Modified Electronic Structure Of Zinc Oxides For Photocatalytic Hydrogen Evolution

Abstract

In this thesis, the concentration was put on the fabrication of ZnO-based heterojunction photocatalysts to improve photocatalytic activities of hydrogen generation from water. The studies have been divided into two parts, including p-n heterojunctions and type II heterojunctions. The mechanism of each type of catalyst under UV and visible light irradiation was clearly illustrated in the thesis. The first part describes the in-situ synthesis of multicomponent ZnO-based photocatalysts for hydrogen production. The fabricated ZnO coupled with Cu-Cu2O nanoparticles and modified reduced graphene oxide (mRGO) ameliorated hydrogen production. The simultaneous introduction of mRGO and Cu-Cu2O enhanced the generation rate of photocatalytic hydrogen to 3085.02 µmol g-1 h-1 due to significant alteration of the electronic structure. The bandgap energy of the prepared catalysts decreased from 3.2 eV for pristine ZnO to 2.64 eV for a composite containing 15% CuCu2O. The optimized designated heterostructure efficiently separates photo charge carriers and prevents charge carriers’ recombination by accelerating charge transfer with the help of mRGO and metallic Cu and as a result leading to efficient hydrogen yields. The second part obviously demonstrates the role of EDTA molecules to enhance the photocatalytic activity of CdS/ZnMn2O4. The composite strongly improved catalytic performance due to the low photo-resistance when bridging EDTA molecules between two materials. Besides that, the optimal composite showed superior hydrogen production at a rate of 26.34 mmol.g-1.h-1. Furthermore, the material possessed better photostability in both acid and basic environments for around 18 h under light irradiations. This research could be useful to validate the efficacy of organic-inorganic systems for photocatalysts because of the positive effect of organic factors in synthesizing heterojunction photocatalysts, promoting charge transfers, and reducing recombination of electron-hole pairs to increase photoactivity.