Rational construction of edge-grafted g-C3N4 via cross-linking aromatic compounds with C F bonds for efficient photocatalytic H2 evolution

Chemical modification of g-C3N4 (CN) for electron directional transport to separate charge carriers is important for its photocatalytic application, but remains a challenge. In this research, Tetrafluoroterephthalic acid (TFBDC) was utilized to modify CN by the crossing-linking reaction of carboxyl groups in TFBDC and terminal NH2 groups in CN. The introduction of fluorine into the CN framework through benzene-ring linkage to CF bonds achieves the dual regulation of electron hybridization structure and electron directional transport from the center to the edge of CN, which can greatly promote the separation of charge carriers in plane, as supported by density functional theory (DFT) calculations and femtosecond transient absorption spectrum (fs-TAS). The decay dynamics analysis from fs-TAS results indicates the slower exciton annihilation and longer shallow electron trapping in TFBDC-50/CN (τ1: 1.3 ps, τ2: 136.4 ps) compared to CN (τ1: 3.3 ps, τ2: 149.4 ps), both of which can be attributed to the graft of benzene rings with CF bonds. This grafting strategy not only promotes the participation of more electrons in the photocatalytic water splitting process, resulting in the hydrogen evolution rate of TFBDC-50/CN being increased to 5.4 times that of CN, but also exhibits remarkable recycle stability, enhancing the overall performance of the photocatalytic system. The results obtained in this work can provide beneficial references for research aimed at exploring chemical modification of CN for the enhancement of photocatalytic performance.