1：Experimental Design and Method Selection:

The study involved preparing Ni(OH)2@g-C3N4/halloysite nanocomposites with varying Ni(OH)2 amounts (

2：5–10 wt%) to enhance photocatalytic hydrogen evolution under visible light. Methods included synthesis, characterization, and activity evaluation. Sample Selection and Data Sources:

Samples were synthesized using urea, thiourea, halloysite nanoclay, and Ni(NO3)2·6H2O. Data came from experimental measurements and simulations.

3：2O. Data came from experimental measurements and simulations. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a muffle furnace, centrifuge, XRD diffractometer (RINT-2100, Rigaku), SEM (S-4500, Hitachi), TEM (EM-002B, TOPCON), UV-vis spectrophotometer (UV-3600, Shimadzu), BET surface area analyzer (BELSORP-mini, BEL Japan, Inc.), XPS (JPS-9010MC, JEOL), gas chromatograph (GC-8A, Shimadzu), and computational software (Accelrys Materials Studio). Materials included urea (>

4：0%, Wako), thiourea (0%, Kanto), halloysite nanoclay (Merck), NaOH (50%, Merck), Ni(NO3)2·6H2O (999%, Merck), and deionized water. Experimental Procedures and Operational Workflow:

g-C3N4 was synthesized by heating urea and thiourea at 550°C. Nanocomposites were prepared by dispersing g-C3N4 and halloysite in NaOH, adding Ni(NO3)2 solution, stirring, centrifuging, washing, and drying. Characterization involved XRD, SEM, TEM, UV-vis DRS, BET, and XPS. Photocatalytic activity was evaluated by dispersing powder in aqueous methanol, irradiating with a 300 W Xenon lamp, and analyzing evolved H2 with GC. Adsorption was modeled using molecular dynamics simulations.

5：Data Analysis Methods:

Data were analyzed using Rietveld refinement for XRD, Kubelka-Munk method for UV-vis, BET equation for surface area, and computational modules for adsorption energies.