ZnFe2O4/TiO2 composites with type-I heterojunction for photocatalytic reduction of CO2

The composites of ZnFe2O4 (ZFO) with TiO2 (anatase, rutile) were synthesized and tested towards the photocatalytic reduction of CO2 to CO in the gas phase. ZFO was obtained through the precipitation from zinc and iron nitrates(V) precursors, followed by hydrothermal treatment, and its physicochemical properties were examined using XRD, FT-IR, XPS, SEM-EDS, and XRF techniques. ZFO was simply ground in the agate mortar with one of the TiO2 polymorphs, forming ZFO/anatase and ZFO/rutile. Spectroelectrochemical (SE-DRS), surface photovoltage (SPV), transient photocurrent and diffuse reflectance UV-vis spectroscopy (DRS) measurements were applied to understand the fate of photogenerated electrons and holes. The results point to the type-I heterojunction that is formed in the case of all ZFO/TiO2 systems. This type of band alignment is responsible for boosted photoactivity of the composites compared to the components used separately. The results confirm that the selection of anatase favours reaching higher yields of CO production, which is attributed rather to better electron mobility within anatase compared to rutile than to preferential, reducing properties of the rutile's conduction band.