Potential mediated electrochemical recycling and sensing of cadmium ions in wastewater over ZnO/SA-g-PPy biocomposite

Abstract

Potentiometric sensing and electrochemical recycling of cadmium ions have been demonstrated over chemically interactive and electrically conducting bio-nanocomposite film comprised of zinc oxide, sodium alginate, and polypyrrole (ZnO/SA-g-PPy) using a laboratory-designed electrochemical setup. The chemical structure, functionality, morphology, crystallinity, conductivity, and physico-mechanical properties of composite and constituents were investigated by infrared spectrometry, X-ray diffractometry, scanning electron microscopy, and other relevant standard techniques. The analytical results reveal the evolution of chemically interactive sites along with electrochemical responsive nature due to the liberation of interactive sites in sodium alginate during composite formation towards the cadmium ions present in solution states along with electrical conductivity. Further, a thin film of composite cast on ITO-coated glass was explored for potentiometric sensing of trace cadmium ions in the range of 0.1 μM to 1000 μM, with a sensitivity of 0.255 mV μM⁻¹ cm⁻², response time of 40 s, recovery time of 10 s, and stability of 80 days, along with 72% extractability after the application of external optimized potential, i.e., 0.48 V, on the used sensing electrode. The mechanism of recycling and sensing has been proposed based on induced potential and applied external potential against electrodes after electrochemical interaction between cadmium ions and ZnO/SA-g-PPy-based electrode along potentiometric reductive desorption of adsorbed cadmium ions due to electrochemical reduction and desorption.