Composite MOF Mixture As Volatile Organic Compound Sensor — a New Approach to Lmof Sensors

Metal-organic frameworks (MOFs) show high potential as luminescent sensors due to the high amount of metal-ligand combinations available and many exploitable luminescent mechanisms. Sensor applications nearly always require materials in the solid state; however, due to the self-quenching mechanisms in the solid state, MOF literature has focused on testing materials in solutions, where pH, polarity, and other solvent effects overcome the self-quenching mechanism. Five luminescent metal-organic frameworks (LMOFs) were synthesized solvothermally to investigate fluorescent enhancement and/or quenching effects in the solid state in the presence of a series of volatile organic compounds (VOCs). Each of the MOFs were characterized with powder x-ray diffraction directly after synthesis, activation, and with emission/excitation studies. Three of the LMOFs, LaBTB (BTB = 1,3,5-tris(4-carboxyphenyl)benzene acid), ZrPDA (PDA = 1,4-phenyldiacrylic acid), and UiO-66-NH₂, were mixed and exposed to a series of VOCs to show the feasibility of solid mixtures in creating fingerprint-like spectroscopic regions for detection and identification of VOCs. The independent responses from each MOF create a predictable response pattern in each spectroscopic region. For a many-MOF mixture, this effectively dilutes self-quenching mechanism. Moving from solution based testing to solid state testing is a large step toward industrial applications or composite materials.