Polymer-grafted silica based hybrid macrobeads for Pb(II) and Cr(VI) removal from water

The presence of heavy metals in water deters its usability for drinking purposes. Indiscriminate disposal of industrial effluent into water bodies further complicates the situation. Accordingly, there is a dire need for a treatment system that can effectively remove the contaminants from water. Although there are solutions like the utilization of membrane and other powder-based adsorbers, challenges like high cost, fouling, scaling, the generation of a new class of waste (post usage), and limited recyclability often limit their usage. Hence, there is a critical need to develop a system that demonstrates high adsorption capacity, is reusable, and is easy to develop. Accordingly, we synthesized silylated polyethyleneimine, grafted it onto silica particles, and tested its efficacy in removing heavy metal contaminants like lead and hexavalent chromium from water. The resultant modified polyethyleneimine modified silica particles (termed as SiEP) outperformed many adsorber materials, including metal-organic framework, zeolite, clay, etc., and it demonstrated a staggering adsorption capacity (Langmuir) of 442 mg/g (pH 6) and 182 mg/g (pH 5) for lead and chromium, respectively at 30 degrees C. The developed nanopowder was further encapsulated inside polyacrylonitrile macrobeads and tested for its efficacy. Although the encapsulation resulted in a decrease in adsorption capabilities, common problems like high-pressure build-up and inefficient contact associated with powder-based adsorber were avoided upon encapsulation. The macrobeads exhibited 37 mg/g and 20 mg/g adsorption capacities for lead and chromium, respectively. For both the powder and the macrobeads, the adsorption capacity was tested in the presence of mixed ions and both the adsorber demonstrated their unique capability to be selective against targeted ions. They were further tested against a real groundwater matrix synthetically spiked with lead and chromium. Such findings open up a new avenue to developing water treatment materials that demonstrate selectivity and recyclability, indicating their potential for large-scale water treatment applications in industrial settings.