Formation of polysulfides as a smart strategy to selectively detect H2S in a Bi(iii)-based MOF material

Abstract

SU-101 was demonstrated to be an effective and efficient detector for H₂S, due to the facile generation of polysulfides, with a remarkable H₂S selectivity. Raman and XPS analyses confirmed the formation of S _n ^2- and S₄ ^2- polysulfide species after the H₂S adsorption (at 0.05 bar, 0.1 bar and 1 bar), without compromising the structural integrity of SU-101. The detection mechanism involves rigidification of the structure by the formation of the polysulfides and blockage of the ligand-metal charge transfer (LMCT) process, which increased the radiative emission. Additionally, theoretical simulations were carried out in order to demonstrate that the interaction of the polysulfide molecules inside the pores of SU-101 is energetically stable. Remarkably, the limit of H₂S detection (LOD) was calculated to be as low as approximately 22 ppm. Finally, SU-101 is nominated as a promising candidate for implementing toxic waste valorisation (i.e., capture of toxic H₂S) toward relevant applications in accurate molecular sensing.

Fig. 1. (a) Schematic of the formation of the SU-101 structure along the channel a-axis and (b) metal cluster and linker arrangement along the a-axis. Atoms label: green: Bi³⁺ octahedra, brown: carbon, and yellow: oxygen.

Fig. 2. (a) Solid-state emission spectra of the ellagic acid linker (brown) and as-synthesized SU-101 (yellow). (b) Comparison of the solid-state emission spectra of activated SU-101 and SU-101 exposed to different H₂S gas pressures. (c) Comparison of the solid-state emission spectra of SU-101 exposed to air, water vapour and different gases. (d) Fluorescence emission spectra of dispersed SU-101 in H₂S solutions in THF.

Fig. 3. (a) XPS survey spectra of activated SU-101 (yellow) and SU-101 saturated with H₂S (green). (b) Bi 4f/S 2p regions for XPS spectra of H₂S-saturated SU-101. (c) Comparison of S 2s regions for XPS spectra of SU-101 saturated with H₂S and pristine SU-101. (d) Raman spectra of activated SU-101 (yellow) and SU-101 saturated with H₂S (green). (e) UV-vis spectra of activated SU-101 (yellow) and SU-101 saturated with H₂S (green). (f) TRPL spectra of activated SU-101 (yellow) and SU-101 saturated with H₂S (green).

Fig. 4. (a) Schematic of the changes in the HOMO–LUMO energy of pristine and H₂S-saturated SU-101 material. (b) Schematic of the Jablonski diagram that would explain the changes in the fluorescence of the system.

Fig. 5. 2D plot of the electron density difference of (a) H₂S/SU-101, (b) H₂S₂/SU-101, (c) H₂S₄/SU-101, (d) H₂S₆/SU-101, and (e) H₂S₈/SU-101. Blue regions of 2D slices represent sites from which the electronic charge was depleted, and the red areas refer to the locations where the charge is accumulated (an isovalue of 0.001 e Å⁻³).