Effective Near-Infrared Light-Driven Photocatalytic Reduction of CO₂ by Dual-Site Doped Carbon Nitrides

g-C3N4 is a nontoxic, stable, and nonmetal photocatalyst that mostly absorbs solar energy in the ultraviolet region. The photocatalytic activity of g-C3N4 was considerably restricted by its low quantum efficiency and fast carrier recombination. In this work, we present a novel P–S codoped black carbon nitride (PSCN) prepared by the solvothermal method. The physicochemical and photoelectrical properties of the prepared catalysts were studied by SEM, XRD, XPS, UV–vis DRS, and PL techniques. By introducing P and S heteroatoms to the C3N4 framework, its bandgap was reduced significantly from 2.71 eV (GCN) to 1.79 eV (PSCN), and its light absorption extended from the UV zone (λ < 420 nm) to the NIR zone (800–1500 nm). When exposed to near-infrared laser radiation (λ = 808 nm), the catalyst demonstrates an unusual photothermal conversion, as evidenced by IR thermography. The CO yields with a PSCN photocatalyst (58.5 μmol·h–1·g–1) under NIR light (λ > 800 nm) are comparable to that irradiated by UV–vis light (300 < λ < 800 nm, 57.0 μmol·h–1·g–1), while the CO yield with GCN under full-spectrum is only 6.2 μmol·h–1·g–1 (UV–vis–NIR). According to DFT simulations, PSCN can lower the energy required to produce COOH*. Furthermore, compared to CO desorption, the energy barriers for forming HCO* on PSCNs were much higher; thus, the selectivity of CO2 reduction to CO was enhanced. Our research provides a new approach for constructing nonmetal photocatalysts with a wide spectral response range and photothermal synergistic catalysis.