Photocatalytic CO₂ Reduction by Mesoporous Polymeric Carbon Nitride Photocatalysts

In this paper, a sol–gel derived mesoporous polymeric carbon nitride has been investigated as a photocatalyst for CO₂ photocatalytic reduction. Noble-metal Pt nanoparticles were deposited on carbon nitride (sg-CN) in order to investigate the performance of both Pt-sg-CN and sg-CN for photocatalytic CO₂ reduction. Physicochemical properties of prepared nanocomposites were comprehensively characterized by using powder XRD, N₂ physisorption, UV-Vis DRS, ICP-AES, FTIR, solid-state NMR, SEM, TEM and photoelectrochemical measurements. Compared with pure sg-CN, the resulting Pt-loaded sg-CN (Pt-sg-CN) exhibited significant improvement on the CO₂ photocatalytic reduction to CH₄ in the presence of water vapor at ambient condition under UV irradiation. 1.5 wt.% Pt-loaded sg-CN (Pt-sg-CN) photocatalyst formed the highest methane yield of 13.9 μmol/g_cat. after 18 h of light irradiation, which was almost 2 times and 32 times improvement in comparison to pure sg-CN and commercial TiO₂ Evonik P25, respectively. The substantial photocatalytic activity of Pt-sg-CN photocatalyst for the yield product of the CO₂ photocatalytic reduction was attributed to the efficient interfacial transfer of photogenerated electrons from sg-CN to Pt due to the lower Fermi level of Pt in the Pt-sg-CN hybrid heterojunctions as also evidenced by photo-electrochemical measurements. This resulted in the reduction of electron–hole pairs recombination for effective spatial charge separation, consequently increasing the photocatalytic efficiency.