Investigation of the network structure of Semi-Interpenetrated Hydrogels for Heavy Metal Removal from Wastewater

Hydrogels find application in many fields like biomedicine, agriculture and water treatment. For the latter, hydrogels have great potential for removing heavy metal ions, but their application presents still several challenges. These regard low adsorption capacity and slow absorption kinetics of cationic species, leading to long application times and complicated regeneration process. Hydrogels of hydroxyethyl methacrylate (HEMA) semi-interpenetrated with poly(ethyleneimine) (PEI) are smart pH responsive materials for enhanced adsorption/release of specific heavy metals pollutants. Detailed structural analysis of these gels is essential for full control of their behavior. Metal absorption and distribution (currently unknown) alter the polymeric structure and topology at the nanoscale. In this beamtime we aim to achieve a comprehensive structural characterisation of pHEMA-PEI hydrogels at different interpenetrating degree (from 0 to 25 wt%). Preliminary SANS/SAXS experiments highlighted modifications of the network structure at the nanoscale as a function of composition, in the absence of absorbed metal ions. These measurements need to be complemented investigating the structure of the gels after copper absorption, and copper distribution. Through contrast-matching conditions of the gels it is possible to exclude the scattering contribution of the polymeric network, thus allowing to trace the distribution of copper coordinating structure of PEI and pHEMA.