Oxides nanomaterials

There is currently considerable interest in processing polymeric composite materials filled with nanosized rigid particles. This class of material called "nanocomposites" describes two-phase materials where one of the phases has at least one dimension lower than 100 nm [13]. Because the building blocks of nanocomposites are of nanoscale, they have an enormous interface area. Due to this there are a lot of interfaces between two intermixed phases compared to usual microcomposites. In addition to this, the mean distance between the particles is also smaller due to their small size which favors filler-filler interactions [14]. Nanomaterials not only include metallic, bimetallic and metal oxide but also polymeric nanoparticles as well as advanced materials like carbon nanotubes and dendrimers. However considering environmetal hazards, research has been focused on various means which form the basis of green nanotechnology. 

According to Ref. [12], template for synthesis of nanomaterials is defined as a central structure within which a network forms in such a way that removal of this template creates a filled cavity with morphological or stereochemical features related to those of the template. The template synthesis was applied for preparation of various nanostructures inside different three-dimensional nanoporous structures. Chemically, these materials are presented by polymers, metals, oxides, carbides and other substances. Synthetic methods include electrochemical deposition, electroless deposition, chemical polymerization, sol-gel deposition and chemical vapor deposition. These works were reviewed in Refs. [12,20]. An essential feature of this... 

Current density, which ranges from 2,000 to 300,000 Am 2, has been probed as an important operational variable for the sonoelectrodeposition process of massive metals [70], sonoelectrodeposition of oxide metals [80], sonoelectrosynthesis of gases [54] and also nanomaterials synthesis [96], where current density can affect crystal size in at least two opposing directions. A smaller size would be expected, on the basis of the small amount of material deposited at a lower current. On the other hand, lower current density allows more time for atomic diffusion processes to occur which can lead to larger crystal size. However, the former effect is dominant [85]. 

Landsiedel, R., Ma-Hock, L., Kroll, A., Hahn, D., Schnekenburger, J., Wiench, K., and Wohlleben, W. (2010) Testing metal-oxide nanomaterials for human safety. Advanced Materials, 22 (24), 2601-2627. 

Herzog, E. et al. (2009) Dispersion medium modulates oxidative stress response of human lung epithelial cells upon exposure to carbon nanomaterial samples. Toxicology and Applied Pharmacology, 236 (3), 276-281. 

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]. 

N anomaterials have been around for hundreds of years and are typically defined as particles of size ranging from 1 to 100 nm in at least one dimension. The inorganic nanomaterial catalysts discussed here are manganese oxides and titanium dioxide. Outside the scope of this chapter are polymers, pillared clays, coordination compounds, and inorganic-organic hybrid materials such as metal-organic frameworks. 

Nanomaterials can also be tuned for specific purposes through doping. Specifically, the effect of the presence of manganese oxides on photocatalysis involving primarily titanium dioxide will be considered in this section. Titanium dioxide is a well-known photocatalyst and will be considered separately. K-OMS-2, which has a cryptomelane structure, is illustrated in Figure 8.4. Not all the literature discussed in this section, however, involves OMS tunnel structure materials. For example, amorphous manganese oxide (AMO) is also discussed as a photocatalyst. Manganite (MnOOH) is also included in battery applications. 

This section covers environmental applications of nanomaterials insofar as they are directly applied to the pollutant of interest. The photocatalytic degradation of organic pollutants and remediation of polluted soils and water are discussed here. The high surface areas and photocatalytic activities of semiconductor nanomaterials have attracted many researchers. Semiconductor nanomaterials are commercially available, stable, and relatively nontoxic and cheap. Prominent examples that are discussed are metal oxides such as Ti02 and ZnO and a variety of Fe-based nanomaterials. 

Metal ions or their oxides were combined with Ti02 nanomaterials in order to improve the catalytic activity and selectivity of the Ti02 photocatalysts. Ag-doped Ti02 was used to degrade gaseous sulfur compounds [158], Ag nanoparticle-doped Ti02... 

Rodriguez J.A. and Fernandez-Garcia,M. (2007) Synthesis, Properties, and Applications of Oxide Nanomaterials, John Wiley Sons, Inc., Hoboken, NJ. 

As mentioned earlier, biological systems have developed optimized strategies to design materials with elaborate nanostructures [6]. A straightforward approach to obtaining nanoparticles with controlled size and organization should therefore rely on so-called biomimetic syntheses where one aims to reproduce in vitro the natural processes of biomineralization. In this context, a first possibility is to extract and analyze the biological (macro)-molecules that are involved in these processes and to use them as templates for the formation of the same materials. Such an approach has been widely developed for calcium carbonate biomimetic synthesis [13]. In the case of oxide nanomaterials, the most studied system so far is the silica shell formed by diatoms [14]. 

The material is presented in 17 chapters, covering topics such as trends in ion selective electrodes, advances in electrochemical immunosensors, modem glucose biosensors for diabetes management, biosensors based on nanomaterials (e.g. nanotubes or nanocrystals), biosensors for nitric oxide and superoxide, or biosensors for pesticides. 

Nakagawa, K. et al., Oxidized diamond as a simultaneous production medium of carbon nanomaterials and hydrogen for fuel cell, Chem. Mater., 15, 4571, 2003. 

Prior to functionalization the carbon nanomaterials were washed in concentrated nitric acid (65% Fisher Scientific) for 8 h using a Soxhlet device in order to remove catalyst residues of the nanomaterial synthesis as well as to create anchor sites (surface oxides) for the Co on the surface of the nanomaterials. After acid treatment the feedstock was treated overnight with a sodium hydrogen carbonate solution (Gruessing) for neutralization reasons. For the functionalization of the support media with cobalt particles, a wet impregnation technique was applied. For this purpose 10 g of the respective nanomaterial and 10 g of cobalt(II)-nitrate hexahydrate (Co(N03)2-6 H20, Fluka) were suspended in ethanol (11) and stirred for 24 h. Thereafter, the suspension was filtered via a water jet pump and finally entirely dried using a high-vacuum pump (5 mbar). 

The book focuses on three main themes catalyst preparation and activation, reaction mechanism, and process-related topics. A panel of expert contributors discusses synthesis of catalysts, carbon nanomaterials, nitric oxide calcinations, the influence of carbon, catalytic performance issues, chelating agents, and Cu and alkali promoters. They also explore Co/silica catalysts, thermodynamic control, the Two Alpha model, co-feeding experiments, internal diffusion limitations. Fe-LTFT selectivity, and the effect of co-fed water. Lastly, the book examines cross-flow filtration, kinetic studies, reduction of CO emissions, syncrude, and low-temperature water-gas shift. 

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