Electrocatalytic reduction and sensing of hazardous Cr(VI) in water samples using in situ functionalized vanillin-catechol derivative/MWCNT-modified electrode

Abstract

Vanillin (VAn), 4-hydroxy-3-methoxybenzaldehyde, is a natural organic compound classified as a phenolic aldehyde. It is the primary component responsible for the distinctive vanilla flavor and aroma found in vanilla beans. Beyond its culinary applications, VAn is utilized in the fragrance and cosmetic industries due to its pleasant scent. In this study, VAn was employed as a precursor for the in situ functionalization of redox-active catechol on multi-walled carbon nanotubes (MWCNTs)–modified electrode surface, designated as GCE/MWCNT@VAn-Redox, where VAn-Redox represents the redox-active product of VAn. This modified electrode functions as a surface-confined redox-active molecular species capable of efficiently electrocatalytically reducing hazardous Cr(VI) species in aqueous solutions. The chemically modified electrode (CME) exhibited a well-defined redox peak at a standard electrode potential, E° = 0.6 V vs Ag/AgCl, with a surface-excess value (Γ) of 14.2 × 10⁻⁹ mol·cm⁻² in a pH 2 HCl + KCl environment. Characterization of the modified electrode was performed using various techniques, including FE-SEM, UV–Vis, Raman, FT-IR, HRMS (organic extract), and control electrochemical experiments. Amperometric i-t and batch injection analyses (BIA) were employed to evaluate the electrocatalytic reduction, transforming the screen-printed CME into a sensitive electrochemical sensor for toxic Cr(VI) species. Notably, this innovative electrode demonstrates no interference with dissolved oxygen or various biochemicals, such as mercury, calcium, zinc, sulfate, chloride, iodide, H₂O₂, cysteine, glucose, and urea.