Iron terephthalate MOF-MWCNTs based composite paste two-electrode system for selective detection of lead in contaminated stream

Abstract

A composite paste combining iron terephthalate metal-organic framework (MOF-235) and multi-walled carbon nanotubes (MWCNTs) was synthesized for potentiometric lead detection in aqueous solutions. Synthesis yielded a homogeneous and well-dispersed composite by blending MOF/CNT with silicon oil as a binder. This novel material combination of materials has been explored for the first time focussing more into potentiometric and electrochemical lead detection with various control settings, including MOF concentration, electrolyte pH, temperature, electrode spacing and saturation time as well as real-life water analysis. Optimal sensor was selected for electrochemical studies, including, cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry for analysis of various electrode configuration and effect of scan rates on peak currents. Amperometric studies assessed the impact of interfering ions, while leachate solution analysis determined the content of different ions from modified electrodes. Linear behaviour of peak current with scan rates indicated adsorption-controlled kinetics. ECSA for unmodified and modified electrodes were 0.033 cm² and 0.053 cm², with surface coverage areas of 8.5 mM cm−2 and 2.3 mM cm−2. Sensor exhibited a quasi-reversible nature with a sensitivities of 3075.5 mA.cm⁻².mg/l⁻¹ and 226.5 mA.cm⁻².mg/l⁻¹ and detection limits of 0.2 µg/l and 39 µg/l over dynamic ranges. This cost-effective sensor, with a material cost of 1893 INR (22.8 US$) per gram of paste, offers an alternative for lead detection.