Selective removal of Pb(II) with lignin-based adsorbent

Abstract: A way to use lignin to remove heavy metal from water has been found. Because heavy metal pollution of the aquatic ecosystem is an environmental issue, ways to selectively bind these metals is of tremendous interest. Past researchers have tried to remove these metals using natural lignin. However, it does not have a specific attraction to lead. Reported here is a way to modify lignin to improve this selectivity. Using the Mannich reaction, a chemical group was added to the lignin, formed a new material in a one step process. The new adsorbent (AFL) displayed enhanced adsorption capacity (Qmax = 91.4 mg/g) with selectivity toward lead ions. Characterizations of the AFL were carried out by FT-IR, NMR, elemental analysis, and X-ray, and all show an intact 1-Aza-18-crown-6 moiety which is responsible for this selectivity. The AFL could be regenerated by desorption of Pb(II) ions and retained > 80% of its adsorption efficiency after four adsorption-desorption cycles. The AFL material will serve as a recyclable and bioresource-based adsorbent material for water purification engineering.