POLYMER/METAL OXIDE MODIFIED CLAY NANOFIBROUS MEMBRANES FOR DECONTAMINATION

Abstract

This research focusses on the development of polyacrylonitrile/zinc oxide modified montmorillonite nanofibrous membranes for the efficient capture of particulate matter from atmosphere as well as decontamination of hexavalent chromium ions from water sources. Montmorillonite clay has been modified with zinc oxide nanoparticles, termed as zinc oxide modified montmorillonite, using three different raw materials namely zinc oxide nanoparticle, zinc nitrate and aloe vera gel. The particle size of zinc oxide modified montmorillonite varies from 16 nm to 48 nm. The surface morphology showed the presence of cuboidal shaped zinc oxide nanoparticles over the surface of the flaky shaped montmorillonite. The modification of montmorillonite to zinc oxide modified montmorillonite enhanced the thermal stability of montmorillonite. Polyacrylonitrile/Montmorillonite nanofibrous nanocomposites were fabricated using electrospinning technique with variation in concentration of montmorillonite from 0.25% to 1.00%. The electrospinning process developed PAN/Mt nanofibrous nanocomposites having reduced fiber diameters and high surface roughness as observed in Field Emission Scanning Electron Microscopy. The nanocomposite nanofibers were characterized by X-ray diffraction and Thermogravimetric analyzer for intercalation and thermal stability respectively. Electrospun polyacrylonitrile/zinc oxide modified montmorillonite nanofibrous nanocomposites with varying concentrations of zinc oxide modified montmorillonite ranging from 0.25% to 1.00% (w/w) were prepared to be used as filtration membranes. The addition of zinc oxide modified montmorillonite to polyacrylonitrile dope solution affects its viscosity and ionic conductivity. The surface morphology of the nanofibrous membranes was studied using field emission scanning electron microscopy. The average diameter of polycrylonitrile nanofibers and its nanocomposites was found to be between 247 nm to 468 nm. The addition iv of zinc oxide modified montmorillonite enhanced the thermal stability of polyacrylonitrile nanofibrous membranes from 188 °C to 310 °C. Ultrafine particulate matter and airborne microorganisms present in atmosphere are responsible for affecting the human health and the global climate. The development of bifunctional membranes which can simultaneously filter the particulate matter and inhibit the growth of microorganisms is the need of the hour. Polyacrylonitrile/montmorillonite nanofibrous nanocomposites were tested for their water vapor transmission rate, air permeability, burst strength and tensile strength. The filtration efficiency of 0.75% Polyacrylonitrile/montmorillonite nanofibrous nanocomposite was found to be 98.7% for PM2.5 particles present in air with a pressure drop of 46.8 Pa. An increase in porosity, air permeability and water vapor transmission rate of the nanofibrous membranes was observed with an increase in concentration of zinc oxide modified montmorillonite in polyacrylonitrile nanofibers upto 0.75%. The filtration efficiency of the nanofibrous membranes was evaluated using environment particle air monitor instrument. Polyacrylonitrile/zinc oxide modified montmorillonite nanofibrous membranes having 0.75% w/w zinc oxide modified montmorillonite exhibited filtration efficiency of 99.9% and a pressure drop of 26.72 Pa. The antimicrobial property of PAN/ZnO-Mt nanofibrous membranes was studied against S. aureus and E. coli bacterial strains showing 99.58% and 99.71% antibacterial activity respectively. The efficient adsorption of hexavalent chromium ions from wastewater using montmorillonite, zinc oxide modified montmorillonite, polyacrylonitrile /montmorillonite and polyacrylonitrile/zinc oxide nanoparticle modified montmorillonite nanofibrous nanocomposites as adsorbents has been studied. The effect of pH, concentration, time and amount of adsorbent on the removal of hexavalent chromium ions from water were investigated. Adsorption of hexavalent chromium ions over the adsorbents follows pseudo- v second-order kinetics, Langmuir and Freundlich isotherm. Polyacrylonitrile/zinc oxide nanoparticle modified montmorillonite and polyacrylonitrile /montmorillonite nanofibrous nanocomposites were found to be more effective adsorbents for Cr (VI) ions compared to zinc oxide modified montmorillonite and montmorillonite.