Why Are Carbon Nanomaterials Favored by Researchers?

History of Development
As early as 1985, the discovery of fullerene with the “football” structure immediately attracted the world’s attention. Then, carbon nanotubes with a hollow cylindrical structure are formed based on mild modifications toward fullerenes. In 1991, Japanese researchers discovered carbon nanotubes in carbon fibers for the first time. In 2004, researchers discovered the 2D planar nanomaterial whose planar thickness is confined to the nanoscale range. At the same time, researchers also developed a practical “scotch tape” technique to separate single-layer graphene from bulk graphene. Buckyballs (fullerenes), carbon nanotubes, and graphene all belong to a large family of carbon allotropes. Meanwhile, their structural differences make these nano-allotropes exhibit diverse but unique properties and great application potential.

Carbon Nanomaterials Open Up New Opportunities

For nearly forty years, carbon nanomaterials, such as fullerenes (0D), carbon nanotubes (1D), carbon nanofibers (1D) and graphene (2D), have been speedily developed due to their unique electronic, optical, thermal, mechanical, and chemical nature. The development of these materials offers opportunities for researchers to achieve major accomplishments in basic and applied sciences as well as advancing disruptive technologies and applications. In fact, nearly every aspect of cutting-edge research areas has been explored utilizing carbon nanomaterials. To name a few, conductive polymers, transparent electrodes, chemical sensors, supercapacitors, clinical diagnostics and therapeutics, food analysis, water treatment and environmental remediation, high-frequency devices, photoelectric sensors, alternative energy and bio-inspired system, etc.

Electronics

As electronic devices shrink in size, the complementary metal–oxide–semiconductor (CMOS) technology that is conventionally used will reach its limited size soon. At the same time, carbon nanotubes (CNTs) are considered one of the most promising candidates for nanoelectronics applications due to their near-ballistic electron transportation capabilities, lack of surface dangling bonds, strong C–C covalent bonds, compatibility with high-k dielectrics, as well as band dependence vector of the gap on diameter and chirality. Furthermore, due to its nanoscale cross-section, electrons travel only along the tube axis, while electron transport involves quantum effects. Not to mention the active development of CNT thin film transistors (TFTs) by recent research groups. For instance, McCarthy et al. developed vertical CNT FETs that showed sufficient current output to drive OLEDs at low voltages, allowing OLEDs to emit red-green-blue lights through a transparent CNT network (DOI: 10.1126/science.1203052).

Diagnosis and Treatment

Although the clinical application of carbon nanomaterials is still an emerging field of research, substantial preclinical evidence demonstrates essential translational potential, e.g., improving drug delivery and imaging. Carbon nanofibers (CNFs), obtained by fabrication techniques such as electrospinning and carbonization, consist of longer lengths and larger hollow inner diameters (from 50 nm to over 400 nm) than CNTs. Due to their flexibility, biocompatibility, and electrical conductivity, CNFs have shown significant potency in neurological applications and in fabricating electrodes in biosensors for the detection of electrically active neurotransmitters.

Furthermore, nanodiamonds (NDs) represent a particularly interesting class of carbon nanomaterials with strong potential in clinical application usages as imaging agents or for nanomedicine drug delivery. For example, the small detonation nanodiamond (DND) with a truncated octahedral structure results in negatively charged or neutral (111) surfaces and neutral (110) surfaces and positively charged (100) surfaces and (100)/(111) edges that enhance imaging and drug delivery by NDs (DOI: 10.1002/adma.201802368).