Photocatalytic reduction of CO2 with H2O vapor under visible light over Ce doped ZnFe2O4

Abstract

In this work, ZnFe₂O₄ spinels doped with different Ce contents were synthesized through a sol–gel method and their morphologies, structures, optical and electronic properties, adsorption capacity for CO₂ and activities for CO₂ photoreduction with H₂O vapor were investigated. The results show that the presence of Ce³⁺ in the ZnFe₂O₄ lattice and CeO₂ particles on the surface of ZnFe₂O₄ can enhance photoabsorption in the visible light region, and promote the effective separation of photogenerated electron–hole pairs. CO₂-TPD and in situ FTIR spectroscopy confirmed that monodentate carbonate (m-CO₃²⁻), bidentate carbonate (b-CO₃²⁻) and bidentate bicarbonate (b-HCO₃⁻) were the main surface species for the coadsorption of CO₂ and H₂O on photocatalyst surfaces. The addition of Ce strengthens the chemical interaction between CO₂ and photocatalyst surfaces and obviously increases the adsorption amount of b-HCO₃⁻ and b-CO₃²⁻ species. As a result, all Ce-doped samples exhibit much higher production rates of H₂, CO and CH₄ when compared to undoped ZnFe₂O₄, and ZFC0.2 has the highest photocatalytic activity among all samples, for which H₂, CO and CH₄ production rates of 19.9, 1.7 and 9.9 μmol g_cat⁻¹ h⁻¹ were achieved, about 4.6, 4.3 and 4.2 times that of undoped ZnFe₂O₄, respectively.