Preparation of black nano-titanium dioxide by a B2O3 sealed magnesium weak reduction method and kinetic analysis

In this paper, black titanium dioxide was prepared by surface weak reduction of white titanium dioxide and its non-isothermal kinetic analysis was conducted. Based on thermogravimetric experiments, there are at least three reactions (TiO₂ + Mg → TiO₂@TiO_2−x + MgO; MgO + TiO₂ → MgTiO₃; Mg + xTiO₂ → xTiO_(2−1/x) + MgO) and one phase transition (Mg(s) → Mg(l)) during the heating process from room temperature to 900 °C. The whole process is caused by magnesium gradually taking away the oxygen in titanium dioxide and causing titanium dioxide to change from a disordered core–shell structure with surface oxygen loss to various titanium oxides. Side reactions and liquid phase changes should be avoided. The results of kinetic analysis show that the Friedman (104.144 kJ mol⁻¹) model-free method has the highest average Adj. R² (0.963) of the four activation energy calculation methods. The activation energy calculation results are used to derive the reaction model and analyze the kinetic mechanism. The dominant model (A8) of the reaction process is characterized by surface nucleation diffusion of the product. Combined with the results of thermogravimetric analysis and reaction mechanism analysis, the temperature control preparation strategy of black titanium dioxide seal is obtained: through B₂O₃ sealing, the surface of titanium dioxide is weakly reduced below the melting point of Mg. Based on this strategy, black TiO₂ with oxygen vacancy defects can be obtained after acid leaching, after heating at 550 °C for more than 2 hours.