Metal-free　photocatalysts　for　peroxymonosulfate　(PMS)　activation　offer　a　sustainable　approach　to　water　purification,　though　achieving　high　efficiency　remains　challenging.　Herein,　we　reported　an　oxygen/methyl-modified　carbon　nitride　(OMCN)　as　efficient　PMS　activator　for　phenolic　pollutant　removal.　Through　facile　one-pot　thermal　copolymerization　of　urea　and　dimethyl　malonate,　the　electronic　structure　of　carbon　nitride　was　engineered　to　generate　a　strong　internal　electric　field　that　significantly　enhances　charge　separation.　OMCN　exhibited　a　stronger　built-in　electric　field　compared　to　oxygen-modified　carbon　nitride　(OCN)　and　methyl-modified　carbon　nitride　(MCN)　individually.　The　optimized　OMCN2　photocatalyst　featured　a　narrowed　bandgap,　enhanced　PMS　adsorption　energy,　and　reduced　activation　barrier　for　PMS　cleavage.　Consequently,　the　visible-light-driven　PMS　(Vis-PMS)/OMCN2　system　achieved　completely　phenol　degradation　within　90　min,　substantially　outperforming　Vis-PMS/CN　system.　The　catalyst　demonstrated　excellent　stability　across　multiple　cycles,　retaining　88.1　%　of　its　initial　catalytic　activity　after　four　consecutive　runs　while　maintaining　broad　pH　tolerance.　Mechanistic　studies　revealed　that　sulfate　radicals　dominate　the　degradation　process.　When　integrated　into　continuous-flow　membrane　reactors,　the　system　maintained　complete　pollutant　removal　at　a　water　flux　of　205　L　m−2　h−1　over　270　min.　Comprehensive　toxicity　assessments　confirmed　effective　detoxification　of　treated　effluents.　These　findings　establish　a　rational　design　framework　for　metal-free　photocatalysts　that　efficiently　combines　solar　energy　utilization　with　persulfate　activation　for　sustainable　water　treatment.　©　2025　Elsevier　Inc.