Nanofiber-To-Hydrogel Conversion Enables a Structurally Integrated PAN Hydrogel with Multifunctional Properties for Efficient Water Treatment

Hydrogels, renowned for their remarkable water absorption capacity, have emerged as promising materials for oil-water separation. Nevertheless, the widespread application of traditional hydrogels remains challenging owing to their insufficient mechanical robustness, particularly in the hydrated and swollen state. In addition, hydrogels that simultaneously exhibit high strength, strong adhesion, excellent swelling capacity, and self-healing ability remain relatively rare. Herein, we present an "all-in-one" polyacrylonitrile (PAN) nanofibrous hydrogel through a "from-nanofibers-to-gel" strategy by controlling the alkaline hydrolysis time of PAN nanofibers. The resulting hydrogel exhibits exceptional mechanical strength and toughness (over 3.36 MPa at a strain of 1230%), adhesion (greater than 520 kPa), self-healing capability, and particularly outstanding swelling performance (more than 3600%). Notably, the hydrogels that have reached swelling equilibrium still remain good mechanical properties and can return to their original state with minimal shrinkage (<5% volume loss) after dehydration, enabling cyclic use. Furthermore, by integrating the thermoresponsive polymer PNIPAm and the photothermal material MXene into a PAN nanofibrous hydrogel, a photothermal-responsive PAN/MXene/PNIPAm hydrogel (PMP hydrogel) were obtained which demonstrates high efficiency in separating dye-contaminated oil/water mixtures. Additionally, as a solar-driven water evaporator, the PMP hydrogel effectively evaporates and degrades dye solutions, enabling the recovery of clean water. Benefiting from the hydrogel's exceptional mechanical strength and swelling capacity, the PMP hydrogel evaporator maintains 99.9% photodegradation efficiency for dyes and an 85.3% water recovery rate after 20 hydration-dehydration cycles.