Sustainable rewritable paper based on photoresponsive tungsten oxide quantum dots for anti-counterfeiting and waterproofing

Ink-free printing using photochromic paper has emerged as a promising technology for information recording, transmission, and secure interaction applications. Tungsten oxide quantum dots (WO 3 QDs), with their rapid UV response, excellent photochemical stability, and outstanding fatigue resistance, exhibit significant potential as an ink-free medium in the construction of sustainable rewritable paper. However, challenges such as low binding force, poor stability, and weak scalability limit the development of reversible photochromic paper based on WO 3 . In this study, a novel sustainable rewritable paper based on a scalable strategy of covalent modification and hydrophobic layer protection has been reported. Specifically, cellulose papers modified with silane coupling agent were directly grafted with amino-modified WO 3 QDs by covalent bonding through the addition reaction between epoxy and amine groups. Subsequently, the sustainable rewritable paper was obtained by the deposition of hydrophobic layer of polydimethylsiloxane (PDMS) via a dip-coating method. The rewritable paper exhibits exceptional properties, including high color contrast, extended color-retention (over 21 days), good rewritability (20 cycles) and excellent resistance to water or stains. Based on ink-free writing technology, the photo-responsive rewritable papers were utilized for anti-counterfeiting and encryption or decryption, demonstrating their great potential for information recording, storage, and security protection.