1：Experimental Design and Method Selection:

A hydrothermal method was used to synthesize BiVO4/BiOCl composites by surface replacement of pre-synthesized BiOCl with BiVO4. This method was chosen to optimize visible light absorption and charge carrier separation through the formation of a p-n junction.

2：This method was chosen to optimize visible light absorption and charge carrier separation through the formation of a p-n junction. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: BiOCl powders were synthesized from Bi(NO3)3?5H2O and KCl in ethylene glycol solution. BiVO4 was synthesized using Bi(NO3)3?5H2O aqueous solution and NH4VO3. Composites with varying BiVO4 molar percentages (10%, 20%, 30%, 40%) were prepared.

3：Composites with varying BiVO4 molar percentages (10%, 20%, 30%, 40%) were prepared. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Chemicals included Bi(NO3)3?5H2O, KCl, NH4VO3, ethylene glycol, deionized water, ethanol, NH3?H2O, Rhodamine B dye. Equipment included Teflon-lined autoclaves, ultrasonic bath, centrifuges, drying oven, XRD diffractometer (XRD-6100, Shimadzu), FE-SEM (SU-1510, Hitachi), HRTEM (Tecnai G2 F20, FEI Company), UV-Vis-NIR spectrophotometer (UV-3600, Shimadzu), XPS (AXIS-ULTRA DLD, Shimadzu), Xe lamp with cutoff filter, electrochemical workstation (CHI-660E, CH Instruments), ITO glass, platinum gauze electrode, Ag/AgCl reference electrode.

4：Experimental Procedures and Operational Workflow:

BiOCl was synthesized by heating Bi(NO3)3?5H2O in ethylene glycol with KCl at 160°C for 12h. For composites, BiOCl suspension was mixed with NH4VO3 solution, pH adjusted to 7 with NH3?H2O, and hydrothermally treated at 180°C for 12h. Products were washed, dried, and characterized. Photocatalytic tests involved degrading RhB under visible light, with samples collected periodically for UV-Vis analysis. Photocurrent measurements used a three-electrode system with visible light cycles.

5：2h. For composites, BiOCl suspension was mixed with NH4VO3 solution, pH adjusted to 7 with NH3?H2O, and hydrothermally treated at 180°C for 12h. Products were washed, dried, and characterized. Photocatalytic tests involved degrading RhB under visible light, with samples collected periodically for UV-Vis analysis. Photocurrent measurements used a three-electrode system with visible light cycles. Data Analysis Methods:

5. Data Analysis Methods: XRD for phase identification, SEM and TEM for morphology, XPS for surface composition, UV-Vis DRS for optical properties, first-order kinetics model for degradation rates, Tauc's plot for band gap calculation, chronoamperometry for photocurrent response.