Efficient photocatalytic reduction of CO2 by improving adsorption activation and carrier utilization rate through N-vacancy g-C3N4 hollow microtubule

The g-C3N4 is considered to be a promising non-metallic semiconductor photocatalyst for converting CO2 into value-added products. However, g-C3N4 undergoes recombination of photogenerated electrons and holes and its low CO2 adsorption capacity. Here, g-C3N4 hollow microtube (TCN) structure with tunable N-vacancy concentrations (TCN-1) was controllably fabricated by hydrothermal self-assembly followed by H2 heat treatment. The resultant N-vacancy with one-dimensional structure g-C3N4 exhibits excellent activity for photocatalytic CO2 reduction, giving the CO generation rate of 7.06 μmol/g/h (TCN-1) under visible-light illumination without any co-catalyst or a sacrificial agent, which is 2.2- and 8.8- times that of TCN (3.12 μmol/g/h) and pristine g-C3N4 (0.75 μmol/g/h). It is well evidenced with experiments and DFT calculations that N-vacancy mainly originates from the selective cleavage of C=N–C sites on the surface of g-C3N4. The N-vacancy can act as electron trap, extending the lifetime of charge carriers. Moreover, the changes in the electron distribution around the vacancies thereby provide the driving force for the dissociation of excitons, which in turn promotes the activation of CO2 adsorption. The bifunctional of g-C3N4 with structural optimization and defect design is a very promising candidate for enhancing the adsorption-activation of reactants and the carrier utilization of photocatalysts in the photocatalytic process.