PROPERTIES OF NANO MATERIALS�LECTURE 2��Nano Chemistry

CHM- 504

BS Chemistry�

Nano Materials

• Commission recommendation definition of nano material
• “A natural, manufactured material containing particles in an unbound state or as an aggregate or as an agglomerate and where for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm – 100 nm”

1 nm = 10 ^-9 m

• 1 nm is approximately the length equivalent to 10 H atoms or 5 si atoms aligned in a line.

Classification of Nanomaterials

Nanomaterials as those which have structured components with at least one dimension less than 100nm.

• One dimension in nanoscale (Other two dimensions are extended)

Thin films

• Surface Coatings
• Computer chips
• Two dimensions in nanoscale (Other one dimension is extended)
• Nanowires
• Nanotubes
• Three dimensions in nanoscale
• Nanoparticles
• Precipitates
• Colloids
• Quantum dots (tiny particles of semiconductor material)

Schematic types of Nano particles

Quantum Dots

• QDs are the class of materials in which quantum confinement effects can be evidenced.
• They are very small semiconductor crystals on the order of nanometer size, containing merely a hundred to a thousand atoms. 

Properties of Nano materials

• The peculiar properties of Nano materials deviate from single crystal or poly crystals (Bulk)
• The unique properties of these intentionally produced Nano materials give them novel mechanical, thermal, electrical, magnetic, optical and catalytic features that are highly desirable for applications in commercial, medical and environmental sector.
• Large number of functional groups can be introduced on these materials or they can be fabricated on other materials to achieve specific properties.
• The physical and chemical properties of material depends on both the size and shape of the microscopic constituent particles.

• When the size and shape of Nano materials change the inter atomic distance between the atoms or ions change.
• This change in inter atomic distance is responsible for change in many properties.
• When inter atomic spacing is reduce in many cases: 1- the motion of electron is restricted. Free electrons tend to localize in Nano crystallites (nc) of metals.
• 2- the magnitude, direction and type of inter atomic interactions also change that may become more repulsive or strongly attracted to each other.

Two principal factors cause the properties of nanomaterials to differ significantly from Bulk materials:

​

• Increased relative surface area

​

• Quantum effects: These factors can change or enhance properties such as reactivity, strength and electrical characteristics.

Surface Effects

• As a particle decreases in size, a greater proportion of atoms are found at the surface compared to those inside.

​

• Nanoparticles are more reactive than large particles (Catalyst).

Quantum Effects

Quantum confinement

• The quantum confinement effect can be observed once the diameter of the particle is of the same magnitude as the wavelength of the electron Wave function.
• Quantum confinement is responsible for the increase of energy difference between energy states and band gap. A phenomenon tightly related with the optical and electronic properties of the materials.
• When materials are this small, their electronic and optical properties deviate substantially from those of bulk materials.

Scale at which Quantum Effects Dominate Properties of Materials�

• When particle size is made to be nanoscale, properties such as melting point, fluorescence, electrical conductivity, magnetic permeability, and chemical reactivity change as a function of the size of the particle.

Physical Properties

• Size, shape, specific surface area, aspect ratio
• Agglomeration/aggregation state
• Size distribution
• Surface morphology/topography
• Structure, including crystallinity and defect structure
• Solubility

​

Chemical Properties

• Structural formula/molecular structure
• Composition of nanomaterial (including degree of purity, known impurities or additives)
• Phase identity
• Surface chemistry (composition, charge, tension, reactive sites, physical structure, photocatalytic properties, zeta potential)
• Hydrophilicity/lipophilicity

​

Nanoscale Gold Particles

• Nanoscale gold particles are not the yellow color.
• Nanoscale gold can appear red or purple.
• At the nanoscale, the motion of the gold’s electrons is confined. Because this movement is restricted, gold nanoparticles react differently with light compared to larger-scale gold particles.
• Their size and optical properties can be put to practical use: nanoscale gold particles selectively accumulate in tumors, where they can enable both precise imaging and targeted laser destruction of the tumor by means that avoid harming healthy cells.

Crystal structures of Nano material

• Small Nano particles or Nano dimension layer may adopt a different crystal structure from that of the normal bulk material.
• Some metals which normally have hexagonal close packing of atoms (bulks) have been reported to adopt a face-centered cubic structure in Nano sizing.

​

Y₂O₃ (cubic in bulk) mono clinic (NC)

ZrO₂ (monoclinic) tetragonal (NC)

​

KEY IDEAS

The properties of Nano material are different from their bulk counterpart.

• The difference in properties is due to their change in physical properties i.e.
• The number of surface atom increases.
• The inter atomic spacing changes.
• The inter particle interaction changes.
• They have wide applications in many fields of sciences i.e. physics, chemistry, biology, medicine, engineering and environment etc..

References

• G.B. Sergeev. 2006. Nanochemistry. Elsevier. 1^st Ed. Netherland.
• A. I. Kirkland. and J. I. Hutchison, 2007. Nanocharacterisation. The Royal Society of Chemistry. U.K.
• R. E. Hester and R. M. Harrison, 2007. Nanotechnology: Consequences for Human Health and the Environment. The Royal Society of Chemistry. U.K

�