Preparation of amide functionalized calix[4]arene based quartz crystal microbalance (QCM) sensors and investigation of their sensing properties towards some anions

In this study, we aimed preparation of new QCM sensors coated with amide functionalized calix[4]arene derivatives and based on calix[4]arene amide, and their investigation of sensing properties for some important anions such as Br-, SO42-, Cl-, NO3-, F-, I-, H2PO4-, CN-, Cr2O72-, ClO4- in aqueous media. For this purpose, firstly, amide group (propyl and ethylene bridged amide) functionalized calix[4]arene 4a and 4b derivatives were synthesized from their lower rim region. Subsequently, calix[4]arene 6a and 6b derivatives were synthesized from their upper rim region to form a regular layer on the QCM crystal surface of these derivatives and thus to obtain a higher sensing. Characterization of the structures of the synthesized compounds was carried out by FT-IR and 1H-NMR spectroscopy. Synthesized thiol group containing calix[4]arene amide derivatives 6a and 6b were coated on the QCM sensor surface by using soaking method, and thus sensing studies of these new QCM sensors were carried out for the selected anions. In addition, in order to make comparisons and to see the structural effects, QCM sensors coated and uncoated with calix[4]arene 2, 3 and 4b derivatives were also prepared and their sensing properties towards the selected anions were examined. As a result of the detection studies, it was seen that the QCM sensor coated with 6b (ethylene-bridged amide), which is one of the calix[4]arene derivatives with amide functionalized, exhibited a significantly higher detection for all anions compared to other sensors. On the other hand, it was remarkable that this sensing was much higher especially towards cyanide (CN-) and fluoride (F-) anions. For the amide functionalized calix[4]arene 6b coated QCM sensor, it was calculated LOD values as 0.0317 mM and 0.0306 mM, adsorption capacities as 224.3 mg/g adsorbent , and the binding constants as 2.399 and 6.770 for CN- and F-, respectively. As a result, in this study, a novel QCM sensor, which coated with calix[4]arene amide 6a bearing ethylene bridge and thiol groups, emerged as an efficient and effective sensor, especially in the sensing of CN- and F- anions.