Preparation Of Novel Ag-Containing Visble-Light-Responsible Photocatalysts And Their Photocatalytic Performence

With the development of the society, the increasingly seriousenvironmental pollution has been a threat to people’s health. Semiconductorphotocatalytic technology can use the sunlight to make the organicpollutants mineralized, which is under the condition of energy conservationto achieve the purpose of the environmental governance. Ag-containingphotocatalyst is a kind of efficient visible light catalyst. But thephotocatalytic activities for the few of silver salts were studied, and therealso exists the shortage that the mechanisms of photocatalysis research lagbehind. To solve these problems, we have preparated two kinds of newvisible light catalysts: BiPO₄/Ag₃PO₄composite photocatalyst andAg₃AsO₄photocatalyst, meanwhile we tested relevant characterization andphotocatalyst activity for these two kinds of photocatalysts, catalyticmechanism of these two kinds of catalysts were explored. The specific workwas as follows:（1） A series of BiPO₄/Ag₃PO₄composite photocatalysts with differentdoping proportion of BiPO₄and Ag₃PO₄were synthesized using AgNO₃Bi（NO₃）35H₂O and NaH₂PO₄as raw materials by a co-precipitation methodat different calcination temperature. The properties of the photocatalysts,including light-absorption band, morphology and photoluminescence, etcwere characterized by UV-Vis diffuse reflectance spectra, scanning electronmicroscopy and fluorescence spectrum. The results showed that thesecomposite photocatalysts can absorb visible light with the wavelength of400-500nm, and hence are novel visible light responsive photocatalysts.The photocatalytic activity of the photocatalysts was tested in degradationof Rhodamine B. With the increase of doping ratio, the photocatalyticactivity decreases. With the enhancement of calcination temperature, thephotocatalytic activity firstly increases, and then decreases. Thephotocatalyst with the BiPO₄/Ag₃PO₄molar percent of5%that was obtainedby calcining at350℃showed the optimal activity, which is the completedegradation of200mL rhodamine B solution with a concentration of12mg/L within40minutes. Catalytic mechanism of the BiPO₄/Ag₃PO₄composite photocatalyst was explored by using three chemical agents, i.e.,benzoquinone, disodium ethylenediaminetetraacetate and tert-butanol. This indicated that photogenerated holes of BiPO₄/Ag₃PO₄are the dominantreactive species.（2） A novel visible-light-responsive photocatalyst Ag₃AsO₄hassuccessfully prepared through a facile and concurrent precipitation method.The properties of the photocatalyst were characterized by UV-Vis diffusereflectance spectra, XRD, fluorescence spectrum and scanning electronmicroscopy, etc. The band gap of the newly developed Ag₃AsO₄photocatalyst was calculated using the results of the UV-Vis diffusereflectance spectra and the formula. The results showed that the wavelengthfor the absorption band edge of the Ag₃AsO₄is at around730nm, so theycan absorb most of the visible light. The catalytic activity result ofdegradation of RhB and MO showed that, the photocatalytic activity ofAg₃AsO₄was higher than that of Ag₃PO₄and AgI, and the catalytic activityof the recycling once of the Ag₃AsO₄was higher than the freshly Ag₃AsO₄samples. Catalytic mechanism of the Ag₃AsO₄photocatalyst was exploredby using three chemical agents, i.e., benzoquinone, disodiumethylenediaminetetraacetate and tert-butanol. This indicated thatphotogenerated holes of Ag₃AsO₄are the dominant reactive speciescontributing. In addition, we have detected the BET of the Ag₃AsO₄,Ag₃PO₄and AgI, respectively. The result is that the surface areas of thephotocatalysts are very low and the difference among them is slight. Theresults suggested that surface area is not the major factor responsible forthe higher photocatalytic activity of Ag₃AsO₄. From the above researchresults we can come to the conclusion that Ag₃AsO₄is a novel and efficientvisible-light-responsive photocatalyst, the excellent photocatalytic activityof Ag₃AsO₄is attributed to its high oxidizing ability of photogeneratedholes, more separated photogenerated carriers and high absorption capacityof visible light.