Evaluation of mechanochemically synthesised fulleretic ZIF-67 MOF composite as a solid-contact in screen-printed ion-selective electrodes.

Abstract

Metal-organic frameworks (MOFs) and their composites have shown potential as solid-contact materials for electrochemical sensors; however, conventional MOF synthetic procedures are often time- and solvent-intensive, while the inherently poor electrical conductivity and limited stability of many MOFs under practical conditions restrict their broader application in electrochemical sensing. Mechanochemically synthesised sodalite cobalt ZIF-67 MOF was investigated as a solid-contact material for screen-printed potentiometric potassium-selective electrodes. The incorporation of fullerene (C60) into the ZIF-67 framework and subsequent MOF-templated nanoporous carbon formation were explored as strategies to improve the hydrophobicity, electrical conductivity, and capacitive behaviour of the solid-contact layer. Fullerene incorporation increased the water contact angle from 82.8 ± 4.4° for ZIF-67 to 135.0 ± 3.2° for the C60@ZIF-67 composite, while pyrolysis further enhanced hydrophobicity to 148.5 ± 1.4°. Structural and morphological analyses showed that C60 improved the thermal stability of the ZIF-67 framework during pyrolysis. The materials were deposited between screen-printed carbon electrodes and potassium-selective polymeric membranes to fabricate solid-contact ion-selective electrodes. The resulting sensors exhibited near-Nernstian responses toward K+ ions over the concentration range of 10-6-10-1 mol dm-3, with a detection limit of 10-5.9 mol dm-3 after C60 incorporation. Sensors based on pyrolysed ZIF-67 and C60@ZIF-67 showed an order-of-magnitude broader linear response range compared with non-pyrolysed materials and bare electrodes, further lowering the detection limit to 10-6.8 mol dm-3 and improving potential stability. These results demonstrate that fullerene-loaded ZIF-67 and its pyrolysis-derived materials are promising solid-contact layers for stable and reproducible screen-printed ion-selective electrodes.

Abstract as supplied by the indexing source. © the authors / publisher.