Carbon-Based Transducers for Solid-Contact Calcium Ion-Selective Electrodes: Mesopore and Nitrogen-Doping Effects

Area of Science:

• Electrochemistry
• Materials Science
• Analytical Chemistry

Background:

• Solid-contact ion-selective electrodes (SC-ISEs) are crucial for portable ion detection, utilizing solid-contact (SC) materials for signal transduction.
• Carbon-based materials offer high electrical double-layer (EDL) capacitance and hydrophobicity, making them ideal SC transducers.
• Enhancing interfacial capacitance is key to improving potential stability in SC-ISEs.

Purpose of the Study:

• To compare the performance of three carbon-based SC materials: nitrogen-doped mesoporous carbon (NMC), reduced graphene oxide (RGO), and carbon nanotubes (CNT).
• To investigate the effect of mesopore structure and N-doping on EDL capacitance and hydrophobicity.
• To develop and evaluate a highly stable Ca2+-SC-ISE using the most promising carbon material.

Main Methods:

• Synthesis and characterization of NMC, RGO, and CNT materials.
• Fabrication of Ca2+-SC-ISEs using each carbon material as the SC layer.
• Electrochemical performance evaluation, including potential stability, EDL capacitance, and Nernstian response.
• Analysis of Ca2+ ions in real-world samples like mineral water and soil leaching solutions.

Main Results:

• NMC exhibited the highest EDL capacitance due to its mesoporous structure and N-doping, while maintaining hydrophobicity and avoiding water-layer effects.
• Ca2+-SC-ISEs based on NMC demonstrated superior potential stability compared to those using RGO and CNT.
• The developed NMC-based SC-ISE achieved a Nernstian slope of 26.3 ± 3.1 mV dec−1 over a wide concentration range (10 μM to 0.1 M) with a low detection limit of 3.2 μM.

Conclusions:

• Mesoporous and N-doping engineering of carbon materials significantly enhances interfacial capacitance and potential stability in SC-ISEs.
• NMC is a superior SC material for developing high-performance Ca2+-SC-ISEs.
• The developed NMC-based SC-ISEs are suitable for practical, portable Ca2+ analysis in environmental and consumer products.