Xu Min, Zada Amir, Yan Rui, Li Haonan, Sun Ning, Qu Yang
College of Science & Technology, Ningbo University, Ningbo 315300, P. R. China.
Phys Chem Chem Phys. 2020 Feb 28;22(8):4526-4532. doi: 10.1039/c9cp05147c. Epub 2020 Feb 12.
It is strongly desired to develop highly active photocatalysts for CO reduction by accelerating charge separation and realizing spatially separated active sites. In this work, TiO/TiO heterophase junctions with enhanced charge separation and spatially separated active sites were facilely prepared via in situ thermal oxidation of commercial TiO in air at an appropriate annealing temperature. The as-prepared TiO/TiO heterophase junctions, especially the temperature-optimized T550 sample, displayed high photocatalytic activity for CO reduction to yield CH (∼0.65 μmol g h), CO (∼2.64 μmol g h) and O (∼5.66 μmol g h), which was 4 times higher than that of bulk TiO and nearly 2 times higher than that of rutile TiO. Based on the surface photovoltage spectra, related produced OH radical measurement and electrochemical reduction, the high photoactivity could be attributed to the metallic TiO, which trapped the photogenerated electrons from TiO through the formed TiO/TiO heterophase junctions to enhance charge separation. Remarkably, it was confirmed from theoretical calculations based on density functional theory, Kelvin probe and CO-TPD measurements that the TiO/TiO heterophase junction possesses spatially separated active sites for CO reduction and water oxidation. Metallic TiO as a reduction site activated and catalyzed CO to produce solar fuels such as CO and CH, while TiO as an oxidation site oxidized HO to produce O and protons. The designed concept of heterophase junctions and simultaneously activating CO and HO at different spatial sites may offer a new strategy to suppress the reverse reactions during photocatalysis for efficient solar energy conversion.
通过加速电荷分离并实现空间分离的活性位点来开发用于CO还原的高活性光催化剂是非常有必要的。在这项工作中，通过在空气中于适当的退火温度下对商用TiO进行原位热氧化，轻松制备了具有增强电荷分离和空间分离活性位点的TiO/TiO异质结。所制备的TiO/TiO异质结，特别是温度优化的T550样品，对CO还原生成CH（约0.65 μmol g h）、CO（约2.64 μmol g h）和O（约5.66 μmol g h）表现出高光催化活性，这比块状TiO高4倍，比金红石TiO高近2倍。基于表面光电压光谱、相关产生的OH自由基测量和电化学还原，高光活性可归因于金属TiO，它通过形成的TiO/TiO异质结捕获来自TiO的光生电子以增强电荷分离。值得注意的是，基于密度泛函理论的理论计算、开尔文探针和CO-TPD测量证实，TiO/TiO异质结具有用于CO还原和水氧化的空间分离活性位点。金属TiO作为还原位点激活并催化CO生成太阳能燃料如CO和CH，而TiO作为氧化位点氧化HO生成O和质子。异质结的设计概念以及在不同空间位点同时激活CO和HO可能为抑制光催化过程中的逆反应以实现高效太阳能转换提供一种新策略。
