The Preparation Of Doped POM/PVP Composite And Its Application In Rewritable Paper

The photochromic properties of the heterochromic-based composites owned make them useful in many fields,but rarely in rewritable paper.The existing color convention materials are not as excellent as POM in performance,color conversion conditions and prices.Henceforth,it is a big highlight in this paper to construct rewritable paper by using doped POM/PVP composite film system,poly-acid-based 350⁴00 nm UV-responsive photochromic nanocomposite system,to construct writable paper.In this paper,phosphomolybdic acid and polyvinylpyrrolidone was firstly chosen to build a POM/PVP composite film system.Based on this,phosphotungstic acid,carbon dots and Silver ions were used to modify the sensitization critical point of the composite film.Transmission electron microscopy?TEM?,X-ray electron spectroscopy?XPS?,infrared absorption spectroscopy?FT-IR?,ultraviolet-visible absorption spectroscopy?UV-vis?and other characterization methods were used to investigate the structure,elemental composition and structure of the resulted composite films.Further,the electron transfer theory was used to explore the photochromic reaction mechanism to provide a theoretical basis for further research.?1?PWA/PMoA/PVP composite film was prepared by doping phosphotungstic acid into POM/PVP composite solution.The results of FT-IR showed that the Keggin structure of phosphotungstic acid and phosphomolybdic acid were still preserved in the final resulted films before and after irritation.There was no distinct adsorption in the visible region before irradiation.Even after 10 coloration-decoloration cycles,the photochromic properties still excellent.The absorption sideband was red-shifted?377nm?398nm?,and the forbidden band width was reduced?3.29 e V?3.11 e V?.XPS results showed that photoreduction reaction occurred and the ratio of Mo⁵⁺/Mo?0.34?0.59?and W⁵⁺/W ratio?0.26?0.47?increased significantly before and after irradiation.?2?The CDots@PMoA/PVP composite film was prepared by doping carbon dots into PMoA/PVP solution.The structure of Keggin structure phosphomolybdic acid were not destroyed in the composite films before and after irradiation.Compared with PMoA/PVP composite membrane,the photochromic response of CDots@PMoA/PVP composite membrane exhibited stronger photochromic response.More precisely,irradiated with visible light for 15 minutes,the adsorption intensity of CDots@PMoA/PVP composite films was 1.13 times than that of the un-doped one.The results of XPS revealed that the photoreduction reaction occurred and the Mo⁵⁺/Mo ratio increased by 32% after irradiation.?3?Ag@PMoA/PVP composite films was prepared by introducing silver ions into the PMoA/PVP composite solution.Various characterizations were used to investigate the structure and photochromic properties and mechanism of Ag@PMoA/PVP composite films.It was showed that Ag and phosphomolybdic acid particles both were uniformly dispersed in the polyvinylpyrrolidone matrix.Under visible light irradiation,the colorless films changed to blue and with the prolonging of irradiation time,the films finally ended as yellow after 14 mins.The analysis of XPS presented that the first color change can be well explained by the reduction reaction between Mo⁶⁺ and Mo⁵⁺.And the appearance of yellow may be contributed to the reduction of Ag⁺,generating Ag nanoparticles,simultaneously,Mo⁵⁺ was oxidized back to Mo⁶⁺.?4?The photochromic properties performance of the three kinds of printing paper,made by composite solutions of PWA/PMoA/PVP,CDots@PMoA/PVP and Ag@ PMoA/PVP repectively,shows that the CDots@ PMoA/PVP papers own the longest pattern fading time.And different from the other two,the color of the Ag@ PMoA/PVP papers are brown,and the pattern can be preserved for quite a long time.It can be explained by the existing of Ag ions.