Lead (II) removal by poly(N,N-dimethylacrylamide-co-2-hydroxyethyl methacrylate)

Traces of certain heavy metals are crucial for the metabolism of living beings, but poisoning occurs when their concentration increases. On the other hand, heavy metals such as lead, mercury, and cadmium lack functionality in higher organisms, resulting in considerable toxicity. Their long-term persistence is an environmental issue, being adsorption an alternative for the removal of metal pollutants, for example in wastewater. Adsorption has many advantages, such as high efficiency, simple design, low toxicity and reusable materials. Among the adsorbents, hydrogels feature improved resistance and high levels of swelling, comparable in costs to other common materials. In this work, we synthesized a copolymer of N,N-dimethylacrylamide (DMAa) and 2-hydroxyethyl methacrylate (HEMA) and evaluated its lead (II) adsorption capacity. The copolymer poly(HEMA-co-DMAa) was synthesized by a free-radical type bulk copolymerization of equal volumes of each monomer. The copolymer was characterized by ¹H and ¹³C NMR, and Raman spectroscopies, and by the temperature and pH dependant-swelling effect of the hydrogel. Quantification of the removed Pb²⁺ from probe solutions was performed by a UV spectrophotometric method as proposed by Krzek et al. Results suggest that at equilibrium, the amount of sorbed Pb(II) increased as the probe solution also increased (gradually from 10 to 200 ppm). Raman and ¹³C spectroscopies confirmed effective copolymerization between HEMA and DMAa. The p(HEMA-co-DMAa) copolymer featured a swelling capacity up to 3.6 times their weight of water and exhibited a LCST in the range of 308–340 K with its geometric center around 313 K. In conclusion, a thermo-and-pH-responsive copolymer was obtained from the HEMA and DMAa monomers with LCST at 313 K and pH critical point at pH = 8, featuring efficient Pb(II) adsorption capabilities. The synthesized p(HEMA-co-DMAa) is promising for applications in heavy metals adsorption in aqueous systems with a broad range of pH and temperature, featuring resistance on adsorption and desorption cycles without mechanical degradation.