Study On The Synthesis And Visible Light Catalytic Activity Of Ag₂CO₃Modfied TiO₂-based Composites

In recent years,with the development of the social economy,the environment conditions as well asdeteriorating,air pollution and water pollution are the two problems that urgently needed to solve.TiO2attracts much attention of many researchers because of its particular and fascinating properties,forexample,high photocatalytic activity,good chemical and thermal stability,no-poison, low cost and so on.Thus they are widely used in various kinds of photocatalytic oxidation degradation on many organicpollutions.Nevertheless, on account of that TiO2can only use ultraviolet light of the solar energy,and thelifetime of photo-generated electrons and holes is short, which greatly limits its application on actualproduction. To make better use of the sunlight，it is imperative to develop new narrow band gapsemiconductor photo-catalyst with visible--light-active.Recently studies have shown that Ag2CO3has visible light catalytic activity, but its inherentphoto-corrosion, can be resulted in inactivation.On the basis of silver carbonate, we synthesized newcatalysts with visible light activity,which can improve the utilization of the solar spectrum of visiblelight.In this paper,we discuss several highly active catalysts that synthesized by silver carbonate anddifferent types of titanium dioxide. In addition,we also prepare photocatalyst that containing Agnano-particles to enlarge visible light activity by using novel metals surface plasmon resonancephenomenon.As-prepared P25-Ag2CO3，Ag2CO3-TiO2-x，Ag@Ag2CO3-TiO2-xmaterials were characterized byDRS,XRD, TEM, SEM, XPS and ESR, and the photocatalytic activity were evaluated by photodegradationof propylene in gas under visible light irradiation. The effects of the crystal structure, size of silvercarbonate, and morphology of TiO2on photocatalytic activities were discussed. The significant results arelisted as follows:(1) Silver carbonate with monoclinic system was prepared, which had a high visible lightphotocatalytic activity on propylene oxidation at the beginning of the irradiation reaction,within30min,degradation rate was up to70%, but then decreased obviously. The catalytic activity of silver carbonatewas discussed in several cycles, and we speculated the possible deactivation mechanism under visible light. Besides, we synthesised P25-Ag2CO3by chemical deposition method. It had a certain photocatalytic activity,and compared to Ag2CO3, photocatalytic stability and lifetime were improved.(2) By using titanic nanotube acid as raw materials, and a series TiO2with various concentration ofoxygen vacancy through different heat treatment temperature were obtained. After chemical deposition,the series of Ag2CO3-TiO2-xcatalysts were prepared. Characterization results of these three catalystssuggested that their photocatalytic activity was inseparable with heat treatment temperature of NTA,crystallinity, crystal size and absorption in the visible region of catalysts. Meanwhile, we found that theorder of the catalytic activity was: Ag2CO3-TiO2-（x600）> Ag2CO3-TiO2-x（450）> Ag2CO3-TiO2-x（300）.And we carried out a kinetic study on Ag2CO3-TiO2-x(600) sample with the highest activity, results werein line with the first order dynamics.(3) Ag@Ag2CO3-TiO2-xseries catalysts were characterized, results indicated that there was mentalsilver generated on Ag@Ag2CO3-TiO2-x(600),which had the best crystal structure, and possessed thehighest photocatalytic activity.The effects of circulating water on Ag@Ag2CO3-TiO2-xseries catalysts ofcatalytic activity were studied. On one hand,in the case of without circling water, the activity of these threesamples were relatively high, Ag@Ag2CO3-TiO2-x(600) degradation rate was up to95.8%;on the otherhand,in the case of with circling water, the activity of these three samples were remarkably reduced,Ag@Ag2CO3-TiO2-x(600) corresponding to57.3%. Circling water around the reactor was to maintaintemperature at a fixed value and absorbe infrared light, thus we can speculate that the reaction temperaturehad a significant influence on the effect of the catalyst activity.