Calixarene-Grafted Adsorbent from Polypropylene Waste for Selective Removal of Strontium Ion from Water

Radioactive pollutants from nuclear reactors have always been an unprecedented risk and pose a significant hazard to all life forms if an unrestrained spillage happens. Strontium (90Sr) is the second largest radioactive discharge from nuclear plants, and it can cause osteosarcoma, birth defects, and damage to the immune system. A polypropylene (PP) waste-based emulsion templated porous scaffold functionalized with chemically modified calixarene (CMC) was developed in the present work for efficient strontium ion (Sr2+) adsorption. Grafting of CMC on PP was achieved via the Fenton reaction at a yield of 22%. A high adsorption capacity of 27.20 mg/g for Sr2+ ions was achieved selectively in the presence of different competitive ions. The Langmuir and Freundlich models were used to study the adsorption isotherm, and the maximum adsorption capacity was found to be 131.74 mg/g. The Freundlich model favored the physisorption process for Sr2+ ion due to the pores present in the scaffold. A pseudo second order kinetic model, based on the best fit of the data, suggested chemisorption of Sr2+ ions by the hydroxyl groups of CMC grafted on the PP scaffold. Based on the high surface area of the scaffold and the functional groups grafted on the scaffold, the approach can be further explored for other toxic heavy metals and numerous applications for selective sorption, purification, and filtration.