1：Experimental Design and Method Selection:

The study employed a hard template synthesis method using SiO2 nanospheres as templates to fabricate mesoporous carbon nitride nanospheres (MCNS) through incomplete polycondensation of cyanamide during thermal polymerization. This method was chosen to introduce cyano groups and enhance surface properties. Theoretical calculations using density functional theory (DFT) were conducted to understand the mechanisms.

2：Sample Selection and Data Sources:

The photocatalysts synthesized included MCNS, nanosheet g-C3N4 (NS C3N4), and bulk g-C3N4. Bisphenol A (BPA) was used as a model pollutant. Materials were sourced from commercial suppliers (e.g., Tokyo Chemical Industry, Sinopharm Chemical Reagent).

3：Bisphenol A (BPA) was used as a model pollutant. Materials were sourced from commercial suppliers (e.g., Tokyo Chemical Industry, Sinopharm Chemical Reagent). List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included SEM (QUANTA FEG 250), TEM (Tecnai G2 F20 S-TWIN), XRD (Bruker D8), XPS (ESCALAB 250 XI), FTIR (Thermo Nicolet), BET surface area analyzer (Micromeritics ASAP 2020), potentiostat (CHI 760D), UV-vis DRS (Shimadzu Solid 3700), xenon lamp (BL-GHX-Xe-300), HPLC (Waters 2695), TOC analyzer (liquic TOC II). Materials included cyanamide, TEOS, ethanol, ammonia, HCl, NH4HF2, BPA, TBA, AO.

4：Experimental Procedures and Operational Workflow:

Synthesis involved preparing SiO2 templates, mixing with cyanamide, thermal polymerization at 550°C in N2, removal of silica with NH4HF2, and freeze-drying. Characterization included SEM, TEM, XRD, XPS, FTIR, BET, electrochemical measurements, and photocatalytic tests with BPA degradation under visible light. DFT calculations were performed using VASP.

5：Data Analysis Methods:

Data were analyzed using Langmuir-Hinshelwood kinetics for degradation rates, statistical methods for comparisons, and software tools for DFT calculations and spectral analysis.