The evaluation of gold nanoparticles embedded on polyvinyl alcohol matrix as oxidation catalyst and biosensor

Abstract

In this study, a method for synthesizing polyvinyl alcohol (PVA) embedded gold film is presented. This approach takes advantage of the high affinity of thiol molecules towards gold. Gold particles, in the size range of 20 to 180 nm, were first prepared by the conventional Turkevitch method by the reduction of tetrachloroauric acid (HAuCl4 ) with sodium citrate in water. The Ultraviolet-Visible (UV-Vis) absorption spectra and dark-field microscopy confirmed the presence of a surface plasmon resonance (SPR), attributed to the nanosized gold particles. The resultant gold particles of sizes as low as 27 nm with nearly spherical in shape were achieved as determined by Transmission Electron Microscopy (TEM) and Field Emission Scanning Electron Microscopy (FESEM). In the preparation of PVA embedded gold (PVA-Gold) film, PVA was functionalized with (3-mercaptopropyl) trimethoxysilane (MPTMS) which produced a thiol functionality on the surface. Then, gold particles were chemisorbed onto the surface of partially dried thiol functionalized PVA to produce PVA-Gold composite. The composite materials were characterized using Fourier transform infrared spectroscopy (FTIR), FESEM, TEM and UV-Vis diffuse reflectance (DRUV) spectroscopy. The TEM results showed that the gold particles embedded on the surface of PVA were polydispersed with the average particle size from 30 nm to 150 nm. The catalytic potential of PVA-Gold for oxidation reaction has been investigated in the liquid phase oxidation of styrene with aqueous tert-butyl hydroperoxide and the results were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). PVA-Gold were found to be highly active catalyst (95% conversion of styrene) and selective towards the oxidation of styrene to give benzaldehyde (73%) as the main product. Moreover, PVA-Gold also showed a very good regenerability in the repeated oxidation of styrene. The unique optical properties of PVA-Gold were also exploited in the interactions with several amino acids such as L-Arginine (Arg), L-Proline (Pro), L-Tryptophan (Trp) and L-Tyrosine (Tyr). The DRUV demonstrated that the surface plasmon resonance peaks for the amino acid – PVA-Gold conjugates were relatively shifted towards longer wavelength as evidence of a successful functionalization of gold with the amine groups of amino acid. The above findings suggest that PVA-Gold have potential application as heterogeneous oxidation catalyst and can be explored as probes for biosensing application.