Synthesis and design of PSf/TiO 2 composite membranes for reduction of chromium (VI): Stability and reuse of the product
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The study demonstrates the 100% repeated recyclability of hybrid membranes without any pretreatment. Composite membranes designed with titanium dioxide (TiO2) nanoparticles (NPs) and polysulfone (PSf) membranes were used for reduction of chromium (Cr) (VI) to Cr (III) under sunlight. Different concentrations of TiO2 NPs varying from 1.5% to 2.5% with the difference of 0.5% were incorporated into the membrane matrix. Increase in weight percentage of TiO2 particles enhances the reduction to 100% within 2.5 h with an increase in recyclable capacity as well. The effect of recycling on the surface of the membrane was studied using x-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscopy (AFM). The observations in general indicate an increase in roughness without affecting the catalytic efficiency up to six recycles. The study on surface membrane morphology and catalytic efficiency with reusability opens a scope for a feasible economical chromium reduction via a membrane process. Macro and micro structure of the membrane before reduction and after recycling were studied and compared with scientific evidence. Based on the results, the kinetic model was proposed for the reduction reactions.
I. INTRODUCTION
Lately, membranes have been of interest in various fields because of their wide applications. The general areas of interest in membrane process include its synthesis, application and post synthesis modification.1 The membrane synthesis process involves techniques and improving materials and methods for manufacturing processes so as to produce a high performance.2 The application and post synthesis process depends on the specific operating parameters of a membrane system. These include selecting the raw water characteristics, operating pressure, and cleaning at regular intervals to allow the system to operate at a maximum efficiency. The different techniques for removal of heavy metals include photoreduction,3–6 ion exchange,7 solvent extraction,8 reverse osmosis,9 separation,10 and absorption.11 Among all the heavy metals, reduction/removal of hexavalent chromium (Cr) has become a major concern because of its toxicity, carcinogenicity, and mutagenicity.12 Photocatalytic reduction of toxic and hazardous Cr (VI) to nontoxic Cr (III) using semiconductor technology is one of the promising methods for the removal of Cr (VI). However, this application demands high purity, crystallinity,
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.169 J. Mater. Res., Vol. 29, No. 14, Jul 28, 2014
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particular phase, and particle size of the semiconductor material. The anatase type of nano titania (titanium dioxide (TiO2)) with an optical bandgap of approximately 3.2 e V has a better catalytic efficiency than rutile phase13–17 probably because of its lower recombination of electron hole pairs. Hence, it was used for reduction of Cr (VI). On internal recombinat
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