In situ electro-organic synthesis of hydroquinone using anisole on MWCNT/Nafion modified electrode surface and its heterogeneous electrocatalytic reduction of toxic Cr(vi) species

Abstract

Owing to its electro-inactive character, anisole (phenylmethyl ether, PhOCH₃) and its related derivatives have been used as electrolytes in electrochemistry. Herein, we report a simple one-step electro-organic conversion of PhOCH₃ to hydroquinone (HQ) on a pristine-MWCNT–Nafion modified electrode glassy carbon electrode surface, GCE/Nf–MWCNT@HQ, in pH 2 KCl–HCl solution within 15 min of working time. The chemically modified electrode showed a highly redox-active and well-defined signal at an apparent standard electrode potential, E^o′ = 0.45 V vs. Ag/AgCl (A2/C2) with a surface excess value, Γ_HQ = 2.1 × 10⁻⁹ mol cm⁻². The formation of surface-confined HQ is confirmed by collective physicochemical and spectroscopic characterizations using TEM, UV-Vis, Raman, FTIR, NMR and GC-MS techniques and with several control experiments. Consent about the mechanism, the 2.1% of intrinsic iron present in the pristine-MWCNT is involved for specific complexation with oxygen donor organic molecule (PhOCH₃) and hydroxylation in presence of H₂O₂ (nucleophilic attack) for HQ-product formation. The GCE/Nf–MWCNT@HQ showed an excellent heterogeneous-electrocatalytic reduction of Cr(VI) species in acidic solution with a linear calibration plot in a range, 5–500 ppm at an applied potential, 0.4 V vs. Ag/AgCl with a detection limit, 230 ppb (S/N = 3; amperometric i–t). As a proof of concept, selective detection of toxic Cr(VI) content in the tannery-waste water has been demonstrated with a recovery value ∼100%.