Carboxymethyl cellulose aerogel decorated MOF-808 with defects via mixed-metallic center and etching for enhanced Pb(II) removal

Pb(II) removal from water is essential for human health due to their high toxicity and carcinogenicity. Metal-organic frameworks (MOFs) have potential to remove heavy metal ions because of their adjustable structure and tunable pore size. However, the microporous structure limits their removal performance because Pb(II) mainly exists in water as hydrated ion, which is larger than the pore size of MOFs. Defect engineering is promising to form suitable pore to capture Pb(II). Herein, we developed an etched Cu0.3Zr0.7-MOF-808 MOF by a mixed-metal strategy followed with an etching process. We replaced part of Zr4+ in the MOF-808 skeleton with Cu2+ through competition between Zr4+/Cu2+ for coordinating with –COOH on 1,3,5-Benzenetricarboxylic acid (H3BTC) to increase its specific surface area. Then H3PO4 and EDTANa2·2H2O as etchants were used to break the coordinate bond between Zr4+/Cu2+ and –COOH on H3BTC to achieve macroporous structure to inhabit Pb(II). The powder property of MOFs limits their practical applications due to their poor recyclability. We crosslinked the MOF on CMC by coordinating Zr4+ on the MOF with –COOH on CMC to form aerogel to facilitate its recyclability. The maximum adsorption capacity for Pb(II) was 542.77 mg/g at 45 °C. The adsorption of Pb(II) conformed to the intra-particle diffusion model and the Langmuir model, illustrating that the adsorption process was monolayer adsorption and affected by intra-particle diffusion. The electrostatic attraction and chelation between Pb(II) and –COOH accounted for the effective Pb(II) removal performance. This work provides a novel idea for the removal of heavy metal ions from water.