity of the films was increased with the increase in temperature for all synthesized samples which showed an increase in the number of effective charge carriers while it was decreased at a specific higher temperature for each film. The observed activation energy for CP4, CP8 and CP10 were 0.431, 0.610 and 0.425 eV, respectively. These properties showed that the films were promising materials to be employed for conducting properties.

The effect of Nanocrystalline cellulose/Gum Arabic conjugates in crosslinked membrane for antibacterial, chlorine resistance and boron removal performance

In this work, we developed hybrid membranes integrated with Nanocrystalline cellulose (NCC)/Gum Arabic (GuA) conjugates using crosslinked Poly (vinyl alcohol) (PVA) as a matrix phase with the addition of PEO-PPO-PEO block copolymer that insured pore formation. At first, the NCC was prepared from microcrystalline cellulose via acid hydrolysis process. The performance property of hybrid NCC/GuA was measured using boron removal. The results showed that the rejection capability enhanced as compared to the control membranes, especially at 0.1wt% of NCC the selectivity is up to 92.4% with the flux rate of 21.3L/m2.h. Moreover, the GuA in NCC/GuA conjugate significantly enhances the antibacterial activity by hindering the bacterial attachment to the surface as both of them carry the negative charge. Also by providing the active sites responsible for hydrogen bonding thus enhancing the hydrophilic character resulted in increased permeation flux rate. Therefore, the NCC/GuA conjugated membranes have great potentials for boron removal.

Fabrication and performance characteristics of tough hydrogel scaffolds based on biocompatible polymers.

Novel silane crosslinked tough hydrogel scaffolds were prepared using chitosan (CS) and polyvinyl alcohol (PVA) to give network structure and scaffolds properties. The influence of crosslinking and PVA concentration on scaffolds were studied. Fourier transform infrared spectroscopy (FTIR) spectroscopy confirmed the presence of incorporated components. Tensile strength (TS) and fracture strain analysis of scaffolds were detected owing to the mutual effect of chemically and physically crosslinked network. Tough hydrogel scaffolds having 90% CS and 10% PVA exhibited TS of 49.18MPa and 10.15% elongation at break. The contact angle is less than 90° exhibited the hydrophilic nature of the scaffold. X-ray diffraction analysis (XRD) indicated the characteristics peaks fitting to CS and PVA and increase in the crystallinity of scaffolds. Cytotoxicity of scaffolds with different human fibroblast cell lines (F121, F192 and F84) for indirect method and human dermal fibroblast cell lines (F121) for direct method was evaluated. This indicated that these biomaterials were non-toxic, viable to the used cell lines, helpful in the growth of these cells and did not discharge toxic material damaging to the living cells.

In-situ crosslinked nanofiber mats of chitosan/poly(vinyl alcohol) blend: Fabrication, characterization and MTT assay with cancerous bone cells

Biocompatible crosslinked nanofiber mats of chitosan (CS)/poly(vinyl alcohol) (PVA) were fabricated using electrospinning technique. CS and PVA blends (7, 9 and 11 weight %) of prepared keeping ratios of CS: PVA to 1:4 and was crosslinked with tetraethoxysilane (TEOS). Fourier transform infrared (FTIR) analysis confirmed the existence of inter- and intramolecular hydrogen bonding between polymer chains and the development of siloxane linkage within the nanofibers. X-ray diffractometry (XRD) analysis showed an increase in the crystallinity of electrospun nanofibers after crosslinking as compared to the uncrosslinked nanofibers and with an increase in CS/PVA content. Scanning electron microscopy (SEM) micrographs exhibited the formation bead-free fibers at higher polymer concentration. The average size of the nanofibers was found in the range of 40 to 100 nm. The concentration and crosslinker content affected the mechanical and thermal properties of the nanofibers. The crosslinker has increased the tensile strength (TS) values upto 120 % and Young’s modulus by 71 % as compared to the uncrosslinked nanofibers while elongation at break was decreased in all nanofibers. The cell viability of the nanofibers was investigated by employing human cancerous bone cells (MG63). The obtained results showed that cancerous bone cells were not proliferated in the presence of nanofibers and the growth of the cells was inhibited confirming the worth of CS/PVA nanofibers against cancerous bone cells. This inherent behaviour can be exploited as base material for anticancer biomedical applications.

Decoration of open pore network in Polyvinylidene fluoride/MWCNTs with chitosan for the removal of reactive orange 16 dye

Inspired by the hydrophilic, biocompatible, adsorbent properties of chitosan. A simple, adaptable, green synthesis method was developed to prepare a thin film composite membranes using chitosan as a pore decorating material for the removal of anionic dye-Reactive orange 16 (RO-16). The hydrophilic chitosan was used to fill up the porous hydrophobic PVDF substrate, modified by MWCNTs. The dye rejection was carried out through the formation of a strong electrostatic interaction between the cationic group of chitosan surface and the anionic group of RO-16 dye. The dye molecules accumulate on the chitosan surface, thus promoting the higher retention rate. The TFC membranes were evaluated using dead filtration plant. It is found that the modified membranes showed RO-16 rejection up to 91% with optimum permeation flux of 170kgm-2h-1. Furthermore, the presence of chitosan on MWCNT/PVDF substrate provides a hydrophilic character thus decreasing the active sites available for foulant attachment which is confirmed by the fouling study. The CTAB foulant showed an increase in flux rate even after physical flushing. The modification procedure is performed under mild conditions, thus it is helpful to fabricate TFC membrane at a commercial scale.