Ordered mesoporous ZnGa2O4 for photocatalytic hydrogen evolution

Abstract

Zinc gallate (ZnGa₂O₄) materials as a mixed oxide of d¹⁰ metal zinc and gallium have a wide range of applications because of their intriguing properties. Considerable effort has been devoted to nanostructuring ZnGa₂O₄ to regulate or enhance its properties and performance, although further investigation would be still necessary. Herein, for the first time, we demonstrated the nanocasting synthesis of ordered mesoporous ZnGa₂O₄ with highly crystalline frameworks by using mesoporous silica as the hard template, which exhibits excellent photocatalytic hydrogen (H₂) evolution performance. The key for fabricating ordered mesoporous ZnGa₂O₄ was its improved stability over individual zinc oxide or gallium oxide in alkaline etching solution during the removal of the silica template, which allows for the maintenance of the ordered mesoporous structure in a finely etching silica process. The resultant ordered mesoporous ZnGa₂O₄ possesses an ultrathin framework of 3–5 nm and a large pore size of 11 nm as well as a relatively high surface area of ∼157 m² g⁻¹. An enhanced photocatalytic H₂ evolution performance of 2.72 mmol h⁻¹ g⁻¹ could be achieved under ultraviolet (UV) light irradiation, which is almost 1.8 and 3.9 times as high as those of ZnGa₂O₄ nanoflowers (1.5 mmol h⁻¹ g⁻¹) and bulk ZnGa₂O₄ (0.7 mmol h⁻¹ g⁻¹).