Facile oxidation and reduction processes to manipulate the nanocomposites of AuAg structure for promoting surface-enhanced Raman scattering and catalysis performance

Abstract

In this study hydrogen peroxide (H2O2)/ phosphate buffered saline (PBS)/ Poly(styrene-alt-maleic acid) sodium salt (PSMA) aqueous solution was used to corrode the AuAg hollow nanoparticles at 80oC During the raction the Ag atoms in the nanoparticles of the AuAg hollow nanoparticles would be oxidized into Ag ions and diffuse to the surface of the nanoparticles Ag ions were captured and fixed by PSMA Then Ag ions would be reduced to Ag atoms on the nanoparticles surface through the reducing agent to enhance the SERS effect We used 5 different reducing agents and found that the structure formed by N2H4‧H2O had the better SERS effect In addition the oxidized-AuAg hollow nanoparticles had AgCl crystals on the surface which let the nanoparticles performed a good photocatalytic property The size and morphology of the nanoparticles were observed using a Transmission Electron Microscopy (TEM) Ultraviolet-Visible Spectrophotometer (UV-vis) was used to monitor the reaction and optical properties X-ray Diffractometer (XRD) helped for studying the lattice of AuAg nanoparticles and the formation of AgCl The surface chemistry of nanoparticles was studied by using Fourier Transform Infrared spectroscopy (FTIR) and Electron Spectroscopy for Chemical Analysis (XPS) This study would also explores different reaction conditions such as temperature different concentration of HAuCl4 and used other AuAg nanoparticles for the same reaction to illustrate the versatility of this study In order to improve the instability of the nanoparticles caused by the Ag on the AuAg nanoparticles surface this study used an antioxidant tannic acid (TNA) to form a protective film on the oxidized AuAg hollow nanoparticles and then added a reducing agent to convert the surface Ag ions to Ag atoms Among them the benzene ring on TNA will form a π - π stacking with the benzene ring on dye molecules such as methyl blue (MB) malachite green (MG) etc MG Raman signal could be measured to 1 nM So when measuring these dye molecules there was a better SERS effect This study measured the Raman spectra of methyl blue malachite green and 4-nitrothiophenol for 28 days After 28 days the detection limit for measuring MG remained linear proving the nanoparticles in aqueous solution were stabile by TNA protective film

Date of Award	2020
Original language	English
Supervisor	I-Wen Sun (Supervisor)