The Construction And Characterization Of Doped-TiO₂/MCM-41 Composites

Ordered mesoporous materials are materials of ordered pore channels which distributed between 2nm to 50nm. They are widely used in material science, catalysis, energy and environment, biotechnology. Traditional approaches focused on synthesizing ordered mesoporous materials using pure chemical reagents as Si and Al source which are of high cost and baffle the industrial production of porous materials. TiO2 nanoparticles is a kind of popular photocatalyst, but the relatively large banding energy (anatase 3.2eV and rutile 3.0eV) which cause low solar energy utilization, as well as the uncontrollable particle sizes, easily occurring of agglomeration during preparation prevent the widely use of TiO2. Taking ordered mesoporous materials as host matrix, functional composites of superior properties can be successfully obtained by incorporating functional composites into the channel of the host matrix. In this paper, Al-MCM-41 was successfully synthesized from natural bentonite which have similar structure unit to mesoporous materials. Doped-TiO2/MCM-41 host guest materials were obtained to control the growth of TiO2 and promote visible light activity.Al-MCM-41 was obtained through directly alkali fuse using natural bentonite as raw materials. Orthogonal experiment was used to optimize the synthesis parameters and the optimum conditions were obtained. The Al-MCM-41 synthesized under the optimum conditions had high specific surface area of 1007.3m2·g-1, big pore volume of 0.91cm3·g-1, and narrow pore distribution centered at 3nm. The effect of Si/Al molar ratio on structures and pore properties of samples was analyzed, the result showed that regular ordered Al-MCM-41 can be obtained easier by controlling Si/Al molar ratio between 30 and 45.High surface areas of ZnFe2O4-TiO2/MCM-41 composites were successfully obtained using sol-gel method. The effect of ZnFe2O4 addition and MCM-41 incorporation on the structure and properties of TiO2 was discussed in detail. It is proved that TiO2 nanoparticles had been incorporated into the pore channel of MCM-41 without destroy the integrity of the host materials. The addition of ZnFe2O4 during the synthesis of TiO2 can not only inhibit the growth of TiO2 particles, but also promote the transformation of TiO2 from anatase to rutile phase. MCM-41 host matrix can also control the growth of TiO2 particles and inhibit the phase transformation of TiO2. The adsorption edges of ZnFe2O4-TiO2/MCM-41 composites red shift to the visible light region obviously with increasing the amount of ZnFe2O4.Ion-doped TiO2/MCM-41 was obtained through sol-gel method. The effect of ion doping on structure and properties of samples was investigated. The results indicated that TiO2 has successfully incorporated into pore channel of MCM-41, and the particle size of TiO2 is effectively controlled. There isn't obvious change of the adsorption edges of samples before and after Ag and Y doping, the adsorption edge of Ni doping samples blue shift while the adsorption edge of Ce doping samples red shift to the visible region markedly. In sample (Ag)TiO2/MCM-41 and (Ni)TiO2/MCM-41, Ti exist as Ti4+of TiO2, Ag occurred self-rich phenomenon on the surface of (Ag)TiO2/MCM-41 composites as metal silver. Ti4+is partly substituted for Ni2+in (Ni)TiO2/MCM-41 composite.