Facet-dependent photocatalytic H2O2 production of single phase Ag3PO4 and Z-scheme Ag/ZnFe2O4-Ag-Ag3PO4 composites

With high surface energy leading to high photocatalytic activity, there have been significant interests in maintaining high surface energy for photocatalyst by controlling the exposed facet. To demonstrate the effect of exposed facet on the performance of composite photocatalyst and understand the corresponding mechanism, we prepared ZnFe2O4 and Ag3PO4 with {111}, {110}, {100}, and mixed exposed facets, and constructed corresponding Z-scheme Ag/ZnFe2O4-Ag-Ag3PO4 heterojunctions using a photo-assisted isoelectric point method. The {111} facet of Ag3PO4, which has higher surface activity, better separation efficiency of photogenerated e- and h+, and higher energy and activity of photogenerated electrons, exhibited the highest activity in photocatalytic H2O2 production under simulated sunlight (146.1 mu mol/L in the presence of 10 vol% methanol as a hole sacrificial agent by 120 min). The H2O2 production efficiency was significantly improved for the Z-scheme Ag/ ZnFe2O4-Ag-Ag3PO4 composites (up to 206.3 mu mol/L in the presence of 10 vol% methanol by 120 min for the one with the {111} facet of Ag3PO4 exposed). The band potentials of ZnFe2O4 and Ag3PO4 were suitable for forming Z-scheme heterostructure, while the recombination of photogenerated e- and h+ was effectively inhibited with the Ag introduced as a conductive channel and co-catalyst in the composite photocatalysts. Photocatalytic H2O2 production in the presence of Ag3PO4 occurred through the direct two-electron oxygen reduction reaction, while that in the presence of Z-scheme Ag/ZnFe2O4-Ag-Ag3PO4 involved sequential two-step single-electron oxygen reduction reaction. The insights obtained in this work could help guide the design and development of highly active composite photocatalysts through crystal facet engineering.

Automated summary

The {111} facet of Ag3PO4 exhibited the highest surface activity and photocatalytic performance, leading to significant improvement in H2O2 production efficiency for the Z-scheme Ag/ZnFe2O4-Ag-Ag3PO4 composites. Introduction of Ag as a conductive channel and co-catalyst effectively inhibited the recombination of photogenerated e- and h+, promoting the production of H2O2. Insights from this work could guide the design of highly active composite photocatalysts through crystal facet engineering.