Self-triggered carboxymethyl chitosan hydrogel for the convenient sustained release of ClO gas with environmental stability and long-term antimicrobial effect

Challenges associated with the storage and uncontrolled release of ClO 2 gas present significant hurdles to its practical application. Herein, a clever strategy for self-triggering the sustained release of chlorine dioxide (ClO 2 ) gas is proposed by crosslinking carboxymethyl chitosan (CMCS) with Zn 2+ to construct a novel CMCS-Zn@NaClO 2 gel with eco-friendly, environmental stability, and convenient, long term, and efficient antibacterial activity. The precursor (NaClO 2 ) in the CMCS solution was alkaline and triggered by the acidic Zn(NO 3 ) 2 6H 2 O solution to achieve sustained self-triggering ClO 2 release. The ClO 2 gas self-release could be sustained on demand at different temperatures for at least 20 days due to the environmental structure stability of the gel. The hydrogels showed an increase in pore size after sustained release. Molecular dynamics simulations showed the spontaneous release of ClO 2 gas at room temperature and the contraction of the CMCS agglomeration, which were consistent with the macroscopic behaviour. The gel displayed a long-acting and high antibacterial efficacy, resulting in a bacteria-killing rate of over 99.9% (inhibitory concentrations of 2.5 mg mL 1 against E. coli and 0.16 mg mL 1 against S. aureus ). The hydrogels could effectively extend the shelf life of fruits and demonstrated an excellent wide range of antibacterial properties. This work provides a new approach to solving the storage difficulty of ClO 2 gas and offers a fresh perspective on the design of materials with convenient self-triggering release by a precursor, as well as the relationship between the material microstructure and sustained-release behaviour. Preparation and application process of the CMCS-Zn@NaClO 2 gel.