CO₂ conversion into methanol under ambient conditions using efficient nanocomposite photocatalyst/solar-energy materials in aqueous medium

A promising route to solve the CO2 issue is its photocatalytic back-conversion to H-based solar fuels/chemicals, particularly methanol - being widely used as a strategic material in chemical/energy-related industries. Herein, the authors address this globally interesting problem and demonstrate how through an effortless hydrothermal route and using earth-abundant elements, two efficient carbon nanotube (CNT)-based heterojunction photocatalyst/solar-energy materials, viz. CNT/NiO and CNT/NiO/Fe2O3 are synthesized and employed for methanol production. The investigations revealed that both binary and ternary composites could selectively (≥93%) produce methanol using CO2 feed in aqueous medium. Moreover, a higher performance (energy efficiency: 1.81%) was witnessed for the ternary photocatalyst. From a catalytic standpoint, the superior activity of the CNT/NiO/Fe2O3 photocatalyst was discussed in detail in terms of its larger surface area, higher absorption of incident light, better charge separation/transfer, and generation of greater photo-voltage/current to effectually split the water medium and achieve the photoconversion process. A mechanistic scheme was finally proposed for the production of methanol and methane, as liquid and gas phase products, respectively.