Internal Electric Field-Induced “Proton Bridge” Mechanism in Photo-Self-Fenton Coupled PMS Systems: A Theoretical Study Based on Nonmetal Surface-Engineered Carbon Nitride

Abstract

Constructing a photoself-Fenton (PSF) coupled peroxymonosulfate (PSF–PMS) system, which exploits the cross-activation between PMS and in situ generated H2O2 to boost reactive oxygen species flux, can overcome the kinetic bottlenecks of single advanced oxidation processes. However, the microscopic mechanisms governing how dual half-reactions overcome electron and proton competition at complex interfaces remain elusive. Herein, density functional theory (DFT) and machine learning (ML) were integrated to unveil the synergistic mechanisms of the PSF–PMS system, using nonmetal surface-engineered carbon nitride as a model. Theoretical calculations reveal that the local internal electric field (IEF) induced by doping and defects drives the spatial separation of redox sites. The downshift of the p-band center strengthens interfacial Lewis acidity, steering PMS activation toward hole-dominated oxidative deprotonation accompanied by in situ proton release; meanwhile, the interfacial charge transfer dictates the rate-determining energy barrier of the two-electron oxygen reduction reaction (2e– ORR) for H2O2 production. Crucially, transition-state kinetic searches and thermodynamic analyses confirm a cross-site “proton bridge” mechanism: driven by the IEF and low kinetic activation barriers (Ea < 0.5 eV), protons released from PMS oxidation spontaneously overcome lattice constraints and migrate across the surface to reduction sites for H2O2 synthesis, establishing a microenvironmental proton cycle that resolves the proton supply–demand imbalance. Furthermore, the Random Forest algorithm based on the Bagging architecture mitigates the multicollinearity of high-dimensional DFT descriptors, achieving high-precision nonlinear predictions of reaction barriers (R2 > 0.9). Extracting descriptor contribution weights demonstrates that the p-band center, valence band maximum, and work function synergistically regulate the proton source, migration driving force, and proton sink. This study elucidates the interfacial dynamics of coupled oxidation systems at the molecular scale, providing a data-driven theoretical foundation for the rational design of IEF-enhanced environmental catalysts.