STUDY OF PHOTOCATALYTIC AND ADSORTIVE BEHAVIOUR OF PURE ZIRCONIUM OXIDE AND CARBON-SULPHUR CO-DOPED ZIRCONIUM OXIDE NANOCOMPOSITES FOR PURIFICATION OF DYE WASTEWATER

Abstract

In this work, ZrO2 nanoparticles were synthesized by green method using Plumeria acuminata leaf extract via the variation of pH. Subsequently, carbon and sulphur were incorporated onto the lattice layer of the prepared ZrO2 nanoparticles by wet impregnation method. The prepared undoped, doped and co-doped zirconium oxide based nanomaterials were characterized for their morphology, phase structure, surface area, microstructure, absorption band, crystallinity and elemental composition using HRSEM, XRD, BET, HRTEM, UV-visible and EDS. The photocatalytic and adorptive properties of ZrO2 based materials for the treatment of local dyeing wastewater were investigated. The photocatalytic and adsorptive performance of ZrO2, C-ZrO2, S-ZrO2 and C-S-ZrO2 nanocomposites were determined by measuring the reduction in the level of .the following indicator parameters in local dyeing wastewater (TOC, COD, BOD, SO42-, CO32-, Cl-, NO3¬- and pH) in the presence and absence of natural sunlight irradiation. HRSEM analysis revealed the formation of agglomerated spherical particles for ZrO2 alone and mixture of spherical and hexagonal shaped particles for C-S co-doped ZrO2 nanocomposites. The EDS confirmed the presence of Zr and O as the dominant elements for ZrO2 alone and also C and S in C-S-ZrO2 nanocomposites. The XRD pattern of pure ZrO2 and carbon doped ZrO2 revealed the formation of tetragonal phase and doping with sulphur revealed orthorhombic, while the co-doped carbon-sulphur ZrO2 revealed a mixture of tetragonal and orthorhombic phases. The crystalline size decreases with addition of the dopants in the order of ZrO2(20.03 nm), S-ZrO2 (17.51 nm), C-ZrO2(16.03 nm) and C-S-ZrO2 (12.40 nm). Optical characterization of the nanomaterial revealed reduction of band gap from 5.2 eV to 3.4 eV for ZrO2 and C-S-ZrO2 respectively. The BET analysis revealed increase in the surface area upon the addition of the dopants in the order of C-S-ZrO2 (80.165 m2/g) >.C-ZrO2 (52.637 m2/g)>.S-ZrO2(24.824 m2/g)> ZrO2 (10.682 m2/g). It was found that the photocatalytic and adsorptive behaviour of the four materials differ with respect to the target pollutants. Of all the four samples studies, C-S-co-doped ZrO2 nanocomposites with highest mesoporosity exhibited excellent photocatalytic activity under natural sunlight than carbon doped ZrO2 , sulphur doped ZrO2 and ZrO2 alone with TOC, COD, BOD, Cl-, NO3¬- and pH removaal efficiency of 97.7%, 77.3%, 87.6%, 63.9%, 84.4%, 70.3%, 83.3% and 19.4% within 120 minutes respectively. The order of adsorptive behaviour of the four samples for the removal of TOC, COD, BOD, Cl-, NO3¬- and pH were C-S-ZrO2 (82.9%) >.C-ZrO2 (82.7%)>.S-ZrO2(81.7%)> ZrO2 (80.3%). This study revealed carbon-sulphur co-doped ZrO2 have excellent adsorption and photocatalytic properties for the removal of target pollutants from local dyeing wastewater except for COD, BOD, Cl-, SO42- and CO32- that were above the permissible limits.