An all-solid-state potentiometric sensor modified with multi-walled carbon nanotubes (MWCNTs) for silicate assessment and water-quality testing

Abstract

A simple and cost-effective approach is proposed for silicate ion determination. The approach is based on designing an all-solid-state potentiometric sensor. The plasticized polyvinyl chloride (PVC) membrane sensor is based on the ion-association complex [Ni(bphen)₃]²⁺[SiO₃]²⁻ as a sensory recognition material. The sensor is modified with multi-walled carbon nanotubes (MWCNTs) as an ion-to-electron transducer material. The performance characteristics of the new silicate-selective electrode were evaluated using a potentiometric water-layer test, potentiometric measurements, impedance spectroscopy, and current-reversal chronopotentiometry. The developed electrodes exhibited a low detection limit (0.11 μg mL⁻¹) over a wide linear range (4.0 × 10⁻⁶ to 1.0 × 10⁻³ M) and near-Nernstian sensitivity (slope = −28.1 ± 1.4 mV per decade). They presented a very short response time (<5 s) over the pH range 6–12 and provided acceptable reliability, ease of design and miniaturization, and high potential stability, in addition to good accuracy and precision. The sensors exhibited enhanced selectivity for silicate over many common interfering anions, such as SO₄²⁻, NO₃⁻, CH₃COO⁻, CO₃²⁻, Cl⁻, S²⁻, and PO₄³⁻. These results could qualify the developed sensor to be used in a successful way for the trace determination of silicate ions in different matrices. The developed method was successfully applied to the potentiometric detection of silicate in different pre-packaged bottled drinking water samples.