UV Suppression in photoluminescence emission and improved photocatalytic activity under sunlight in nanoassemblies and nanocrystals of ZnO

Abstract

The objective of present study is to analyse the impact of alterations in the shape and size of ZnO on PL emission and photocatalytic activity of ZnO nanostructures. The study also aims at addressing the knowledge gap between synthesis approach and its role in governing the optical, morphological and photocatalytic behaviour. Here, we report the facile and controlled synthesis of nanoassemblies (NA) and nanocrystals (NC) of ZnO via soft chemical approach. The synthesized ZnO nanostructures were characterized using TEM, SEM, UV–vis and photoluminescence (PL) measurement. The morphology of ZnO is tuned by adjusting the molar ratio of DEG and water whose impact is also noticed on the PL emission spectra. PL analysis revealed that the UV emission (378 nm) and defect levels attributed to Zn interstitial (Zni) and oxygen interstitial (Oi) are stabilized at ambient condition. However, UV band gap emission peak is significantly reduced making it lesser distinct by introducing appropriate amount of water in diethylene glycol (DEG) solvent during ZnO synthesis. Such controlled nanostructured growth demonstrates potential for sustainable photocatalytic activity under both UV and Sunlight irradiation. The study shows 100% photodegradation efficiency for ZnO NA and it get completely irradiated methylene blue dye within 90 min under UV light, whereas only 70% dye is degraded in 100 min for ZnO NC. Under natural Sunlight, ZnO NA has been achieved 97% degradation efficacy in 75 min; however, ZnO NC has degraded only 89% of dye. Further, the degradation of dye over ZnO was observed to follow pseudo first order reaction kinetic model that is used to determine the rate constant of the reaction.