Development of Highly Visible-light Sensitive Photocatalyst by Controlling Surface Nano-structure of TiO_2 with Cold Plasma Treatments

采用磁控管式冷等离子体反应器，用氩、氮等离子体串联处理TiO_2颗粒膜。XRD分析表明，氮掺杂使锐钛矿（101）平面的半值宽度增大，并使锐钛矿的晶格明显变形。这种晶格畸变将源于Ti-N键和氧缺陷的形成。等离子体处理后的薄膜除了吸收紫外线外，还吸收了可见光。出现可见光活性，对应于可见光吸收。可见光活性的出现是由Ti-N键的形成引起的。通过对氮掺杂TiO_2带结构的理论分析，发现Ti-N键的形成足以缩小可见光活性TiO_2的带隙。最佳的Ti-N键含量是获得最高可见光活性的必要条件。过量的Ti-N键会导致氧缺陷的增加，从而降低粒子的可见光活性。研究表明，冷等离子体处理可以控制TiO_2颗粒的表面纳米结构。冷等离子体处理可以加速Ti-N键的形成，抑制颗粒中氧缺陷的形成，并且通过颗粒中可见光活性的出现可以开发出高灵敏度的光催化剂。

A film composed of TiO_2 particles was treated with argon and nitrogen plasmas, in series, with magnetron-type cold plasma reactor. According to XRD analysis, half-value width of anatase (101) plane was increased with nitrogen-doping and it becomes apparent that crystal lattice of anatase was distorted with nitrogen-doping. Such lattice distortion will be originated with formations of Ti-N bonds and oxygen defects.The plasma-treated film revealed visible-light absorption, in addition to ultraviolet-light absorption. Visible-light activity appeared, corresponding to the visible-light absorption. The appearance of the visible-light activity will be originated by the formation of Ti-N bonds. According to theoretical analysis of band structure for the nitrogen-doped TiO_2, the formation of Ti-N bonds will be adequate for narrowing of the band gap in the visible-light active TiO_2. Optimum content of Ti-N bonds is necessary to obtain the highest visible-light activity. A large excess of Ti-N bonds will bring about an increase in oxygen defects which depress the visible-light activity of the particles.In this work, it becomes apparent that surface nano-structure of TiO_2 particles can be controlled by the cold plasma treatments. It is possible by the cold plasma treatments to accelerate the formation of Ti-N bonds and depress the formation of the oxygen defects in the particles, and highly sensitive photocatalyst can be developed by the appearance of the visible-light activity in the particles.