A Physical Route to High Performance Heterojunction Composites: Experiments, Mechanism and Applications
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A Physical Route to High Performance Heterojunction Composites: Experiments, Mechanism and Applications Delong Li1,2, Chengzhi Luo2, Chunxu Pan1,2 1 Shenzhen Research Institute, Wuhan University, Shenzhen, Guangdong 518057, China. 2 School of Physics and Technology, Wuhan University, Wuhan, Hubei 430072, China. ABSTRACT In order to enhance the photocatalytic efficiency of oxide semiconductors, variant processes have been proposed. The creation of the heterojunction composites has attracted considerable attentions and developed into an important research area for the high performance photocatalyst preparation. In this paper, we introduce the research progress on heterojunction composites which were prepared via a novel physical route with relatively high temperature treatments. It is hope that this mini-review can inspire research interest in the realm of heterojunction synthesis based on the thermal diffusion mechanism. INTRODUCTION Oxide semiconductors have attracted wide attention in the past decade, due to the its proven ability to function as a photocatalyst and facilitate important environmentally beneficial reactions, such as water splitting to generate hydrogen, dye-sentitized solar cells, sensors and treatment of polluted air and water. However, its applications are still limited because of its inherent defects involving wide band gap and high recombining ratio of photo-induced electron-holes [1]. Therefore, it is still a challenging topic to design and synthesize visible light response photocatalytic materials with higher utilization efficiency of solar energy. In order to overcome these disadvantages, many processes have been proposed in the last several years, such as tuning synthesis method, compounds, metal and nonmetal doping, surface modifications, etc. [2-6]. Generally, coupling with oxide semiconductor is a simple and efficient method to improve photocatalytic efficiency. Up to now, many photocatalytic composites have been prepared by using variant methods, such as metal-organic vapor-phase epitaxy, hydrothermal process, chemical vapor deposition (CVD), and microwave assisted method, etc [7-10]. It has been wellknown that a crucial point for obtaining a high-quality composite system is to achieve a tight contact interfaces between different phases, i.e. to form a heterojunction structure. However, the tight contact heterojunction is difficult to be formed via regular chemical methods at low temperatures. In general, there exists only a mechanical contact at the interface which has many “gaps”, resulting in problems with stability and service life during long-term usage. Obviously, the above chemical routes provide simple and facile processes to get semiconductors composites. But due to low temperature, it is difficult to form a full lattice coherent or partial lattice coherent heterojunction between the two kinds of semiconductors. In this paper, we introduce a novel physical route for preparing heterojunction composites based on thermal diffusion mechanism. By using high temperature treatment proce
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