1：Experimental Design and Method Selection:

A two-step hydrothermal method was used to synthesize SrTiO3/SnCoS4 heterojunctions, with photocatalytic activity evaluated under visible light irradiation using methyl orange degradation as a model reaction.

2：Sample Selection and Data Sources:

Samples included pure SrTiO3, SnCoS4, and various composites with different SnCoS4 loadings (1%,

3：5%, 5%, 5%, 10%), prepared using analytical grade reagents. List of Experimental Equipment and Materials:

Materials included tetraisopropyl orthotitanate, strontium nitrate, sodium hydroxide, cobalt chloride hexahydrate, stannic chloride pentahydrate, L-cysteine, anhydrous ethanol, acetic acid, and methyl orange. Equipment included a Teflon-lined stainless-steel autoclave, centrifuge, Shimadzu XRD 6000 diffractometer, SUPRA 55 FESEM with EDX, JEOL JEM 2100 TEM, ThermoFisher ESCALAB 250X XPS, Shimadzu UV-3600 spectrophotometer, FS5 fluorescence spectrophotometer, and a 250 W Xe arc lamp with UV cut-off filter.

4：Experimental Procedures and Operational Workflow:

SrTiO3 was synthesized hydrothermally at 180°C for 24 hours. Composites were prepared by dispersing SrTiO3 in deionized water, adding precursor solutions, and hydrothermally reacting at 180°C for 24 hours. Photocatalytic tests involved adding catalyst to MO solution, stirring in dark for adsorption equilibrium, irradiating with visible light, sampling periodically, centrifuging, and measuring absorbance.

5：Data Analysis Methods:

XRD for crystal structure, SEM/TEM for morphology, XPS for elemental analysis, UV-Vis DRS for light absorption, PL spectra for charge separation, and degradation kinetics analyzed using pseudo-first-order model.