| Anatase titanium dioxide(TiO2)is one of the most widely studied photocatalysts,there are various advantages:wide applications,non-toxic and good chemical stability;rich in elements and being synthesized easily.The photochemical activity,refractive index and other physicochemical properties of TiO2 semiconductor materials as well as their applications are closely related to the morphology,size and microstructure of the materials.Therefore,controllable synthesis of anatase TiO2 effectively so as to better realize the various functions of TiO2 nano-materials and expand the application field of materials are very impotant.Although the traditional hydrothermal synthesis of TiO2 crystals' controllable facets have been widely studied,there are few systematically experimental studies on the effects of morphologies on its photocatalytic properties by microwave hydrothermal method.Therefore,anatase TiO2 single crystals with a dominant synthesis was prepared by a novel microwave-assisted method and the effects of reaction time,concentrations of HF on morphology and photocatalysis of TiO2 single crystals were systematically studied.Since visible light cannot be effectively absorbed via anatase TiO2 crystals owing to its wide band gap,we further developed the stable,narrow-band inorganic semiconductor graphitic nitride carbon(g-C3N4),which can form heterojunction with TiO2 nanosheets.The compounds of TiO2 nanosheets and g-C3N4 will acted as a stable and efficient photocatalyst.The main contents of this work are as follows:Firstly,the microwave-assisted technique was used to study the effect of reaction time on controllable synthesis of anatase TiO2 single crystals and its photocatalytic performance.Tetrabutyl titanate(TBOT)was used as Ti source and hydrofluoric acid(HF)acted as morphology controlling agent.Herein,anatase TiO2 single crystals exposing high percentage of {001} facets were synthesized successfully.The results indicate that the size of anatase TiO2 single crystals increases with increasing reaction time in a certain range(45min-105min),while percentage of exposed {001} facets and truncation degree are almost unchanged with 180 mM HF as morphology controlling agent at 210?.Furthermore,EDS shows that F was preferentially adsorbed on the surface of anatase TiO2 single crystals and the morphology is kept same after high temperature annealed.The photocatalytic degradation results reveal clearly that smaller crystal size gives rise to higher decomposition rate under similar percentage of exposing {001} facets.Secondly,based on the experiments in the previous chapter,The influence of HF concentration on controllable synthesis of anatase TiO2 single crystals was studied.The results show that the size of anatase TiO2 single crystals gradually increases with increasing HF concentrations(120 mM-210 mM)at 210 ? for 90 min reaction time,and the percentage of {001} facets as well as truncation degree are enhanced with increasing HF concentrations in certain range.The result of photocatalytic degradation shows that the size and exposed fraction of {001} facets synergistically affect the photocatalytic activity of anatase TiO2 single crystals.Under the optimal condition(size is 2.0 ?m,truncation degree is 0.75,exposed fraction of {001} facets is 34%),the photocatalyst exhibits the highest activity towards MB.Finally,the photocatalytic performance was studied through g-C3N4/TiO2 composites as photocatalyst,which was synthesized via the calcination process.Firstly,TiO2 nanosheets and two-dimensional layered g-C3N4 were synthesized separately.TBOT was used as Ti precursor and HF as morphology controlling agent.TiO2 nanosheets were successfully synthesized by hydrothermal reaction at 200 ? for 14 h.Urea was used as carbon precursor to prepare g-C3N4 by calcination process in the muffle furnace at 550 0C for 2 h,then the synthesized TiO2 nanosheets and two-dimensional layered g-C3N4 were homogenously mixed in a certain proportion and then calcined in a muffle furnace at 400? C for 2 h,herein,g-C3N4/{001}TiO2 composites were successfully prepared.The results show that the addition of g-C3N4 does not affect the phase structure of the samples,indicating that the combination of the two materials is a physical behavior.Secondly,the addition of g-C3N4 broadens the visible light range of TiO2 photocatalyst and significantly improves the photocatalytic degradation activities. |
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