Manipulating Active Sites of 2D Metal–Organic Framework Nanosheets with Fluorescent Materials for Enhanced Colorimetric and Fluorescent Ammonia Sensing

Abstract

Abstract2D metal–organic frameworks (MOFs) offer high surface area and unique accessibility to active adsorption sites making them appealing for gas sensing applications. 2D MOFs‐based sensors are gaining traction for detecting hazardous flu‐gases such as ammonia selectively at low concentrations. Fluorescent and colorimetric sensing are promising techniques offering high sensitivity, selectivity, and rapid response in simple applications. In this work, Zn‐BTC is synthesized as 2D‐MOFs nanosheet with approximate thickness of 2.52 nm via a fast, facile, direct synthesis technique. The introduction of 8‐hydroxyquinoline during synthesis forms fluorescent compounds with zinc (ZnQ) which is encapsulated and decorated onto Zn‐BTC. Inherent charges on ZnQ lead to the agglomeration of multiple 2D‐flakes forming ZnQ@Zn‐BTC multi‐flaked nano‐discs. The synthesized material shows visible color change upon exposure to ammonia from white to ivory. In addition, selective fluorescence quenching is observed under ultraviolet illumination (λex = 365 nm) when ZnQ@Zn‐BTC is exposed to ammonia. The limit of detection reaches 0.27 ppm as a dried film for gaseous sensing and 60.8 nm in liquid phase fluorescence quenching, respectively. The observed high sensitivity and selectivity are attributed to the manipulation of active sites of 2D‐MOFs nanosheet with ZnQ. Functionalization also limits the degradation and breakdown of ZnQ@Zn‐BTC.