Carbon spheres

Scientists identified the first carbon nanotubes in 1991. They sealed two graphite rods inside a container of helium gas and sent an electric discharge from one rod to the other. Much of one rod evaporated, but out of the inferno some amazing structures emerged (see illustrations). As well as the tiny 60-atom carbon spheres known as buckminsterfullerene—which had been known since 1985—long, hollow, perfectly straight carbon nanotubes were detected. 

Maynollo J., Kraeutler B. Diels-Alder Reactions of the [60]Fullerene From Regularly Functionalized Carbon Spheres to Cyclophanes Fullerene Sci. Technol. 1996 4 213-226... 

Fullerenes possess electronic and photophysical properties which make them natural candidates for the preparation of functional dendrimers. The attachment of a controlled number of dendrons on a core provides a compact insulating layer around the carbon sphere, and the... 

By changing the ultrasound power, changes in the mesoporosity of ZnO nanoparticles (average pore sizes from 2.5 to 14.3 nm) have been observed. In addition to the changes in mesoporosity, changes in the morphology have also been noted [13]. Recently, Jia et al. [14] have used sonochemistry and prepared hollow ZnO microspheres with diameter 500 nm assembled by nanoparticles using carbon spheres as template. Such specific structure of hollow spheres has applications in nanoelectronics, nanophotonics and nanomedicine. 

Stockli T, Bonard JM, Chatelain A (2000). Plasmon excitations in graphitic carbon spheres measured by EELS. Phys. Rev. B. 61 5751-5759. 

Li et al. reported first on the decoration of hydrothermal carbon spheres obtained from glucose with noble metal nanoparticles [19]. They used the reactivity of as-prepared carbon microspheres to load silver and palladium nanoparticles onto then-surfaces, both via surface binding and room-temperature surface reduction. Furthermore, it was also demonstrated that these carbon spheres can encapsulate nanoparticles in their cores with retention of the surface functional groups. Nanoparticles of gold and silver could be encapsulated deep in the carbon by in situ hydrothermal reduction of noble-metal ions with glucose (the Tollens reaction), or by using silver nanoparticles as nuclei for subsequent formation of carbon spheres. Some TEM images of such hybrid materials are shown in Fig. 7.4. 

Fig. 7.4 (a) Carbon spheres loaded with silver nanoparticles at room temperature (b) carbon spheres loaded with palladium nanoparticles by refluxing (c) silver core of carbon spheres from encapsulation of silver nanoparticle seeds, (d) layered structure with an silver core, a platinum shell, and a carbon interlayer, formed by seeded encapsulation followed by the reflux method. 

Model a campfire spark as a carbon sphere (pc = 3 g/cm ) surrounded by a boundary layer... 

The physical and chemical complexity of primary combustion-generated POM is illustrated in Fig. 10.1 (Johnson et al., 1994), a schematic diagram of a diesel exhaust particle and associated copollutants. The gas-phase regime contains volatile (2-ring) PAHs and a fraction of the semivolatile (3- and 4-ring) PAHs. The particle-phase contains the remainder of the semivolatile PAHs ( particle-associated ) along with the 5- and 6-ring heavy PAHs adsorbed/absorbed to the surface of the elemental carbon spheres that constitute the backbone of the overall diesel soot particle. Also present is sulfate formed from oxidation of sulfur present in the diesel fuel and gas- and particle-phase PACs. 

The second model aerosol is composed of gray spheres that is, the absorber is incorporated in the nonabsorbing particles rather than separate from them. We might visualize this as small carbon spheres uniformly embedded in plum pudding fashion throughout much larger nonabsorbing spheres. 

Over the past 15 years, we have assisted in a huge development of the covalent chemical functionalization of the Ceo carbon sphere aimed at generating many new fullerene-based materials,6 7 in which the outstanding properties of the fullerenes would combine synergistically with those of other molecular materials, polymers, dendrons, liquid crystals, and more, in general, with photo-, electro-, or biologically active units (Scheme 9.1). 

Pure carbon spheres of Cf,(l the fullerenes—react avidly with free radicals with a higher antioxidant ability than the naturally occurring vitamin E (21). Endohedral fullerenes have been shown to be capable of encapsulating a variety of atoms such as radiotracers or noble gases, thereby making them efficient excipients in the delivery of radioisotopes to cancer cells or in magnetic resonance imaging (MRI) (22). 

The regiospecific thermolysis of crystalline mono-adduct 8 gives a (1 1) mixture of C6o and the trans-1 bis-adduct 9 in 48% yield. The two anthracene addends of 9 served, in solution, to direct four bromomalonate addends regiospecifically into e-positions, yielding hexakis-adduct 10. The subsequent thermal removal of the two anthracene molecules led to a tetrakis-adduct with an equatorial belt of bis[(ethoxycarbonyl)methano] addends on the carbon sphere [14], representing a valuable building block for further specific functionalization. 

It may be speculated that C60Hf, is best represented by structure 15. It is noteworthy that the formation of fullerene ions from acetylenic 14 is observed in the negative ion mode, which is considered to be milder than the positive ion mode which was previously used to detect ionized carbon spheres. It thus appears that 14 is structurally predisposed for fullerene formation. However, attempts to perform the exhaustive decarbonylation on a macroscopic scale by irradiating dilute THF solutions of 14 with pulsed laser light did not lead to the formation of buckminsterfullerene C6o-... 

---