Bidirectional electron transfer enabled by dual electric fields for efficient 4-nitrophenol removal on a bifunctional FeCoNiP/PCN heterojunction

Although extensive research has explored modulating the built-in electric field (BIEF) and interfacial dipole electric field (IDEF) individually, a strategy leveraging their synergistic interplay for bidirectional electron regulation remains scarcely explored. Herein, a bifunctional FeCoNiP/P-doped g-C 3 N 4 (FeCoNiP/PCN) heterojunction was constructed and confirmed by TEM analysis. XPS and DFT analyses confirmed the co-existence of synergistic dual electric fields: a BIEF directed from PCN to FeCoNiP and an oppositely oriented IDEF, which cooperatively establish a bidirectional charge-transfer channel. This unique dual-field configuration drove highly efficient spatial charge separation, as evidenced by significantly quenched photoluminescence (PL), diminished charge-transfer resistance (EIS), and a markedly enhanced photocurrent response. The synergistic electric fields enabled bidirectional electron flow, thus enabling the simultaneous photooxidation of 4-nitrophenol (4-NP) and its selective reduction to 4-aminophenol (4-AP). The optimized FeCoNiP/PCN heterojunction showed significantly enhanced catalytic performance, achieving a 91 % degradation of 4-NP within 1.5 h with a rate constant 4 times and 25 times higher than pristine PCN and FeCoNiP, respectively. Moreover, it exhibited bifunctional performance, reducing 100 mg/L 4-NP nearly completely to 4-AP within only 4 min. The superior performance is primarily attributed to the synergistic interplay between the BIEF and IDEF, which efficiently lowers energy barriers and orchestrates directional electron transfer, as elucidated by combined experiments and theory. This study proposes a feasible strategy to regulate bidirectional electron flow via synergistic dual electric fields in heterojunctions, which opens a new avenue for designing high-performance bifunctional catalysts to tackle complex environmental issues.