Highly hydrophobic solid contact based on graphene-hybrid nanocomposites for all solid state potentiometric sensors with well-formulated phase boundary potentials

• Hybrid nanocomposites of graphene and a lipophilic silver salt were synthesized.
• The hybrid nanocomposite was used as the solid contact for all solid state ISEs.
• The overall potential difference can be theoretically formulated.
• Hydrophobic nanocomposite can suppress the water layer and the potential drift.

The properties of solid contact (SC) transducer are crucial for obtaining stable solid state ion selective electrodes (ISEs). We report in this work that the hybrid nanomaterial composed of graphene and sliver tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (AgTFPB), designated graphene&AgTFPB, can be sandwiched between an ion selective membrane (ISM) containing TFPB− and a silver conducting substrate (CS) and effectively work as the SC transducer to provide ion-to-electron translation. Thus developed solid state ISEs, designated Ag/graphene&AgTFPB/K+-ISM electrodes, demonstrated a Nernstian response to K+ with a slope of 56.46 (±0.25) mV/decade (n = 5) in a concentration range of 10−5.2–10−2.9 M with a detection limit of 10−5.73 M, as well as a sufficient stability against O2, CO2 and light. Furthermore, the Ag/graphene&AgTFPB/K+-ISM electrodes displayed a standard electromotive force (EMF) of 550.42 (±1.34) mV with a batch-to-batch deviation of 1.26 mV. We believe that the superior potential stability and reproducibility can be ascribed to the graphene&AgTFPB nanocomposites SC. We believe that the doped AgTFPB can provide the ion-to-electron transduction via the Ag/AgTFPB/TFPB− redox conversion at the SC/CS interface and the ion-exchange equilibrium of TFPB− at the ISM/SC interface. Thus, the overall potential difference across the potentiometric measurement cell can be theoretically formulated in terms of thermodynamic equilibrium at two interfaces. Moreover, the highly hydrophobic nature of graphene&AgTFPB nanocomposites can also substantially suppress the formation of water layer.

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