Efficient Capture of Pb (II) Ions From Aqueous Solutions Using Metal Organic Frameworks@Covalent Organic Framework Composites With Abundant Carboxyl Groups

ABSTRACT The development of efficient adsorbents with high selectivity is essential for mitigating environmental pollution. This study introduces a novel adsorbent comprising a metal–organic framework (i.e., MIL‐101(Fe)‐NH 2 ) and a covalent organic framework (COF) enriched with carboxyl groups, which is designated MIL‐101(Fe)‐NH 2 /COF‐COOH. The adsorbent is synthesized through a Schiff base reaction followed by carboxymethylation and is subsequently employed for Pb (II) adsorption. The structure of MIL‐101(Fe)‐NH 2 /COF‐COOH is confirmed using various characterization techniques, including Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, thermogravimetric analysis, and Brunauer, Emmett, and Teller surface area analysis. The adsorption capacity (q e ) value of MIL‐101(Fe)‐NH 2 /COF‐COOH is estimated through batch adsorption experiments . The effects of several factors, including pH, adsorbent dosage, contact time, Pb (II) concentration, solution ionic strength, and temperature, on the adsorption process are systematically assessed. MIL‐101(Fe)‐NH 2 /COF‐COOH achieves the highest adsorption of 184 mg/g at pH 6. The adsorption kinetics, isotherms, and thermodynamics indicate that the adsorption process occur through a spontaneous monolayer chemical process. Moreover, MIL‐101(Fe)‐NH 2 /COF‐COOH displays remarkable anti‐interference capability, and its q e decreases by only 10% after 10 cycles. Based on the characterization results, the Pb (II) adsorption mechanism is determined to be primarily electrostatic and chelation interactions between Pb (II) and O‐ and N‐containing functional groups. Thus, this highly efficient and recyclable adsorbent exhibits considerable potential for removing Pb (II) from aquatic ecosystems.