1：Experimental Design and Method Selection:

The study used thermal polymerization method to synthesize nano-layer structured g-C3N4 (NL-CN) from melaminium dinitrate (MDN) precursor, comparing it with bulk g-C3N4 (CN) from melamine. The rationale was to leverage the energetic decomposition of MDN for exfoliation.

2：Sample Selection and Data Sources:

MDN was synthesized from melamine and nitric acid; samples included NL-CN and CN for comparison.

3：List of Experimental Equipment and Materials:

Equipment included muffle furnace, XRD (Rigaku D/max 2500 V/PC), FTIR (Nicolet-560), XPS (MULTILAB2000, VG), SEM (JSM-6390A), TEM (FEI TecnaiG20), BET surface area analyzer (Tristar II-3020), UV-Vis spectrometer (U-3010), PL spectrometer (Hitachi-4600), element analyzer (FLASH1112A), ESR spectrometer (Bruker ER200-SRC), electrochemical workstation (CHI 660E), photocatalytic H2 evolution system (LabSolar), gas chromatograph (GC-1690, Jiedao), UV-Vis spectrophotometer (721 model), TOC analyzer (Liqui TOC II). Materials included melamine, nitric acid, alumina crucible, acetyl acetone, ethanol, FTO glass, triethanolamine, RhB, benzoquinone, isopropanol, ammonium oxalate, DMPO.

4：Experimental Procedures and Operational Workflow:

MDN synthesis involved adding nitric acid to melamine solution, cooling to precipitate, filtering. NL-CN preparation: calcine MDN at 500°C for 2h at 10°C/min in muffle furnace. CN preparation: same but with melamine. Characterization involved XRD, FTIR, XPS, SEM, TEM, BET, UV-Vis DRS, PL, elemental analysis, ESR. Photoelectrochemical tests used three-electrode system with FTO electrode. Photocatalytic H2 evolution: 50mg catalyst in triethanolamine solution under Xe lamp with cutoff filter, H2 detected by GC. RhB degradation: 0.01g catalyst in RhB solution under Xe lamp, concentration measured by spectrophotometer, stability tested over cycles.

5：01g catalyst in RhB solution under Xe lamp, concentration measured by spectrophotometer, stability tested over cycles. Data Analysis Methods:

5. Data Analysis Methods: Band gap calculated using Kubelka-Munk equation, kinetic analysis for RhB degradation, AQE calculation for H2 production, statistical analysis of characterization data.