Biomimetic patternable polyhydroxyl nanocellulose/MXene films sequentially bridged through a synergistic hydrogen and ionic interaction with tunable multi-photoresponsive performances

High-performance electronics based on transition-metal carbides/nitrides (MXene) have attracted extensive attention due to their two-dimensional structure, modifiable surface chemistry and excellent conductivity. However, because of the weak interconnections between adjacent nanosheets, the construction of robust and flexible macroscopic MXene-based films for wearable electronics remains a challenge. Herein, mechanically tough, highly electroconductive and multi-photoresponsive films (TTM-Al) with a hierarchical nacre-like structure composed of tannic acid-modified 2,2,6,6-tetramethylpiperidin-1-yloxy-oxidized cellulose nanofibers (TA@TOCNs) and MXene are developed via sequentially bridged hydrogen and ionic bonds. TA@TOCNs with abundant phenolic hydroxyl groups as the intercalation layer can enhance the hydrogen bonding interactions with adjacent MXene nanosheets and improve the dispersibility, film-forming ability, mechanical toughness, as well as the in-plane orientation of MXene nanosheets, which can facilitate the construction of well-aligned “brick and mortar” structure. The ionic bonds induced by aluminum ions and oxygen-containing groups in TA@TOCNs and MXene can not only strengthen the interlocking ability and mechanical toughness of TTM-Al, but also promote the electron transfer and heat conduction between MXene nanosheets. Benefiting from the synergism of sequentially bridged hydrogen and ionic bonds, the optimized ultra-thin TTM-Al (∼40 μm) integrates high mechanical strength (∼118.56 MPa), toughness (∼6.84 MJ m−3), electroconductivity (∼5587 S m−1), photoelectric response (photosensitivity ∼ 3050%) and fast photothermal conversion capability (saturation temperature up to 181.6 °C in only 20 s) under near-infrared irradiation. The patternable and flexible devices based on polydimethylsiloxane encapsulated TTM-Al demonstrate the tunable photoelectric/photothermal dual response, enhanced mechanical and waterproof properties, delivering an alternative construction strategy for next-generation multifunctional photoresponsive wearable devices.