Solution-Gel Synthesis and In Situ Transformation of CuFeO2 and CuFe2O4 into Active Catalysts for Photothermal CO2 Conversion

Abstract This study evaluates CuFeO2 and CuFe2O4 as promising catalysts for photothermal CO2 conversion and their ability to form plasmonic Cu nanoparticles in situ. A straightforward, reproducible, aqueous citrate-based solution-gel method with high stoichiometric control was developed to synthesize both catalysts from the same starting materials. XRD, Raman, and ICP-OES confirmed nearly phase-pure materials with appropriate bandgaps (1.13 eV for CuFeO2 and 1.55 eV for CuFe2O4), determined by UV–vis spectroscopy. SEM and BET analyses showed a dense morphology for CuFeO2 and a slightly more porous CuFe2O4 architecture. The catalysts were tested in a photoreactor, where they selectively form CO via the reverse water–gas shift reaction. The combination of light and heat causes exsolution of copper onto the surface. These nanoparticles exhibit the localized surface plasmon resonance effect (LSPR), which facilitates CO2 conversion. The CuFeO2 catalyst produces 62 mmol of CO gcatalyst–1 h–1, and CuFe2O4 produces 65 mmol of CO gcatalyst–1 h–1, both using a combination of reactor heating and catalyst illumination. The key advancements are the development of a universal aqueous solution-gel route to structurally distinct copper iron oxides and the identification of an in situ Cu exsolution mechanism that converts these materials from pre-catalysts into active photothermal catalysts.