A sustainable redox-active electrocatalyst utilizing natural quercetin-infused MWCNT for ultra-sensitive detection of environmental Cr(VI) contaminants

Abstract

Hexavalent chromium (Cr(VI)), classified as a Group 1 carcinogen, is a widely acknowledged water pollutant, posing significant public health risks. The persisting challenge involves the development of sensitive and cost-effective methods for the detection and monitoring of Cr(VI) species at the concentration level recommended by the World Health Organization (WHO), which is 50 ppb (960 nM), in water sources. In the electrochemical detection of Cr(VI), modified electrodes utilizing precious metals (Au and Ag) and toxic organic redox mediators (Thionine, methylene blue, quionone, bisphenol and phenosafranine) have been employed. In this work, as an new platform, green electrochemical approach based on parsley-plant based natural quercetin (Qn-Redox) infused MWCNT modified glassy carbon electrode, designated as GCE/MWCNT@Qn-Redox, has been introduced for highly-effective electrocatalytic reduction and sensing of Cr(VI) species in pH 2 KCl-HCl solution. The as prepared GCE/MWCNT@Qn-Redox showed highly redox active surface confined peak at Eo = 0.550 V vs Ag/AgCl with surface excess value, 10.31 × 10−9 mol cm−2. Extensive physicochemical, spectroscopic, molecular characterization, and electrochemical control experiments confirm the identity of the entrapped molecular species in the green electrode as quercetin. By using scanning-electrochemical technique, the electroactive site of the green-electrode was imaged using Fe(CN)63−/Fe(CN)64− redox couple. The green-electrode showed excellent electrocatalytic Cr(VI) reduction signal where the Qn-Redox peak appears without any fouling problem. As a practical application, a portable batch-injection analysis coupled with three-in-one screen-printed electrode modified with MWCNT@Qn-Redox, which exhibitted a detection limit of 203 nM (S/N = 3), has been demonstrated for real time monitoring of toxic Cr(VI) species in tannery industries contaminated water samples. Given the electrochemical foundation of this approach, it holds promise for various sustainable electroanalytical assays in the future.