Studies On The Preparation Of A Series Of Silver Salt Photocatalytic Composites And TiO₂Doped With La And Their Photocatalytic Performance

There has been extensive interest in photocatalitic technology, owing totheir non-toxic, no repollution and low price properties and great potentialapplications in many fields such as energy, environment protection.Although various photocatalysts have been synthesized to achive higherphotocatalitic activity, an effective, stable photocatalyst is still one of themajor challenges used in practice. My job is based on the previous works,the elaboration as follows:（1） The Ag₂S/Ag₃PO₄synthesis was successfully synthesized by ionexchange method. The S/P molar ratio and calcination temperature havesignificant effect on photocatalytic activity of degradation on rhodamine B（RhB） under visible light. The samples were characterized by the means ofTG-DTA, XRD, TEM, XPS, UV-Vis diffuse reflectance. The photocatalyticactivity data suggested that photocatalysts calcinated at250and350℃present higher photocatalytic activity. The best S/P molar ratio is20%, itcan completely eliminate8mg/L100mL RhB in20minutes when itcalcinated at250℃, which much higher than pure Ag₃PO₄. The results ofcharacteristic showed that doping Ag₂S could be propitious to form theAg₃PO₄which has smaller particle size and more specific morphology athigh temperature. The crystalline phase of Ag₃PO₄could be broken whenthe temperature is higher than450℃. When photocatalysts was calcinatedat250and350℃, crystalline phase of Ag₂S and Ag were formed and theabsorption band edge of shifts to680nm. The HRTEM showed that theformed silver particle was located between Ag₂S and Ag₃PO₄. Combinedwith the characteristics and photocatalytic activity, higher photocatalyticactivity is acribed to the higher absorption to visible light, the smallerparticle size and ohmic junction to effective separation of photogeneratedcharge carriers.（2） A series of Ag@Ag₃PO₄photocatalysts were prepared byhydrothermal method assisted by different addition of pyridine.Ag₂S/Ag@Ag₃PO₄which the molar ratio of S/P is20%were prepared by anin situ anion-exchange method and characterized by fluorescence spectroscopy, scanning electron microscopy, UV-visible diffuse reflectanceand X-ray diffraction characterization. The potocatalytic activity of thecatalyst was evaluated by degradation of rhodamine B under visible lightirradiation. The effects of scavengers, such as t-butanol, p-benzoquinone,EDTA-Na2, were examined in attempt to elucidate the reaction mechanism.The addition of pyridine has effect on photocatalitic activity, when2mL isbest,1mL followed. The composite photocatalysts exhibited lower activitythan that of pure Ag₃PO₄. The experimental results indicated that theappropriate amount of Ag contribute to the formation of Ag₂S crystalline.Due to the synergistic effect between Ag and Ag₂S, the absorption bandedge of AS/APP-2shifts to680nm and lower electron-hole recombinationrate, which is corresponding to higher photocatalytic activity. Theexperimental results which are adding different scavengers proved that h+played the major role for RhB degration and O2-secondary. Thephotoinduced electrons trapped by Ag futher react with O2to finallygenerate OH then have impact on photocatalytic activity.（3） A series of Ag₃PO₄/Ag₂CO₃composite photocatalysts withdifferent doping proportion of Ag₃PO₄and Ag₂CO₃were synthesized by anion exchange method. The photocatalytic activity of the photocatalysts withdifferent P/C doping ratio and calcination temperatures was tested indegradation of Rhodamine B under the visible light. The properties of thephotocatalysts were characterized by fluorescence spectrum, scanningelectron microscopy, UV-Vis diffuse reflectance spectra and X-raydiffraction. The results showed that photocatalytic activity of thephotocatalysts weakened with the rise of the calcination temperature andwas not improved while the best silver phosphate doping amount with themolar ratio of P/C for40%. Metallic Ag particles appear in the wholesystem through the analysis of the characterization results, and silvercarbonate decomposition when the calcinations at high temperature200℃.It decreases the photocatalytic activities of degradation of RhB undervisible light.（4） By means of controlling the molar ratio of monomer and initiator,three hyperbranched polyglycerols （HPG） with different molecular weightwere prepared by a step ring-opening polymerization of glycidol. Morever，as a templating agent, it was used to synthesized lanthanum doped titanium dioxide catalyst. These HPG were characterized by1H、13C NMR spectrum,GPC and FT-IR to analysise their structure and molecular weight. Thecatalysts were characterized by TG-DTA、 SEM、 TEM、 HRTEM and XRD.The photocatalytic eliminations of the methanol was used as modelreactions to evaluate the photocatalytic activity of the catalysts underultraviolet light irradiation. The results show that the bigger the formulaweight of HPG, the better catalytic activity of the catalysts calcined at550℃. So by this way, the catalytic activity of the lanthanum doped titaniumcatalysts can be improved. Methanol degradation in UV light of thecatalysts followed Langmuir-Hinshelw ood kinetics.