Study On The Oxidation And The Improvement Of The Photocatalytic Activity Of Silver Nanoparticles

The localized surface plasma resonance（LSPR）of silver nanoparticles（AgNPs）can induce visible-light driven photocatalysis and thus AgNPs has potential applications in environment protection.Former studies in our group have demonstrated that oxygen plasma irradiation（OPI）could improve the photocatalytic activity（PA）of AgNPs greatly.In order to explore the mechanism of the PA improvement,this paper studies the oxidation of AgNPs and the decomposition of silver oxides.Then,copper nanoparticles（CuNPs）were successfully applied to improve the PA of AgNPs.The technology process and the mechanisms were explored.Firstly,oxidation of AgNPs and decomposition of silver oxides were studied.The AgNPs were prepared by evaporation of high pure silver under high vacuum.The oxidation was performed by oxygen plasma irradiation（OPI）in vacuum and the decomposition was conducted via annealing the silver oxides in nitrogen ambient at various temperatures.The absorption spectra,surface enhanced resonance scattering（SERS）,X-ray photoelectron spectroscopy（XPS）and field emission scanning electron microscopy（FESEM）images of those samples were characterized.A model explaining the oxidation and decomposition process was established.The results have shown that AgNPs are not easy to be completely oxidized in oxygen plasma and prolonging the irradiation time the Ag₂O will be over oxidized into silver oxides with higher valence.The LSPR of AgNPs without being oxidized is damped by Ag₂O which combined with electrophilic oxygen is responsible for the PA improvement.Secondly,the PA improvement of Ag composited with Cu nanoparticles was explored.This work was developed from three aspects,the influence of configuration of AgNPs and CuNPs,the ratio of Ag to Cu,and the influence of OPI.The nano-Ag/Cu or Cu/Ag thin films were prepared by vacuum evaporation.The configuration was changed by changing the deposition order of AgNPs and CuNPs.The tuning of ratio is through controlling the deposition time of Ag and Cu.The samples were characterized by absorption spectra,FESEM images and the photocatalytic activity were tested.The results show that the configuration affects PA improvement of AgNPs greatly.Excellent photocatalytic activity of nano-Ag/Cu thin films could be gained by adjusting the ratio of Ag/Cu.The maximum improvement could reach 342%.The PA could be improved further by 35%by OPI.The mechanisms about the PA improvement were proposed.This study is of scientific significance for the research of the photocatalytic performance improvement mechanism and method of AgNPs,which promotes the application of AgNPs in the field of photocatalysis.