A 2D Mesoporous Hydrazone Covalent Organic Framework for Selective Detection and Ultrafast Recovery of Au(III) from Electronic Waste

Developing a material that can simultaneously detect and recover Au(III) is economically desirable. Herein, we constructed a two-dimensional mesoporous fluorescent covalent organic framework named TY-Hz COF by integrating 1,3,6,8-tetra(4-formylphenyl)pyrene (TY) and terephthalic dihydrazide (Hz) into a pi-conjugated framework for simultaneous detection and recovery of Au(III). The TY-Hz COF suspension can rapidly (10 s) and sensitively response to Au(III) with electron transfer-induced fluorescence quenching and visual color change from bright yellow to dark green, and the limit of detection is as low as 17 nM. Moreover, TY-Hz COF can capture more than 92 % Au(III) in the solution with extremely fast kinetics (within 2 min) and excellent selectivity with a maximum adsorption capacity of 1008.30 mg g-1. It is worth mentioning that TY-Hz is the first type of COF that achieves Au(III) detection, adsorption and chemical reduction simultaneously. Mechanistic studies reveal that the detection and adsorption behaviors can be attributed to the synergistic effect of reduction, coordination interaction between neutral amide functional groups and Au(III), and hydrogen bonding between protonated amides and AuCl4-. These results suggest that TY-Hz COF shows great potential for Au(III) detection and recovery in electronic waste (e-waste).