Electrostatic Assembly of Photochromic TiO₂/Phosphomolybdic Acid Composite Nanoparticles for Light-Responsive Rewritable Papers

Light-responsive rewritable paper (LRP) based on photochromic materials has attracted extensive attention to alleviating the problems of environmental sustainability, energy saving, and forest conservation. However, the development of LRP with long legible time of information and high reusable time still remains a great challenge for practical applications. Herein, an LRP with long legible time is fabricated based on photochromic phosphomolybdic acid (PMoA) composite nanoparticles by integrating photoreductive TiO2 nanoparticles with redox-driven color-switchable PMoA clusters. The TiO2/PMoA composite nano particles with close interfacial contact are obtained through the electrostatic interaction between positively charged TiO2 nanoparticles and negatively charged PMoA clusters, which ensures the highly efficient photoreversible color switching properties. Owing to the slow oxidation kinetics of reduced PMoA and excellent photochromic properties of TiO2/PMoA composite nanoparticles, LRP exhibits longawaited properties, such as long legible time of printed information (> 60 days), fast coloration time (?50 s), on-demand erasing time (from 1.75 to 90 min), high reusable times (> 70 cycles), and positive imaging mode. As LRP is easy for large-scale production by a simple dip-coating method, we believe that LRP has great opportunities for practical applications in long-term temporary information reading and recording purposes.