Preparation Of TiO 2 /diatomite Composite And Study On Dye Adsorption & Degradation

A huge quantity of dye wastewater is discharged by textile and dyeing industries every year. As many dyes are complex organic contained azo and poly aromatic ring, which may cause people abnormal, cancerous and mutagenic. The removal of dyes from these wastewaters is a very important subject. Lots of dyes are resistant to oxidation and degradation, so adopting traditional methods to remove the dyes may not be effective. TiO₂ semiconductor photocatalytic oxidation has received considerable attention for the treatment of biorefractory wastewater. However, TiO₂ can only utilize a relative small part (less than 5%) of the solar spectrum for photocatalytic oxidation. In addition, artificial UV light sources are expensive and the powder is difficult to separate which are main barriers to marketing the TiO₂ photocatalytic processes. Therefore, immobilization of TiO₂ and the use of visible light of solar energy which is free and inexhaustible, has recently drawn considerable attention.In this paper, TiO₂/Diatomite composite photocatalysts were prepared by a sol-gel method and TiO₂ was modified by Fe³⁺ ion. As a result, an efficient composite photocatalyst which can efficiently adsorption and photocatalytic degradation dye under solar has been prepared. Hence, the system study of preparation process, materials characterization, dye-adsorption°radation property, the kinetics of reactant in dye photocatalytic degradation system and degradation mechanism & pathway of dye was carried out. The main achievements are as follows:The better preparation process showed that the contents of the composite in TiO₂ were V_Ti(OC₄H₉)₄:V_C2H5OH:V_HCl:V_H2O=1:5:0.05:0.2; the contents of the TiO₂ in composite TiO₂-mounted diatomite were 37.5%; the calcine condition were 500℃for 1 hour. As a result, TiO₂-mounted diatomite decomposed efficiently dye under UV irradiation. With the increasing of dye concentration or decreasing of photocatalysts concentration, the removal of dye descended but was not direct proportion. The removal of dye at the lower pH value is better than that at the higher pH value.When the contents of Fe³⁺ were appropriate, Fe was trapped in the crystal lattice of TiO₂ as ion. When the contents of Fe³⁺ were overdose, photocatalysts contains segregated iron oxide in addition to Fe³⁺ doped TiO₂. The better contents of Fe³⁺ were 0.2% in this paper. Compared with undoped photocatalysts, Fe-doped TiO₂ samples exhibit red shifts of absorption edge and significant enhancement of light absorption at 400～600nm. The removal of dye under solar by Fe-doped TiO₂/diatomite was better than that by undoped TiO₂/diatomite.The adsorption process of Rhodamine B dye can be described by the Langmuir model. The photocatalytic kinetics model can be described by the Langmuir-Hinshelwood model. With the assistance of HPLC, five N-deethylated intermediates were calculated: rhodamine, N-ethylrho- damine, N,N-diethylrhodamine, N-ethyl-N'-ethylrhodamine,N,N-diethyl-N'-ethylrhdamine. According to GC/MS, eight small molecular organic acids were identified: 3-Hydroxybenzoic acid,Terephthalic acid,Succinic acid,Phthalic acid,Adipic acid,Propionic acid,Benzoic acid and caprylic acid. It was considered that four photocatalytic degradation processes, including N-de-ethylation, chromophore cleavage, opening-ring and mineralization, were in this photocatalytic system.