Study On The Preparation And Application Of TiO₂ And Its Graphene-based Composite

Titanium dioxide(TiO2);as a widely used photocatalyst,with unique physical and chemical properties,has the advantages of non-toxicity,stable chemical properties and low cost,and has significant practical value in the degradation of organic pollutants in water and related fields.However,the photocatalytic activity of TiO2 is limited by the band gap(rutile 3.0 eV,anatase 3.2 eV),which can only be excitated by ultraviolet light with its wavelength being below 380nm.So,TiO2 also has its own limitations.In addition,in the photocatalytic process of TiO2 under light radiation,photogenerated electron-hole pairs can recombine quickly internally other than migrate to the surface of the catalyst,resulting in limitation of the photocatalytic activity of TiO2.In order to solve the above problems,there have been many methods that can change the band gap of TiO2 and inhibit the recombination of electron-hole pairs,such as the incorporation of noble metal particles,metal oxide,carbon materials and controlling synthesis of special morphology of TiO2.A ideal TiO2-based composite photocatalyst can be prepared by these methods.Graphene is a two-dimensional carbon material composed of monolayer carbon atoms sp2.It is widely used for its excellent mechanical,electrical and thermal stability.Exsisting studies show that there exsists sevral problems in the TiO2/graphene(TiO2-rGO)composite research field,such as complicated preparation method,many by-products,expensive titanium source,easy hydrolysis of titanium source et al.Therefore,in this paper,the controlling synthesis of TiO2 with special morphology were studied,and the graphene-based special morphology TiO2 composite was prepared and its photocatalytic performance was investigated.In this paper,the water soluble titanium solution was perpared,which was used as titanium.Three anatase/rutile mixed-phase TiO2 with different morphology were synthesized by sol-gel method and TiO2-rGO composite photocatalyst was prepared by solvothermal method and its performance was studied.The main work of this thesis includes the following five aspects:1.Ti solution was prepared,the solution was bright yellow at room temperature,and has good stability and water solubility,can effectively control the hydrolysis of TiC14.This method of controlling the hydrolysis of titanium source,also has a certain effect on the stability of other titanium source,suitable for many kinds of synthetic methods for preparation of various titanium dioxide nanoparticles material.2.Three different TiO2 samples with different morphology were perpared by sol-gel method under different reaction conditions,using Ti solution as titanium source and CTAB as surfactant.We can see from Raman and XRD analysis results,all obtained samples are anatase/rutile mixed phase TiO2,and the proportion of rutile phase in rod like TiO2 is the highest.As is shown in the SEM and TEM picture,the box like TiO2 crystals are tiled over silicon,with crystal being shape an,edge and angles being distinct,surface being smooth and boundary being clear.TiO2 microspheres clearly show a yolk-eggshell structure,with spheres surface being sough,shape being regular and boundary being clear.The reunion phenomenon present in the sample and small particles attached to the spherical show sample dispersion is not homogeneous.It may also be caused by excessive titanium source.The ring in selected area electron diffraction(SAED)pattern shows that TiO2 microspheres are composed of many small particles instead of single crystal.In addition,TiO2 nanorods arranged in irregular,some agglomerate together,resulting in trend of formation of heterojunction flower structure.3.Graphene oxide(GO)with good dispersion was prepared by the modified Hummer' method,which is single or few layer structure,containing abundant oxygen-containing functional groups,such as hydroxyl(-OH),carboxyl(-COOH),epoxy(-CH(O)CH-).Due to the existence of oxygen functional groups,GO has enhanced dispersion in aqueous solution and provides large amounts of active sites for TiO2 crystal nucleation and growth in the process of preparation of composite materials.4.Through a simple green solvothermal method,TiO2-based nanocomposites was prepared,where TiO2 particles successfully supported GO substrate.TiO2-rGO nanocomposites were characterized by a series of intruments to study crystal structure of composites and morphology and oxygen-containing functional groups.XPS and FTIR patterns show GO were reduced competely,meanwhile,SEM and TEM figures show TiO2 crystals with particle size being about 100 nm were loaded on GO subsurface.These crystals can effectively reduce the path of photogenerated electron-hole pairs transfered to the surface,which may further promote high photocatalytic efficiency.5.Finally,the photocatalytic degradation performance of TiO2,P25,TiO2-rGO with different amount GO added in composites were studied under simulated sunlight irradiation,and analyze the reasons.The results show that reduced graphnene oxide can enhance the photocatalytic performance of TiO2,and TiO2-rGO(3%)has the best photocatalytic performance,which can degradate methylene blue in 50 minutes.The degradation kinetics curve of different photocatalyst show the quasi first-orde reaction law.The reasons are mainly the strong adsorption ability of rGO and inhibition of recombination of electron-hole pairs and caption of electron-hole pairs of rutile phase TiO2 in mixed crystal TiO2.