Liquid-Phase Nanoparticle Synthesis

For mixed metal oxides obtained from their hydroxide or carbonate precursors after calcination, it is generally difficult to determine whether the as-prepared precursor is a single-phase or multiphase solid solution [35]. Non-aqueous solvents appear superior for achieving two dissimilar metal oxides such as MM Oz or MM 04 precipitates such reactions cannot be carried out simultaneously in aqueous solution due to the large variations in pH necessary to induce precipitations [41,42]. Table 6.1 summarizes some of the nanoparticulate semiconducting metal oxides and mixed metal oxides prepared via co-precipitation techniques. The general procedure of achieving metal loaded nanoparticles on an oxide support is shown in Fig.6.5. 

I able 6.1 Summary of the reactions for the synthesis of oxides nanopartieJe by difTcrcnl methods 

CuE11tK UtKls SlmliiM Paxii jiUj iun CbdttliEij) iitjeiu PoK muii ComJilionsi ( C) Prod Hid M/.e (nm) Rd  

Bi Celyltrimelliylanimoniuin bromide PVA Polyvinyl alcohol CA Cilric Acid EG  

Ethy leiie Glycol PAA Polyacrylic acid G.AA Glacial Acetic Acid PT Propanelriol 

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The synthesis of Pd/ACF (0.42wt.% Pd) catalyst with monodispersed nanoparticles carried out at cuo = 3 is illustrated, as well as its catalytic performance in a liquid-phase hydrogenation of 1-hexyne in comparison with a traditional powdered Lindlar catalyst. 

Since nanoscale metal nanoparticles are applicable to a number of areas of technological importance, the nano-structured materials chemistry will occupy much attention of scientists. It is certain that controlling the primary structures of metal nanoparticles, that is, size, shape, crystal structure, composition, and phase-segregation manner is still most important, because these structures dominate the physical and chemical properties of metal nanoparticles. Now the liquid phase synthesis facilitates the precise control of the primary structures. 

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

In the specific case of silica nanoparticles-pH EMA hybrid materials, the synthesis relies on obtaining a fine dispersion of silica nanoparticles (with a mean diameter of 7nm) in HEMA monomers (liquid phase). When a homogeneous solution is obtained, a free radical initiator is added at a concentration based on the weight of the monomer mixture. After the initiator dissolution, the solution can be poured into molds or between two glass plates to obtain monoliths or uniform films, respectively, after being cured at temperatures around 60-85 °C for several hours. 

The concept of using colloids stabilized with chiral ligands was first applied by Bonnemann to hydrogenate ethyl pyruvate to ethyl lactate with Pt colloids. The nanoparticles were stabilized by the addition of dihydrocinchonidine salt (DHCin, HX) and were used in the liquid phase or adsorbed onto activated charcoal and silica [129, 130]. The molar ratio of platinum to dihydrocinchonidine, which ranged from 0.5 to 3.5 during the synthesis, determines the particle size from 1.5 to 4 nm and contributes to a slight decrease in activity (TOF = l s ). In an acetic acid/MeOH mixture and under a hydrogen pressure up to 100 bar, the (R)-ethyl lactate was obtained with optical yields of 75-80% (Scheme 9.11). 

We have proposed the method of synthesis of carbon nanostructures and composites on their base by arc discharge in the liquid phase. In this connection the work on production of ultradispersed metal powders by the electroerosion method [1-4] began in the eighties years and still continues today. Besides carbon nanostructures produced by evaporation of carbon electrodes in the liquid phase, there appears a possibility of producing metal-carbon composites by sublimation of metal in the carbon-containing liquid. In this case the metal nanoparticles form with carbon nanostructures on their surface. 

On the one hand, these complete and rapid one-step solid-state reactions are due to the pseudo-liquid phase properties of solid-state HPAs. On the other hand, suitable crystal water of HPAs is important to the synthesis of POM nanoparticles. The HPA precursors with about twenty crystal water molecules are the best candidate for the preparation of uniform nanoparticles as observed in the TEM images (Figure 1). HPAs with excessive or lacking crystal water could not become the appropriate precursor. 

Conventional methods of preparation of magnesium oxide yield products that have large and varied grain sizes and fairly low surface areas. The most popular method of nanoparticle synthesis has been via sol-gel processing. Other liquid-phase methods involve the use of hydrothermal synthesis, which has yielded rod, tube, and needle-shaped morphologies (Ding et al., 2001). Klabunde (2001) has reviewed the various synthetic methods. 

Some potential applications for TSILs have been briefly highlighted in Figs. 2.3-3 and 2.3-4. Many more examples can be found throughout this book. The reader interested in catalytic applications of TSILs is referred to Chapter 5, Section 5.3 for more details. Section 5.5 describes explicitly the role of task-specific ionic liquids as new liquid supports in combinatorial syntheses. This section also provides more details on the synthetic procedures leading to the specific functionalized ionic liquids that have turned out to be particularly suitable for this purpose. While Section 5.6 expands on the role of alkoxysilyl functionalized ionic liquids for surface modification in the preparation of supported ionic liquid phase (SILP) catalysts, Section 6.3 is devoted to the synthesis of nanoparticles and nanostructures in which TSILs often play a decisive role as templates or particle stabilizing agents. 

The synthesis of magnetic nanoparticles has been developed over 30 years. The raw materials have been used from metal to nonmetal and from gas to liquid phases. The most commonly used metal oxides are the Fe, Co, Mg, and Mn with their alloy compounds. In recent years, many experiments have been done on the control of shape, crystalline, and stable surfaces of magnetic nanoparticles. As mentioned earlier, the shape and orientation affect the chemical properties greatly. The most common way is coprecipitation, thermal synthesis, and microemulsion. The following section will focus on each of the techniques. 

The bottom-up technique refers to synthesis based on atom-by-atom or molecule-by-molecule arrangement in a controlled manner, which is regulated by thermodynamic means (Keck et al. 2008). The process takes place through controlled chemical reactions, either gas or liquid phase, resulting in nucleatiOT and growth of nanoparticles. Bottom-up techniques (like supercritical fluid antisolvent techniques, precipitation methods etc.) create heavily clustered masses of particles that do not break up on reconstitution (Shrivastava 2008 Mishra et al. 2010). 

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