Density Functional Theory Calculations and Experimental Studies of Surface Defect Effects on Photocatalytic Properties of Metal Oxide Semiconductors

表面缺陷對半導體金屬氧化物光催化性能影響的理論與實驗研究

Student thesis: Doctoral Thesis

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Award date11 Feb 2019

Abstract

Introducing surface defects into the lattice of metal oxide semiconductors is one of the most efficient strategies for expanding the coverage of the solar spectrum. However, there are still unknown areas in the design and synthesis of highly functional surface defect metal oxide semiconductor materials. By tuning reaction parameters and setting up convincing models that include cluster and periodic structures combined with experimental and theoretical results, the effects of the oxygen vacancies, hydrogen heteroatoms and metal vacancies on the electronic structures can be revealed. This finding will be helpful for developing highly efficient surface defect metal oxide semiconductor materials.

TiO2 is a promising photocatalytic material owing to its low cost, good stability, high photoelectric properties and environmental compatibility. However, the practical applications of this material are limited by its large band gap. The oxygen-deficient TiO2 provides a solution to this problem. We first used small clusters to estimate the geometric and electronic structures, including the band gap, energy level and projected density of states, to reveal the composition dependent reactivity of TiO2 clusters. Among the different titanium oxide species that we investigated, the most stable structures are TinO2n, however, their reactivities are relatively lower than the clusters with smaller O atom ratios. Due to the extremely small sizes, the properties of small clusters cannot be applied to periodic structures directly. Therefore, the persuasive periodic modeling of TiO2 and H heteroatoms adsorbed oxygen-deficient surfaces of TiO2 were set up to achieve the in-depth, detailed theoretical results based on the experimental measurements. The oxygen-deficient TiO2 were obtained via a calcination process under hydrogen environment. Through our theoretical calculations and experimental studies, the influence of the adsorbed H heteroatoms on the electronic structures of oxygen-deficient TiO2 has been revealed.

Although TiO2 remains center stage in metal oxide semiconductor materials, increasing academic interest has been focused on Bi2O3, which has a moderate band gap and wider coverage of the solar spectrum than TiO2. In this study, we produced metallic bismuth nanoparticles and bismuth vacancies on the surface of Bi2O3 via different reaction temperatures and set up corresponding models to describe the different bismuth-deficient surfaces of Bi2O3. The influence of the surface metallic bismuth nanoparticles and bismuth vacancies on the electronic structures of Bi2O3 has been revealed. Moreover, after thermal vacuum treatment, the as-prepared Bi2O3 samples exhibit higher efficiency photo(electro)chemical performance. Combining the experimental results with the theoretical calculations can help us to obtain a deeper understanding and new insights into the surface defect structures of Bi2O3.

The simple thermal treatments and the convincing theoretical calculations in this work not only offer guidance for the synthesis and understanding of the surface defects of functional semiconductors but also provide a reliable solution for dealing with the shortage of energy and the problem of environmental contamination.

    Research areas

  • TiO2, Bi2O3, DFT, Photocatalysis, Surface defect