Alkali blue 6B-attached poly(EGDMA-HEMA) microbeads for removal of heavy-metal ions

Abstract

In this study, we investigated a new sorbent system, i.e., Alkali Blue 6B-attached poly(EGDMA-HEMA) microbeads, for removal of heavy-metal ions from aqueous solutions. Poly(EGDMA-HEMA) microbeads were prepared by suspension copolymerization of ethyleneglycoldimethacrylate (EGDMA) and hydroxyethylmethacrylate (HEMA) by using poly-(vinylalcohol), benzoyl peroxide and toluene as the stabilizer, the initiator, and the diluent, respectively. Alkali Blue 6B molecules were then covalently attached to these microbeads. Microbeads (150–200 μm in diameter) with a swelling ratio of 55%, and carrying 23.6 μmol Alkali Blue 6B/g polymer were used in the adsorption/desorption studies. Adsorption rate and capacity of the microbeads for the selected metal ions, i.e., Cd(II), Cu(II), Zn(II) and Pb(II) were investigated in aqueous media containing different amounts of these ions (1–500 ppm) and at different pH values (1.5–7.5). Very high adsorption rates were observed at the beginning, and adsorption equilibria were then gradually achieved in about 5–90 min. The maximum adsorptions of metal ions onto the Alkali Blue 6B-attached microbeads were 5.5 mg/g for Cd(II), 2.3 mg/g for Cu(II), 41.4 mg/g for Zn(II), and 125 mg/g for Pb(II). However, when the metal ions competed (in the case of the adsorption from their mixture) the amounts of adsorption for Cd(II), Zn(II) and Pb(II) were quite close. Desorption of metal ions were studied by using 0.1 M HN03 (pH 1.0) for Cd(II), Cu(II), Zn(II) and Pb(II) ions. High desorption ratios (more than 90%) were achieved in all cases. Adsorption/desorption cycles showed the feasibility of repeated use of this novel sorbent system.