A Tb-based-metal–organic framework prepared under ultrasound for detection of organic amines in aqueous solution through fluorescence quenching

A luminescent Tb–benzenetricarboxylate (BTC) metal–organic framework (MOF) was synthesized, ultrasonically, and used (without any functionalization) for selective detection of organic amines through fluorescence quenching of the Tb-metal. Several amines, with various basicity, such as ethylenediamine (ED), diethanolamine (DOA), diethylamine (DEA), triethylamine, pyridine, aniline, and pyrrole were chosen as representative analytes. The quenching efficiency of the amine solutions relied on the basicity of the analytes and steric hindrance between the analytes and MOF. A Tb–BTC MOF, synthesized using ultrasound irradiation, shows better results than MOF synthesized using conventional electrical or microwave heating, which might be the effect of a better dispersion of the MOF due to smaller particle size, higher analyte diffusivity, and higher defect-site contents. The change in the luminescence of the Tb–MOF was attributed to the interaction of amines with the Tb-metal ions of the MOF through coordination/complexation. By applying the luminescent Tb–MOF (prepared with ultrasound), aliphatic organic amines like ED, DOA, and DEA could be detected up to 100 μM and 2 μM, with naked eyes and fluorescence spectrophotometry, respectively. However, other chemicals, such as alcohol, ketone, hydrocarbon, and hydrogen peroxide did not quench appreciably the fluorescence of Tb–MOF, suggesting the possible selective detection of amines.