Efficient Photocatalytic Reduction of CO₂ to CO Using NiFe₂O₄@N/C/SnO₂ Derived from FeNi Metal–Organic Framework

Use of light is considered an effective approach to convert CO2 into usable chemical energy. In the present study, an iron- and nickel-containing bimetallic metal–organic framework (MOF) was synthesized via a simple solvothermal route. SnO2 was then composited with the said MOF, and the obtained material was calcined and annealed to fabricate a series of nanophotocatalysts. The annealed sample displayed superior photocatalytic activity to the calcined sample, possibly due to the carbon–nitrogen layer formed after annealing mediating the charge-transfer process. The results of photocatalytic experiments indicated that using [Ru(bpy)3]Cl2·6H2O as a photosensitizer and triethanolamine (TEOA) and acetonitrile (MeCN) as sacrificial agents, the catalyst sample was annealed at 450 °C (NiFe2O4@N/C/SnO2-450) to afford the highest CO yield from CO2 (2057.41 μmol g–1 h–1). The increase in the photocatalytic ability of the nanocomposites is basically attributed to multiple synergistic effects between NiFe2O4 and SnO2, which reduce the recombination probability of the photo-induced electrons and holes. Ultimately, a photocatalytic reaction mechanism is proposed for NiFe2O4@N/C/SnO2 in the reduction of CO2.