Photocatalytic pure water splitting activities for ZnGa2O4 synthesized by various methods

• High temperature solid state reaction, hydrothermal, sol-gel methods were applied.
• All ZnGa2O4 samples show UV-light catalytic activities on pure water splitting.
• Bulk ZnGa2O4 has a good photocatalytic activity per specific surface area.
• Sol-gel is a superior method to prepare nanosized ZnGa2O4 with a high activity.
• The AQY for SG-ZnGa2O4 is 2.6% for pure water splitting under 313 nm irradiation.

We studied and compared the photocatalytic water splitting performances for ZnGa2O4 prepared by high temperature solid state reaction (HTSSR), hydrothermal (HY) and sol-gel (SG) methods. HTSSR-ZnGa2O4 has a relative large photocatalytic activity per surface area (1.6 μmol/h/m2) in pure water by UV irradiation due to its high crystallinity. The HY- and SG-samples both have small particle sizes (20∼30 nm) and therefore high surface area (20 and 29 m2/g, respectively), which leads to superior photocatalytic H2 evolution rates per unit mass (11.5 and 28.5 μmol/h/g). The apparent quantum yield of SG-ZnGa2O4 for pure water splitting under 313 nm irradiation is 2.6%. The existence of substantial surface defects is the major problem for HY- and SG-ZnGa2O4. Consequently, the usage of sacrificial agents could greatly enhance the activities and indeed the H2 evolution rates in 20 Vol. % methanol aqueous solution increase to 100 and 142 μmol/h/g for HY- and SG-ZnGa2O4, respectively.

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