Scalable one-pot hydrothermal N-Co/biochar from spent coffee grounds achieving ultrahigh PMS utilization and continuous-flow validation

The advanced oxidation studies have prioritized removal rates, yet quantitative evidence on PMS utilization is scarce. This study used coffee grounds as the carbon source to construct N-Co/biochar (N 50 CoCG) through a one-step hydrothermal method, and a scaled batch was prepared in a 500 mL autoclave (N 50 CoCG-500). The two catalysts exhibited highly consistent morphology, wettability, and surface chemistry, and showed comparable peroxymonosulfate (PMS) activation. Under the experimental conditions of 50 mg/L catalyst dosage and 0.02 mM PMS concentration, nitenpyram (NPR) removal reached 100 % and PMS utilization was >90 %. In a 10-day fixed-bed run, both NPR removal and PMS utilization remained >90 %, while Co leaching stayed below 6.87 μg/L. Open-circuit potential and chronoamperometric responses showed rapid, reversible electron transfer between PMS/NPR and Co N sites, enabling a reversible Co 3+ /Co 2+ cycle enabling >90 % PMS utilization. The one-pot hydrothermal strategy unites scalability with ultrahigh oxidant utilization, offering a scalable, oxidant-efficient catalyst oriented toward the “oxidant economy” and validated under continuous-flow conditions.