Novel synthesis of carbon nanorings and their characterization
Graphical abstract
A novel route to the synthesis of amorphous carbon nanorings is reported for the first time using the carbonized structures of Pluronic P123 polymer within the mesoporous SBA-15. The diameter of the ring structures obtained were between 2 and 10 μm with a rim thickness of ∼50 nm.
Introduction
Nanostructured materials with ring-like morphology are expected to display unique features different from the rod, ribbon, wire or sphere-type structures [1], [2], [3], [4], [5], [6]. For example, carbon nanorings, a variant of carbon nanotubes are reported to show negative magnetoresistance at low temperatures [7]. Owing to their importance as nanoconstructs in the fabrication of nanodevices, attempts have been made to prepare materials with ring-like structures either by self-organization of smaller units or by using sacrificial templates. For example, organically passivated nanocrystals were organized into 2D ring structures by evaporation-assisted self-assembly method [8], [9], [10], [11], [12], [13], [14]. In a similar approach, porphyrin based molecules are assembled to form ring like superstructures under certain conditions [15], [16], [17]. Wang et al. observed the formation of ZnO nanorings by the spontaneous self-coiling of ZnO polar nanobelts during the high temperature growth process [18], [19]. The propensity to form ring and coil structures by the carbon nanotubes upon end-to-end functionalization and subsequent bundling by van der Waal’s interaction received much attention in recent years [1], [20], [21]. Although graphitic carbon nanotubes with ring and coil structures are known [22], their amorphous counterpart is so far not reported. In this article, we report for the first time the formation of amorphous carbon rings by the self-assembly of polymeric nanostructures of carbon generated inside the pores of mesostructured SBA-15 nanorods prepared within the pores of anodic alumina membranes.
Section snippets
Experimental
SBA-15 mesoporous silica rods were synthesized inside the porous anodic alumina membrane (AAM) using a literature procedure [23]. In a typical synthesis, 0.6 g of Pluronic P123 was dissolved in 1 ml of ethanol followed by the addition of 1 ml of tetraethoxyorthosilicate (TEOS) and 0.4 ml of 0.1 M HCl solution. An anodic alumina membrane (13 mm diameter, 60 μm thick with a uniform pore size of 200 nm, Whatman Anodisc 13) was soaked in the above sol for overnight. The membrane was dried after taking out
Results and discussion
In Fig. 1a, we show a FESEM image of a sample obtained (after 24 h acid treatment) to reveal rings of diameter ranging from 0.5 to 20 μm. The histogram in Fig. 1a inset shows a wide distribution of ring sizes with the maximum at 2 μm diameter. Rings of smaller diameter (<2 μm) are clearly seen in the higher magnification image. The bright circles manifested with the larger rings could be accounted for variation in the rim thickness. The smaller rings are exhibiting a smooth, but slightly tapered
Conclusion
In summary, amorphous carbon nanostructures have been organized to form rings at the liquid–liquid interface. These nanostructures were obtained by carbonizing the Pluronic P123 template of mesostructured SBA-15 confined in an anodic alumina membrane. These carbon nanorings can be used as versatile templates to make inorganic oxide and metal replica with hollow ring structures.
Acknowledgements
We thank Prof. C.N.R. Rao for valuable discussion and support in carrying out this work. We also thank Prof. Vikram Jayaram, Metallurgy department IISc, Bangalore for help with the EELS measurements.
References (23)
- et al.
Physica E
(2002) - et al.
Science
(2001) - et al.
Phys. Rev. Lett.
(2002) - et al.
Phys. Rev. B
(2001) - et al.
Phys. Rev. B
(2005) - et al.
J. Chem. Phys.
(2000) - et al.
Phys. Rev. B
(2000) - et al.
Phys. Rev. Lett.
(2000) - et al.
Langmuir
(1999) - et al.
J. Am. Chem. Soc.
(2002)