Design of modified carboxymethyl cellulose adsorbent for effective removal of Pb (II) and cd (II) from aqueous solutions

In this study, carboxymethyl cellulose (CMC) was grafted with 3-mercaptopropyl trimethoxy silane, crosslinked and then freeze-dried to fabricate the modified CMC-based adsorbent with three-dimensional network structure. The adsorbent showed the advantages of low price, environmental protection and high stability, and could effectively remove lead ion (Pb (II)) and cadmium ion (Cd (II)) from wastewater. The adsorption equilibrium for two metal ions could been achieved within 60 min with the maximum adsorption capacity of 322.96 mg/g and 199.35 mg/g for Pb (II) and Cd (II), indicating fast adsorption rate and high adsorption efficiency. Under the coexistence of multiple ions, the adsorbent still exhibit high Pb (II) and Cd (II) adsorption, demonstrating the good ion selectivity. Furthermore, the adsorption conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm, indicating that the adsorption process was mainly chemical adsorption. After five adsorption-desorption cycle tests, the adsorbent still maintain high adsorption efficiency and integrity, proving the good recyclability and reusability. Density functional theory calculations revealed that the HOMO-LUMO gaps decreased after adsorption, implying the enhanced charge transfer via orbital hybridization with functional groups. This work provides a new idea for preparing low-cost, environmentally friendly, efficient, and reusable adsorbents to capture toxic heavy metal ions.