1：Experimental Design and Method Selection:

The study involved fabricating Z-scheme heterojunctions by combining β-FeOOH with g-C3N4 to enhance photocatalytic hydrogen evolution under visible light. Methods included thermal condensation, hydrothermal synthesis, and calcination.

2：Sample Selection and Data Sources:

Samples included pure g-C3N4, β-FeOOH, and composites with varying FeCl3·6H2O amounts (CN/Fe-x, x=0.25 to 2 mmol). Data were obtained from material characterizations and photocatalytic tests.

3：25 to 2 mmol). Data were obtained from material characterizations and photocatalytic tests. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included XRD diffractometer (PANalytical X’pert MPD Pro), TEM (FEI Tecnai G2F30 S-Twin), FTIR spectrophotometer (Bruker Vetex70), BET analyzer (Micromeritics ASAP 2020), XPS (Kratos Axis Ultra DLD), UV-Vis spectrophotometer (Agilent Cary 5000), PL spectrophotometer (PTI Quanta Master 40), photoelectrochemical setup with three-electrode system, photocatalytic reactor with 300 W Xenon lamp, and gas chromatograph. Materials included urea, FeCl3·6H2O, ethylene glycol, triethanolamine (TEOA), H2PtCl6·6H2O, Nafion solution, and others.

4：Experimental Procedures and Operational Workflow:

g-C3N4 was synthesized from urea at 600°C. Composites were prepared by dispersing g-C3N4 and FeCl3·6H2O in water, evaporating, and calcining at 200°C. Pure β-FeOOH was synthesized separately. Characterizations involved XRD, TEM, FTIR, BET, XPS, UV-Vis, PL, photoelectrochemical measurements, and photocatalytic H2 evolution tests with Pt cocatalyst and TEOA sacrificial reagent under visible light (λ ≥ 420 nm).

5：Data Analysis Methods:

Data were analyzed using standard techniques for each characterization method. Photocatalytic activity was quantified by H2 evolution rate and apparent quantum efficiency (AQY) calculations.