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.