Study On Modification Of Nanometer TiO₂ And Photocatalytic Degradation Of Ormaldhyde

In recent 20 years, Titanium dioxide has attracted much attention in the field of photocatalytic application for environmental purification, decomposition of hazard substances and utilization of solar energy. because it is highly photoactive, cheap, non-toxic, chemically and biologically inert and photostable. However, there are some drawbacks, such as the low photocatalytic quantum efficiency and low availability of sunlight, which hamper successful application of TiO₂ on industrial scale operation for wastewater treatment. To acquire high photocatalytic in decomposing various harmful substances in gas or liquid, TiO₂ materials need to be fabricated with small size, high specific surface areas and highly porous structures for effective contact with reactant substances.This thesis was supported by national 863 project"New Effective Physico-Chemical Combination Technology and Apparatus"(2002AA601300). The aims of this work is to fabricate high photocatalytic TiO₂ by optimizing technique paramrters in the Sol-gel process and modifying TiO₂ using acid and Heteropolyacids HPAs. At the same time, sub-critical water treatment was applied in the process of fabricating TiO₂. The main findings are as following:(1) The Sol-gel preparation process of TiO₂ photocatalyst was optimized using Ti(OC4H9)4 as precursor. Using the photodegradation rate of formaldehyde solution as an indicator, the effects of the dosage of water, ethanol(C2H5OH), nitric acid (HNO3) and CH3COCH2COCH3(AcAc) on the photocatalytic activity of TiO₂ were investigated by using experimental design methods of single factor analysis, the L16(44) Orthogonal Design and Simplex Design respectively. The results showed that the Simplex Design could decrease the experiment time, but achieve better activity of the catalyst. The simplex optimized results are n n(H₂O)/n[Ti(OBu)₄]=3.43, n(C₂H₅OH)/n[Ti(OBu)₄]=16.49, n(HNO₃)/n[Ti(OBu)₄]=0.77, n(AcAc)/n[Ti(OBu)4]=2.29. The result of Orthoganal design showed that the important sequence of the factor affecting TiO₂ photocatalysis is dosage of AcAc > dosage of water > dosage of nitric acid >dosage of ethanol.(2) TiO₂ was respectively modified by sulfuric acid(H2SO4), nitric acid(HNO3), hydrochloric acid(HCl) and phosphoric acid(H3PO4) in sub-critical water. The prepared acid modified TiO₂ powders were characterized by X-ray diffraction(XRD), and transmission...