1：Experimental Design and Method Selection:

A solvothermal method was used to synthesize BiOBr hierarchical structures, with citric acid as a capping agent and methanol as the solvent to control crystal growth and morphology. The design aimed to investigate the effects of citric acid amount, reaction time, temperature, and solvent on the product.

2：Sample Selection and Data Sources:

Bismuth nitrate (Bi(NO3)·5H2O), potassium bromide (KBr), citric acid, methanol, and distilled water were used as starting materials. Samples were synthesized under various conditions (e.g., different CA/Bi3+ ratios, temperatures, solvents).

3：List of Experimental Equipment and Materials:

Equipment included a Teflon-lined stainless steel autoclave for solvothermal reactions, X-ray diffractometer (Rigaku D/MAX 2200 PC), X-ray photoelectron spectrometer (Thermo Fisher Scientific Escalab 250), field emission scanning electron microscope (JEOL-6340F), transmission electron microscope (JEOL JEM-2100F), UV-vis spectrophotometer (Shimadzu UV-3600), BET surface area analyzer (NOVA-2200e), UV light source (100 W high pressure mercury lamp), simulated sunlight source (300 W Xe lamp), and UV-vis spectrophotometer (Techcomp UV-2600). Materials included Bi(NO3)·5H2O, KBr, citric acid, methanol, distilled water, methyl orange.

4：0). Materials included Bi(NO3)·5H2O, KBr, citric acid, methanol, distilled water, methyl orange. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: In a typical procedure, Bi(NO3)·5H2O was dissolved in methanol, followed by addition of KBr and citric acid. The mixture was stirred, transferred to an autoclave, heated at 150 °C for 12 h, cooled, washed, and dried. Controlled experiments varied CA amount, reaction time, temperature, and solvent. Photocatalytic activity was evaluated by dispersing the sample in methyl orange solution, stirring in dark for equilibrium, then exposing to light and measuring concentration changes over time.

5：Data Analysis Methods:

XRD for phase identification, XPS for elemental analysis, SEM and TEM for morphology, UV-vis for optical properties, BET for surface area, and UV-vis spectrophotometry for photocatalytic degradation kinetics.