A Novel Method for the Synthesis of MOF-199 for Sensing and Photocatalytic Applications

Abstract

Multifunctional Cu (II)-based Metal Organic Framework (MOF) [Cu₃(BTC)₂] has been synthesized by a facile electrochemical method. Crystallographic and morphological characterizations of synthesized MOF have been done using Powder X-ray Diffractometer and Scanning Electron Microscope (SEM), respectively, whereas Fourier Transform Infrared Spectroscopy (FT-IR), Energy Dispersive X-ray Spectroscopy (EDS), UV-Vis Absorption Spectroscopy and Energy Resolved Luminescence Spectroscopic studies have been used for the detailed qualitative, quantitative as well as optical analyses. Sharp PXRD peaks indicate the formation of highly crystalline MOF with face centered cubic (fcc) structure. Flakes (average length = 0.71 µm and width = 0.10 µm) and rods (average aspect ratio = ((0.1:8.3) µm) like morphologies have been observed in SEM micrographs. The presence of C, O and Cu has been confirmed by EDS analysis. Photocatalytic activity potential of the synthesized MOF has been tested using methylene blue dye (MB) as a test contaminant in aqueous media under sunlight irradiation. Selective and sensitive fluorescent sensing of different Nitroaromatic compounds (NACs) like 4-Nitroaniline (4-NA), 2-Nitroaniline (2-NA), 3-Nitroaniline (3-NA), 4-Nitrotoulene (4-NT), 2,4-Dinitrotoulene (2,4-DNT), 1,3-Dinitrobenzene (1,3-DNB), 2,6- Dinitrotoulene (2,6-DNT) has been done by exploring the photoluminescent behaviour of chemically stable Cu₃(BTC)₂. Synthesized MOF is extremely sensitive towards 4-NA, which is having PL quenching efficiency of 82.61% with highest quenching rate till reported. Indeed, a large quenching coefficient KSV = 34.02 × 10^-7 M^-1 and correlation coefficient R² = 0.9962 in K_SV plot have been elucidated with limit of detection (LOD) = 0.7544 ppb. The possible ways of luminescence quenching are successfully explained by the combination of Photoinduced Electron Transfer (PET) and Resonance Energy Transfer (RET) mechanisms. Additionally, the Density Functional Theory (DFT) calculations have been employed to support the experimental results. Cu₃(BTC)₂ fully demonstrates the power of a multi component MOF, which provides a feasible pathway for the design of novel material towards fast responding luminescence sensing and photocatalytic degradation of pollutants.

Keywords: Crystallography; Cu (II)-MOF; Density Functional Theory; Fluorescence Sensing; Morphology; Nitroaromatic Compounds; Photocatalysis; Photoinduced Electron Transfer; Resonance Energy Transfer.