Enhanced Performance of Photocatalytic Water Splitting on B-Doped g-C3N4

Graphitic carbon nitride (CN) is a promising photocatalytic material, but its practical application is limited by small specific surface area, narrow light absorption range, and high photogenerated carrier recombination rate. To address these issues, this study synthesized boron-doped carbon nitride (BCN) and sulfuric acid-exfoliated boron-doped carbon nitride (BCND). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirmed that boron was successfully doped into the CN skeleton via B-N bonds. Scanning electron microscopy (SEM) and N2 adsorption–desorption (BET) characterizations showed that acid exfoliation significantly increased the specific surface area of BCND to 68.80 m2·g−1, much higher than that of CN (9.54 m2·g−1) and BCN (15.98 m2·g−1). UV–visible diffuse reflectance spectroscopy (UV-Vis DRS) analysis revealed that BCND had the narrowest bandgap (2.59 eV) among the three materials, which enhanced its visible-light absorption efficiency. Photoelectrochemical tests demonstrated that BCND exhibited the smallest charge transfer resistance and the highest transient photocurrent density (eight times that of CN), indicating efficient separation of photogenerated electron–hole pairs. Photocatalytic water splitting experiments showed that BCND achieved the highest Hydrogen production rate of 792.34 μmol·g−1·h−1, which was about 4 times that of CN (158.41 μmol·g−1·h−1) and 1.36 times that of 2.5% BCN (584.30 μmol·g−1·h−1). Free-radical trapping experiments indicated that hydroxyl radicals (·OH) played a crucial promotional role in Hydrogen production, while superoxide anions (·O2−) exerted an inhibitory effect. The enhanced performance of BCND was attributed to the synergistic effects of boron doping (narrowing bandgap) and acid exfoliation (increasing specific surface area). A possible photocatalytic Hydrogen production mechanism was proposed based on the experimental results. This study provides a feasible strategy for the structural modification and performance optimization of g-C3N4-based photocatalysts for water splitting.