耦合包覆层协同共振电子转移提高二氧化钛纳米线表面三价钛光催化稳定性研究

Photocatalysis is a promising, environmentally friendly technology for the conversion of solar energy into chemical energy. Among various semiconductor photo-catalysts, TiO2 remains the most popular material and can be considered as a benchmark in the field of photocatalysis. The many advantages of TiO2 include high photo-reactivity under UV-light, good stability with time, low cost, and environmentally friendly nature. . Among diverse modified methods to reduce the band-gap of TiO2, Ti3+ received more research attention, due to the localized state forming in the band gap at ∼0.8−1 eV below the conduction band edge of TiO2, which make TiO2 could absorb visible-light and have high electrical conductivity. However, the surface Ti3+ is easily oxidized into Ti4+ by absorbed oxygen and hydroxyl, thus losing visible-light activity. To address this key issue, in this application, we plan to employ the strategy of charge transfer resonance mechanism to stabilize Ti3+ by non-metal species situated in interstitial and/or substitutional positions, and further coupled charge transfer resonance with rGO coating to improve the photocatalytic stability of surface Ti3+. In the view of the advantage of one-dimension (1D) nano-material and our previous work (graphene wrapped TiO2 nano-tube with Ti3+ synthesized under high temperature), we intend to realize the above mentioned strategies on the model of rGO coated 1D TiO2 nanowire material. Specific, the coated 1D TiO2 material would be calcined under various atmosphere to dope N, S or C, to investigate the effect of electronegativity on Ti3+ stabilize mechanism by charge transfer resonance; then the structure of coating carbon would be modified, including Ti-C bond, a strategy of Ti-C bond introduced by carbon coating coupled charge transfer resonance would be done to improve the stability of surface Ti3+. Thus, we would obtain the detailed mechanism of charge transfer resonance, and the role of surface coating layer for the stability of surface Ti3+, these results and strategies could be applied in other TiO2 system or semiconductor- photocatalyst, and set a theory for commercialization of TiO2 photocatalysis under visible light.

二氧化钛光解水产氢具有解决化石能源短缺和温室效应等问题的巨大潜力。三价钛使二氧化钛在可见光下具有良好的光催化活性，但表面三价钛不稳定，易被氧化。本申请拟采用高温气氛还原的方法在二氧化钛纳米线表面制备三价钛，并进一步提出耦合石墨烯包覆层协同共振电子转移的策略来提高表面三价钛光催化稳定性。首先，通过不同气氛高温煅烧石墨烯包覆二氧化钛纳米线，在还原产生Ti3+的同时，并对它掺杂非金属，研究不同非金属元素通过共振电子转移对表面三价钛稳定作用机理，获得其影响规律；再通过氨气高温煅烧石墨烯包覆钛酸纳米线，耦合包覆层（产生Ti-C键），研究耦合包覆层协同氮掺杂稳定表面Ti3+机理，揭示共振电子转移、耦合包覆层和三价钛光催化稳定性的关系，获得具有稳定光催化活性的可见光响应二氧化钛纳米线。这一策略可以推广到其它二氧化钛结构或半导体光催化剂体系的稳定性研究，并为提高二氧化钛表面三价钛稳定性打下坚实的理论基础。

光解水产氢能通过光驱动催化反应产生氢气，提供一种高效的清洁能源。二氧化钛(TiO2)因无毒，良好的光化学稳定性和紫外光下高产氢活性而被认为是最有前景的半导体光催化剂。但是，TiO2只能吸收紫外光激发至导带使用，而紫外光只占太阳光谱的3%。三价钛会使二氧化钛吸收可见光；并且提高二氧化钛导电性，从而加速光激发电子空穴分离。因此，三价钛（Ti3+）是一种有效的二氧化钛可见光改性方式。但表面三价钛（3d1）不稳定，容易被吸附氧氧化成四价钛（3d24s2），从而使二氧化钛失去可见光催化活性。本申请课题拟以石墨烯包覆二氧化钛（钛酸）纳米线为基体材料，提出通过耦合石墨烯包覆层协同共振电子转移的策略，围绕二氧化钛表面三价钛光催化稳定性这一基础科学问题展开研究。. 研究内容主要包括：（1）二氧化钛纳米管表面三价钛制备研究；（2）不同掺杂非金属元素通过共振电子转移对稳定表面Ti3+的影响；（3）耦合包覆层协同共振电子转移对二氧化钛纳米管表面Ti3+稳定性影响。我们以上研究制备出了N掺杂石墨烯包覆的二氧化钛纳米管，在高温氩气还原和碳热还原作用下，实现了N-C共掺杂，并且石墨烯层起到有效的管状形貌维持作用和导电作用。此复合物在可见光下展示出良好的光解水活性，产氢率达到720 μmol g−1 h−1，并且经过一年多的空气气氛存放后，表面三价钛浓度和光催化活性无明显下降，从而进一步证实了N, C共掺杂在光催化过程中通过共振电子转移机制提高了表面三价钛的化学稳定性。