Synthesis Of TiO₂ Pillared Bentonite And Its Adsorptive And Photocatalytic Activity

In this paper,TiO₂-pillared bentonite and TiO₂-pillared bentonite with transitional metal ions doping are synthesized by acid catalyzed sol method using bentonite as the carriers.The morph ology,structure and composition of the composites are characterized by TEM,XRD,FT-IR,TG-DTA,BET,XPS and DRS.The factors,which affect the synergistic effect on adsorptive and photocatalytic degradation of dyes,and the mechanism and pathways of degradation of dyes with different structure,are also investigated.Here,reslutes are summed up as follows:(1) TiO₂-pillared bentonite is prepared,and the influence of calcination temperature and the content of TiO₂ on the structure and degradated activity are studied.It has been found that TiO₂-pillared bentonite has the best samdwich and TiO₂ nanoparticles,the crystal type of which is Anatase,are distributed into the layers of bentonite.The d001 basal spacings,BET special surface area,the thermal stability and adsorptive and photocatalytic activity of composites are all enhanced compared with bentonite.Results indicate that TiO₂-pillared bentonite with 50%TiO₂ content,which is calcinated at 473K, exhibite the highest adsorptive and photocatalytic activity.(2) TiO₂-pillared bentonite composites with different metal ions doping are prepared. Results show that doped metal ions lie in the shape of noncrystal,which have no effect on the d001 basal spacings.Compared with TiO₂-pillared bentonite,BET special surface area has been increased slightly.The adsorptive and photocatalytic activity change from high to weak according to the regularity as follows:Fe-Ti-Na-MMT＞Y-Ti-Na-MMT＞La-Ti-Na-MMT＞Zn-Ti-Na-MMT＞Ni-Ti-Na-MMT＞Cu-Ti-Na-MMT＞Ti-Na-MMT,which is similar with the change regularity of the ratio between ionic charges and ionic radius.For Y³⁺-doped TiO₂-pillared bentonite,1.5%Y³⁺ content have the highest adsorptive and photocatalytic activity.(3) Kinetic model of adsorption and photocatalysis is investigated using Y³⁺-doped TiO₂-pillared bentonite in dyes solution.Adsorptive kinetic analyses indicate that the process of adsorption accords with Bangham and Langmuir equation.Meanwhile,the adsorptive capability of the composites can be well described using Freundlich and Langmuir isotherm adsorption equation.Photocatalytic kinetic analyses indicate that the photodegradation rates of methyl orange can usually be approximated as pseudo-first-order kinetic,according to the Langmuir-Hinshelwood model.Several factors such as pH,substrate concention,the presence of H₂O₂ and the structure of dye molecule,which affect the efficiency of adsorptive and photocatalytic degradation,are discussed.It has been found that the efficiency of degradated dyes can be enhanced by appropriate pH,substrate concention and H₂O₂ additive.The regularity of adsorptive and photocatalytic degradation of dyes with different structure is as follows:rhodamine B＞methyl orange＞congo red＞reactive blue.(4) The photocatalytic degradation of dyes with different structure has been investigated with the use of Y³⁺-doped TiO₂-pillared bentonite.It has been found that dyes adsorbs on the composites and undergoes a series of oxidation stepds,which lead to decolorization and formation of a number of intermediates,mainly aromatic and aliphatic acids.These molecules are further oxidized toward compounds of progressively lower molecule weight and,eventually,to CO₂ and inorganic ions,such as sulfate,nitrate and ammonium ions.There is a synergistic effect on the process of adsorption and photocatalysis using the composites,and the increase of adsorptive capabilitiy will enhance the photocatalytic activity.The reaction model of adsorption and photocatalysis is built for the first time.