1：Experimental Design and Method Selection:

The study employed a simple precipitation method to synthesize BiOBrxCl1-x solid solutions without adding any organic template. The photocatalytic reduction of CO2 was carried out as a gas–solid heterogeneous reaction under simulated solar light irradiation.

2：Sample Selection and Data Sources:

Bismuth nitrate pentahydrate and ammonium halide were used as precursors. The samples were characterized by XRD, SEM, TEM, BET, UV–vis DRS, PL, XPS, EPR, and photoelectrochemical measurements.

3：List of Experimental Equipment and Materials:

Equipment included a diffractometer (D8 Advanced, Bruker Co., Germany), SEM (JSM-6700F), TEM (JEM-2100), UV-3600 spectrophotometer, FLS 920 Fluorescence and Phosphorescence spectrometer, XPS (VG, Physical Electrons Quantum 2000), EPR (Brucker EPR A200), and a gas chromatograph (Agilent GC-7890B).

4：Experimental Procedures and Operational Workflow:

The photocatalytic reduction of CO2 was performed in a 40 mL Schlenk flask under simulated sunlight. The reaction products were analyzed using gas chromatography.

5：Data Analysis Methods:

The data were analyzed using various characterization techniques to understand the structure, optical properties, and photocatalytic activity of the samples.