Applications of Carbon Nanomaterials

Since the discovery of fullerenes in 1985, carbon nanotubes in 1991 and graphene in 2004, their unique properties have been exploited for technical, medical and environmental applications. Carbon-based nanomaterials can be combined with molecules via strong covalent bonds which yield kinetically stable compounds.

Typically, however, only pristine particles are used in studies on their impact on living organisms. This approach hardly reflects realistic natural conditions.

Physical

The unique physical properties of carbon nanomaterials enable them to be used as components in very sensitive sensor devices that can detect low concentrations of chemical compounds. Such sensors have a broad range of environmental applications. They can replace activated carbon (AC) in wastewater filtration, and they are also useful in agricultural processes.

Carbon nanotubes are tubes made of carbon with diameters in the nanometer range. They have superior mechanical strength and electrical conductivity. They can be single-walled or multi-walled. Single-walled ones can be zigzag or armchair-shaped. They can have surface functional groups that increase their chemical reactivity and add new properties. Based on their chiral vector, they can be metallic when n is equal to 1 and semiconducting when n is equal to 2 or 3. The morphology of carbon nanotubes determines their absorption spectra.

Chemical

Carbon nanomaterials exhibit remarkable chemical properties that can be exploited for a broad spectrum of applications. These materials have the potential to replace traditional activated carbon (AC) in wastewater filtration systems and as promising drug/gene delivery systems.

Carbon can exist in a number of molecular forms (allotropes) that differ in their properties. The most well-known are diamond and graphite.

Carbon nanomaterials can be tube-shaped, horn-shaped or spherical and are also referred to as fullerenes. The structure of a carbon nanomaterial determines its physicochemical characteristics, with the most important being solubility and surface chemistry. In addition, the morphology of a carbon nanomaterial can be modified by chemical functionalization. For example, by oxidation of carbon nanotubes, carboxylic groups can be introduced on their surfaces to enhance solubility.

Electrical

Carbon atoms can form three different allotropes that differ in their strength, electrical properties and other characteristics. Two of these allotropes, graphene and carbon nanotubes, are attracting great interest because they can be used to make incredibly strong, light, conductive materials.

The shapes of carbon nanoparticles determine their electrical properties. Particles that are tube-shaped are called carbon nanotubes, those that are horn-shaped are called nanohorns and those that are spherical or ellipsoidal belong to the group known as fullerenes.

Single-wall carbon nanotubes that are metallic have the highest electrical conductivity of any material. SWCNTs that are semi-conducting have lower conductivity than metallic ones. The chirality of the tubes also affects their conductivity.

Biomedical

Carbon nanomaterials such as fullerenes, graphene and carbon nanotubes exhibit unique mechanical, electrical, thermal and chemical properties that make them attractive candidates for many biomedical applications. These include drug delivery, tumor therapy, targeted bio-sensing, tissue engineering and cellular imaging.

A major challenge in the field of biomedical applications is the toxicity of carbon nanomaterials, which can be caused by the production and processing techniques as well as by their intentional or accidental release into natural and agricultural ecosystems.

To address this issue, the surface of carbon nanomaterials can be functionalized in order to increase their affinity for adsorbates. This can be achieved by adding ligands, polymers and other nanoparticles, which also improve their biocompatibility. In addition, the size of carbon nanomaterials can be adjusted to achieve desired target tissue accumulation.

Energy

Carbon nanomaterials – including nanohorns, nanofibers and the more popular carbon nanotubes have unique properties which have opened up new areas for research. They all share the sp2 hybridization of carbon atoms, a hexagonal pattern and high mechanical strength but their individual sizes, shapes and chirality distinguish them from one another.

The discovery of multi-wall and single-wall carbon nanotubes (MWNTs and SWNTs respectively) brought a new dimension to the field. They resemble a graphene sheet rolled into a tube and capped at both ends.

Carbon nanoparticles exhibit remarkable adsorption capabilities and can be employed in many different environmental applications. In particular, they are able to effectively remove and monitor pollutants in urban and agricultural ecosystems. They can also be used to detect and remove contaminants in food chains with potentially hazardous effects on living organisms.

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