Photocatalytic reduction of CO 2 to methanol over ZnFe 2 O 4 / TiO 2 (p–n) heterojunctions under visible light irradiation

BACKGROUND The development of visible light photocatalysts for CO 2 reduction into methanol is a challenge, as most of the reported photocatalysts can only work in a UV light environment. Slow kinetics and poor selectivity of CO 2 towards methanol are currently two significant drawbacks limiting the practical application of CO 2 reduction into methanol. RESULTS A ZnFe 2 O 4 /TiO 2 heterojunction with a ratio of unity was found to lead to the highest methanol yield of 693.31 μmol (g cat) −1 under a light intensity of 100 mW cm −2 . This photocatalyst also possessed the highest BET surface area of 6.5211 m 2 g −1 and better morphological structure, as compared with other ratios (1:2, 2:1 w/w). Interestingly, a loading of 1 g L −1 of ZnFe 2 O 4 /TiO 2 (1:1) heterojunction photocatalyst in the pre‐annealing treatment of ZnFe 2 O 4 at 900 °C and post‐annealing treatment of ZnFe 2 O 4 /TiO 2 (1:1) composite at 500 °C revealed that there was an enhancement in the interfacial interaction, and subsequently an efficient photoreduction of CO 2 into methanol. CONCLUSIONS This study demonstrates facile fabrication of p–n heterostructured phototcatalysts for reduction of CO 2 with marked improvement in methanol yield under visible light irradiation. It provides a viable route for exploring the effects of composition, hydrothermal treatment, and pre‐/post‐annealing treatment of hybrid semiconductor composites used to scale up photocatalytic CO 2 conversion in solar fuel‐based devices.