Preparation, Adsorption And Photocatalytic Property Of Nano-TiO₂ Supported On Zeolite

Nano-TiO₂ has received much attention due to its strong redox ability, chemical stability,non-toxicity, and cheapness. However, the nano-TiO₂ powder is easy to lose in liquid-phasephotocatalytic reaction and difficult to be collected after the reaction, which disturbs therecycle of photocatalyst and hampers the practical applications of nano-TiO₂ powder.Immobilization of nano-TiO₂ overcomes the difficulties in separation and recycles ofphotocatalyst, enhances the concentration of substrates near the TiO₂, as well as restrainsaggregation and deactivation of the catalyst particles. In this work, the research on nano-TiO₂supported on zeolites or porous silica and their hydrophobical modification was reviewed.Therefore, the significance of theory and practice about the study on photocatalyticdegradation of MO over TiO₂/HZSM-5, as well as adsorption and photocatalytic properties ofTiO₂/MCM-41, which includes cationic template within the framework of MCM-41-drymaterials, has been shown in this paper.TiO₂/HZSM-5 photocatalysts were prepared by impregnation, sol-gel, and solid statedispersion methods, using ammonium titanyl oxalate, tetrabutyl titanate, and P-25 as titaniumsource, respectively. The photocatalytic reactivity of the prepared samples for the degradationof methyl orange (MO) under UV light irradiation were investigated. The catalyst prepared bysimple, easy to control and organic-solvent-free impregnation method showed a higherphotocatalytic activity than that prepared by sol-gel and solid state dispersion methods. Inaddition, effect of Si/Al ratios and TiOB2 Bloadings on catalyst, which prepared by impregnation,for photocatalytic activity of degradation of MO were investigated. It was found that, at 15wt% and Si/Al=500, TiO₂/HZSM-5 showed a higher photocatalytic activity. The structure ofthe catalysts were characterized by XRD,UV-vis DRS and BET technologies. It was foundthat TiO₂/HZSM-5 prepared by impregnation had a higher surface area and the nano-TiO₂particles well dispersed on the surface of zeolite leading to a higher photocatalytic activity.The effect of surfactant template in MCM-41 on the removal of o-CP and o-CNB wasinvestigated. The comparison of adsorption of o-CP and o-CNB on uncalcined MCM-41noted as MCM-41-dry) and calcined MCM-41 (noted as MCM-41-cal) was investigated.MCM-41-dry exhibited significant adsorption capacity for o-CP and o-CNB as compared to MCM-41-cal, which may be because of the hydrophobicity created by surfactant template inMCM-41-dry. In addition, batch adsorption studies were carried out to study the effect ofvarious parameters like adsorbent dose, pH, initial concentration and the presence ofco-existing ions. It was found that adsorption of o-CP and o-CNB depends upon the solutionpH as well as co-existing ions present in the aqueous solution. . From the sorption studies itwas observed that the uptake of o-CP was higher than that of o-CNB. The equilibriumadsorption data for o-CP and o-CNB was analyzed by using Freundlich adsorption isothermmodel.The photocatalytic activity of TiO₂ supported on MCM-41-dry and MCM-41-cal wasinvestigated using the photooxidation of o-CP as test reactions. The photocatalytic activity ofTiO₂ supported on MCM-41-dry was observed to be higher than that of TiO₂ supported onMCM-41-cal. Moreover, it was found that the photocatalytic activity of TiO₂/MCM-41-dryincreased with the increase in pH value of reactant solution and decrease in initialconcentration of o-CP.