1：Experimental Design and Method Selection:

The study employed a facile hydrothermal reaction to synthesize Na-doped α-Bi2O3. The phase formation was investigated via XRD patterns and structural refinements. The effects of oxygen vacancies on optical properties and photocatalysis were discussed.

2：The phase formation was investigated via XRD patterns and structural refinements. The effects of oxygen vacancies on optical properties and photocatalysis were discussed. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The samples consisted of well-crystalized nanoplates with smooth surfaces. The optical absorption was measured at room temperature, and photocatalytic activities were evaluated on photo-degradation of RhB.

3：List of Experimental Equipment and Materials:

XRD patterns were conducted on a diffractometer (Rigaku D/Max). A Cary 5000 UV–vis-NIR spectrophotometer was used for optical absorption measurements. Photocatalytic activities were tested in a 500 ml reactor with a 500 W xenon lamp.

4：Experimental Procedures and Operational Workflow:

The hydrothermal synthesis involved dissolving Bi(NO3)3·5H2O in dilute nitric acid, adding ethylene glycol, and then mixing with Na2CO3 solution. The solution underwent hydrothermal reactions at 170 °C for 12 h.

5：Data Analysis Methods:

The band gap was estimated via Wood-Tauc formula. The photocatalytic effects were evaluated by the optical absorption in RhB solutions.