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Effective use of photogenerated electrons and holes in a system: Photocatalytic selective oxidation of aromatic alcohols to aldehydes and hydrogen production

Meng, Sugang, Ye, Xiangju, Zhang, Jinghu, Fu, Xianliang, Chen, Shifu
Journal of catalysis 2018 v.367 pp. 159-170
alcohols, aldehydes, carbon dioxide, electrons, energy, hydrogen, hydrogen production, indium, ions, irradiation, molybdenum, nanoparticles, nitrogen fixation, oxidation, oxygen, photocatalysis, platinum, protons, sulfides, zinc
Effective utilization of photogenerated electrons and holes in a system is always a research hotspot. Photocatalysis has been identified as a promising solution to tackle the current environmental and energy issues. However, photogenerated holes or electrons were wasted in the traditional photocatalytic process. In the paper, a dual-function photocatalytic reaction system was constructed using dispersed Ptx-modified 2D-3D Zn3In2S6 hierarchical structures (x = 1–4). In the system, aromatic alcohols were photocatalytically selectively oxidated into aldehydes and protons were reduced to hydrogen by photogenerated holes and electrons, respectively. In the reaction process, one aromatic alcohol is first dehydrogenated into aromatic aldehyde and two H+ via the corresponding carbon-centered radical by consuming of two holes, and then two H+ ions dehydrogenated from OH group and α CH of alcohol are evolved into H2 by depleting of two electrons. Atomically dispersed Ptx could offer the maximum atom efficiency and significantly promote visible light absorption and separation of photogenerated electron-hole pairs. The cooperative photoredox system exhibits remarkable photocatalytic activity for visible light-driven splitting of aromatic alcohols. Under visible light irradiation for 6 h, The H2 output over 2.14% Pt/Zn3In2S6 reaches up to 950 μmol, which is around 7.5, 5.3 and 3.8 times higher than that over Zn3In2S6, Pt-nanoparticle/Zn3In2S6 and MoS2/Zn3In2S6, respectively. The apparent quantum efficiency (AQE) of 2.14% Pt/Zn3In2S6 at 400 nm is about 4.6%. The utilization rate of photogenerated electrons to holes could be achieved 98.2%. Moreover, Pt/Zn3In2S6 hybrid shows high stability even when Zn3In2S6 was stored for 12 months. Compared with two half-reactions: the photocatalytic selective organics transformation under O2 atmosphere and the water splitting with sacrificial reagents, such designed dual-purpose photocatalytic reaction not only could effective use of photogenerated electrons and holes for organics transformation and hydrogen production simultaneously but also shows much higher photocatalytic activity than two half-reactions. At the same time, the work also expands the research field of photocatalysis, such as N2 fixation and CO2 reduction by using of the as-produced H+.