Dendrimer-encapsulated nanoparticles (DENs) are nanoparticles ranging from 1.5 to 10 nm that are synthesized by a template approach using

dendrimers Dendrimers are highly ordered, branched polymeric molecules. Synonymous terms for dendrimer include arborols and cascade molecules. Typically, dendrimers are symmetric about the core, and often adopt a spherical three-dimensional morphology. The ...

. Monometallic, bimetallic and semiconductor nanoparticles have been synthesized using this method. The primary use for DEN's is as a catalyst due to their extremely high surface area to volume ratio. Advantages that DENs have over other nanoparticles is that they are monodisperse and easy to make.

Synthesis

The first component in DEN synthesis is the

dendrimer Dendrimers are highly ordered, branched polymeric molecules. Synonymous terms for dendrimer include arborols and cascade molecules. Typically, dendrimers are symmetric about the core, and often adopt a spherical three-dimensional morphology. The ...

itself. By using different sizes, or generations, of

it is possible to control the size of the nanoparticle to be synthesized. Although there are many types of

, the most common is the poly(amidoamine) (PAMAM)

. These types of

are predominantly terminated with either amine or hydroxyl groups. The notation for these dendrimers are in the form of Gx-R, where x is generation of the

and R is the terminal group of the

(in most cases R= -OH or -NH₂) When metal ions are introduced to a

in aqueous solution they form a complex with the tertiary amines of the

notated as Gx-R(M^p+)_n, where M^p+ refers to the metal ions used and n refers to the average number of metal ions complexed within each

. After a complex has formed, a reducing agent such as

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applic ...

is introduced in a high molar excess and the metal ions are reduced to their zerovalent form and come together within the

to form the DEN notated as Gx-R(M_n) where M is the zerovalent metal used and n is the number of metal atoms.

Characterization

DENs can be characterized mainly by

ultraviolet–visible spectroscopy UV spectroscopy or UV–visible spectrophotometry (UV–Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relative ...

. The

charge-transfer complex In chemistry, a charge-transfer (CT) complex or electron-donor-acceptor complex describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic forc ...

that forms between the metal ions and the dendrimer exhibits a ligand-to-metal charge transfer, or LMCT, band in the UV-Vis spectrum, indicating that a complex has formed. The specific wavelength of occurrence for these LMCT peaks are different for each metal.

References

{{reflist Nanoparticles by surface chemistry