Gold-Nanocluster-Doped Inorganic−Organic Hybrid Coatings on Polycarbonate and Isolation of Shaped Gold Microcrystals from the Coating Sol

Abstract

Au-nanocluster-doped inorganic−organic hybrid coatings on polycarbonate substrates were prepared for the application of abrasion-resistant colored coatings as well as nonlinear optical material. The Au-doped sol was prepared by incorporating HAuCl4·4H2O into a composite sol derived from 3-(glycidoxypropyl)trimethoxysilane, tetraethylorthosilicate, and 3-(methacryloxypropyl)trimethoxysilane via hydrolysis−condensation and epoxy polymerization reactions. When the coated substrates were exposed under UV light, three reactions occurred simultaneously: (i) reduction of Au ions into metallic Au nanoclusters, (ii) polymerization of methacrylate groups, and (iii) strengthening of the silica network. As a result, the UV-cured coatings became reddish-purple and more abrasion-resistant than the polycarbonate substrate. UV−vis spectroscopy and TEM of the films showed a peak at 530 nm due to the surface plasmon resonance of Au nanoclusters and the presence of 8−10 nm spherical Au nanoclusters, respectively. XRD of the films also showed the characteristic peaks of metallic Au nanoclusters. The inorganic−organic hybrid network at the sol stage also acted as a new breeding medium for the generation of shaped (triangular, hexagonal, prismatic, etc.) Au microcrystals from the Au-doped sol without UV irradiation. Electron diffraction suggests that these were single crystals with a preferential growth along the Au (111) plane.