Carboxyl-functionalized lotus seedpod: A highly efficient and reusable agricultural waste-based adsorbent for removal of toxic Pb2+ ions from aqueous solution

Converting agricultural wastes into efficient adsorbents is a promising pathway that helps mitigate environmental problems and reduce the waste of natural resource. Herein, agriculturally wasted lotus seedpod (LSP) was functionalized with carboxyl groups for the first time through a simple chemical modification and developed as a novel adsorbent for removal of Pb2+ ions from aqueous solution. Compared to raw LSP, the carboxyl groups-functionalized LSP (CLSP) retained the well-defined fibrous morphology while featuring a high content of carboxyl groups (1.025 mmol g(-1)) on its surface. By means of a surface complexation mechanism, the CLSP exhibited an excellent performance for Pb2+ removal and the maximum adsorption capacity reached up to 111.1 mg g(-1), which was significantly higher than those obtained by many previously reported adsorbents. Moreover, the adsorption of Pb2+ onto CLSP proceeded very fast, achieving equilibrium within only 10 min. Besides, the adsorption capacity of CLSP could remain almost unchanged in the presence of common foreign ions, indicating a satisfactory anti-interference ability for Pb2+ removal. Test of reusability revealed that this adsorbent was easily regenerated and the removal efficiency maintained over 99% after 6 cycles. Therefore, the agricultural waste-based material (CLSP) developed in this work can be considered as a promising candidate for replacement of the current expensive Pb2+ adsorbents from the view of sustainability.