Solid-state Chemical Synthesis And Properties Study Of Several Silver-based Photocatalytic Materials

Recently,water pollution caused by dyestuffs in dyeing wastewater is increasingly worsening,which will pose a serious threat to human health.The photocatalytic technology as an effective green technology can make organic pollutants degrade into non-toxic small molecules through simple catalytic oxidation steps.Therefore,it has became a promising strategy in the field of water pollution treatment.At present,the utilization rate of sunlight for traditional photocatalytic materials is restricted due to wide bandgap,which mainly absorb ultraviolet light to degrade organic contaminant.The silver-based catalytic materials can absorb visible light and exhibit excellent photocatalytic activity in the fields of photocatalysis,which can effectively solve the problem of low visible-light utilization for photocatalyst.However,silver-based catalytic material usually have bad stability caused by photocorrosion that was greatly limited its future development and application.Generally,silver-based materials are prepared through liquid-phase method,and the related reports about solid-state reaction method is limited.Hence,our work adopts room-temperature solid-state chemical reaction to synthesize high-efficiency silver-based photocatalysts,and study photocatalytic degradation performance under visible light irradiation.In order to further improve the degradation activity and stability of silver-based photocatalytic materials,we prepared silver-based composite catalytic materials via matching semiconductors with appropriate position of band gaps and energy gap,which can not only improve its visible-light absorption,but also promote effective transfer and separation of the photoexcited electrons and holes pairs.Consequently,stable Ag-based photocatalysts with high degradation efficiency for organic pollutants under visible light were obtained as we expected.?1?Ag₂WO₄ was synthesized by solvent-free method in room temperature.Then,a novel multiphase composite photocatalyst of Ag/AgCl/Ag₂WO₄ was successfully fabricated,in which the Ag and AgCl were subtlely generated from the one-step reaction between Ag₂WO₄ particles and HONH₃Cl as reductant and chlorine source.The photocatalytic activities of as-synthesized composites were investigated by degradation of MO,MB,RhB dyestuffs under the visible light illumination,which can be used to study the influence of dyestuff charge for photocatalytic performance.Since the Zeta potential spectrum of ternary composite sample in neutral solution shows a negative surface potential,it exhibits excellent degradation efficiency for cationic dyestuff MB.In addition,the ratios of Ag and AgCl in composites have significant effect on photodegradation efficiency.The 20%-Ag/AgCl/Ag₂WO₄ sample with optimum composite ratio shows optimal photocatalytic activities and the degradation rate reached to 95.5%within 120 min under visible light,which was better than that of pure Ag₂WO₄.The improved performance of Ag/AgCl/Ag₂WO₄can be ascribed to the surface plasma resonance?SPR?effects of metal Ag and the synergistic effect among composites,accordingly effectively promote the transfer and separation of photoinduced electron-hole pairs,widen the absorbance range in the visible light.Moreover,the formation of raspberry-like Ag/AgCl/Ag₂WO₄ composites can increase specific surface area of Ag₂WO₄ support and facilitate the contact of dye molecules and photocatalysts.?2?Ag/Ag₂O composites with excellent visible-light photocatalytic activity were prepared via an extremely simple solvent-free chemical technique.The obtained Ag/Ag₂O samples simultaneously include desirable absorption property of Ag₂O and surface plasmon resonance of metal silver on the surface of semiconductor Ag₂O.The visible-light degradation efficiency of as-obtained Ag/Ag₂O samples were explored using MO,MB,Rh B,phenol,bisphenol A,2,4-dichlorophenol as model pollutants.Experimental results show that the Ag/Ag₂O composite photocatalyst exhibited outstanding photocatalytic activities and reusability for azo dyestuffs and phenols.The composite photocatalyst shows the optimum photocatalytic efficiency for MO degradation that is about 80%within 12 min.Performance is much better than commercial Ag₂O?P25 is almost without degradation activity?.The improved visible-light photocatalytic performance for Ag/Ag₂O composite could be attributed to the formation of metallic Ag on the surface of Ag₂O and synergistic effect between Ag⁰ and Ag₂O,which could broaden visible-light absorption,promote highly efficient separation of photogenerated electron-hole pairs of Ag₂O,and achieve the effective suppression of photo-etching phenomenon.With the assistance of scavengers and ESR technique,the h⁺and·O₂^-were proved to be crucial reactive species in the pathways of photocatalytic degradation reaction,then the relevant photocatalytic mechanism were proposed.?3?The pure Ag₂CO₃ was synthesized by one-step solid-phase method at room temperature.The corresponding photodegradation properties were studied and the photocatalytic mechanism was speculated.The single Ag₂CO₃ has good photocatalytic activity,which can degrade MB completely in 12 minutes?better than P25?under ultraviolet light and decompose the MB by 80%within two hours under the visible light irradiation.The dominating active species of·O₂^-and h⁺played a crucial role in photocatalytic process.However,single Ag₂CO₃ exhibited bad recyclability due to the severe photoetching phenomenon.?4?In order to improve the photocatalytic properties and stability of pure Ag₂CO₃semiconductor,the p-n Ag₂O/Ag₂CO₃ heterojunction photocatalysts with different weight ratios of Ag₂O and Ag₂CO₃ were successfully fabricated via a facile one-step solid-state route at room temperature.The content of the two components was controlled by changing the ratio of the reactants AgNO₃ and Na₂CO₃ in the synthesis process.In this paper,the degradation of various organic contamination including colored dyes and phenols were explored and the photodegradation mechanism was proposed.Due to the different charge of dyestuff,the heterostructure sample performs more excellent degradation capacities for the cationic MB dye?the MB removal can reach 100%within 25 minutes?and the apparent rate constant is up to 20-fold higher than that of the pure Ag₂CO₃.The photo-decomposing rate of MB still remains 70%after the six successive cycles.Compared to pure Ag₂O and Ag₂CO₃,the formed heterostructure with relatively matchable band edge positions can facilitate visible-light photodegradation because of the increased light-harvesting ability and the minimized recombination efficiency of charge carriers.Furthermore,the capture experiments and the electron spin resonance technology confirmed the dominating active species of·O₂^-and h⁺played a crucial role in photocatalytic decomposing contaminants with visible-light radiation.