Preparation And Properties Of TiO₂?B?-based Crystal Phase Controllable Photocatalytic Materials

At present,most of the catalysts used in the field of photocatalysis are n-type semiconductor materials,including TiO₂,CdS,SnO₂,ZnO,ZnS,etc.,wherein the photocatalytic effect of TiO₂ is more photochemical than other semiconductor photocatalysts.It is non-toxic,harmless,has a wide range of sources,and has higher photocatalytic efficiency and strong oxidizing power.It has wide applications in the fields of wastewater treatment,photodecomposition of water to produce hydrogen,reduction of CO₂ to prepare CH₄,and battery materials.The researchers have prepared eight crystal phase structures of titanium dioxide in the laboratory,including:anatase,rutile,brookite,monoclinic TiO₂?TiO₂?B??,TiO₂-R,TiO₂-H,TiO₂-II and TiO₂-III.Among them,anatase,rutile and brookite are relatively common,and have been widely studied by scholars,while the other five crystal forms have not received much attention,mainly because of their difficult synthesis and unstable crystal structure.It is easy to transformed into anatase phase and rutile phase under high temperature heat treatment conditions.In the field of photocatalysis research,anatase,rutile and brookite have also been recognized by researchers.Since monoclinic TiO₂ was first discovered by Marchand in 1980,there has been little research in the field of photocatalysis.In addition to structural instability,the main reason is that the forbidden band width is large,and the photogenerated electron-hole pairs are easily recombined,resulting in low photocatalytic efficiency.The work of this thesis is mainly to prepare TiO₂?B?nanosphere structure,and to prepare black anatase phase TiO₂ with TiO₂?B?as precursor and to synthesize composite with graphene to improve its photocatalytic activity.The specific content and main findings of the paper are as follows:?1?A new type flower-like nanosphere structure of TiO₂?B?was synthesized by solvothermal method.Ti³⁺self-doped TiO₂?B?nanospheres were prepared by X-ray diffraction and transmission electron microscopy using Ti³⁺ions carried by TiCl₃.The morphological structure of the sample was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy.The photocatalytic activity of TiO₂?B?was studied by using methylene blue as the simulated organic wastewater.The results show that the photocatalytic activity of nano-TiO₂?B?prepared by glycol solvothermal method is lower than that of commercial P25.The main reason is that the surface of nano-TiO₂?B?has large defect density,and adsorbs ethylene glycol,which can not directly diffuse organic pollutants.Nano-TiO₂?B?photocatalyst surface,but this new TiO₂?B?nanoflower-like structure is significantly reduced compared to nanosheets.?2?Using black TiO₂?B?as a precursor,calcination was carried out in a 320?temperature tube furnace under nitrogen atmosphere to prepare black anatase phase TiO₂.In the preparation of precursor TiO₂?B?,the effects of different conditions of TiO₂?B?and black anatase phase TiO₂ on the catalytic activity of methylene blue were studied by changing the pretreatment stirring time and solvothermal temperature.It is found that,within a certain range,with the increase of pretreatment stirring time and the increase of solvothermal temperature,the crystal phase structure of the sample has no significant difference before annealing,but after annealing at 320?,the sample will be monoclinic TiO₂.Gradually transformed into anatase phase structure.The sample prepared under optimized conditions is a flower-shaped nanosphere titanium dioxide composed of nano-sheets with a specific surface area of 210 m²/g,an initial concentration of methylene blue of 2×10^-5 mol/L,and the photocatalytic degradation efficiency can reach 99.6%.?3?The nano TiO₂?B?prepared by the above method is a precursor,and is loaded with graphene oxide at 180?by using sol-gel method using anhydrous ethanol as a medium.,and finally anatase phase titanium dioxide/graphite oxide is obtained.The effects of the mass ratio of TiO₂?B?and graphene oxide on the photocatalytic properties of the composites were investigated.The results show that TiO₂?B?is converted into anatase phase structure after compounding at 180?.When the mass ratio of graphene oxide to TiO₂?B?is 2:1,the photocatalytic efficiency of the composite is 6 times higher than that of black anatase phase titanium dioxide,and the photodegradation efficiency can still reach 99.8%.