Thermoresponsive adsorbents for efficient lead removal and easy regeneration using hot water

Chemical regeneration of metal adsorbents remains a critical challenge in low- to medium-income countries (LMICs) due to limited resources and infrastructure. In this study, we developed a novel thermoresponsive adsorbent, a cellulose bead grafted with methoxy triethyleneglycol (mTEG)-modified β-cyclodextrin (mTEG-β-CD), designed for chemical-free regeneration using hot water. By substituting β-CD's hydroxyl groups with mTEG units, mTEG-β-CD exhibits thermoresponsive behavior with a lower critical solution temperature (LCST) of 70 °C. We evaluated the adsorption performance of the beads for Pb²⁺ and Zn²⁺ at 25 °C and 75 °C, temperatures below and above the LCST, respectively. The beads demonstrated significantly higher adsorption of Pb²⁺ due to their ability to form stable 2:1 complexes with mTEGs, effectively mimicking the size-specific ion recognition of crown ethers. Above the LCST, the adsorbent efficiently desorbed Pb²⁺ by disrupting these interactions. Our observations revealed that mTEG-β-CD maintains outstanding Pb²⁺ selectivity and achieves about 90 % regeneration efficiency across multiple adsorption/desorption cycles, even in the presence of competing co-ions. These results emphasize the practical potential of this thermoresponsive material, which can be repeatedly regenerated through simple hot water cleaning. Given that water heated to 75 °C is readily accessible in most settings, including rural communities, this technology represents a significant advancement in sustainable, chemical-free regeneration for resource-limited areas.