What Are Nanomaterials?

Nanomaterials are materials that have at least one external dimension, or an internal structure or surface feature, in the range of 1 to 100 nanometers. At these dimensions, materials exhibit optical, electrical, magnetic, mechanical, and catalytic properties that differ substantially from those of the same material in bulk form, because quantum confinement effects, surface energy, and the ratio of surface atoms to interior atoms all change dramatically as grain or particle size decreases toward the nanoscale. The study and engineering of nanomaterials form the physical basis for nanotechnology and underpin applications across electronics, energy, medicine, and environmental science.

The field draws on solid-state physics, chemistry, surface science, and materials engineering. The classification scheme most widely used groups nanomaterials by dimensionality: zero-dimensional (nanoparticles and quantum dots), one-dimensional (nanowires, nanotubes, and nanorods), two-dimensional (nanosheets and thin films), and bulk nanostructured materials. As reviewed in nanoparticle classification and physicochemical properties published in the Journal of Nanobiotechnology, each class exhibits distinct property-structure relationships that govern its suitability for specific applications.

Properties and Synthesis

The defining characteristic of nanomaterials is that a large fraction of their atoms reside at or near a surface, where bonding configurations, coordination numbers, and chemical reactivity differ from bulk atoms. This elevated surface-to-volume ratio accelerates catalytic reactions, increases solubility compared to the bulk material, and shifts absorption and emission spectra to energies that depend on particle size. Quantum confinement in semiconductor nanocrystals (quantum dots) produces discrete electronic energy levels whose spacing can be tuned by adjusting particle diameter, enabling wavelength-selectable fluorescent labels for biological imaging. Synthesis routes for nanomaterials divide into top-down methods, such as ball milling, laser ablation, and lithographic patterning, and bottom-up methods, such as chemical precipitation, hydrothermal synthesis, sol-gel processing, and chemical vapor deposition. The bottom-up routes generally produce narrower size distributions and better crystallinity, while top-down methods scale more readily to production volumes. NIST maintains an active nanofabrication and manufacturing research program that develops measurement standards and process benchmarks for nanomaterial synthesis and characterization.

Classification by Composition

Nanomaterials are also classified by chemical composition into three broad groups: carbon-based, inorganic, and organic. Carbon-based nanomaterials include fullerenes (spherical C60 and higher cages), carbon nanotubes (single-wall and multi-wall), graphene sheets, and carbon nanodots; their mechanical strength, electrical conductivity, and chemical stability make them useful as reinforcing agents, electrode materials, and drug carriers. Inorganic nanomaterials include metal nanoparticles (gold, silver, platinum), metal oxide nanoparticles (titanium dioxide, zinc oxide, iron oxide), and semiconductor nanocrystals; their optical, magnetic, and catalytic properties are tunable by size, shape, and surface chemistry. Organic nanomaterials such as liposomes, dendrimers, and polymeric nanoparticles are used primarily in drug delivery because their compositions can be tailored for biocompatibility and controlled release.

Nanopackaging

Nanopackaging applies nanomaterials to improve the performance of packaging materials, particularly in food safety, electronics, and pharmaceutical storage. Incorporating silver or zinc oxide nanoparticles into polymer films provides antimicrobial activity that extends shelf life without conventional preservatives. Nanoclay platelets and graphene oxide dispersed in a polymer matrix reduce oxygen and moisture permeability well below what the base polymer achieves alone. In electronics packaging, nanomaterial-filled thermal interface materials transfer heat away from semiconductor dies more effectively than conventional greases and pads. The Springer review of nanomaterials in food packaging applications examines the trade-offs between barrier performance, mechanical integrity, and safety considerations for consumer-facing nanocomposite packaging.

Applications

Nanomaterials have applications in a wide range of fields, including:

• Electronics and photonics, where quantum dots and nanowires enable displays, photodetectors, and transistors with engineered optical and electronic properties
• Energy storage and conversion, using nanostructured electrodes in lithium-ion batteries, supercapacitors, and solar cells to increase surface area and shorten ion diffusion paths
• Nanomedicine and drug delivery, where nanoparticles serve as carriers for targeted therapy and contrast agents for imaging
• Environmental remediation, where photocatalytic and adsorptive nanomaterials remove pollutants from water and air
• Structural materials, where carbon nanotubes and nanoclay reinforcements improve the strength-to-weight ratio of composites