Hydrazone-LinkedNanoporous Covalent Organic Frameworkfor the Selective Detection and Efficient Removal of Chromium(III)

Heavy metal ions are highly toxic and widely spread as environmental pollutants. Developing methods that can simultaneously detect and remove these ions is critical. In this study, we leverage the intrinsic properties of covalent organic frameworks (COFs) to design fluorescent COFs for sensing applications. Specifically, we synthesized an ethoxy-functionalized hydrazone-linked nanoporous COF material, COF-43, via a Schiff-base reaction for selective Cr³⁺ detection and efficient removal. COF-43 exhibits a uniform, finger-like morphology with an average length of ∼400 nm and a width of ∼200 nm. In its fluorescent mode, the fluorescence signal of COF-43 is quenched in the presence of Cr³⁺, displaying a linear response to concentrations ranging from 0 to 50 μM. Additionally, COF-43 undergoes a visible color change from yellow to dark green as Cr³⁺ concentrations increase. The material also demonstrates efficient removal of Cr³⁺ from aqueous solutions. The adsorption capacity (<i>q</i>_t) for Cr³⁺ adsorption is 189 mg/g, and the removal efficiency (η) of 94% is obtained, underscoring its potential for practical applications. Results indicate that Cr³⁺ adsorption within COF-43 occurs primarily through chelation rather than through covalent bonding. This work presents the dual function of fluorescent COF for both metal ion sensing and removal while offering a straightforward approach for constructing functional COF for environmental remediation.