Natural Sunlight Assisted Bentonite-ZnO Mixed Oxide Catalyst for Organic Pollutant Removal in Leather Post Tanning Wastewater with Solar Reactor

Abstract

Organic pollutants in leather post tanning wastewater weredegraded by the advanced oxidation process using semiconductivephotocatalysis technique. A mixed oxide nanocatalyst Bentonite-ZnO was employed for the degradation process and the same hasbeen prepared by hydrothermal method. The morphological andoptical characteristics of the nanocatalyst was well characterizedby using X-ray diffraction (XRD), Scanning Electron Microscope(SEM), Diffuse Reflectance Spectroscopy (DRS) and FluorescenceSpectrophotometer studies. The diffraction peak of the mixedoxide catalyst confirms the formation of wurzite structure of ZnOwith the incorporation of bentonite clay particles. The SEM imagedisplayed the formation of nanosized particles with porousspherical texture. The optical band gap of the bare ZnO (3.3 eV)and Bentonite-ZnO (2.5eV) catalysts were measured by DRSstudies. A comparative study of photoluminescence spectra ofZnO and Bentonite-ZnO showed the suppression of charge carrierrecombination in case of Bentonite-ZnO than bare ZnO. Existenceof suitable charge carriers and vectorial transportation betweenbentonite and ZnO makes Bentonite-ZnO as an appropriatecatalyst for degradation of organic pollutants present in leatherpost tanning liquor. The semiconductive photocatalysis on leathertannery post tanning wastewater was carried out in a speciallydesigned pilot scale solar light reactor with Bentonite-ZnO, theresults are compared with bare ZnO catalyst, where thedegradation property with mixed oxide catalyst Bentonite-ZnO isbetter than bare ZnO. The decrease in COD with Bentonite-ZnOnanocatalyst is found to be 35.3% for three hours of continuousreaction under solar light. Such percentage of COD reductionsuggest to offer this nanocatalyst treatment as preliminary step forbetter performance of further treatment process.