1：Experimental Design and Method Selection:

The study involved synthesizing MgO/g-C3N4 nanocomposites via calcination of mixtures of magnesium nitrate hexahydrate and g-C3N4 under nitrogen atmosphere to form heterojunctions for improved charge separation.

2：Sample Selection and Data Sources:

Samples included bare g-C3N4 and MgO/g-C3N4 composites with varying MgO contents (

3：25, 5, 1, 3, 15 wt%), prepared from melamine and magnesium nitrate hexahydrate. List of Experimental Equipment and Materials:

Materials used were melamine, triethanolamine, magnesium nitrate hexahydrate, ethanol, tetrabutylammonium hexafluorophosphate, and other reagents from Sinopharm Chemical Reagent Co. Ltd. Equipment included tube furnaces for calcination, FT-IR spectrometer (Bruker Tensor 27), thermogravimetric analysis instrument (Q1000DSC + LNCS + FACS Q600SDT), X-ray diffractometer (D/Max-3c), SEM (FEI Quanta 200), TEM (JEOL JEM-2100), ASAP 2420-4 adsorption analyzer, UV-Vis spectrophotometer (PerkinElmer UV-Lambda 950), XPS instrument (HI5700ESCA), fluorescence spectrometer (Shimadzu F-7000), ICP-MS (Leeman), electrochemical instrument (CHI 660), Xe lamp (Beijing Perfect Light Co. 300 W), gas chromatograph (Techcomp GC7900).

4：0). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: g-C3N4 was prepared by calcining melamine at 550°C under N

5：MgO/g-C3N4 composites were made by dissolving magnesium nitrate in ethanol, adding g-C3N4, ultrasonicating, evaporating solvent, and calcining at 400°C under NPhotocatalytic tests involved irradiating catalyst suspensions with visible light using a Xe lamp and cut-off filter, measuring hydrogen evolution with GC. Characterization included FT-IR, TGA, PXRD, SEM, TEM, BET, UV-Vis DRS, XPS, PL, electrochemical measurements. Data Analysis Methods:

Data were analyzed using techniques such as PXRD for crystal structure, BET for surface area, UV-Vis for band gap calculation, PL for charge recombination, electrochemical methods for impedance and photocurrent, and statistical analysis of photocatalytic rates.