Synthesis of MnO₂–Ag Nanojunctions with Plasmon-Enhanced Photocatalytic and Photothermal Effects for Constructing Rewritable Mono-/Multi-Color Fabrics

Semiconductor-mediated photoreversible color switching systems (PCSSs) have great potential to replace traditional photochromic materials, and the key is to obtain semiconductors with unique photocatalytic and photothermal features. Herein, we have developed MnO2–Ag nanojunctions with plasmon-enhanced photocatalytic and photothermal effects for PCSSs. MnO2–Ag nanojunctions are solvothermally synthesized with Mn(CH3COO)3, KMnO4, and AgNO3 in diethylene glycol as precursors, and they are composed of MnO2 nanoparticles (∼30 nm) that are decorated by Ag nanodots (∼6 nm). The presence of Ag confers an enhanced visible photoabsorption with a narrow band gap for MnO2 (Eg = 1.82 eV) and a weak/broad photoabsorption tail (∼875 nm) compared to that of pure MnO2 (2.45 eV, ∼625 nm). By coupling MnO2–Ag nanojunctions with various redox dyes, some PCSS inks can be obtained, and especially, the inks containing hydroxyethyl cellulose could be used to prepare rewritable fabrics. When inks and fabrics are irradiated by 475 nm light, rapid discoloration can occur, resulting from the photocatalytic reduction of the dye. Contrarily, the irradiation of 808 nm light promotes the rapid recoloration since Ag nanodots with plasmonic effects in the nanojunctions can absorb light to generate heat, which facilitates the oxidization of leuco dyes in air. Consequently, remote printing of figures was attained on the rewritable fabrics via 475 nm light illumination, and then, the erasure was performed by 808 nm light illumination in an O2 atmosphere, with high reversibility and cycling stability. Therefore, MnO2–Ag nanojunctions have tremendous promise for rewritable media, and the introduction of metal–semiconductor junctions as a nanophotocatalyst offers new insights for PCSSs.