Construction of P-N charge-transfer bridge in porous g-C3N4 for highly efficient visible-light-driven photocatalytic N2 fixation

Solar N2 fixation is a green and pollution-free technology to realize solar energy to chemical energy. Here, P doped g-C3N4 nanosheets (PCNx) with porous structure has been fabricated via a one-step calcination process for efficient ammonia generation. The optimal PCN0.6 catalyst provided an improved visible light photoperformance with an ammonia generation rate of 3110 mu g L- 1h- 1g- 1, 15 times higher than that for pristine gC3N4 (CN). And the quantum efficiency at 400 nm monochromatic light reached 3.29%. Characterization results revealed that the implantation of P-N bonds in g-C3N4 resulted in expanded optical response, larger accessible active sites and efficient separation of electron-hole pairs than that of bulk counterpart. Wavefunction contour maps revealed a more localized charge density distribution upon P doping, leading to a favorable electron-rich structure. The calculated N2 adsorption energy and N2-TPD tests showed the strong capacity of nitrogen chemadsorption by PCN0.6. Charge density differences and Bader charge demonstrated the electrons transfer from the P doping sites of g-C3N4 to adsorbed N2, thus activating N2 molecules for effective NH4+ generation. This work offered significant insights into the heteroatom doping engineering to construct active sites and steer the charge migration pathways in g-C3N4 for efficient photo-reduction of N2.