Search

Electrografting is a relevant process that allows getting modified electrodes where organic molecules are covalently bonded to the electrode surface. The modification is typically performed using electrochemical reactions, where the transient passage by free radicals allows the formation of covalent bonds with the electrode surface. These intermediaries are generated over a wide potential window, and they are commonly prone to a second electron transfer (oxidation or reduction). Thus, this reaction competes with the surface reactions, slowing down the formation of films on the electrode. In the case of carboxylate oxidation, these competitive processes have been minimized by using a redox‐catalysed process which occurs at low oxidation potentials. The rate at which modifications procedures occur is relevant in the sense that they determine the properties of the polymeric films covalently attached to the electrode surfaces. Therefore, this review focuses on the main aspects of the direct and redox‐catalysed oxidation of carboxylates as a tool for the covalent modification of the surface of different carbon electrodes. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of 6‐ferrocenylheptanoate was used to modify the surface of glassy carbon electrodes with thin films bearing ferrocene molecules. These films grow layer by layer and behave as surface redox catalyst during the electrografting. The electrografted films have a structure with pinholes or channels, whose existence was deduced from the redox behavior of the film in acetonitrile solution containing different supporting electrolytes and organic additives. The electron transport through this film requires the presence of the electrolyte anions in the film channels. However, the voltametric feature of the grafted films is sensitive to the electrolyte cation size. The supporting electrolyte anions inside the film channels stabilize the ferrocenium species during the film oxidation. However, the presence of the cations is required to keep the inner charge balance. The inclusion of both anions and cations inside the grafted film determines the surface coverage obtained from the voltammetric experiments. [ABSTRACT FROM AUTHOR]

The oxidation of 4‐(4‐nitrophenyl)butyrate ions in acetonitrile was used to modify glassy carbon surfaces with films bearing 3‐(4‐nitrophenyl)propyl groups. The main features of the voltammetric reduction of the grafted nitrophenyl groups were studied in two different supporting electrolytes; n‐Bu4NPF6 and Me4NPF6. The best response was obtained with the less bulky electrolyte, which was explained by the major capability of these ions to diffuse inside the channels of the grafted film, as well as the better stabilization of the radical anions generated during the reduction process. It was also shown that the films electrografted in presence of the bulky n‐Bu4NPF6 are thicker but less compact than those prepared in Me4NPF6. The amount of nitrophenyl groups in the grafted film that can be reduced depends on the size of the electrolyte ions. The permeation of the electrolyte ions inside the film channels determines also the voltammetric behavior of ferrocene as redox probe. A current rectification phenomenon was observed in acetonitrile solutions of bulky and hydrophobic electrolytes like n‐Bu4NPF6 and n‐Hx4NPF6, whose marginal inclusion inside the film channels promotes both the entrance of ferrocene and the expelling of ferrocenium ions from these ones. This phenomenon was emulated through a CEC mechanism in solution, where the diffusion inside the channels was described as single chemical equilibria. [ABSTRACT FROM AUTHOR]

Solid urban wastes are a primary source of local and global contamination. One approach to slow their accumulation is by using them to obtain addedvalue products. One common example of these waste materials is the fiber from the husks of coconuts, i.e. coir. However, it is also known that microorganisms such as fungi can attack products containing natural fibers. In this respect, this study aimed to evaluate how the mechanical properties of an extruded composite made of 60% recycled HDPE and 40% discarded coir were affected due to accelerated weathering and Phanerochaete chrysosporium attack. The effect of P. chrysosporium on the materials' mechanical properties before and after weathering, using an accelerated weathering (AW) test device, was evaluated by means of tensile and flexural analysis following ASTM standards. Samples were also characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR spectroscopy and SEM showed that both types of treatment degraded the surfaces of the tested samples. However, the mechanical performance was not seriously affected, which means that other fungal species would affect the composites to a lesser extent. [ABSTRACT FROM AUTHOR]