Investigation On The Fabrication And Photocatalytic Properties Of AgCl@Ag Nanocubes

The surface plasmon(SP)effect of noble metal nanomaterials have showed great application in various areas,e.g.sensor,photoelectric conversion,medical detection,photocatalysis etc.Since the SP of noble metal nanomaterials can be triggered by visible light,which accounts for?43%of the solar energy,thus SP-mediated photocatalysis is treated as a promising strategy to drive the green catalytic processes.Moreover,when noble metal nanoparticles(NPs)are deposited on semiconductor support,the catalytic performance can be enhanced if there exist charges transfer between them under solar irradiation.Therefore,how to design and utilize metal-semiconductor hybrid materials to further enhance the photocatalytic activities has become one of the most investigated areas.However,generally it's difficult to control the morphology of metal nanostructures deposited on semiconductor materials.Thus in this dissertation,we considered an opposite way to cover noble metal nanomaterial by wide-bandgap semiconductor material layer,and the corresponding photocatalytic activities were investigated.Ag NCs were selected as a model nanostructure,an ultrathin layer of wide-bandgap semiconductor,silver chloride(AgCl),was covered on the surface of Ag NCs to fabricate AgCl@Ag core-shell nanostructure.Theoretical local electric field(E-field)contours generated by SP around an individual Ag NC or an individual AgCl@Ag NC were carried out by discrete dipole approximation(DDA)method.Then surface enhanced Raman spectroscopy(SERS)was used to studied photocatalytic activities on Ag NCs and AgCl@Ag NCs samples,respectively.The details of this dissertation are as follows:(1)Ag NCs with good uniformity were synthesized by hydrothermal method.The Ag NCs with?83 nm in edge length was fabricated by adjusting the parameters such as reaction temperature,concentration of precursors and so on.(2)AgCl NCs were synthesized by hydrothermal method.The size and morphology of AgCl NCs were controlled by adjusting parameters such as reaction temperature,concentration of precursors and so on,where the temperature could affect the uniformity of AgCl and the concentration of precursors could determine the size of AgCl.(3)AgCl@Ag core-shell NCs structure was fabricated by depositing AgCl on the surface of Ag NCs.A 2 nm-thick AgCl layer was covered on the surface of Ag NCs by reducing the concentrations of the precursors,Ag NO₃and HCl,in equal proportion.(4)The properties,e,g,mophology,chemical component,crystal structure,etc.,of Ag NCs and AgCl@Ag NCs were analyzed by using scanning electron microscopy(SEM),ultraviolet-visible spectroscopy(UV-VIS),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS)and so on.(5)Theoretical local E-field contours generated by SP around an individual Ag NC or an individual AgCl@Ag NC were carried out by DDA method.The simulation results suggested that the maximum|E|~2/|E₀|~2value of AgCl@Ag NC was lower than that of Ag NC.Since the plasmonic photocatalytic activity is directly proportional to the square value of E-field intensity generated by SP,it seemed that AgCl@Ag NCs would display inferior SP-mediated photocatalytic activities relative to those of Ag NCs.However,the results obtained by SERS displayed that AgCl@Ag NCs presented superior photocatalytic activities relative to those of Ag NCs,which was contrary to the DDA simulation.(6)The p-aminothiophenol to p,p'-dimercaptoazobenzene(PATP-to-DMAB)oxidization was used as a model reaction to explore the photocatalytic conversions.It was observed that the AgCl@Ag NCs presented better photocatalytic activities than those of Ag NCs under 633 nm excitation.The divergent results suggested that there existed charges transfer between Ag NC and AgCl layer.To reveal the mechanism behind the superior activities of AgCl@Ag NCs,the PATP-to-DMAB conversions were also carried out in ambient argon(Ar).The results showed that Ag NCs exhibited inferior photocatalytic performance in ambient argon(Ar)compared to that in air ambient.However,the AgCl@Ag NCs sample demonstrated higher conversions in ambient Ar than those carried out in air ambient.The mechanism could be explained based on the separation of electron-hole pairs in AgCl through SP effect of Ag NC.The free electrons were collectively oscillated by the E-field of incident light.At a certain time,the free electrons aggregated at one side in the Ag NC,and meanwhile the empty states of electrons were left on the other side.Then the electrons at the valence band(VB)of AgCl could be excited to the empty states of Ag,leaving holes in the AgCl and participating in the oxidation of PATP to DMAB.Thus our work provides a facile avenue to enhance SP-mediated photocatalytic activities on plasmonic metallic nanostructures by the cover of an ultra-thin layer of wide bandgap semiconductor.