Study On Preparation, Characterization, Visible Light Photocatalytic Activity Of Plasmonic Photocatalyst Ag/AgBr And Ag/AgBr/TiO₂

AgBr powder was synthesized by double jet method using NaBr aqueous solution and [Ag(NH3)2]+ aqueous solution. Ag/AgBr powder, which consists of silver nanoparticles (NPs) deposited on AgBr surface, was prepared by chemical reduction method under visible light irradiation. Ag/AgBr photocatalyst was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-vis-diffuse reflectance spectroscope (UV-vis DRS), X-ray photoelectron spectroscopy (XPS) and specific surface area (SSA). The SEM images reveal that silver NPs with a diameter in the range of 20-40 nm are formed on the surface of AgBr particles with a diameter in the range of 0.8-2.5μm. The XRD pattern of the Ag/AgBr catalyst shows that the cubic phase of Ag coexists with the cubic phase of AgBr. The high absorption of Ag/AgBr in the visible region is attributed to the plasmon resonance of silver NPs deposited on the AgBr particles. The SSA of Ag/AgBr, which is 1.3 m2 g-1, is much lower than those of TiO2-P25 (55.2 m2 g-1) and N-TiO2 (250.7 m2 g-1).The photocatalytic activities of Ag/AgBr were studied by degradation of methyl orange (MO). The photocatalytic reaction follows first-order kinetics and the rate constant (k) for the degradation of MO photocatalyzed by Ag/AgBr is 102 and 16 times of that by commercial TiO2-P25 and mesoporous N-TiO2, respectively, which indicates that the Ag/AgBr photocatalyst has outstanding visible light photocatalytic activities. The recycling runs experiment shows that the photocatalytic stability of Ag/AgBr photocatalyst is excellent. Total organic carbon (TOC) experiment indicates that Ag/AgBr photocatalyst can easily mineralize MO.The effects of initial concentration of MO, catalyst dosage, pH of MO solution and scavenger of electrons or holes on MO visible light photodegradation with Ag/AgBr as catalyst were investigated. The degradation rate is found to increase with an increase in initial concentration of the MO from 5 to 10 mg L-1 and then decrease over 10 mg L-1. The effect of catalyst dosage on the photocatalytic degradation of MO was studied by varying the amount of Ag/AgBr from 0.5 to 5 g L-1 and the results indicates that the degradation rate increases with increasing the catalyst dosage. The photodegradation rate of MO decreases with an increase of pH in the initial solution. The photogenerated holes might be the main active species in MO degradation photocatalyzed by Ag/AgBr.Combined with the H2O2 formation experiment and the carriers scavenger experiment, the mechanism of the degradation of MO by Ag/AgBr was discussed. The high stability could be attributed to the strong absorption of silver NPs in the visible light region, so that the photogenerated electrons in Ag/AgBr are absorbed by the silver NPs rather than being transferred to the Ag+ of the AgBr lattice. The electrons are transferred to the surface of the silver NPs, and then reduce the adsorbed dissolved oxygen to produce superoxygen anionic free radicals·O2-. The HO·and H2O2 could be further formed from·O2-. The holes could be transferred to the AgBr surface, leading to the formation of Br0 atoms from the oxidation of Br- ions. The Br0 atoms are powerful oxidizing agent and attacks organic pollutants present at or near the surface of Ag/AgBr.AgBr/TiO2 composites was synthesized by sol-gel method. Mesoporous Ag/AgBr/TiO2 plasmonic photocatalyst (Ag/AgBr/TiO2), which consists of silver NPs deposited on AgBr/TiO2 surface, was prepared by chemical reduction method under visible light. Ag/AgBr/TiO2 was characterized by Small angel X-ray diffraction (SAXRD), Wide angel X-ray diffraction (WAXRD), UV-vis-diffuse reflectance spectroscope (UV-vis DRS) and N2 isothermal adsorption-desorption. The Ag/AgBr/TiO2 photocatalyst exhibits strong absorption in visible light region because of the plasmon resonance of silver NPs.The photocatalytic activities of Ag/AgBr/TiO2 were studied by degradation of Rodamine B (RB). The photocatalytic reaction follows first-order kinetics and the rate constant (k) for the degradation of RB photocatalyzed by Ag/AgBr/TiO2 is 10.7 and 8.8 times of that by commercial TiO2-P25 and M-TiO2, respectively, which indicates that the Ag/AgBr/TiO2 photocatalyst has outstanding visible light photocatalytic activities. The recycling runs experiment shows that the photocatalytic stability of Ag/AgBr photocatalyst is excellent.