Cysteine functionalized poly(hydroxyethyl methacrylate) monolith for heavy metal removal

The aim of this study was to investigate the performance of monoliths composed of hydroxyethyl methacrylate (HEMA) to which N-methacryloyl-(L)-cysteine methyl ester (MAC) was polymerized for removal of heavy metal ions. Poly(HEMA-MAC) monolith was produced by bulk polymerization. Poly(HEMA-MAC) monolith was characterized by FTIR and scanning electron microscopy (SEM). The poly(HEMA-MAC) monolith with a swelling ratio of 89%, and containing 69.4 μmol MAC/g were used in the adsorption studies. Adsorption capacity of the monolith for the metal ions, i.e., Cu2+, Cd2+, Zn2+, Hg2+, and Pb2+ were investigated in aqueous media containing different amounts of the ions (10–750 mg/L) and at different pH values (3.0–7.0). The maximum adsorption capacities of the poly(HEMA-MAC) monolith were 68.2 mg/g for Zn2+, 129.2 mg/g for Cu2+, 245.8 mg/g for Pb2+, 270.2 mg/g for Hg2+, and 284.0 mg/g for Cd2+. pH significantly affected the adsorption capacity of MAC incorporated monolith. The competitive adsorption capacities were 587 μmol/g for Zn2+, 1646 μmol/g for Cu2+, 687 μmol/g for Pb2+, 929 μmol/g for Hg2+, and 1993 μmol/g for Cd2+. The chelating monolith exhibited the following metal ion affinity sequence on molar basis: Cd2+ > Cu2+ > Hg2+ > Pb2+ > Zn2+. The formation constants of MAC–metal ion complexes have been investigated applying the method of Ruzic. The calculated values of stability constants were 5.28 × 104 L/mol for Cd2+, 4.16 × 104 L/mol for Cu2+, 2.27 × 104 L/mol for Hg2+, 1.98 × 104 L/mol for Pb2+, and 1.25 × 104 L/mol for Zn2+. Stability constants were increased with increasing binding affinity. The chelating monoliths can be easily regenerated by 0.1 M HNO3 with higher effectiveness. These features make poly(HEMA-MAC) monolith a potential adsorbent for heavy metal removal.