Multifunctional cysteine-rich hyaluronic acid-based hydrogel for efficient Cd²⁺ and Cu²⁺ removal and sorghum growth promotion via synergistic mechanisms

The infiltration of heavy metals poses a significant threat to both crop growth and economic revenue. Although hydrogels are promising adsorbents, developing materials with integrated high capacity, long-term stability, and agronomic compatibility remains challenging. Here, a cysteine-rich hyaluronic acid (HA)-based hydrogel (HDTCys) was synthesized by grafting dopamine (DA), tannic acid (TA), and L -cysteine (Cys) onto the HA backbone. The introduced thiol group (–SH) provide strong chelation sites, endowing HDTCys hydrogel with high adsorption capacities of 241 mg/g for Cd²⁺ and 177 mg/g for Cu²⁺. Notably, it retains 85.7% (Cd²⁺) and 80.2% (Cu²⁺) of its initial capacity after five consecutive adsorption-desorption cycles, demonstrating excellent reusability and operational stability. Mechanistic studies reveal a synergistic coordination-redox pathway: Cd²⁺ is predominantly sequestered by chelation, whereas Cu²⁺ undergoes selective reduction to Cu(I) and forms stable precipitates. The process was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. In pot experiments, HDTCys hydrogel reduces the bioavailability of Cd²⁺ and Cu²⁺ in sorghum by 54.9% and 70.3%, respectively, significantly alleviating metal toxicity and promoting plant growth. By integrating Cys into an HA-DA-TA multi-network, this work presents a dual-functional platform that couples superior heavy-metal immobilization with crop-protective effects, offering a sustainable strategy for soil remediation and safer agriculture. • Cysteine-rich HDTCys hydrogel shows high Cd²⁺ and Cu²⁺ adsorption capacity. • Maximum adsorption: 241 mg/g for Cd²⁺ and 177 mg/g for Cu²⁺ via chelation and redox. • Cu²⁺ is reduced to Cu(I) precipitate; Cd²⁺ mainly captured by chelation. • HDTCys hydrogel enhances sorghum growth in heavy metal-contaminated soil. • Low-cost, bio-based hydrogel offers potential for soil remediation and crop economy.