Enhanced activity of β-Ga2O3 by substitution with transition metal for CO2 photoreduction under visible light irradiation

Gallium oxide semiconductors have been developed as effective photocatalysts for water splitting driven by UV light irradiation, but there is no relevant study for the CO 2 photoreduction application. Herein, we report the first investigation of β -Ga 2 O 3 applying to photocatalytic CO 2 reduction under visible light irradiation by doping transition metal ions ( M  = V, Cr, Mn, Fe, Co, Ni and Cu) onto the framework. Using sol-gel method, a series of transition metal ions incorporated β -Ga 2 O 3 have been successfully obtained, in which the transition metal substitution content is 2 mol%. The β -Ga 2 O 3 : M photocatalysts are characterized completely by diverse tests (e.g., XRD, XPS, UV–Vis DRS, SEM). The effective replacement of Ga 3+ ion by M ions significantly expands the scope of spectral response from UV light to visible light, and Fe 3+ , Co 2+ , Ni 2+ significantly enhance the photocatalytic activity under visible light irradiation. In these cases, CO and H 2 are evolved as the reduction products from CO 2 and H + by the generated electrons, respectively. Among these effective catalysts we prepared, β -Ga 2 O 3 :Ni exhibits the most substantial CO formation rate of 14.3 μmol/h at 30 °C, and the selectivity for CO evolution exceeds 60.9%. Furthermore, the CO formation rate increases to 24.6  μ mol/h after loading of Ag as the co-catalyst. The stability of the Ag/ β -Ga 2 O 3 :Ni are verified after five cycle of CO 2 photoreduction under visible light.