NiO-SiO2 sol-gel nanocomposite films for optical gas sensor

Recently nanocomposites with sensoring function are becoming a new area of interest in the field of optical gas sensor. In fact, the optical transmittance of nano-particles or thin films has been reported to be changed by atmosphere gases. In particular it was found that NiO, Co3O4 and Mn3O4 thin films showed reversible decrease in the Vis-NIR absorption due to CO. Aim of this work is the synthesis and the characterization of SiO2 sol-gel glass films doped with NiO nanocrystals. Films of composition (100-X)SiO2-XNiO with X = 10, 20, 40, were obtained by mixing a matrix solution of Si(OC2H5)(4) (TEOS) and CH3Si(OC2H5)(3) (MTES) as SiO2 precursors, with a doping solution containing NiCl2 as precursor for NiO particles. 3-Aminopropyltriethoxysilane (3-APTES), bearing either an ammine group capable of coordinating the Ni ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix, was used as bifunctional ligand. Transmission electron microscopy micrographs showed a uniform distribution of round shaped nanoparticles in film heated at 500degreesC with a mean diameter of 2.5 nm. The film composition evaluated from Rutherford backscattering spectrometry was in good agreement with the nominal one. As expected the density of the films heated at 1000degreesC is much higher than the density of the film heated at 500degreesC due to a residual porosity. Fourier transform infrared spectra also confirmed the presence of residual porosity in the films heated at 500degreesC.