Evaluation of photocatalytic performances of PEG and PVP capped zinc sulfide nanoparticles towards organic environmental pollutant in presence of sunlight.

Advanced oxidation processes triggered by nanoscale materials are promising owing to the in-situ generation of reactive radicals that can degrade toxic organic pollutants. In the present study, zinc sulfide (ZnS) nanoparticles with polyethylene glycol-4000 (PEG-4000) and polyvinylpyrrolidone (PVP) cappings were prepared using the chemical precipitation method and characterized thoroughly. Optical and structural characteristics of the capped ZnS nanoparticles were investigated and compared with those of uncapped ZnS nanoparticles. Results showed that PVP and PEG capped ZnS nanoparticles exhibited smaller crystallite size of 1.42 and 1.5 nm, respectively, as compared to uncapped ZnS (1.93 nm). Consequently, band gap energies of capped ZnS nanoparticles were higher which enable them to work as solar photocatalyst. The photocatalytic performance of the PEG, PVP-capped, and uncapped ZnS nanoparticles were evaluated against methyl orange (MO) dye and showed 85%, 87%, and 80% dye removal efficiencies, respectively. Degradation rate constant derived using Langmuir-Hinshelwood model revealed faster degradation kinetics bycapped ZnS photocatalysts owing to broader light absorption range. A possible dye degradation mechanism based on the energy levels positions was proposed to explain the route of photocatalytic degradation of MO by ZnS materials. It was inferred that the generation of reactive oxygen species by photogenerated electron-hole pairs facilitate degradation of MO dye molecules under sunlight illumination. It is expected that this work will provide insights into the development of strategies employed to achieve enhanced photocatalysis by nanoscale materials through organic capping.