Synthesis, Properties, and Applications of Hydrophilic Hollow Carbon Nanoparticles from C 60 and its Soot
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Synthesis, Properties, and Applications of Hydrophilic Hollow Carbon Nanoparticles from C60 and its Soot Ken Kokubo, Hiroshi Ueno, Yuji Nakamura, Shizuka Yamakura, and Takumi Oshima Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan ABSTRACT We have developed a facile synthetic method for highly water-soluble, hollow carbon nanoparticles with a diameter of ~1 nm, as a so-called fullerenol. The method was extended to fullerene soot to obtain the corresponding hydrophilic carbon materials, and the products were subjected to IR and elemental analysis. Particle size analysis demonstrated the relatively high dispersion of particles with diameters of ~70 nm, in water. The surface analysis using FE-SEM showed the difference in morphology between fullerene soot and activated carbon as well as between before and after hydrophilic treatment of the soot with hydrogen peroxide. Moreover, this hydrophilic fullerene soot exhibited high antioxidant activity as compared with fullerenol and C60. INTRODUCTION Hydrophilic carbon particles have been used in the past for black calligraphy ink and are presently used in ink-jet printer ink. This material is readily available and is lightweight, and it has low cost and relatively low toxicity. It can also be used as an adsorbent for undesired and/or toxic compounds, depending on the hybridization and surface area of the carbon structure, in the form of porous activated carbon (AC). Recently, the dispersion of fullerene, carbon nanotubes, graphene, nanodiamonds, and other nanocarbons in aqueous solution through the introduction of hydrophilic substituents or the use of surfactants has attracted growing attention [1–3]. Hydrophilic carbon materials, especially nanoscale materials that disperse easily in aqueous solution, have great potential for applications in materials chemistry because of their versatile properties and facile modifications. One promising candidate is polyhydroxylated fullerenes, socalled fullerenols (Scheme 1).
Scheme 1. Synthesis of various fullerenols.
Of the various fullerenols having different numbers of hydroxyl groups developed so far [4,5], our synthetic method using hydrogen peroxide can produce the highly hydroxylated and water-soluble fullerenols C60(OH)36 [6] and C60(OH)44 [7]. The fullerene surface is covered with many hydroxyl groups (an average 36 or 44 per 60 carbon atoms, forming a complex mixture of regioisomers) and thus is highly hydrophilic. However, due to the introduction of such a large number of hydroxyl groups, unavoidable high strain on fullerene cage often results in skeletal rearrangement along with C–C bond cleavage, forming holes. Therefore, such a fullerene multiadduct is not a true fullerene anymore but can be considered a hydrophilic hollow carbon nanoparticle. Although the structure can be defined only as an estimated average structure, much interest and effort have been devoted to studies of its antioxidant activity [8,9], related bioactivities [10–12], and othe
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