nanomaterials

Nanomaterials are materials with structural features at the nanoscale, typically 1 to 100 nanometers, in at least one dimension. At this scale, many materials exhibit properties that differ from their bulk counterparts due to quantum effects and a high surface-area-to-volume ratio. These properties can include enhanced strength, altered electronic and optical behavior, and increased chemical reactivity, which can be tailored by controlling size, shape, composition, and surface chemistry.

Common forms include nanoparticles (0D), nanorods and nanotubes (1D), nanosheets (2D), and quantum dots; nanocomposites combine nanoscale structures with a surrounding matrix. Synthesis methods are broadly categorized as top-down approaches, which start from bulk materials and reduce their size by milling or lithography, and bottom-up approaches, which assemble atoms or molecules into nanoscale structures via chemical routes, self-assembly, or crystallization. Typical techniques include chemical vapor deposition, sol-gel processing, precipitation, hydrothermal synthesis, and electrodeposition.

Applications span electronics and optoelectronics, energy storage and conversion, catalysis, environmental remediation, sensors, coatings, and biomedicine (drug delivery, imaging).

Characterization relies on electron microscopy (TEM, SEM), atomic force microscopy, X-ray diffraction, spectroscopy, and surface-area measurements (BET).

Safety and regulation: nanomaterials may pose unique health and environmental risks due to their size and reactivity; risk assessment and appropriate handling are active areas of regulation and guidance. Life-cycle analysis and "safe by design" strategies are increasingly emphasized to minimize adverse impacts.

Challenges include reproducibility, scalable manufacturing, cost, standardization of definitions and measurement, and incomplete toxicology data.