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Date of Award


Document Type

Campus Access Master's Thesis

Degree Name

Master of Science in Materials Science and Engineering (MS)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Yun Hang Hu

Committee Member 1

Stephen A. Hackney

Committee Member 2

Kazuya Tajiri


Great effort has been made to solve environmental and energy issues by developing photocatalytic processes, which can convert solar energy into chemical fuels. However, most of photocatalysts can only absorb ultraviolet light because of their wide band gap. Therefore, catalysts with narrower band gaps are necessary for visible-light driven photocatalytic water splitting. In this research, high energy ball milling, which is a possible technique to narrow the band gap, was employed to tune band structure of ZnO. The ball-milled particles were evaluated by XRD, FE-SEM, UV-Vis, and EIS measurements.

XRD measurements showed that the average particle size of ZnO nanoparticles was significantly decreased by ball milling. This was supported by FE-SEM images. Furthermore, it was found that the ball-milling created defects, resulting in a narrower energy gap (Eg). However, the conduction band potential, which is calculated from the Mott-Schottky plots, remained almost unchanged. Therefore, an energy level above the valence band of ZnO should be generated, which can be attributed to the formation of zinc vacancies (Vzn). The longer the ball-milling time, the more the oxygen content, the lower the energy level of Vzn. In addition, it was demonstrated that the ball-milling-induced defects in ZnO can be partially repaired by an annealing process, enlarging its band gap. This further proves that the formation of Vzn is a reason for the narrowed band gap of ball-milled ZnO.