Shape-selected nanoparticles

The arrows in the figure indicate the hydrogen desorphon peaks for the different facets. The shape-selected nanoparticles show very pronoimced peaks compared to the carbon-supported... 

TEM studies were performed in order to reveal changes in the shape of the shape-selected nanoparticles upon cycling (Figure 10.6). These still confirmed a large number of... 

FIGURE 10.5 Change in the CV response of shape-selected nanoparticles upon repeated cycling between —0.3 V and 1.25 V vs. RHE. 

FIGURE 10.6 TEM images of the shape-selected nanoparticles after accelerated aging by cycling to high potentials. 

The intention of this chapter is to provide a general survey on the preparative methodologies for the size- and shape-selective synthesis of metallic nanoparticles that have emerged from the benches of chemical basic research during the last few decades and become established as practical standard protocols. Industrial scale-up, however, has only just started to test the economic viability of these procedures and to determine whether they can meet the challenges of a number of very specific applications. The commercial manufacture of such thermodynamically extremely unstable nanoparticles in defined sizes and shapes on the kilo-scale is still confronted by a number of major problems and it remains to be seen how these can be solved. 

Figure 3. Several strategies on controlling the shape of nanoparticles (a) organic molecules or polymers as capping agents, (b) inorganic molecules as face-selective catalysts, and (c) inorganic molecules as face-selective etchants.

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

Size and Shape Selective Synthesis of Metal Nanoparticles by Seed-Mediated Method and the Catalytic Activity of Growing Microelectrodes (GME) and Fully Grown Microelectrodes (FGME)... 

Size and Shape Selective Synthesis of Metal Nanoparticles... 

In conclusion, we can say that the synthesis of metal nanoparticles and tuning of their sizes is achievable through seed-mediated synthetic route. Again, this method helped us to obtain shape selective evolution of... 

Starch-mediated shape-selective synthesis of Au nanoparticles with tunable longitudinal plasmon resonance. Langmuir, 20, 3520-3524. 

Zeolites are widely used as acid catalysts, especially in the petrochemical industry. Zeolites have several attractive properties such as high surface area, adjustable pore size, hydrophilicity, acidity, and high thermal and chemical stability. In order to fully benefit from the unique sorption and shape-selectivity effects in zeolite micropores in absence of diffusion limitation, the diffusion path length inside the zeolite particle should be very short, such as, e.g., in zeolite nanocrystals. An advantageous pore architecture for catalytic conversion consists of short micropores connected by meso- or macropore network [1]. Reported mesoporous materials obtained from zeolite precursor units as building blocks present a better thermal and hydrothermal stability but also a higher acidity when compared with amorphous mesoporous analogues [2-6]. Alternative approaches to introduce microporosity in walls of mesoporous materials are zeolitization of the walls under hydrothermal conditions and zeolite synthesis in the presence of carbon nanoparticles as templates to create mesopores inside the zeolite bodies [7,8]. 

This kind of selective nanoparticle assembly, combined with e-beam lithography — which offers (i) nanoscale resolution, (ii) flexibility in any pattern shape and (iii) integral control over the location of the features — represents a new methodology for patterning complex nanostructures from nanoparticles on surfaces, as relevant, for example, to biosensors, electronics and optical devices. 

Fig. 2.15 Shape selective synthesis of Pt nanoparticles using PVP as the capping agent.

Size- and Shape-selective Preparation of Metal Nanoparticles in the Zerovalent Form 255... 

---