In this study, the research aim is to enhance the activity index of activated coal gangue and study its activation mechanism. The activation process of coal gangue was optimized through orthogonal tests, and the Back-Propagation (BP) neural network model was improved using a genetic algorithm. With the effects of grinding duration, calcination temperature, and calcination duration, the morphological changes and phase transformation processes of coal gangue were studied at the micro and meso levels to clarify the activation mechanism. The results indicated that the effect of calcination temperature on the strength activity index of coal gangue was most significant, followed by grinding duration and calcination duration. The potential activity of coal gangue can be effectively stimulated through mechanical and thermal activation, and the content of potential active minerals in coal gangue powders was also increased. The activation process of coal gangue for the optimal scheme was obtained as grinding at 76 min first and thermal treatment at 54 min at 749 °C. As the thermal activation under 950 °C, some unstable external hydroxyls, and internal hydroxyls in kaolinite from coal gangue were removed, the Al^Ⅵ-O octahedron was destroyed, and kaolinite was transformed into spatially disordered metakaolinite with very high activity.

With growing global emphasis on green and low-carbon development, energy-related challenges have attracted heightened scholarly and public attention. Polyoxometalates (POMs)—well-defined anionic metal–oxygen clusters—exhibit exceptional capacity for rapid, reversible multi-electron transfer while maintaining structural integrity. In this study, graphitic carbon nitride (g-C₃N₄) was protonated using hydrochloric acid to yield the cationic derivative g-C₃N₄–H⁺Cl⁻. Subsequently, three nanostructured g-C₃N₄-based composite photocatalysts—denoted as g-C₃N₄-H-MMo₆ (M = Ni, Fe, Co)—were synthesized via electrostatic assembly between the protonated support and POM anions. Comprehensive characterization was conducted to elucidate phase purity, morphology, surface properties, elemental composition, and chemical states. Under visible-light irradiation, photocatalytic H₂O₂ production performance was significantly enhanced: g-C₃N₄-H-NiMo₆ achieved a 3.91-fold increase in activity relative to pristine g-C₃N₄. Catalytic efficiency followed the trend g-C₃N₄-H-NiMo₆ > g-C₃N₄-H-FeMo₆ > g-C₃N₄-H-CoMo₆. Electrochemical tests confirmed the role of MMo₆ (M = Ni, Fe, Co). The photogenerated electrons of g-C₃N₄ are transferred to the anchored POMs and reduce dissolved O₂ to H₂O₂ (O₂ + 2H⁺ + 2e⁻ → H₂O₂), while the photogenerated holes oxidize H₂O to H₂O₂ (2H₂O + 2h⁺ → H₂O₂ + 2H⁺), achieving sacrificial-agent-free H₂O₂ photosynthesis with an overall reaction of O₂ + 2H₂O → 2H₂O₂. Collectively, electrostatic immobilization of POMs onto protonated g-C₃N₄ affords robust, high-performance photocatalysts with simultaneously improved activity, stability, and structural fidelity.