Abstract
Enhancing the performance of nanofibrous carbons requires the specific chemical functionalization of the surface, while limiting material degradation or causing other detrimental changes in the surface area and pore structures. We compare traditional oxidation protocols using HNO3, HNO3/H2SO4, and KMnO4 with the much less used oxidants RuO4 and OsO4, in tandem with secondary oxidants (such as KMnO4 or Oxone®), for their ability to form carboxylic acids on the surface of polyacrylonitrile-based activated carbon nanofiber membrane (ACNF) materials. While the traditional methods increased the carboxylic acid contents, they also destroyed the macrostructure of the ACNF, concomitant with the loss of up to 17 wt.% of the material. RuO4-mediated oxidations proved also to be too harsh. On the contrary, some of the OsO4-based protocols were characterized by very high mass yields; significant increase in carboxylic acid functionalization (6.3 µmol/mg) compared with the unmodified ACNF (1.7 µmol/mg), but with no concomitant loss of macrostructure, as measured by the retention of the Brunauer-Emmett-Teller (BET) surface area; and average pore width. While there was some reduction in micropore volume, the microporosity of the material remained high. The temperature-programmed desorption mass spectrometry (up to 1000 °C) indicated the presence of both single and adjacent carboxylic acid groups. We thus identified mild and highly effective reaction conditions for the functionalization of carbon nanomaterials without undue degradation of their physical properties.
Highlights
IntroductionCarbon nanomaterials with their tunable chemical, physical, electrical, and mechanical properties, are useful as adsorbents, sensors, filters, antimicrobial agents, or in energy storage devices [1].For example, materials such as carbon nanotubes (CNT) [2,3,4], carbon nanofibers (CNF) [5,6,7], carbon cloth [1,8,9,10], or activated carbon nanofiber (ACNF) [11,12,13], have all been used for these purposes.The properties of nanocarbon adsorbents with short intra-particle diffusion distances, controllable pore sizes, and the option for high specific surface areas make them suitable for contaminant binding [14]
We report here on the chemical oxidation of polyacrylonitrile (PAN)-based activated carbon nanofiber (ACNF) membranes, using a range of well-known and novel oxidation methods
We inspected the physical appearance of the ACNF membrane after the oxidations
Summary
Carbon nanomaterials with their tunable chemical, physical, electrical, and mechanical properties, are useful as adsorbents, sensors, filters, antimicrobial agents, or in energy storage devices [1].For example, materials such as carbon nanotubes (CNT) [2,3,4], carbon nanofibers (CNF) [5,6,7], carbon cloth [1,8,9,10], or activated carbon nanofiber (ACNF) [11,12,13], have all been used for these purposes.The properties of nanocarbon adsorbents with short intra-particle diffusion distances, controllable pore sizes, and the option for high specific surface areas make them suitable for contaminant binding [14]. Carbon nanomaterials with their tunable chemical, physical, electrical, and mechanical properties, are useful as adsorbents, sensors, filters, antimicrobial agents, or in energy storage devices [1]. Materials such as carbon nanotubes (CNT) [2,3,4], carbon nanofibers (CNF) [5,6,7], carbon cloth [1,8,9,10], or activated carbon nanofiber (ACNF) [11,12,13], have all been used for these purposes.
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