Au nanoparticles, stabilization

Figure 15.28 TEM images of (a) Au nanoparticle arrays in mesoporous silica film (b) superlattice of extracted Au nanoparticles stabilized with 1-dodecanethiol.

Fig. 9.2. High Resolution Transmission Electron Microscopic (HRTEM) image of Au nanoparticles stabilized by dodecanethiol ligand molecules after SMAD and digestive ripening procedure. (Reprinted from Stoeva, S. et al J. Phys. Chem. B, 2003,107,7441-7448, Fig. 11(c), by permission of the American Chemical Society, copyright 2002, American Chemical Society.)...

Liu, J.C., Anand, M. and Roberts, C.B. (2006) Synthesis and extraction of beta-D-glucose-stabilized Au nanoparticles processed into low-defect, wide-area thin-films and ordered arrays using CO2-expanded liquids. Langmuir, 22 (9), 3964-3971. 

Charged polysaccharides can also serve as templates for the growth of metallic, semiconductor and magnetic nanoparticles. For instance, chitosan has been reported as a catalyst and stabilizing agent in the production of gold nanoparticles by the reduction oftetrachloroauric (III) acid by acetic acid. The biopolymer controls the size and the distribution of the synthesized Au nanoparticles and allows the preparation... 

Three general preparative schemes are of particular interest due to their success in preparing nanoparticles on the order of 1 to 3 nm. The first, commonly known as the Brust method for preparing thiol stabilized Au nanoparticles, is discussed in detail in the chapter by Zhong et al. in Section IV of this book. The second method, which originates from Prof El-Sayed s group, is noteworthy for preparing particles with extremely well-defined shapes (tetrahedra, cubes, etc). ° The third method. 

An attempt to prepare PVP-stabilized Au/Pd bimetallic nanoparticles was made by the successive reduction procedure (40). When preparation of Au nanoparticles precedes the reduction of Pd ion, only mixtures of Pd and Au monometallic nanoparticles were produced. On the other hand, when the preparation of Pd nanoparticles precedes the reduction of Au ions, some bimetallic nanoparticles were found. However, the Au/Pd bimetallic nanoparticles thus obtained did not have a core/shell structure, although the bimetallic nanoparticles obtained by the coreduction have such a structure (Fig. 9.1.4). 

As mentioned above, the grafting to technique enables in a one-pot reaction the synthesis of Au NPs stabilized by sulfur-containing polymers, which bear functional groups such as dithioester, trithioester, thiol, thioether and disulfide at the end of a polymer chain or in the middle. This method leads to nanoparticles similar to those obtained by the Brust-Schiffrin method in which alkanethiol-protected Au NPs of small size are obtained. This grafting to technique leads to very stable nanomaterials that also present a high surface graft density of polymer brush on the Au NP surface. 

Polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (Pluronic) block copolymer is a very efficient reducing agent and nanoparticle stabilizer. Au NPs of about 10 nm can be stabilized with PEO-PPO-PEO block copolymer solutions in water and at room temperature and using HAuC14 as precursor. The formation of gold nanoparticles is controlled by the overall molecular weight and relative block length of the block copolymer [118]. 

Figure 10.5 Spherical ensembles of citrate-stabilized Au nanoparticles onto polymer-coated Si02 cores. Au/Si02 particle sizes (a) 40/330 nm (b) 60/460 nm (c) 80/550 nm. Scale = 200 nm.34 (Reprinted with permission from B. Sadtler and A. Wei, Chem. Commun. 2002, 1604-1605. Copyright the Royal Society of Chemistry.)...

Paraschiv et al. demonstrated a functionalized surface with locally isolated functional groups (Fig. 13.1).9 Au nanoparticles d 3 nm) stabilized with propanethiol and monofunctionalized with (mercaptopropyl)methyldimethoxysilane (MPMD) were first prepared by a place-exchange reaction. The Au nanoparticles were covalently assembled onto the surface via a single methyldimethoxysilane unit by reaction with Si-OH surface groups. AFM images revealed the attachment of Au nanoparticles... 

Similar polymer/Au nanoparticle multilayer thin films were made by Wu et al. in a study of pH-sensitive dissociation behavior of poly (3-thiophene acetic acid) (PTA A) and PAA in a LbL film (of 8 bilayers).50 Unlike the pure polymer LbL film, the Au nanoparticles-containing LbL films were difficult to be released from the substrate by varying the pH. It was suggested that the gold particles act as a cross-linker in between the multilayers, thus further enhancing the stability of the LbL films. 

In-situ synthesis of the clay stabilized Au nanoparticles was also carried out by dissolving 1.68 g of MgCl2-6H20 (8.26 mmol) in 20 mL of 3.8 mM solution of HAuCL followed by the addition of 2 mL of 3-aminopropyltrimethoxysilane. The yellow slurry obtained was stirred overnight at room temperature and then kept at 75 °C for 24 h. It slowly turned pink in colour due to the formation of gold nanoparticles by thermal reduction. The pink transparent film obtained was washed with ethanol and then dried again. 

Figure I. Optical absorption spectra of the structures including PVC (a) and PEPC (b) films pure polymer films (1), films with Ag and Au nanopaiticles (2), films with thiol-stabilized Ag and Au nanoparticles (3).

The proposed approach is a universal method that can be applied for successful fabrication of metal-clay nanocomposites with high thermal stability, high dispersity of metal nanoparticles inside the clay matrix and catalytic activity. This work provides original insights into the production of layered naiocomjwsites loaded with inorganic nanoparticles. The ultrasonic treatment accelerates the incorporation process. The Au nanoparticle /clay nanocomposites can be useful for creation of different devices such as nanocondenser systems, sensors, optoelectronic elements. 

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