Papers by Hafiz Zahid Shafi
Desalination and Water Treatment, 2016
Membrane surface modification with the aim of lowering foulant to surface affinity, has recently ... more Membrane surface modification with the aim of lowering foulant to surface affinity, has recently gained considerable attention. In this article, we report improved performance (permeate flux, salt rejection, and resistance to alginate fouling) of surface-modified reverse osmosis (RO) membranes, under cross-flow filtration conditions. The surface of RO membranes was modified by amphiphilic hydroxethyl methacrylate-co-perfluorodecyl acrylate (HEMA-co-PFDA) copolymer films. The amphiphilic coatings were deposited via an all-dry and solventless vapor deposition technique, termed as initiated chemical vapor deposition. Scanning electron microscopy revealed that a dense and continuous layer of alginate formed on the surface of the unmodified membranes, whereas foulant deposition on the surface-modified membranes was found to be more sporadic and discontinuous. The coatings were found stable even after 6 h of exposure to sodium alginate at higher pressure (800 psi), as evidenced by ATR-FTIR analysis of the post-fouled membranes.
In this work we report surface modification of commercial reverse osmosis membranes by depositing... more In this work we report surface modification of commercial reverse osmosis membranes by depositing ultrathin copolymer coatings, which could potentially enhance the biofouling resistance of RO membranes. Hydrophilic monomer hydroxyethyl methacrylate (HEMA) and a hydrophobic monomer, Perfluorodecyl acrylate (PFDA) were copolymerized directly on the active layer of commercial aromatic polyamide reverse osmosis (RO) membranes using an initiated Chemical Vapor Deposition (iCVD) technique. Attenuated total reflective Fourier transform infrared spectra (ATR-FTIR) verified the successful modification of the membrane surfaces as a new FTIR adsorption band around 1730 cm -1 corresponding to carbonyl groups in the copolymer film appeared after the deposition. X-ray Photoelectron spectroscopy (XPS) analysis also confirmed the presence of the copolymer film on the membrane surface by showing strong Fluorine peaks emanating from the fluorinated alkyl side chains of the PFA molecules.
Key Engineering Materials, 2010
ABSTRACT GeC thin films have been prepared by reactive pulsed laser ablation technique. Methane p... more ABSTRACT GeC thin films have been prepared by reactive pulsed laser ablation technique. Methane pressure (P(CH4)) was varied from 0 to 75 milli torrs (mT). Optical analysis of all the samples was performed by spectroscopic ellipsometry (SE). The optical constants i.e. refractive index (n), extinction coefficient (k), absorption coefficient (alpha) and thickness of deposited film(s) were obtained by modeling and simulations of ellipsometric data. It was found that deposition parameter (change in pressure of methane) has a profound effect on the properties of the deposited films. To support our results of optical analysis, other important diagnostic techniques like atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) etc. were employed.
Desalination, 2014
thin film deposition using all-dry technique at ambient temperature.
• Surface modification of commercial RO desalination membranes • p(4VP-co-EGDA) co-polymerization... more • Surface modification of commercial RO desalination membranes • p(4VP-co-EGDA) co-polymerization via initiated chemical vapor deposition • Functionalization of the co-polymer to carboxybetaine zwitterion surface moieties • Significant reduction of bacterial cell attachment on modified membrane surface • Perm selectivity under cross flow conditions comparable to virgin membranes a b s t r a c t Copolymer films of poly(4-vinylpyridine-co-ethylene glycol diacrylate) (p(4-VP-co-EGDA)) were synthesized and first deposited on various substrates via initiated chemical vapor deposition (iCVD). As-deposited copolymer films were converted to surface zwitterionic structures containing poly(carboxybetaine acrylic acetate) (pCBAA) units by a quaternization reaction with 3-bromopropionic acid (3-BPA). Conversion to a zwitterionic structure was confirmed by FTIR and high-resolution XPS N1s scans. Biopolymer adsorption of the deposited copolymer coatings was investigated by quartz crystal microbalance with dissipation (QCM-D) using a model foulant‐ bovin serum albumin (BSA). The optimized copolymer films were then deposited onto commercial RO membranes and with subsequent zwitterionicalization. Inertness to bacterial adhesion of the modified membranes was investigated by counting the number of Escherichia coli and Pseudomonas aeruginosa cells attached on the membrane surface under static conditions. Bacterial adhesion studies revealed an almost 98% reduction in microorganism attachment onto the surface of modified membranes compared to bare membranes, which clearly demonstrates the effectiveness and superior performance of the zwitterionic coating against bacterial adhesion. The salt rejection performance of the modified membranes resulted in improved salt rejection (98%); however, permeate flux was slightly compromised compared to virgin membranes. AFM analysis demonstrated that modified membranes showed lower RMS roughness compared to virgin membranes.
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Papers by Hafiz Zahid Shafi