Ultrafast fabrication of lignin carbon dot hydrogels with self-mending properties and dehydration-visualizable phosphorescence for chemical sensing and information encryption

Abstract

Conventional hydrogels, such as polyacrylamide and polyacrylic acid, rarely exhibit both mechanical and optical properties under ambient conditions, which limits their application as optical materials. We propose a facile strategy to prepare hydrogels with enhanced mechanical properties (tensile strength from 2 to 8 kPa and compressive strength from 180 to 400 kPa), extension ratios (up to 720%), and excellent optical properties (lifetimes as long as 1.13 s) by introducing lignin carbon dots (L-CDs) as functional nanofillers into polymers, resulting in the interactions between the CDs and the network of polymers. In detail, a dynamic redox reaction was achieved between the catechol groups of the L-CDs and Fe³⁺, which could promote the rapid gelation of acrylamide (AM) monomers within 1–2 minutes. Besides, inheriting the fluorescence properties from the L-CDs, the hydrogels possess unique optical properties which can be used for self-visualization of dehydration. The dehydration process can be visualized by the appearance of phosphorescence, as the polymer chains can effectively suppress the non-radiative relaxation, thus enabling the visualization of the dehydration of the hydrogel. In addition, the unique phosphorescence properties of the hydrogels expand their application to chemical sensing and information encryption. We expect that this fast gelation strategy will pave a facile pathway for fabricating versatile and multifunctional hydrogels.