Dendrimer-encapsulated nanoparticle

Figure 21.1 A-Structure of the host PAPAM dendrimer. B-Fabrication procedure for metal-dendrimer nanocomposites. C- Pd and Pt dendrimer encapsulated nanoparticles prepared by displacement reactions [66]. D, E -External and internal dendrimer nanocomposite topologies, respectively [70,77],...

The possibility of using electrostatic charge attraction has been exploited in the preparation of gold dendrimer encapsulated nanoparticles (DENs), which under appropriate conditions can be fully distributed along the surface of monodispersed MWCNTs (Fig. 3.21) [103]. 

Debye—Waller, 161 decomposition, 236 degree of alloying, 315 dehydro-condensation, 140 dehydrocyclyzation, 139 dendrimer, 2, 91, 94, 96,97, 98,99,100,101, 102, 103,105,108, no dendrimer encapsulated nanoparticles, 94 dendrimer-assisted method, 2, 3... 

Using an approach similar to that discussed previously, Pd nanoparticles were prepared within amine-terminated PAMAM dendrimers. To prevent coordination of Pd + to the primary amine groups of the dendrimers, the solution pH was adjusted to around 2, which preferentially protonates the exterior amines to a greater extent than the interior tertiary amines. Accordingly, Pd + binds preferentially to the interior tertiary amines and upon reduction Pd particles form only within the dendrimer interior. G4-NH2 dendrimer-encapsulated nanoparticles can then be quantitatively transported from an aqueous phase into toluene by addition of 10-20% of dodecanoic acid to the organic phase (Fig. 21) [19]. This transition is readily visualized by the color change the brown aqueous solution of Pd nanoparticles becomes clear after addition of the acid, while the toluene layer turns brown. Our studies have shown that this is a consequence of... 

Indeed, recent results from our laboratory indicate that dendrimer-encapsulated CdS QDs can be prepared by either of two methods [192]. The first approach is analogous to the methodology described earlier for preparing dendrimer-encapsulated metal particles. First, Cd and S salts are added to an aqueous or methanolic PAMAM dendrimer solution. This yields a mixture of intradendrimer (templated) and interdendrimer particles. The smaller, dendrimer-encapsulated nanoparticles may then be separated via size-selective photo etching [193], dendrimer modification and extraction into a nonpolar phase [19], or by washing with solvent in which the dendrimer-encapsulated particles are preferentially soluble. An alternative, higher-yield method relies on sequential addition of very small aliquots of Cd + and S " to alcoholic dendrimer solutions. 

Because the dendrimer-encapsulated nanoparticles are so small, they do not have the properties of bulk metals. Therefore, it is not possible to calculate the reduction potential for the exchange reactions from tabulated literature data... 

We are developing a new method for preparing heterogeneous catalysts utilizing polyamidoamine (PAMAM) dendrimers to template metal nanoparticles. (1) In this study, generation 4 PAMAM dendrimers were used to template Pt or Au Dendrimer Encapsulated Nanoparticles (DENs) in solution. For Au nanoparticles prepared by this route, particle sizes and distributions are particularly small and narrow, with average sizes of 1.3 + 0.3 nm.(2) For Pt DENs, particle sizes were around 2 nm.(3) The DENs were deposited onto silica and Degussa P-25 titania, and conditions for dendrimer removal were examined. 

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. 

Crooks, R. M., Zhao, M., Sun, L., Chechik, V., Yeung, L. K., and Lemon, B. I., Dendrimer-encapsulated nanoparticles Synthesis, characterization, and applications to catalysis, private communication. 

Scott RW1, Wilson OM, Crooks RM (2005) Synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles. 1 Phys Chem B 109 692-704... 

Synthesis and Characterization of Dendrimer Encapsulated Nanoparticles 11JJ... 

Scheme 11.2 Dendrimer-encapsulated nanoparticle synthesis (Reprinted with permission from reference [112]...

In this specific case, the colloid stabilizers are dendrimers, for instance, polyamidoamine (PAMAM), which are hyperbranched polymers that ramify from a single core and form a porous sphere [103, 104] (Scheme 17.1). Dendrimer-encapsulated nanoparticles (DENs) are synthesized by sequestering metal ions within appropriate dendrimers, and then by chemically reducing the resulting composite. They can be synthesized in various media, such as water or ethanol. The size of the nanoparticles is usually nearly monodisperse, and can be tuned by varying the metal-to-dendrimer ratio prior to reduction. Supported catalysts can then he prepared by immobilizing DENs onto a sohd support. As in the case of colloids, the last step, which consists in the removal of dendrimers hy thermal treatment, may lead to an increase in both the metal-particle size and particle-size distribution. 

H. Lang, R.A. May, B.L. Iverson, B.D. Chandler, Dendrimer-Encapsulated Nanoparticle Precursors to Supported Platinum Catalysts, Journal of the American Chemical Society 125, 14832, 2003. 

R.W.J. Scott, O.M. Wilson, R.M. Crooks, Synthesis, Characterization, and Applications of Dendrimer-Encapsulated Nanoparticles, Journal of Physical Chemistry B 109, 692, 2005. 

L.W. Beakley, S.E. Yost, R. Cheng, B.D. Chandler, Nanocomposite Catalysts Dendrimer Encapsulated Nanoparticles Immobihzed in Sol-Gel Silica, Applied Catalysis A General 292, 124, 2005. 

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