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

A novel hydrazone covalent organic framework (TY-Hz COF) has been constructed for simultaneous detection and recovery of Au(III) with high sensitivity and excellent selectivity. The unique fluorescent properties of TY-Hz COF can be exploited to selectively detect Au(III) via fluorescence quenching, and the abundant hydrazone groups on TY-Hz COF can capture Au(III) by coordination and hydrogen bonding interactions and further reduce Au(III) to Au(0) through redox, thus possessing a high recovery efficiency and a fast kinetics (within 2 min) for Au(III) from electronic waste. [Display omitted] •A fluorescent hydrazone covalent organic framework (TY-Hz COF) has been constructed.•The TY-Hz COF can be exploited for selective and sensitive detection of Au(III).•The hydrazone groups of TY-Hz COF facilitate fast Au recovery from electronic waste.•TY-Hz COF can efficiently capture Au by coordination, hydrogen bonding and further redox. 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 π-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).