Controllable Synthesis And Photocatalytic Properties Of 3-D Hierarchical TiO₂ Microspheres

In this paper,the hierarchical titanate microspheres were synthesized using tetrabutyltitanateastitaniumprecursor,ploy?ethylene-glycol?-blok-ploy?ethylene-glycol?-blok-ploy?ethylene-glycol?as a structure-directing agent and stabilizer through a simple solvothermal treatment.Then three-dimensional hierarchical titanium dioxide?TiO₂?microspheres with controlled morphology derived from calcination treatment of hierarchical titanate microspheres were fabricated.The obtained hierarchical TiO₂ microspheres with diameters of 1?m to 2?m were composed of polycrystalline anatase nanosheets with thickness of 10 nm,and has large specific area(110.3¹20.5m² g^-1)and rich mesoporous structure.The morphology was manipulated by simply adjusting the molar ratio of tetrabutyl titanate/P123.At a low molar ratio of17.04,TiO₂ microspheres composed of a large number of nanosheets closely packed together were obtained.With the increase of the molar ratio from 17.04 to 25.6,the decrease in the number of nanosheets led to the formation of low density microspheres.At a high molar ratio of 34.08,TiO₂ hybrid architectures with polycrystalline anatase hierarchical microspheres and single-crystal anatase mesoporous?approximately 5 nm?nanospheres were obtained,and the nanosheets became more sparse,mesoporous nanospheres with sizes of approximately 200 nm were packed tightly on the surface of nanosheets.From the time-dependent observation of the titanate precursor,the growth mechanism involved in the multistep pathway of such hierarchical TiO₂ microspheres was revealed,and the role of P123 was also investigated.The formation of hierarchical TiO₂ microspheres has undergone a series of condensation,aggregation,dissolution,nucleation,assembly,growth,and calcination processes.In the reaction system,P123was used as stabilizer and structure directing agent to promote the stability of the system and induce the formation of a well-defined hierarchical structureThe photocatalytic performances of the obtained samples were investigated by the degradation of methylene blue and papermaking wastewater.The effects of catalyst dosage and solution initial pH on the degradation of papermaking wastewater and recycling capacity of catalyst were studied.When the catalyst dosage is and solution initial pH is 5,catalyst exhibited the highest photocatalytic activity.When compared with commercial P25,because of its excellent structural properties,the obtained hierarchical TiO₂ microspheres exhibit superior photocatalytic activity,high degradation efficiency,and good reproducibility.The product with hybrid architectures exhibited the highest photocatalytic activity.The chemical oxygen demand and the chroma removal rate of papermaking wastewater achieved 85.5%and 100%,respectively,after 12 h of photodegradation.More interestingly,the prepared materials exhibited excellent photocatalytic performances for practical application to papermaking wastewater treatment,with the COD_Cr removal rate of papermaking wastewater being maintained at65.8%on the fourth run.