Matrix Doped C3N4 with Hierarchical Microstructures and High Vis–NIR Light Photoactivity

The efficient use of solar energy for photocatalytic CO2 reduction is still challenging. GCN (graphitic carbon nitride) has bulky structures and weak absorption in the Vis–NIR range. Herein, we report a series of homogeneously P-doped carbon nitrides (PCN) with tunable microstructures and high Vis–NIR light activities. PCN samples were prepared via a solvothermal method, followed by a calcination step. Unique morphologies, including pinecones, hourglasses, and furry balls, were obtained in a controlled way. The structural development of PCN in the synthesis process was investigated (by SEM and XRD). PCN samples have larger specific surface areas (by BET analysis) and much stronger Vis–NIR adsorption (400–1500 nm, by UV–vis absorption spectra and near-infrared thermal imaging). The enhanced photoactivities under solar light originated from an elevated valence band (by Mott–Schottky analysis and XPS-VB). Strikingly, the band gap was reduced from 2.71 eV (GCN) to 1.43 eV (PCN). Theoretical calculations (DFT) confirmed that P doping led to the spatial separation of carbon nitride HOMO and LUMO orbitals, which essentially inhibited the recombination of photogenerated carriers and promoted the separation of photogenerated carriers. Photocatalytic CO2 reduction results indicated that matrix P-doping and the microstructural changes synergistically enhanced the CO2 to CO reduction rate (9.2 times of GCN). These results highlight the general applicability of the present method to prepare efficient solar-light-active carbon nitride-based photocatalysts.