Preparation And Catalytic Activities Of Titania/montmorillonite Composites

Montmorillonite(MMT)is a silicate mineral with the nano interlayer structures.It can be widely used as catalyst support because of its high cation exchange capacity(CEC)and large internal surface as a two-dimensional confinement reactor that is beneficial for the preparation of high-dispersed nanosized metal and semiconductor particles with narrow particle size distribution loaded on MMT.In this thesis,the nanosized metal/MMT and TiO₂/MMT composites with higher dispersivity and thermal stability were prepared using an intercalation assembling method.The preparation routes,structure and catalytic activity of composites were also systematically studied.Studies indicate that a highdispersed Pd/MMT composite catalysts with uniform distribution of particle size of palladium ranging from 10-20nm located on the platelet of exfoliated MMT was prepared,in which MMT was used as support,PdCl₂ as precursor,KBH₄ as reductant, and the mixed water and ethanol as reaction resolvent.It is found that this catalyst shows an excellent catalytic degradation activity to methylene blue near room temperature.The results indicate that the catalytic activity mainly depends on the dispersivity and loading amount of nano palladium on MMT together with characterizations via X-ray diffractometer(XRD),Transmission Electron Microscopy(TEM).Studies also indicate that Pd-TiO₂/MMT composite photocatalyst was synthesized by using TiCl₄ hydrolysis to introduce nanosized TiO₂ into the interlayer space of MMT.For obtaining pillared TiO₂/MMT with stable structure it was calcined at 500℃,then palladium was loaded by a chemical reduction route.Photocatalytic tests indicate that the Pd-TiO₂/MMT and TiO₂/MMT have the better photocatalytic degradation activities to methylene blue than the commercial TiO₂(P25).The nanosized composite photocatalysts of titania pillared montmorillonite were synthesized via solvothermal method by using water and ethanol as solvent,hexamethylene tetramine as precipitant as well as precursor of titanium trichloride.The phase composition,particle morphology,specific surface area,element content etc were employed to characterize these samples by using XRD,TEM,BET and AAS techniques.The effect of different ratio between TiCl₃ and montmorillonite on the photocatalytic activity for degrading methylene blue in aqueous solution was investigated.The results indicate that the precursor of TiCl₃ as pillaring agent can effectively insert into the layer of montmorillonite,creating a good mesoporous structure with the distribution of pore diameters centered at 6 to 10 nm,and furthermore, obviously increasing its specific surface area.The composite photocatalyst with the ratio of 0.2:1 between TiO₂ and montmorillonite has the best photocatalytic activity because of its larger specific surface area and suitable pore size distribution.On the basis of this research, Ag-TiO₂/MMT composite photocatalyst was synthesized subsequently. Photocatalytic tests indicate that Ag-TiO₂/MMT has the lower adsorption activities and the better photocatalytic degradation activities to methylene blue than TiO₂/MMT(0.2:1).