1：Experimental Design and Method Selection:

A facile solvothermal method was used to synthesize pyrimidine/g-C3N4 composites. The photocatalytic activity was assessed by degrading RhB under visible light.

2：Sample Selection and Data Sources:

Samples included pure g-C3N4, pyrimidine, and composites with varying pyrimidine content (

3：5 wt%, 1 wt%, 2 wt%, 5 wt%, 3 wt%). RhB solution was used as the pollutant. List of Experimental Equipment and Materials:

Equipment included FT-IR spectrophotometer (MB 154S-FTIR, Bomen), SEM (S4800, Hitachi), TEM (JEM-2010F, JEOL), BET surface area analyzer (NOVA 2000e), XPS (RBD upgraded PHIe5000C ESCA, PerkinElmer), UV-Vis spectrophotometer (UV-2450, Shimadzu), PL spectrofluorimeter (Fluoro-Max-P), electrochemical workstation (CHI 614D, CH Instrument), and a 350 W Xe-lamp with a 420 nm cut-off filter (Nanshen Company). Materials included RhB, dicyandiamide, tetrahydrofuran, and pyrimidine derivative.

4：Experimental Procedures and Operational Workflow:

Synthesis involved dispersing g-C3N4 and pyrimidine in THF, ultrasound and stirring, solvent removal, and drying. Characterization was performed using the listed techniques. Photocatalytic tests involved suspending catalyst in RhB solution, dark adsorption for 30 min, irradiation with visible light, sampling at intervals, and analysis via UV-Vis spectroscopy. Radical trapping experiments used TBA, EDTA-2Na, and VC as scavengers.

5：Data Analysis Methods:

Data were analyzed using pseudo-first-order kinetics model for degradation rates. XPS, FT-IR, SEM, TEM, BET, DRS, PL, photocurrent, and EIS data were interpreted to understand structure, composition, and charge transfer properties.