Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Tsun-Kong Sham

Abstract

Transition metal oxides, including titanium dioxide (TiO2), zinc oxide (ZnO) and Tin dioxide (SnO2) are widely recognized semiconducting photocatalysts. This project engages in a detailed examination of the phase transition of TiO2 and the synthesis of heterostructured metal oxides using an eco-friendly method of ball-milling. A variety of spectroscopy and microscopy techniques have been used to analyze the products. Synchrotron-based techniques: X-ray Absorption near-edge spectroscopy (XANES), X-ray Emission Spectroscopy and X-ray excited optical luminescence (XEOL) can demonstrate the local structure and bonding. The finding highlights a phase transition in TiO2 and the formation of new zinc titanium compounds at speeds of 300rpm and 500rpm. However, at the 150rpm ball milling speed, heterostructured TiO2/ZnO and TiO2/SnO2 formed. This study offers valuable insights into the impact of ball-milling on the synthesis and transformation of semiconducting transition metal oxides, providing a pathway toward the advancement of high-performance semiconductors.

Summary for Lay Audience

Semiconductors, with their significant utility in the electronic industry, include optoelectronic devices, photoelectrochemical technologies, and high-power electronics, which are continually evolving to meet rising performance demands. Semiconducting transition metal oxides are the most common and extensively characterized heterogeneous photocatalysts such as titanium dioxide (TiO2), zinc oxide (ZnO) and Tin dioxide (SnO2). Researchers have widely recognized the potential of mixed-phased and heterostructured semiconductors to significantly enhance the photocatalytic properties of semiconductors. Compared to other synthesis methods, ball-milling is renowned as a cost-effective, eco-friendly approach. Ball milling is a mechanical technique widely used to grind samples into a smaller size. During the ball milling process, the centrifugal forces cause speed differences between the balls and jars, creating friction and point collisions and releasing high pulverization energy.

This thesis engages in a comprehensive analysis of the phase transition of TiO2 and the synthesis of heterostructured metal oxides (TiO2/ZnO and TiO2/SnO2) through ball-milling. For the phase transition of TiO2, X-ray absorption near-edge structures (XANES) offer greater sensitivity in assessing the chemical and structural environment, and linear combination fitting (LCF) is utilized to determine the chemical ratio within the product. Moreover, the changes in the chemical and electronic environment after the formation of heterostructure TiO2/ZnO and TiO2/SnO2 can be detected by the synchrotron techniques, including X-ray Absorption near-edge spectroscopy (XANE), X-ray Emission Spectroscopy, X-ray excited optical luminescence (XEOL), and 2D X-ray Absorption Near Edge Structure-X-ray Excited Optical Luminescence (2D-XANES-XEOL).

The finding highlights a phase transition in TiO2 and the formation of new zinc titanium compounds at the speed of 300rpm and 500rpm. However, at the 150rpm ball milling speed, heterostructured TiO2/ZnO and TiO2/SnO2 formed. This study offers valuable insights into the impact of ball-milling on the synthesis and transformation of semiconducting transition metal oxides, paving the path towards the development of high-performance semiconductors.

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