Rapid Preparation Triggered by Visible Light for Tough Hydrogel Sensors with Low Hysteresis and High Elasticity: Mechanism, Use and Recycle‐by‐Design

Abstract Hydrogels have emerged as promising candidates for flexible devices and water resource management. However, further applications of conventional hydrogels are restricted due to their limited performance and lack of a recycling strategy. Herein, a tough, flexible, and recyclable hydrogel sensor via a visible‐light‐triggered polymerization is rapidly created. The Zn 2+ crosslinked terpolymer is in situ polymerized using g‐C 3 N 4 as the sole initiator to form in situ chain entanglements, endowing the hydrogels with low hysteresis and high elasticity. In the use phase, the hydrogel sensor exhibited high ion conductivity, excellent mechanical properties, fast responsiveness, high sensitivity, and remarkable anti‐fatigue ability, making it exceptionally effective in accurately monitoring complex human movements. At the end‐of‐life (EOL), leveraging the synergy between the photodegradation capacity of g‐C 3 N 4 and the adsorption function of the hydrogel matrix, the post‐consumer hydrogel is converted into water remediation materials, which not only promoted the rapid degradation of organic pollutants, but also facilitated collection and reuse. This innovative strategy combined in situ entangling reinforcement and tailored recycle‐by‐design that employed g‐C 3 N 4 as key blocks in the hydrogel to achieve high performance in the use phase and close the loop through the reutilization at EOL, highlighting the cost‐effective synthesis, specialized structure, and life cycle management.