Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Ajay Ray

Abstract

Among different approaches to overcome current environmental concerns, heterogeneous photocatalysis is recognized as a promising one. While there are various applications of photocatalysis including water splitting and water treatment, the overall efficiency of this process is still fairly low due to the two dominant drawbacks of current semiconductors, namely wide band gap and fast recombination of photo-generated charges, which restrict the photocatalytic reactions. Designing a hybrid photocatalyst composed of semiconductor hetero-junctions is a viable approach to address these challenges.

The objective of this research project is developing efficient photocatalysts via simple and practical synthesis methods in order to enhance the solar photocatalytic water splitting and water treatment. In this regard, hetero-structure photocatalysts from various groups are synthesized and characterized. Furthermore, the performance of such photocatalysts for photocatalytic reactions are evaluated and compared with single semiconductors.

The experiments presented in this study use solar simulator as the light source. Platinum is loaded on TiO2 photocatalyst by solar photo-deposition method. Pt/TiO2 as a metal-semiconductor hetero-structure is used for sacrificial photocatalytic hydrogen generation and Formaldehyde acts as sacrificial agent. The performance of the Pt loaded TiO2 is shown to be superior to that of the pure TiO2. Furthermore, a detailed parametric study is carried out on photocatalytic hydrogen generation using Pt/TiO2 and formaldehyde and it is shown that the solution pH, platinum content (wt %) on TiO2, catalyst concentration, light intensity, and initial formaldehyde concentration all affect the process.

In order to study the performance of a noble-metal-free-co-catalyst-semiconductor hetero-structure for photocatalytic hydrogen generation, molybdenum sulfide is grown on TiO2 by applying the in-situ solar photo-deposition method in a dye-sensitized photocatalytic system. It is observed that the presence of molybdenum sulfide in the system improves the solar photocatalytic hydrogen generation. A systematic statistical analysis is performed to investigate the effect of different reaction parameters as well as their interaction effects and to maximize the hydrogen generation under solar light irradiation.

Graphene-based TiO2 and ZnO are synthesized by hydrothermal method and their performances for photocatalytic water treatment are studied. Optical and structural properties of the composites are obtained using XRD, XPS, Raman spectroscopy, UV-vis spectroscopy, TEM, and SEM. Due to the beneficial effects of graphene, using the two composites results in better degradation of photocatalytic phenol. The parametric study for optimizing the reaction conditions is also presented.

The study conducted in this research thesis establishes that the efficiency of solar photocatalytic is greatly enhanced by using a hybrid photocatalyst, since such photocatalyst can significantly suppress the recombination of photo-generated charge carries and absorb the wider range of solar light.

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