One-dimensional nanomaterials

S. R. C. Vivekchand received his BSc degree from The American College. Madurai in 2001. He is a student of the integrated PhD programme of Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore and received his MS degree in 2004. He has worked primarily on material chemistry aspects of one-dimensional nanomaterials. 

We have developed the solvothermal synthesis as a convenient approach for controlling morphology, by which non-oxides nanomaterials, such as nanoparticles, one-dimensional nanomaterials and those with very special shapes have been fabricated, which include nano-metered tubes, rods, wires, balls, hollow spheres and peanut-like nanostructures, etc. 

Carbon nanotubes (lijima, 1991 Dresselhaus et al., 1996) are a specific type of one-dimensional nanomaterial that has sparked people s imaginations. A cover story in American Scientist magazine a few years ago noted that carbon nanotubes could be used to build a space cable connecting the Earth and moon. News from NASA indicates that, in the near future, spacecraft may be based solely on carbon material—powered by either fuel cells based on carbon materials or lithium-iron batteries based on nanomaterials. Carbon materials also were featured very prominently in the recent national nanotechnology initiative and were mentioned in the President s State of the Union address, in which he referred to carbon nanotubes as a thousand times stronger than steel. 

Despite of many advantages of DSSCs, still lower efficiency compared to commercialized inorganic solar cells is a challenging area. Recently, one-dimensional nanomaterials, such as nanorods, nanotubes and nanofibers, have been proposed to replace the nanoparticles in DSSCs because of their ability to improve the electron transport leading to enhanced electron collection efficiencies in DSSCs. 

Carbon nanotubes (CNTs) are one-dimensional nanomaterials with cylindrical structures consisting of sp carbon bonds [9]. It is believed that CNTs are ideal nanofillers due to its super mechanical [10], thermal [11, 12], and electrical properties. Two main commercial players for PNCs are multiwalled carbon nanotubes (MWCNTs) with a diameter range from 4 to 30 nm and single-walled carbon nanotubes (SWCNTs) with a diameter range from 0.4 to 2-3 nm. This section will follow the in-situ approaches to incorporate CNTs into PU elastomer, solvent-based and waterborne PU. 

Hao J, lian Y, Guan L, Yue D, Guo X, Zhao S, Zhao Y, Ibrahim K, Wang J, Qian H, Dong J, Yuan H, Xing G, Sun B. Supercritical synthesis and characterization of SWNT-based one dimensional nanomaterials. Nanoscale 2011 3 3103-8. 

Chen, Y., Li, C.R, Chen, H., Chen, Y. One-dimensional nanomaterials synthesized using high-energy ball milling and annealing process. Sci. Technol. Adv. Mater. 7, 839-846 (2006)... 

Among one dimensional nanomaterials, synthetic procedures, properties and applications of polymers have been extensively reported in a dedicated chapter of a recent review [89]. 

Over the last 2 decades, there has been an increasing interest in the development of one-dimensional nanomaterials, such as carbon nanotubes (Ounaies et al., 2003), bacterial nanofibers (Yano et al., 2005), silica nanotubes (Miyaji et al., 2003), and titanium dioxide nanotubes and nanowires (Yuan and Su, 2004). These new materials have relatively large specific surface areas and high aspect ratios hence, they are suitable for use as reinforcements, chemical probes, sensors, hydrogen storage, displays, and templates. One-dimension material/polymer nanocomposites allow us to take advantage of the extraordinary properties of one-dimension nanomaterials. 

In addition to structural and electronic properties that are explored in zero-dimensional materials, one-dimensional materials also exhibit rather interesting elastic properties. We shall begin this section with a brief review of elastic considerations regarding one-dimensional nanomaterials and afterward move onto structural and electronic properties. 

Due to the axial periodicity of one-dimensional nanomaterials, plane wave-based methods which are traditionally used for crystals are very often employed. In the work of Arantes and Fazzio (2007), where they study free and passivated Ge nanowires, the band gap of passivated and unpassivated nanowires were determined using a plane wave-based GGA-DFT method. The nanowires were grown in the (110) and (111) directions and their band gaps were calculated as a function of nanowire diameter. In spite of the well-known underestimation of the band gap by LDA and GGA methods, a trend can be obtained rather reliably. The band gaps are seen to vary with respect to direction and size. 

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