Room-Temperature One-Pot Synthesis of pH-Responsive Pyridine-Functionalized Carbon Surfaces

Carbon surfaces (glassy carbon, graphite, and boron-doped diamond) were functionalized with layers composed of linked pyridinium and pyridine moieties using simple electrochemical reduction of trifluoroacetylpyridinium. The pyridinium species was generated in situ in solution by the reaction of trifluoroacetic anhydride and pyridine precursors and underwent electrochemical reduction at -1.97 V vs Fc/Fc⁺, as determined by cyclic voltammetry. The pyridine/pyridinium films were electrodeposited at room temperature, on a timescale of minutes, and were characterized using X-ray photoelectron spectroscopy. The as-prepared films have a net positive charge in aqueous solution at pH 9 and below due to the pyridinium content, confirmed by the electrochemical response of differently charged redox molecules at the functionalized surfaces. The positive charge can be enhanced further through protonation of the neutral pyridine component by controlling the solution pH. Moreover, the nitrogen-acetyl bond can be cleaved through base treatment to purposefully increase the neutral pyridine proportion of the film. This results in a surface that can be "switched" from functionally near neutral to a positive charge by treatment in basic and acidic solutions, respectively, through manipulation of the protonation state of the pyridine. The functionalization process demonstrated here is readily achievable at a fast timescale at room temperature and hence can allow for rapid screening of surface properties. Such functionalized surfaces present a means to test in isolation the specific catalytic performance of pyridinic groups toward key processes such as oxygen and CO₂ reduction.

Oxygen Interactions with Covalently Grafted 2D Nanometric Carboxyphenyl Thin Films—An Experimental and DFT Study

Surface modification is a hot topic in electrochemistry and material sciences because it affects the way materials are used. In this paper, a method for covalently attaching carboxyphenyl (PhCOOH) groups to a gold electrode is presented. These groups were grafted onto the electrode surface electrochemically via reduction of aryldiazonium salt. The resulting grafted surface was characterized using cyclic voltammetry (CV) before and after the functionalization procedure to validate the presence of the grafted layer. The grafting of PhCOOH groups was confirmed by analyzing electrode thickness and composition by ellipsometry and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations indicated that the grafted layers provide a stable platform and resolved, for the first time, their interactions with oxygen.

Electrochemical evaluation of the antioxidant capacity of natural compounds on glassy carbon electrode modified with guanine-, polythionine-, and nitrogen-doped graphene

An electrochemical sensor based on guanine-, polythionine-, and nitrogen-doped graphene modified glassy carbon electrode (G/PTH/NG/GCE) was fabricated and applied for antioxidant capacity evaluation of natural compounds and complexes in electrochemical method since natural sources of active compounds exhibited various antioxidant activities. When the antioxidants existed in the system, the generated hydroxyl radicals were scavenged and the damage to guanine immobilized on the electrode was reduced less resulting in the oxidation peak current increased in square wave voltammetry. After the modifications of polythionine- and nitrogen-doped graphene, the oxidation peak current was improved. The effects of pH, incubation time, and concentrations of guanine and Fe2+ ions on the performances of the electrode were investigated and optimized. The G/PTH/NG/GCE showed good linearity, reproducibility, and storage stability for antioxidant capacity evaluation of ascorbic acid at the optimum conditions. The antioxidant capacities of three flavonoids and three plant extracts were measured using the G/PTH/NG/GCE and DPPH methods. Myricetin showed the highest antioxidant capacity in both electrochemical and DPPH methods. The proposed G/PTH/NG/GCE exhibited easy fabrication procedure, rapid detection time, and low cost for the detection of antioxidant activity for various kinds of samples.