Surface reactivity of polypropylene grafted with carboxylate groups (COO−) in the competitive adsorption of Pb2+, Cu2+, and Cd2+ in aqueous solution

Abstract

In this study, we developed a new material (PPAAcO⁻Na⁺) charge with carboxylate groups to remove metal ions (Pb²⁺, Cd²⁺, and Cu²⁺) through ion exchange of multimetal solutions, (PPAAcO)_nM²⁺. The polymeric surface of polypropylene (PP) was functionalized with carboxylate groups (PPAAcO⁻Na⁺) through grafting and the acid-base reaction of carboxylic acid (PPAA). FTIR-ATR corroborated the change of –COOH (1711 cm⁻¹) to COO⁻Na⁺ (1562 cm⁻¹) on functionalized PP. TGA-DSC showed a decrease in the melting energy of PPAA (75.09 J/g) and PPAAcO⁻Na⁺ (44.98 J/g). The effect of the grafting degree of COO⁻ and its relationship with the concentration of acrylic acid (AA) was studied with grafting of 30%, 80%, and 154% on PPAAcO⁻Na⁺. SEM-EDS evidenced the relationship of the AA concentration, showing a thickening of the PPAAcO⁻Na⁺ fibers. The performance of PPAAcO⁻Na⁺ as a function of the grafting degree in the removal of Pb²⁺, Cd²⁺, and Cu²⁺, showed the following trend: Pb²⁺>Cd²⁺>Cu^2+, achieving an efficiency greater than 90%. The fast adsorption of the metallic ions (120 min) suggests an ion exchange process, promoting a chemical interaction between PPAAcO⁻Na⁺ and the metallic ions, resulting in a polymer-metal complex (PPAAcO)_nM²⁺. PPAAcO⁻Na⁺ has the potential to be a new, easily obtained material capable of coordinating and stabilizing metal ions on its surface.