Cu-(Ga0.2Cr0.2Mn0.2Ni0.2Zn0.2)3O4 heterojunction derived from high entropy oxide precursor and its photocatalytic activity for CO2 reduction with water vapor

The construction of metal–semiconductor heterojunction has been proven to be an effective way to improve the separation efficiency of photogenerated electrons and holes, thus enhancing photocatalytic activity of semiconductor with narrow band gap. Here, we construct a Cu-(Ga0.2Cr0.2Mn0.2Ni0.2Zn0.2)3O4 high entropy oxide (HEO) heterojunction by using Cu-containing HEO precursor, and the effect of Cu addition method on the photocatalytic performance was investigated. The results show that the addition method of Cu has a great influence on the size of Cu nanoparticles, heterojunction amount and photocatalytic activity of Cu-HEO catalysts. Cu-HEO samples prepared by direct introduction method possess much smaller Cu particles due to the uniform distribution and stronger diffusion hysteresis effect of Cu in HEO, and exhibit superior photocatalytic activity and CH4 selectivity for CO2 reduction. With the increase of Cu loading, the photocatalytic activity of Cu-HEO samples firstly increases and then decreases. Among these photocatalysts, Cu0.5-HEO obtained by the direct introduction method displays the highest CO2 reduction activity, and the yields of CO and CH4 reach to 5.66 and 33.84 µmol/h/gcat, respectively. This work innovatively uses HEO precursors with unique properties to construct metal-HEO heterojunctions with smaller metal particles and more active sites.