Synergistic promotion of solar-driven H2 generation by three-dimensionally ordered macroporous structured TiO2-Au-CdS ternary photocatalyst

A ternary photocatalyst TiO2-Au-CdS based on three-dimensionally ordered macroporous TiO2 (3DOM TiO2) was successfully prepared to enhance the light absorption, extend the light responsive region, reduce the recombination rate of charge carriers and promote the efficiency of water splitting H2 evolution ultimately. The obtained 3DOM TiO2-Au-CdS powder has a pure anatase phase of TiO2 and greenockite structured CdS according to the XRD results and TEM analysis. Au nanoparticles (AuNPs) and CdS were evenly distributed in the 3DOM structure which enhances H2-generation rate under visible light by improving light harvesting and utilizing its mass transfer facilitation. As a result, the hydrogen generation rate (1.81 mmol h−1 g−1) using 3DOM TiO2-Au-CdS photocatalyst under visible light irradiation was 13-fold higher than the binary 3DOM TiO2-CdS reference photocatalyst. Under ultraviolet-visible light, the photogenerated electrons in TiO2 would be transferred to recombine with the holes of CdS and under visible light, electrons would move to the conduction band (CB) of TiO2 from CdS via AuNPs. The two different types of internal electron-transfer process in the ternary photocatalyst under ultraviolet and visible light were proposed respectively and both would efficiently reduce the recombination rate of photogenerated electrons and holes thus stimulate H2 evolution rate. The present work demonstrated an excellent example of the synergistic effect of the light absorption enhancement by 3DOM structure, the photosensitizing and electron reservoir effect of AuNPs and the reduction of recombination rate of charge carriers by CdS to highly promote the photocatalytic activity in water splitting reaction.