PAMAM dendrimers particle diameter

Immobilizing DENs within a sol-gel matrix is another potential method for preparing new supported catalysts. PAMAM and PPI dendrimers can be added to sol-gel preparations of silicas " and zinc arsenates to template mesopores. In one early report, the dendrimer bound Cu + ions were added to sol-gel silica and calcined to yield supported copper oxide nanoparticles. Sol-gel chemistry can also be used to prepare titania supported Pd, Au, and Pd-Au nanoparticle catalysts. Aqueous solutions of Pd and Au DENs were added to titanium isopropoxide to coprecipitate the DENs with Ti02. Activation at 500°C resulted in particles approximately 4 nm in diameter. In this preparation, the PAMAM dendrimers served two roles, templating both nanoparticles and the pores of the titania support. 

PAMAM dendrimers are large (G4 is 4.5 nm in diameter) and have a hydrophilic interior and exterior accordingly, they are soluble in many convenient solvents (water, alcohols, and some polar organic solvents). Importantly, the interior void spaces are large enough to accommodate nanoscopic guests, such as metal clusters, and are sufficiently monodispersed in size so as to ensure fairly uniform particle size and shape. As we will show later, the space between the ter-... 

Abstract We review the preparation, characterization, and properties of dendrimer-templated bimetallic nanoparticles. Polyamidoamine (PAMAM) dendrimers can be used to template and stabilize a wide variety of mono- and bimetallic nanoparticles. Depending on the specific requirements of the metal system, a variety of synthetic methodologies are available for preparing nanoparticles with diameters on the order of 1-3 nm with narrow particle size distributions. The resulting dendrimer-encapsulated nanoparticles, or DENs, have been physically characterized with electron microscopy techniques, as well as UV-visible and X-ray photoelectron spectroscopies. 

The results obtained from the analysis of TEM measurements show that the functionalization of the amino groups with carbohydrate chains leads to nanoparticles with narrower size distribution and smaller mean particle diameter than for PEI (Figs. 7 and 8). In this case, the resulting particle sizes are comparable to the ones obtained with PAMAM dendrimers [89,91,92]. 

More recently. Oh and coworkers" developed PAMAM dendrimers with both primary amines and quaternary ammonium groups at the dendrimer periphery, in an attempt to facilitate templating of Au precursors within the dendrimer. Upon reduction by NaBH4, gold nanoparticles on the order of 1 to 2 nm were formed for DMNs containing between 55 and 300 Au atoms. Utilizing this polycationic dendrimer precursor results in the formation of gold particles with smaller and more controlled particle diameters than those previously reported. - Just as in the case of Pt, however, more work needs to be performed to elucidate the mechanism of Au nanoparticle formation. 

---