Halogen anions (F−, Cl−, Br−) modulated the localized microstructure of g-C3N4 to facilitate charge separation and transport and enhance photocatalytic activities†

Modification of functionalized functional groups on catalyst surfaces is an effective strategy to modulate surface active sites, regulate carrier dynamics and hence deeply investigate the structure–activity relationships. Herein, graphitic carbon nitride (g-C₃N₄, abbreviated as CN) was selected as an ideal catalyst and subjected to a facile impregnation treatment with dilute hydrohalic acid (HX, X = F, Cl and Br) aqueous solution at room temperature of 25 °C to obtain halogen ion surface-modified CN (denoted as CN-X). Characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and zeta potential (ζ) was used to systematically investigate the composition and structural information of CN-X catalysts. Impressively, the photocatalytic degradation performances of rhodamine B (RhB), phenol and hydroxyl radical (·OH) generation over CN-X were all significantly improved compared with that of pristine CN. The enhanced photocatalytic performance of CN-X can be attributed to the enhanced concentration of charge carriers, suppressed recombination and effective separation and transfer of charge carriers, which is validated by photoelectrochemical (PEC) measurements, surface photovoltage (SPV), and steady-state fluorescence (PL) and time-resolved fluorescence (TRPL) spectra. This work provides a facile surface modification strategy to promote carrier separation and transport of CN, which may be informative for solar energy conversion of other semiconductor materials.