1：Experimental Design and Method Selection:

The study employed a thermal copolymerization method to synthesize salicylic acid modified polymeric carbon nitride (CN-SA) from urea and salicylic acid. The design rationale was to incorporate aromatic rings into the carbon nitride structure to enhance light absorption and charge carrier separation. Theoretical models included band structure analysis using Mott-Schottky plots and valence band XPS.

2：Sample Selection and Data Sources:

Samples included pristine polymeric carbon nitride (PCN) and CN-SA with varying SA amounts (CN-SA-0.02, CN-SA-0.05, CN-SA-0.1). Pollutants used were tetracycline (TC) and sulfamethazine (SMZ) in aqueous solutions. Data sources included synthesized materials and standard chemical reagents.

3：02, CN-SA-05, CN-SA-1). Pollutants used were tetracycline (TC) and sulfamethazine (SMZ) in aqueous solutions. Data sources included synthesized materials and standard chemical reagents. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment: Muffle furnace (for synthesis), Rigaku D/max-2500 XRD, BioRad FTS-600 FT-IR, Helios NanoLab 600i SEM, Tecnai G2F20 TEM, Brunauer-Emmett-Teller surface area analyzer, ESCALAB 250Xi XPS, Cary 300 UV–vis DRS, Perkin Elmer LS 50B PL spectrometer, 300 W xenon lamp with 420 nm filter, UV–vis spectrophotometer, HPLC-UV, CHI 760E electrochemical workstation, ESR spectrometer. Materials: Urea, salicylic acid (Sinopharm Chemical Reagent Co., Ltd), MilliQ water, ethanol, Na2SO4, N,N-dimethylformamide, FTO glass, Ag/AgCl electrode, Pt electrode, isopropyl alcohol (IPA), TEMPOL, EDTA-2Na.

4：Experimental Procedures and Operational Workflow:

Synthesis: Urea and SA were dissolved in water-ethanol, stirred, ultrasonicated, dried, and heated at 550°C. Characterization: XRD, FT-IR, SEM, TEM, BET, XPS, DRS, PL, photoelectrochemical measurements. Photocatalytic tests: Catalysts dispersed in pollutant solutions, irradiated with visible light, samples taken at intervals, centrifuged, and analyzed by UV–vis or HPLC. Photoelectrochemical: Working electrode prepared by dispersing catalyst on FTO, measured in Na2SO4 under light.

5：Data Analysis Methods:

Kinetic analysis using pseudo-first-order model, band gap calculation from Tauc plots, flat band potentials from Mott-Schottky plots, charge carrier lifetimes from time-resolved PL, active species identification from trapping experiments and ESR.