The conversion of CO₂ to low-carbon fuels using solar energy is considered an economically attractive and environmentally friendly route. The development of novel catalysts and the use of solar energy via photocatalysis are key to achieving the goal of chemically reducing CO₂ under mild conditions. TiO₂ is not very effective for the photocatalytic reduction of CO₂ to low-carbon chemicals such as methanol (CH₃OH). Thus, in this work, novel Cu₂O/TiO₂ heterojunctions that can effectively separate photogenerated electrons and holes were prepared for photocatalytic CO₂-to-CH₃OH. More visible light-active Cu₂O in the Cu₂O/TiO₂ heterojunctions favors the formation of methanol under visible light irradiation. On the other hand, under UV-Vis irradiation for 6 h, the CH₃OH yielded from the photocatalytic CO₂-to-CH₃OH by the Cu₂O/TiO₂ heterojunctions is 21.0–70.6 µmol/g-catalyst. In contrast, the yield of CH₃OH decreases with an increase in the Cu₂O fraction in the Cu₂O/TiO₂ heterojunctions. It seems that excess Cu₂O in Cu₂O/TiO₂ heterojunctions may lead to less UV light exposure for the photocatalysts, and may decrease the conversion efficiency of CO₂ to CH₃OH.

Nanosize-controllable Cu, Ag, Pd, Ni, CuPd alloy and Cu–Ag bimetal encapsulated in inert carbon shells can be synthesized by carbonization of metal–cyclodextrin complexes with a remarkable capability of experimentally determining the size-dependent melting temperature depression of many metal or alloy nanoparticles.