Exploring the visible light-assisted conversion of CO₂ into methane and methanol, using direct Z-scheme TiO₂@g-C₃N₄...

The rapid growth of carbon dioxide (CO₂) emissions raises concern about the possible consequences of atmospheric CO₂ increase, such as global warming and greenhouse effect. Photocatalytic CO₂ conversion has attracted researchers' interests to find a sustainable route for its elimination. In the present study, a direct Z-scheme TiO₂/g-C₃N₄ composite (T-GCN) was fabricated via a facile hydrothermal route for the photocatalytic reduction of CO₂ into methane (CH₄) and methanol (CH₃OH), under visible light irradiation without an electron mediator. The microstructure of the as-obtained TiO₂/g-C₃N₄ nanocomposites was fully characterized for its physicochemical, structural, charge separation, electronic, and photo-excited carrier separation properties. The effect of CO₂ and H₂O partial pressure was studied to find the best operational conditions for obtaining maximum photocatalytic efficiency; the P_CO2 and P_H2O were 75.8 and 15.5 kPa, respectively, whereas, by increasing the light intensity from 20 to 80 mW/cm², a remarkable improvement in the reduction rate takes place (from 11.04 to 32.49 μmol.gcat^-1.h^-1 methane production, respectively). Finally, under the most favorable light, P_CO2 and P_H2O conditions, high methanol and methane rates were obtained from the CO₂ photocatalytic reduction through T-GCN (1.44 μmol.gcat.^-1.h^-1 and 32.49 μmol.gcat.^-1.h^-1, respectively) and an integrated proposition for the Z-scheme mechanism of photocatalytic reduction was proposed. This study offers a promising strategy to synthesize a Z-scheme T-GCN heterojunction with high photocatalytic performance for effective CO₂ conversion.