A 2D Acridine-Based Covalent Organic Framework for Selective Detection and Efficient Extraction of Gold from Complex...

Developing candidate materials which possess the ability of both selective detection and efficient capture of precious metal gold is highly desirable for environment and economy. However, most of reported materials only focus on single function, which seriously restricts their practical application as probes or adsorbents. Herein, a two dimensional (2D) acridine-based covalent organic framework (TpDa-COF) is prepared via the linkage of imine bonds for gold detection and adsorption. The synthesized COF can achieve both fluorescence and colorimetric dual sensing for Au³⁺ in a low concentration range (0.1-1.5 ppm) with the limit of detection (LOD) of 0.036 ppm. Impressively, the selectivity of TpDa-COF for the detection of Au³⁺ is admirable (Fe³⁺, Fe²⁺ and Cu²⁺ for negligible influence on its fluorescence). In addition, TpDa-COF exhibits ultrahigh adsorption capacity of 982.5 mg ⋅ g^-1 for gold at pH=4, which is attributed the synergistic effect of both selective coordination and reductive process of Au(III) to Au(0). Meanwhile, both positive entropy change (ΔS=76.07 J ⋅ mol^-1 ⋅ K^-1) and high distribution coefficient (K_d=12484.8 mL ⋅ g^-1) confirm the good affinity between TpDa-COF framework and gold. This work gives us a new insight to prepare COF with pyridine nitrogen sites for gold detection and adsorption.