Preparation And Visible-light Photochromism Of Multi-component Composite Films Based On Heteropolyacid

With the progress of science and technology and the continuous attention to photochromic materials,the energy spectrum of the excitation light source of photochromic materials will be transferred from the ultraviolet region to the visible region,because visible light is the most common light source around us.This will be the general trend in the study of photochromic materials.In this paper,aiming at the current status of less research on visible light photochromic system of polyoxometalates,multi-component composite thin films based on polyoxometalates with visible-light photochromism was synthesized through compositing between polyoxometalates,organic polymer material polyvinylpyrroli-done(PVP),and visible-light induced inorganic semiconductor ZnO nanoparticles.Transmission electron microscope(TEM),infrared absorption spectroscopy(FT-IR),ultraviolet visible absorption spectroscopy(UV-vis)and X-ray photoelectron spectroscopy(XPS)were used to study the influence of the proportion composition and structure of heteropoly acid and inorganic material ZnO on photochromic properties of composite films.Based on the theory of charge transfer and energy level transition,the possible photochromic mechanism of polyoxometalates-based multi-component composite thin films was proposed,which provided a theoretical basis for the study of related photochromic systems.The main research contents are summarized as follows:(1)PMoA/ZnO/PVP composite thin films were prepared by compositing ZnO sol-gel as visible light photosensitive material with phosphomolybdate(PMoA)in different proportions and introducing it into polyvinylpyrrolidone ethanol system.The original structures of PMoA,ZnO and PVP were retained intactly in the composite film formation and in the photochromic process.The composite film changed from colorless to blue under the irradiation of visible light,and the photochromic process followed the first-order kinetic equation.ZnO generates photoelectron under the excitation of visible light,then PMoA obtains the photoelectron and produces photoreduction reaction to generate heteropolyblue.The photochromic process of PMoA/ZnO /PVP composite thin films is carried out according to the photoelectron transfer mechanism.(2)From the perspective of the reversibility of photochromic materials,phosphotungstate acid(PWA)with low redox potential was introduced into the above prepared PMoA/ZnO/PVP composite thin films to prepare mPMoAnPWA/ZnO/PVP composite thin films with different proportions.Photochromic experiments were conducted under the irradiation of visible light.The composite thin film changed from colorless to dark blue under the excitation of visible light,and showed a reversible photochromic property under the action of oxygen.Under the heating condition,the composite film faded rapidly,which could realize the cycle of multiple coloring-fading.The photochromic process of mPMoAnPWA/ZnO/PVP composite films is also carried out according to the photoelectron transfer mechanism.(3)Select mPMoAnPWA/ZnO/PVP composite thin film with the best photochromic performance and load it onto the paper.Use an ink-free printing device based on a visible light source laser as the light source to type on the prepared A4 paper.According to the reversibility of photochromic materials,the prepared paper can be repeatedly used.