1：Experimental Design and Method Selection:

Hydrothermal synthesis method was used to prepare bismuth molybdate photocatalysts by adjusting pH without organic solvents to avoid adverse impacts on CO2 reduction.

2：Sample Selection and Data Sources:

Bismuth nitrate pentahydrate and sodium molybdate were used as precursors, dissolved in nitric acid and deionized water, with pH adjusted to 5 or 11 using NaOH.

3：List of Experimental Equipment and Materials:

Chemicals included Bi(NO3)3·5H2O (Tianjin Damao Chemical Reagent Factory, 99%), Na2MoO4 (Tianjin Kermel Chemical Reagent Co. Ltd., 99%), HNO3 (Sinopharm Chemical Reagent Co. Ltd., 65-68%), NaOH (Shanghai Titan Scientific Co. Ltd., 98%), deionized water. Equipment included Teflon-lined stainless steel autoclave, Bruker D8 Advanced diffractometer for XRD, Nanosem 430 field-emission scanning electron microscope, Talos F200 field-emission transmission electron microscope, Shimadzu UV-3600 spectrophotometer for UV-vis DRS, Thermo SCIENTIFIC Escalab 250 for XPS, Horiba Scientific Flurolog-3 fluorescence spectrophotometer for PL, CHI660E electrochemical working station for electrochemical measurements, 300 W Xe lamp for irradiation, gas chromatography (GC-8 A, Shimadzu) for product analysis.

4：Experimental Procedures and Operational Workflow:

Precursors were dissolved, mixed, pH adjusted, hydrothermally treated at 160°C for 12 h, washed, dried. Characterization involved XRD, SEM, TEM, BET, UV-vis DRS, XPS, PL, photocurrent, EIS. Photocatalytic CO2 reduction was performed in a gas closed system with 30 mg catalyst, 3 mL water, 70 kPa CO2, irradiated by Xe lamp, gas samples analyzed by GC.

5：Data Analysis Methods:

XRD patterns compared to PDF standards, Raman spectra analyzed for bonding states, BET surface areas calculated, band gaps estimated from UV-vis DRS, XPS binding energies referenced to C 1s, PL and electrochemical data used to assess charge behavior, CO yields measured and rates calculated.