| Photoreversible color switching materials have received increasing attentions owing to their important applications in optoelectronic devices,sensors,security features,and rewritable paper.At present,great progress has been achieved in the development of various photochromic organic molecules,however,the practical applications of these molecules still face several challenges,such as progressive degradation upon prolonged ultraviolet(UV)illumination,complex synthesis procedure and poor stability.In contrast to organic photochromic molecules,inorganic counterparts have apparent advantages including high thermal and chemical stability,nontoxicity,and low cost,which can make up for the shortcomings of organic photochromic materials.Among them,the tungsten-based photochromic materials have been widely investigated,such as phosphotungstic acid(H3PW12O40·xH2O),tungsten oxide and its hydrates(WO3·xH2O,x=0-2),and so on.However,it remains a great challeng for tungsten-based photochromic materials to achieve fast light-responsive speed,long-term stability and reversibility simultaneously,which limit their application.To solve above problems,titanium dioxide/phosphotungstic acid(TiO2/PWA)composite nanoparticles and titanium dioxide/tungsten oxide hydrates(TiO2-x/WO3·0.33H2O)hetero-nanoparticles were prepared by electrostatic attraction and seed growth strategy,respectively.By combining the photoreduction activity of TiO2 nanoparticles with the excellent redox color switching properties of phosphotungstic acid and hydrated tungsten trioxide,the excellent reversible photochromic properties were achieved.In addition,the applications of these composite nanoparticles in photoprintable rewritable paper and solar UV radiation monitors were studied.The main research contents and results are as follows:1.Photochromic properties of TiO2/PWA composite nanoparticles.TiO2 nanoparticles with positive surface charge and Self-doped Ti3+species were prepared by solvothermal method,and TiO2/PWA composite nanoparticles were synthesized by using the electrostatic attraction between the TiO2 nanoparticles and PWA.Ti3+species and oxygen defects in TiO2 nanoparticles can endow TiO2/PWA composite nanoparticles with photoreduction activity by the role of sacrificial electron donors.Meanwhile,the TiO2/PWA composite nanoparticles promote the transfer efficiency of photogenerated electrons.Under the UV illumination,the TiO2/PWA composite nanoparticles produce photogenerated electrons/holes pairs.Photogenerated holes are consumed by Ti3+species and oxygen defects.Meanwhile,photogenerated electrons transfer from TiO2 to PWA,reducing W6+ in PWA to W5+,resulting in the color change for the TiO2/PWA composite nanoparticles from white to dark blue.The dark blue TiO2/PWA composite nanoparticles were oxidized to white by oxygen in the air subsequently.The TiO2/PWA/PVA film was prepared by combining TiO2/PWA composite nanoparticles with polyvinyl alcohol(PVA).The TiO2/PWA/PVA film exhibits excellent reversible photochromic properties,including color changing from white to blue in 30 s under UV illumination,and superior stability after 60 cycles.We applied this TiO2/PWA/PVA film in the field of rewritable media,which shows excellent time-limited information storage capability.2.Light-responsive color switching of self-doped TiO2-x/WO3·0.33H2O hetero-nanoparticles for highly efficient rewritable paper.The seed is TiO2 nanoparticles which synthesized by thermal injection method,and the TiO2-x/WO3·0.33H2O hetero-nanoparticles were synthesized by a simple seed growth strategy,where the Ti3+species self-doped in TiO2-x nanoparticles and Ti-O-W linkages formed between TiO2-x nanoparticles and WO3·0.33H2O.The self-doping of Ti3+species can effectively capture the photogenerated holes in the TiO2-x/WO3·0.33H2O hetero-nanoparticles to survive sufficient photogenerated electrons upon UV illumination.The Ti-O-W linkages formed between TiO2-x and WO3·0.33H2O ensure the nanoscale interfacial contact,thus greatly promoting the photogenerated electrons transfer from TiO2-x to WO3·0.33H2O to trigger the redox reaction between W5+ and W6+.Therefore,the TiO2-x/WO3·0.33H2O hetero-nanoparticles exhibit fast light responsive speed(<15 s)and long reversible color switching cycles(>180 times).Two flexible rewritable paper for long-term or short-term reading were prepared by combining TTiO2-x/WO3·0.33H2O hetero-nanoparticles with hydroxyethyl cellulose(HEC)or PVA.These rewritable paper exhibit low toxicity and low cost fast writing speed,high resolution,and long rewritable life.3.Sunlight-responsive titania-hydrated tungsten oxide hetero-nanoparticles/paper-based color-switching film for solar ultraviolet radiation monitors.A sunlight-responsive paper-based color-switching film is developed by combining TiO2-x/WO3·0.33H2O hetero-nanoparticles with a sticker paper substrate,which possesses the advantage of the excellent sensitivity and selectivity to solar UV radiation for the TiO2-x/WO3·0.33H2O hetero-nanoparticles and the high flexibility of the sticker paper substrate simultaneously,showing great potential for solar UV radiation monitors.Specificly,the color of paper-based color-switching film changes from colorless to blue and even dark blue with the solar UV intensity increasing from 0.75 to 3.25 mW·cm-2.Moreover,the color change of the paper-based color-switching film under solar UV irradiation featuring 40 s is calibrated to indicate the solar UV radiation intensity.Taking the advantage of the excellent sensitivity and selectivity to solar UV radiation,reversibility,flexibility,and low cost,we futher fabricate a wristband solar UV radiation monitor using the paper-based color-switching film as the detection part,which provides a simple and effective method for designing cheap and portable solar ultraviolet radiation monitors. |
PDF Full Text Request