Synthesis of Effective NiO/Ni/g-C₃N₄ Photocatalysts for CO₂ Reduction under Visible Light Irradiation

Photocatalytic reduction of CO₂ is one of the promising strategies for synthesising valuable organic compounds and solving both energy and environmental problems. In the present work, NiO/Ni/g-C₃N₄ photocatalysts were synthesised. Initially, g-C₃N₄ was prepared by calcination of melamine and urea and then modified by photodeposition of a NiO/Ni co-catalyst on its surface. The structure of the photocatalysts was confirmed by X-ray phase analysis, UV–Vis diffuse reflection spectroscopy, and high-resolution transmission electron microscopy. The highest activity in the reaction of photocatalytic CO₂ reduction was demonstrated by 2 wt % (NiO/Ni)/g-C₃N₄ and 3 wt % (NiO/Ni)/g-C₃N₄, equal to 13.2 and 12.4 μmol g^–1 h^–1, respectively. It is worth noting that in this case, an almost 3-fold increase in the reaction rate was achieved compared to the pristine g-C₃N₄. The deposition of NiO/Ni on g-C₃N₄ solves two fundamental problems: adsorption of CO₂ and separation of photogenerated electrons and holes. The present work demonstrates an approach to the synthesis of active catalysts, in particular an approach to design a hybrid NiO/Ni co-catalyst for efficient photocatalytic CO₂ conversion.