| Dinitrophenolic compounds are generally recognized as a kind of important organic pollutants with the feature of strong toxicity and difficulty to biochemical degradation. The toxicity of azo dyestuffs is lower, but they are easily reduced into carcinogenic aromatic amine compounds due to the fracture of azo groups. The two types of compounds are indispensable in industrial and agricultural production. In the process of production and human living, a great deal of organic wastewater will be produced, which can bring a series of environmental issues. So it is necessary to put great importance to comprehensive treatment of the wastewater. The photocatalysis oxidation of TiO2 as a new technique of wastewater treatment has been developing rapidly in recent 20 years due to its non-toxic, low selectivity and good chemical stability. However, the photocatalytic activity of TiO2 is strongly influenced by crystal structure, particles size and surface property. To improve the photo catalytic activity of TiO2, a variety of technichques are used to modify TiO2 in recent years. Silica aerogels have attracted considerable attention due to its low-density, high surface area and high thermal stability. In this paper, we report the preparation of SiO2 aerogel/TiO2 composite photocatalysts by combining titanium dioxide with silica aerogels, making a special study for treating dinitrophenols and azo dyes in the simulated wastewater. And the work can be divided into the following three parts:(1) SiO2 aerogel was synthesized by sol-gel technique at ambient pressure using tetraethyl orthosilioate as precursors. The SiO2 aerogel/TiO2 composite photocatalyst was prepared by doping silica aerogel into the nanosized TiO2 particles. The microstructure and morphology of the photocatalysts were characterized by XRD, TEM, FT-IR and UV-Vis techniques. The results showed the addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination, can slightly affect the particle size and UV-Visible absorption region of the TiO2. The photocatalytic degradation of DNBP was investigated under solar light irradiation, the composite photocatalyst calcined at 500℃with an optimal silica aerogel content of 7.5 wt.% afforded the highest photocatalytic activity.(2) The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) and 2,4-dinitrophenol (2,4-DNP) were studied with SiO2 aerogel/TiO2 composite under sunlight illumination. The experimental parameters such as pH values, initial concentration, catalyst dosage, and reaction temperature were systematically studied in the work. The result indicated that the composite photocatalyst showed much higher adsorption capacity and photocatalytic degradation efficiency than the pure TiO2 catalyst. The photocatalytic reaction was discussed in terms of Langmuir-Hinshelwood model and followed pseudo-first order kinetics in low concentration. Moreover, it is also useful to remove the color and COD of real nitrophenols wastewater.(3) Photocatalytic decoloration of Reactive Black 5 dyes wastewater was studied using SiO2 aerogel/TiO2 composite photocatalyst under sunlight illumination. The results indicated that the catalyst exhibited higher adsorptive capacity to dye molecules. The decolorization rate of Reactive Black 5 was above 97% within 120 min. In addition, the photocatalyst was easy to recycle after dried or calcined at high temperature.
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