SOLUTION METHOD FOR PRODUCTION OF OPTICALLY ACTIVE MULTILAYER TITANIUM DIOXIDE -NANOSILVER COATINGS ONTO POLYETHER SUBSTRATE

Abstract

Photochromic multilayer TiO2/Ag/TiO2 coating was prepared on plastic PET substrate using a solution method. The titanium dioxide sol was successfully produced using the titanium tetraisopropoxide as precursor and the nitric acid as peptizing agent via the low-temperature sol-gel synthesis in aqueous medium. Titanium dioxide films were prepared by a sol-gel dip coating method from a colloid solution of nanocrystalline TiO2 sol. Thus, nanocrystalline titanium dioxide sol and an aqueous solution of silver complex [Ag(NH3)2]NO3 followed by a photolysis for the reduction of silver ions to Ag nanoparticles with a plasmon resonance have been alternately deposited layer-by-layer. In result, heterostructures possessing photochromic properties were formed. The TiO2/Ag/TiO2 coating was investigated by UV-Vis spectroscopy, X-ray diffraction and atomic force microscope (AFM) with different resolutions. The TiO2 crystal phase formed during temperature dehydration possesses high photoactivity as the generated nanoparticles size of about 10 nm is an optimum for the most effective absorption of a light quantum and the generation of electron–hole pairs on the surface. It was found the use of silver nanoparticles also promotes an increase in the photoactivity of a film owing to larger water adsorption on the surface of a composite due to the nanoparticle surface effect, which is promoted by a high concentration of the photogenerated holes whose presence is confirmed by composite conductivity type. Thus, the photochromic multilayer TiO2/Ag/TiO2 coating described in this work are expected to find important applications to the fabrication of photochromic materials, optical filters or sensors.