Ca2Fe2O5 was prepared by a sol–gel method and loaded with nickel by an impregnation method. The catalyst NiO/Ca2Fe2O5 was studied in the photocatalytic splitting of water in the presence of carbon dioxide. It is found that the photocatalytic
activity increased markedly when CO2 was bubbled into the water. It is believed that CO2 may react with water to form HCO3− and CO32−, which promote the scavenging of h+ by HO·, and thus enhance the photocatalytic activity. At the same time, a portion of CO2 is photocatalytically reduced to formic acid.