Showing papers by "Lawrence B. Alemany published in 2013"
TL;DR: An unconventional view of GO chemistry is proposed and the corresponding "dynamic structural model" (DSM) is developed, which provides an explanation for the acidity of GO aqueous solutions and accounts for most of the known spectroscopic and experimental data.
Abstract: The existing structural models of graphene oxide (GO) contradict each other and cannot adequately explain the acidity of its aqueous solutions. Inadequate understanding of chemical structure can lead to a misinterpretation of observed experimental phenomena. Understanding the chemistry and structure of GO should enable new functionalization protocols while explaining GO’s limitations due to its water instability. Here we propose an unconventional view of GO chemistry and develop the corresponding “dynamic structural model” (DSM). In contrast to previously proposed models, the DSM considers GO as a system, constantly changing its chemical structure due to interaction with water. Using potentiometric titration, 13C NMR, FTIR, UV–vis, X-ray photoelectron microscopy, thermogravimetric analysis, and scanning electron microscopy we show that GO does not contain any significant quantity of preexisting acidic functional groups, but gradually generates them through interaction with water. The reaction with water r...
534 citations
TL;DR: In this article, a methodology to synthesize fluorinated graphene oxide by oxidizing the basal plane of fluorinated graphite, allowing for tunable hydrophobicity of GO, is reported.
Abstract: The richly functionalized basal plane bonded to polar organic moieties makes graphene oxide (GO) innately hydrophilic. Here, a methodology to synthesize fluorinated graphene oxide by oxidizing the basal plane of fluorinated graphite, allowing for tunable hydrophobicity of GO, is reported. Fluorine exists as tertiary alkyl fluorides covalently bonded to graphitic carbons, and using magic-angle spinning (MAS) 13C NMR as a primary tool chemical structures for the two types of synthesized fluorinated graphene oxides (FGOs) with significantly different fluorine contents are proposed. The low surface energy of the C–F bond drastically affects GO's wetting behavior, leading to amphiphobicity in its highly fluorinated form. Ease of solution processing enables the fabrication of inks that are spray-painted on various porous/non-porous substrates. These coatings maintain amphiphobicity for solvents with surface tensions down to 59 dyn/cm, thus bypassing existing lithographic means to create similar surfaces. The approach towards fluorinating GO and fabricating graphene-based surfaces with tunable wettability opens the path towards unique, accessible, carbon-based amphiphobic coatings.
106 citations
TL;DR: A 13C T1 inversion‐recovery experiment provides much more detailed information than in previous studies of long‐chain n‐alkanes, demonstrates a steady increase in the relaxation times of the ten different carbons proceeding from the middle to the end of the chain, and thus confirms the assignments for the interior carbons.
Abstract: New information has been obtained from very-high-resolution 13C NMR studies of a series of long-chain n-alkanes. These compounds are fundamentally important in the petroleum industry and are essential to the life of some plants, flowers, and insects. At least partial resolution of the ten different 13C NMR signals of n-C20H42 is observed at 11.7 T for solutions in C6D6 or C6D5CD3. A 13C T1 inversion-recovery experiment provides much more detailed information than in previous studies of long-chain n-alkanes, demonstrates a steady increase in the relaxation times of the ten different carbons proceeding from the middle to the end of the chain because of segmental motion, and thus confirms the assignments for the interior carbons. In contrast, there is significant overlap for the signals for C-7 and the more interior carbons in a solution of n-C16 or longer chain alkanes in CDCl3. Not only are the chemical shifts sensitive to the solvent used, but also the relative chemical shifts change. Signals for the interior carbons of the odd-number alkanes in CDCl3 are better resolved than in the spectra of their even-number counterparts. Some mixed aromatic solvent systems give increased dispersion of the cluster of C-6 through C-10 signals of n-C20H42, n-C21H44, and n-C22H46. However, none of the solvents used could even partially resolve the C-10 and C-11 signals of n-C21H44 or n-C22H46 at 11.7 T, which may result from a different distribution of conformers for n-C21H44 or n-C22H46 than for n-C20H42 and shorter n-alkanes. Copyright © 2013 John Wiley & Sons, Ltd.
2 citations