Abstract:Radical-dominated advanced oxidation processes often suffer from low selectivity and inefficient oxidant utilization in water treatment. In this work, the quasi-pyrolysis regulation of NiFe-BDC at 400 ℃ successfully transformed the sulfamethoxazole (SMX) degradation pathway during peroxymonosulfate(PMS) activation from a radical-driven process to a nonradical-dominated one. This modulation strategy aims to improve PMS utilization and achieve selective oxidation under environmentally relevant conditions. Specifically, SMX degradation and PMS decomposition were quantified by high-performance liquid chromatography (HPLC) and UV-vis spectrophotometry. The temperature-dependent structural evolution of NiFe-BDC was characterized by SEM, TGA, XRD, FTIR, and Raman spectroscopy. Electron paramagnetic resonance(EPR) and quenching experiments were conducted to identify the dominant types of reactive oxygen species, while XPS combined with correlation analysis elucidated the electronic interactions between oxygen vacancies (OV) and Ni active sites. HPLC-MS was employed to determine the degradation intermediates and pathways, while the environmental stability was evaluated through ion interference, recyclability, and inductively coupled plasma (ICP)-based leaching tests. The NiFe-BDC-400/PMS process achieved 99.5% SMX removal with a PMS utilization efficiency of 8.49%, far exceeding that of pristine NiFe-BDC/PMS(SMX removal: 26.1%, PMS efficiency: 3.27%). Structural characterizations demonstrated that quasi-pyrolysis at 400 ℃ partially preserved the carbon framework while exposing abundant Ni and Fe sites, leading to the in-situ formation of uniformly dispersed NiO/NiFe2O4 nanoparticles on the carbon matrix. This configuration enhanced both the accessibility of active sites and the efficiency of charge transfer. Mechanistic investigations revealed that both OV and NIII species acted as the key active sites for singlet oxygen (1O2) generation. OV activated O2 to produce , contributing approximately one-third of the total 1O2, whereas inner-sphere complexation between NiIII and PMS produced  intermediates responsible for the remaining two-thirds. Moreover, OV facilitated charge transfer and induced the NiII→NiIII transformation, enriching high-valence NiIII centers and establishing intrinsic electronic coupling between the two active sites. This synergistic interaction enhanced 1O2 formation, which mediated the selective SMX degradation pathway. LC-MS identified nitro-substituted intermediates as the main degradation products, typically associated with 1O2-dominated pathways. The catalyst maintained high activity in the presence of common anions and humic acid, with Ni leaching below 0.5 mg/L after three cycles, meeting the Class V water discharge standard. Overall, this study demonstrates that quasi-pyrolysis effectively regulates active sites and electron-transfer channels in NiFe-BDC, enabling a stable and selective nonradical oxidation pathway with high PMS utilization efficiency. Furthermore, the formation of NiFe2O4 nanoparticles endowed the catalyst with magnetic properties that facilitated recovery and reuse. These results highlight the need for further investigation into how OV density and electronic coupling quantitatively influence 1O2 generation. Future work may explore controlled defect engineering and heteroatom modulation to optimize the balance between stability and selectivity. The present findings provide mechanistic insights and a methodological reference for developing recyclable, OV-rich catalysts for sustainable pollutant removal and related environmental redox processes. Close-