Mg2Fe2O5 Nanoparticle-Decorated Ca2Fe2O5–CaFe2O4 Heterostructure for Efficient Photocatalytic CO2 Conversion

In this work, a CaFe2O4 porous network and a Mg2Fe2O5 nanoparticle (NP)-decorated Ca2Fe2O5–CaFe2O4 heterostructure are synthesized using the solution combustion method. Ca2Fe2O5 and Mg2Fe2O5 NPs are incorporated into the CaFe2O4 network based on density functional theory (DFT) calculations for enhancing the CO2 adsorption of the heterostructure. With the addition of Ca2Fe2O5 and Mg2Fe2O5 NPs, this CaFe2O4-based heterostructure demonstrates significantly improved photocatalytic activity for CO2 conversion compared to the pristine CaFe2O4 network. CH4 and CH3CHO are produced, and there is no H2 detected from the photocatalytic conversion of CO2 and H2O over the Mg2Fe2O5 NP-decorated Ca2Fe2O5–CaFe2O4 heterostructure. Selectivities of 81.7 and 18.3%, respectively, for CH4 and CH3CHO are achieved in this process. DFT calculations indicate that among the three components in the heterostructure, Ca2Fe2O5 is the active site with the lowest activation energy for the conversion of CO2 and H2O to CH4. Type-II charge transfer dynamics is suggested to take place in the staggered CaFe2O4–Ca2Fe2O5 heterojunction to improve charge separation, which allows the photoelectrons to be well collected on the Ca2Fe2O5 side for the reduction of CO2. Accordingly, the CO2 adsorption, charge separation, and surface CO2 conversion efficiencies are all enhanced with the incorporation of Ca2Fe2O5 and Mg2Fe2O5 into the CaFe2O4 porous network, resulting in the boosted photocatalytic activity for CO2 conversion in the Mg2Fe2O5 NP-decorated CaFe2O4–Ca2Fe2O5 heterostructure.