Efficient Photoreduction of CO ₂ to CH ₄ under UV–vis Light Using a Metal-Free 2D-C ₇ N ₆ Photocatalyst: A Nonadiabatic Molecular Dynamics Study

The visible-light-driven conversion of CO2 into value-added chemical fuels such as CO, CH3OH, and CH4 presents a highly promising solution to pressing global challenges such as climate change and energy shortages. However, the practical efficiency of this process is significantly limited by the high overpotential of the CO2 reduction reaction (CO2RR) and the rapid recombination of photoexcited charge carriers. To overcome these limitations, we employed density functional theory (DFT) and nonadiabatic molecular dynamics (NAMD) simulations to investigate the photocatalytic potential of a metal-free 2D C7N6 monolayer. Our results demonstrate that 2D-C7N6 exhibits excellent thermal stability, favorable band edge positions with a photogenerated electron potential of 2.11 eV, and strong UV–vis light absorption. Moreover, NAMD simulations reveal a long electron–hole recombination time of 1.97 ns, which provides sufficient time for the photoexcited electrons to engage in the CO2RR. Gibbs free energy calculations further confirm that the reduction reaction is thermodynamically favorable under light irradiation. Overall, our findings highlight 2D-C7N6 as a highly efficient, metal-free photocatalyst for converting CO2 to CH4 under UV–vis light.