Efficient approach for simultaneous CO and H₂ production via photoreduction of CO₂ with water over copper nanoparticles loaded TiO₂

Photoreduction of CO₂ with water to alternative fuels using low cost meterials is an efficient approach to mitigate CO₂. The present work describes a series of copper nanoparticles (Cu-NPs) loaded on TiO₂, here copper nanoparticles were separately prepared by chemical reduction method, and then loaded on freshly synthesized TiO₂. Oxidized and reduced forms of Cu/TiO₂ nanoparticles were obtained by calcination under air and H₂ respectively. Prepared catalysts were characterized by XRD, SEM, EDX, HR-TEM, XPS, BET surface area analysis, TPR, UV-vis diffuse reflectance spectroscopy and spectrofluorometry. Catalytic potential of prepared catalysts was checked for photocatalytic reduction of CO₂ with water vapor under UV-C irradiation. The effect of oxidation state and loading amount of Cu as well as irradiation wavelength was also investigated. CO and H₂ were observed as photocatalytic products. Among all the photocatalysts, 1% Cu-Red/TiO₂ exhibited the highest photoactivity, with an initial rate of CO and H₂ production of 334 and 452 μmol g^-1 h^-1 respectively, under UV-C light. The photocatalytic role of the Cu-NPs surface giving contribution to overall reaction was confirmed by using Cu-NPs, 1% Cu-Oxi/SiO₂ and 1% Cu-Red/SiO₂. A plausible mechanism of CO₂ reduction is suggested and computationally confirmed. Reaction mechanism includes stages of CO₂ adsorption at the Cu-TiO₂ interface, reduction into HCO₂, and dissociation into adsorbed hydroxyls and CO. The most energy demanding step was found to be CO desorption that could be facilitated by 254 nm quanta.