Preparation And Application Of Hierarchically Porous Titanium Dioxide-based Materials

Nanocrystalline TiO₂ has attracted wide attention from researchers because of its advantages such as low cost,easy availability,non-toxicity,security,high activity and good stability.However,it is greatly limited in practical application due to its difficulties in recycling and the large band gap.The mesoporous TiO₂ material with hierarchical structure can maintain the high reactivity of the nanocrystals and is easy to recycle and regenerate.On the other hand,if the heterojunction recombination between the nanocrystalline TiO₂ and the graphite-like carbon nitride?g-C₃N₄?with narrow band gap can be realized,the visible light response range can be effectively expanded.Therefore,it is of great theoretical significance and practical application value to explore the preparation of hierarchically porous TiO₂ and TiO₂/g-C₃N₄ composite.In this paper,Ti?SO₄?₂ was used as the titanium source,NH₄Cl was used as the additive,and ethanol solution was used as the reaction system.The hierarchical TiO₂ microspheres were prepared by hydrothermal method.Then g-C₃N₄ prepared by melamine was added to the reaction system with Ti?SO₄?₂ as the titanium source to obtain hierarchically porous TiO₂/g-C₃N₄ composite.The as-synthesized products were characterized by SEM,TEM,XRD,EDS,BET,FT-IR and UV-vis.The formation mechanism of hierarchical TiO₂ microspheres was discussed and the photocatalytic activity of different structured samples was compared by the degradation of Rhodamine B?RhB?dye.The results showed that?1?the TiO₂ microspheres with critical crack on spherical shell have the best photocatalytic activity.The size of the microsphere was about 2.5?m and the specific surface area was 107.6 m²/g.The degradation efficiency of RhB reached 99.24%after500 W xenon lamp irradiation for 100 min.The pseudo-first-order kinetics fitting showed that the degradation rate constant was about 1.9 times as large as that of P25.The corresponding preparation process was that the volume ratio of ethanol to water was 1:1?The total volume was 75 mL?,Ti?SO₄?₂ was 7.5 mmol,NH₄Cl was 15 mmol,and the reaction was carried out at180°C for 2 h.?2?The prepared TiO₂/g-C₃N₄ composite sample had a specific surface area up to 130 m²/g.The degradation efficiency of RhB reached 98.78%after 500 W xenon lamp irradiation for 90 min.The pseudo-first-order kinetics fitting showed that the degradation rate constant was about 9.4 and 9.1 times as large as that of nanocrystalline TiO₂ and g-C₃N₄,respectively.The corresponding preparation process was that Ti?SO₄?₂ was 7.5 mmol,water was 75 mL,g-C₃N₄ was 0.6 g,and the reaction was carried out at 180? for 2h.