High-Performance Electrocatalytic Reduction and Sensing of Hazardous Hexavalent Chromium Using a Redox-Active Binol Species-Impregnated Carbon Nanofiber-Modified Electrode

Abstract

Electrochemical reduction of the hexavalent chromium compounds, a serious environmental pollutant and carcinogen, to a nontoxic Cr(III) species is of significant research interest in interdisciplinary areas. Due to its high oxidation potential (1.36 V vs RHE) and associated surface fouling problems with organic-electrocatalyst systems, expensive precious metalbased electrodes like Au, Ag, Pt, and Pd have been widely used for this purpose. Herein we report, an in situ electrochemically prepared highly redox-active Binol species (Binol-Redox)-impregnated carbon nanofiber-modified electrode (CNF@Binol-Redox), E o ′ = 0.50 V versus Ag/AgCl and surface excess value (Γ Binol-Redox ) = 32.5 × 10 −9 mol•cm −2 , as a low-cost, stable, and highperformance molecular electrocatalyst for selective electrochemical reduction of Cr(VI) species in pH 2 HCL/KCl. The new electrode material was characterized using SEM, FTIR, Raman, GC-MS, 1 H NMR (active site isolated as an ethanolic extract), and scanning electrochemical microscopy (SECM) techniques. It has been revealed that an intermediate electrochemical oxygen reduction reaction to H 2 O 2 occurred at CNF@Binol ads , which is a key step for the surface-adsorbed Binol-precursor oxidation to redox-active molecular electrocatalyst. CNF@Binol-Redox showed a high-performance reduction reaction at a reduction potential of 0.5 V versus Ag/AgCl (low overpotential, η = 0.5 V), which is much better than that of several conducting polymers and Pd-based electrocatalysts (high η = 1.5−0.6 V) and closer to the performance of a bulk gold electrode system. Further, this new electrode does not show any dissolved oxygen interference or surface-fouling problem. The Andrieux-Savent electrochemical kinetic model was adopted to calculate the heterogeneous rate constant (k chem ) as 4.29 × 10 5 mol −1 •dm 3 •s −1 . As practical applications, a prototype electrochemical Cr(VI) sensor operatable by one-drop analysis and bulk electrochemical detoxification of Cr(VI) to Cr(III) have been successfully demonstrated.

In Situ Electrochemical Trapping and Unraveling the Mechanism of the Toxic Intermediate Metabolite N-Acetyl-p-Benzoquinone Imine of the Acetaminophen Drug and Its Biomimetic Mediated NADH Oxidation Reaction

“…The result describes a symmetric energy barrier for the electron transfer reaction. The obtained k s value is comparable with that of redox-active hydroquinone derivative 30,31 and 1,10-phenanthroline-quinone 32 molecular system-immobilized carbon nanomaterialmodified electrodes. Furthermore, this new redox system showed a proton-coupled electron transfer characteristic (slope = −59 ± 3 mV dec −1 ) obeying the Nernstian mechanism with the participation of an equal number of protons and electrons in the electrochemical reaction (real value, −58 mV dec −1 ) (Figure 1E,F).…”

A π–π Bonding-Assisted Molecular-Wiring of Folded-Cytochrome c and Naphthoquinone and Its Electron-Relay-Based Bioelectrocatalytic H2O2 Reduction Reaction Visualized by Redox-Competitive Scanning Electrochemical Microscopy

“…Plausibly, at highly bioelectrocatalytic spots, the local H 2 O 2 concentration within the gap between the substrate and the Pt-Tip is depleted, which leads to a marked Pt Tip current decrement over the substrate. Bioelectrocatalytic spots of different nature, activity, and inhomogeneities within the surface cause specific variations in the imaging current signals . Previously, our group has utilized this technique for analyzing the in situ formation of nickel hexacyanoferrate and molecular oxidation reactions. , Figure A is an illustration of the RC-SECM operational procedure, wherein simultaneous reduction of H 2 O 2 by the GCE/CB@NQ/Cytc (at open-circuit, Step-1) and the Pt Tip (Step-1′) has been explored.…”

“…Figure S5C Next, a redox-competition SECM (RC-SECM) technique was adopted in couple with an H 2 O 2 electrochemical reduction reaction as an in situ redox probe. 63 The variation in the kinetics of the H 2 O 2 reduction reaction between the substrate and the tip electrode was turned for the imaging. 63 If the Pt Tip position is in close proximity to an active electrocatalyst site, a marked decrement in the SECM-Tip current (imaging) will be noticed.…”

“…63 The variation in the kinetics of the H 2 O 2 reduction reaction between the substrate and the tip electrode was turned for the imaging. 63 If the Pt Tip position is in close proximity to an active electrocatalyst site, a marked decrement in the SECM-Tip current (imaging) will be noticed. Plausibly, at highly bioelectrocatalytic spots, the local H 2 O 2 concentration within the gap between the substrate and the Pt-Tip is depleted, which leads to a marked Pt Tip current decrement over the substrate.…”

Wheel-shaped molybdenum(v) cobalt-phosphate cluster as a highly sensitive bifunctional photoelectrochemical sensor for the trace determination of Cr(vi) and tetracycline

“…The above experimental results demonstrated that hybrid 1 is a promising bifunctional PEC sensor for the detection of Cr(VI) and TC. [44][45][46] To gain more insights, the catalytic mechanisms of the electrocatalytic Cr(VI) reduction 47 and electrooxidation of TC 48 over hybrid 1 were investigated by the chronoamperometry technique. Fig.…”