Enhancing the sensitivity of a water stable MOF as a H2S gas sensor by the fabrication of a mixed-matrix membrane

Abstract

Hydrogen sulfide (H₂S) is a smelly, colorless, and hazardous gas even at sub-ppm level, produced predominantly from natural and anthropogenic sources. It is also called a ‘knock-down gas’ as its inhalation at higher concentrations can cause death. Therefore, several researchers are working on designing sensors with high stability and robustness for the real-time detection of H₂S gas. Apart from many other materials, metal–organic framework (MOF)-based fluorescent probes are of high interest for the detection of H₂S. Herein, we present a cost-effective acryl-amide functionalized 2D Zn-bdc MOF, which was shown to function as an excellent probe for the real-time detection of H₂S in liquid as well as in the gaseous form through a nucleophilic addition mechanism to olefinic bonds of the MOFs. Interestingly, in the aqueous phase, Zn-bdc was found to exhibit turn-off and subsequent turn-on fluorescence spectra with the gradual addition of H₂S. Furthermore, the realistic sensing of H₂S by the MOF was investigated by preparing a mixed-matrix membrane of MOF with PVDF as a binder. Notably, the membrane with 60% loading of Zn-bdc increased the probe's sensitivity by two-fold. Furthermore, we note that this is the first example of an essential metal based mixed-matrix membrane for H₂S detection with the LOD value as low as 5.3 μM. In vitro cell imaging of Zn-bdc in the presence of H₂S displays a vibrant bright red fluorescence signal of LN-18 glioblastoma cells.