Studies On The Synthesis And Activity Evaluation Of Novel Visible-light-driven Photocatalysts

With the development of the global industrialization, severer environmental pollution have been encountered. Photocatalytic technology, as a typical representative of green chemistry, attracts increasingly interest. There are many methods for disposing pollutant, among which the multiphase photocatalysis has been widely used. Titanium dioxide is the most important photocatalyst because it exhibits a high durability, corrosion resistance and high oxidation potential of the valence band that cnsures a general applicability to activate a broad range of substrates. However, there are important drawbacks that severely limit the application of titanium dioxide photocatalyst as a general tool either to degrade organic pollutants in the gas or liquid phase or to perform useful transformations of organic compounds. One of the most important limitations is the lack of TiO2 photocatalytic activity with visible light.The reason for this is that TiO2 in the anatase form is a wide band gap semiconductor with a bandgap of 3.2 cV, corresponding to an onset of the optical absorption band at about 350 nm. This onset of the TiO2 absorption is also inadequate to achieve efficient solar light photocatalytic activity, since less than 5% of the solar light energy can be absorbed by TiO2. The photocatalytic activity of TiO2 has been markedly improved through efforts of many research groups. All the efforts to improve the activity can be categorized into three approaches. First, many researchers attempted to improve the quantum yield. Second, attempts have been made to enhance the photocatalytic activity by extending light absorption from the UV region into the visible region. Third, successful attempts have been made to suppress the recombination of electron-hole pairs in TiO2 Besides TiO2, there are other photocatalyst system have been studied cxtcnsivcly, such as ZnO,WO3 and other metal oxide semiconductors.In the present work, we try to improve on the fabrication methods and conditions so as to get series of visible-light-driven photocatalyst with various structures and morphology. The morphology and microstructure characteristics of prepared photocatalyst were characterized by means of the N2 adsorption-esorption measurements, thermal gravimetric and differential thermal analysis (TG-DTA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet-visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD).The main results of the present work were summarized as follows:1.Studies on nanocomposite visible-light-driven photocatalyst of S-ZnO/TiO2Sulfur doped ZnO/TiO2 nanocompositc with high photocatalytic activity were successfully synthesized through sol-gel method, which take thiourca as S source, Zn(CH3COO)2 as Zn source and tetrabutyl tianate as Ti source. The photocatalytic activity evaluation were performed by the decomposition of Rhodamine B (RhB) under visible light irradiation. The mole percentage of ZnO to TiO2 and calcine temperature have been optimized and S-3.0ZnO/TiO2-500 exhibited the most excellent photocatalytic activity under visible light irradiation among the samples, which was the 2.6 times higher than Degussa P25. The enhancement of the activity can be attributed to suitable energetic positions between ZnO and TiO2, the acidity site caused by sulfur doping and the enlargement of the specific area.2.Studies on visible-light-driven plasmonic photocatalyst of Ag/AgCl@TiO2Visiblc-light-driven plasmonic photocatalysts of Ag/AgCl@TiO2 were synthesized through deposition-precipitation and photo-reduction method. The photocatalytic activity evaluation were performed by the decomposition of RhB and 4-chlorophenol under visible light irradiation. The photo-reduction duration and content of Ag-AgCl have been optimized.1.0Ag-AgCl-TiO2-20 exhibited the most excellent photocatalytic activity under visible light irradiation among the samples, which was the 8 times higher than Degussa P25 for decomposition of 4-chlorophcnol. The ratio of Ag/Ag+ was an important factor for the activity of photocatalyst. Ag-AgCl was confirmed as the main active species in the photocatalytic process.3. Studies on visible-light-driven plasmonic photocatalyst of magnetic Ag-AgI/Fe3O4@SiO2 nanopaticleA new plasmonic photocatalyst of Ag-AgI/Fe3O4@SiO2 with paramagnetic property was prepared by deposition-precipitation and photoreduction method. The catalyst exhibited efficient photocatalytic activity for the degradation of Rhodamine B dye and 4-Chlorophenol under visible light irradiation. The degradation rate of Rhodamine B and 4-Chlorophcnol over 9()Ag-AgI/Fe3O4@SiO2 was about 1() times and 4.1 times faster than that of N-TiO2, respectively. The catalyst could be easily recovered due to its paramagnetic property. The ratio of Ag/Ag+was an important factor for the activity of photocatalyst. Ag-AgI was confirmed as the main active species in the photocatalytic process.4. Studies on visible-light-driven plasmonic photocatalyst of Ag-AgCl/WO3 A new plasmonic photocatalyst of Ag-AgCl/WO3 was prepared by deposition-precipitation and photoreduction method. The catalyst exhibited efficient photocatalytic activity for the degradation of 4-Chlorophenol under visible light irradiation. The degradation rate of 4-chlorophenol over 30Ag-AgCl/WO3 was about 11.7 times faster than that of WO3-50(), respectively. The ratio of Ag/Ag(?) was an important factor for the activity of photocatalyst. The high photocatalytic activity can be attributed to SPR effect of Ag particle. The coexist of Ag-AgI was confirm as the main factor for the enhancement of activity.