High-Density Salicylaldehyde-Hydrazone in Covalent Organic Frameworks for Ultrafast and Highly Efficient Copper Removal

Copper ion (Cu(II)) contamination poses a serious threat to water quality and public health due to its high toxicity and nonbiodegradability. Herein, we develop for the first time high-density salicylaldehyde-hydrazone covalent organic frameworks (COFs) for ultrafast and highly efficient Cu(II) removal. The resulting DhaTG_Cl-COF exhibits excellent adsorption performance, achieving a record-high adsorption kinetics (<i>k</i>₂ = 160.58 mg·g^-1·min^-1) and one of the highest capacities of 569 mg·g^-1 among all adsorbents reported to date. Notably, the material also demonstrates the lowest residual Cu(II) concentration (0.01 ppm) within 30 min. The outstanding performance is attributed to the uniform distribution of high-density, strong-affinity tridentate N,N,O-chelating moieties derived from salicylaldehyde-hydrazone within the well-aligned two-dimensional pore channels, which facilitate rapid diffusion and coordination of Cu(II) to the binding sites and ensure exceptional adsorption efficiency even for trace-level Cu(II). This work not only sets a new benchmark for Cu(II) adsorbents but also opens a promising avenue for the design of high-performance COFs for heavy metal ion removal.