1：Experimental Design and Method Selection:

Hydrothermal synthesis was used to fabricate MnO2 nanoparticles and NG-MnO2 nanocomposite, with characterization via XRD, SEM, TEM, FTIR, Raman, TGA, and VSM. Photocatalytic tests were conducted under visible light.

2：Sample Selection and Data Sources:

Samples included reduced graphene oxide (RGO), nitrogen-doped graphene (NG), MnO2, and NG-MnO2 nanocomposite, synthesized from analytical grade chemicals.

3：List of Experimental Equipment and Materials:

Equipment included D8 X-ray diffractometer (Bruker), Tecnai G2 S-Twin TEM, FEI Nova Nano SEM 450, Shimadzu FTIR spectrometer, Lakeshore 7410 VSM, Perkin Elmer SGSA 6000 thermal analyzer, UV-Visible Spectrophotometer (PG instrumentations, US T-90), Renishaw Raman spectrometer. Materials included graphite powder, urea, KMnO4, MnSO4.H2O, H2O2, methyl orange dye, and deionized water.

4：H2O, H2O2, methyl orange dye, and deionized water. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Synthesis involved hydrothermal methods for RGO, NG, MnO2, and NG-MnO2. Photocatalytic tests involved mixing catalyst with MO dye, stirring in dark, and exposing to visible light, with absorbance measurements at intervals.

5：Photocatalytic tests involved mixing catalyst with MO dye, stirring in dark, and exposing to visible light, with absorbance measurements at intervals. Data Analysis Methods:

5. Data Analysis Methods: Crystallite size calculated using Scherrer's formula, photocatalytic degradation efficiency assessed from UV-Vis absorbance changes, and magnetic properties analyzed from VSM data.