Nanopartides properties

Tab. 6.3. Effect of various deposition parameters on the CdSe nanopartides properties in...

The sol-gel process - either aqueous or nonaqueous - is one of the most important processes for the preparation of oxidic nanopartides. For silica particles, the sol-gel-based Stober process is definitely the most used wet chemical preparation route. Particularly, the mild reaction conditions combined with the excellent control over nanopartides properties malce it a universal method for the production of colloids for various applications. In recent years, the metal oxide routes have also become more and more sophisticated. Another reason for the attractiveness of the preparation route is the activity of the derived particles toward surface functionalization. Such modified particles can be easily incorporated into polymer matrices to obtain nanocomposites with extraordinary properties. 

Bimetallic nanoparticles, either as alloys or as core-shell structures, exhibit unique electronic, optical and catalytic properties compared to pure metallic nanopartides [24]. Cu-Ag alloy nanoparticles were obtained through the simultaneous reduction of copper and silver ions again in aqueous starch matrix. The optical properties of these alloy nanopartides vary with their composition, which is seen from the digital photographs in Fig. 8. The formation of alloy was confirmed by single SP maxima which varied depending on the composition of the alloy. 

Daniel, M.-C. and Astruc, D. (2004) Gold nanopartides assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology. Chemical Reviews, 104, 293-346. 

Several mixtures of hexanethiol capped gold nanopartides and triphenylene based discotic LCs have been studied. These mixtures display liquid crystal behavior (columnar mesophases) and an enhancement in the DC conductivity, due to the inclusion of gold nanoparticies into the matrix of the organic LC [70]. Other studies of mixtures of gold nanoparticies with mesogens indude a series of cholesteryl phenoxy alkanoates. The inclusion of the nanopartides does not change the inherent liquid crystal properties of the cholesteryl derivative but the mesophases are thermally stabilized [71]. 

Cseh, L. and Mehl, G.H. (2007) Structure-property relationships in nematic gold nanopartides. Journal of Materials Chemistry, 17, 311-315. 

Yonemura, H., Yanagita, M., Horiguchi, M., Nagamatsu, S. and Yamada, S. (2008) Characterization of mono- and multilayered films with Mn +-doped ZnS nanopartides and luminescence properties of the monolayered films prepared hy applying magnetic fields. Thin Solid Films, 516, 2432—2437. 

Haeiwa, T., Segawa, K. and Konishi, K. (2007) Magnetic properties of isolated Co nanopartides in Si02 capsule prepared with reversed micelle. Journal of Magnetism and Magnetic Materials,... 

Coskun, M., Korkmaz, M., Firat, T., Jaffari, G.H. and Shah, S.I. (2010) Synthesis of Si02 coated NiFe204 nanopartides and the effect of Si02 shell thickness on the magnetic properties. Journal of Applied Physics, 107 (9), 3. 

Cao, S.W., Zhu, Y.J., Cheng, G.F. and Huang, Y.H. (2009) ZnFe204 nanopartides microwave—hydrothermal ionic liquid synthesis and photocatalytic property over phenol. Journal of Hazardous materials, 171 (1—3), 431—435. 

Rivera Gil, P. et al. (2010) Correlating physico-chemical with toxicological properties of nanopartides the present and the future. ACS Nano, 4 (10), 5527-5531. 

Hydrothermal synthesis is a powerful method used for the fabrication of nanophase materials due to the relatively low temperature during synthesis, facile separation of nanopartides in the product, and ready availability of apparatus for such syntheses. Versatile physical and chemical properties of nanomaterials can be obtained with the use of this method that involves various techniques (e.g., control of reaction time, temperature and choice of oxidant and its concentration). Several extensive reviews are available that discuss the fundamental properties and applications of this method [2, 3]. These reviews cover the synthesis of nanomaterials with different pore textures, different types of composition [2, 4—6], and different dimensionalities in terms of morphology [6-8]. 

Studies on the use of hydrothermal, microwave-assisted, and reflux synthesis methods for the development and application of nanomaterials have been reviewed. An important aspect of the green synthesis of metallic nanopartides involves techniques that make use of biological materials such as plant extracts and microorganisms. The design of nanomaterials and control of their desired properties have been reviewed. The unique properties of manufactured nanomaterials offer many potential benefits. 

Sreeja, V. and Joy, P.A. (2007) Microwave—hydrothermal synthesis of (l-Fe. O nanopartides and their magnetic properties. Materials Research Bulletin, 42, 1570-1576. 

There are many published examples in which the coupling of two different materials leads to an increase in the photocatalytic activity. Many of them concern coupling and junctions between different nanopartides, considering also different topologies, like coupled and capped systems [72]. Tentative explanations based on possible heterojunction band profiles are given. However, in-depth analysis of the hetero junction band alignment, the physical structure of the junction, the role of (possible) interfadal traps and of spedfic catalytic properties of the material is still lacking. Some recently published models and concepts based on (nano)junction between different materials are briefly reviewed here. 

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