Microwaves treatment

Sample Time of microwave treatment / min Content of ash (%) SBETfm g VT(ml-g 1) VM(ml-g 1) 

Note Vt is total pore volume and is the volume of the mesopore. 

The study has shown that under the protection of the nitrogen, activated carbons treated by microwave for five minutes, can increase the catalytic activity without obvious change in the surface area and the pore volume. Therefore, microwave treatment can avoid sintering of metal particles in special range of temperatures and it is possible to enhance the performance of catalysts. 

A lot of studies have shown that different treatment methods have different effect on the characters of activated carbons and finally on the performance of catalysts. The surface of activated carbon as supports should have different performances for different active components and different catalytic reactions. Therefore, the activated carbon as supports, proper treatment based on given catalytic reaction can 

The application of microwave (MW) irradiation as an energy source during hydrothermal treatment has been developed in recent years. The crystallinity degree reached is similar to that with hydrothermal treatment in conventional furnaces, but the solids show a smaller particle size and then a larger specific surface area. The process requires shorter periods of time, saving in energy consumption [119]. 

Electromagnetic radiations with wavelength between 1-100 cm (frequency between ca. 300 MHz and 300 GHz) are known as microwaves as laser beams, they are highly coherent and polarized. Those with a frequency of 2.45 GHz (wavelength 12.2 cm, 1.02 10 eV) [120] are used for commercial and chemical applications. Not all materials are sensitive to MW and thus the materials can be classified in conducting, insulators and absorbents [121], although very few materials are purely absorbents or insulators or fully MW-conducting. 

The main advantages of MW heating are [124] (i) higher heating rate, 

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The dielectric permittivity as a function of frequency may show resonance behavior in the case of gas molecules as studied in microwave spectroscopy (25) or more likely relaxation phenomena in soUds associated with the dissipative processes of polarization of molecules, be they nonpolar, dipolar, etc. There are exceptional circumstances of ferromagnetic resonance, electron magnetic resonance, or nmr. In most microwave treatments, the power dissipation or absorption process is described phenomenologically by equation 5, whatever the detailed molecular processes. 

From recent literature it is known that the disintegration of lignified cell walls can be achieved by steam explosion treatments resulting in solubilization of partially depolymerized hemicelluloses [91,92]. The application of this method on wheat bran yielded feruloylated GAX with different feruUc acid content [93]. Partly depolymerized water-soluble, acetylated AGX was obtained from spruce wood by employing microwave treatment [94]. 

Laboratory studies on the extraction of pectin from orange peels, pretreated in an electromagnetic field of hyper frequency, were carried out. The influence of intensity of microwave treatment (P ) and time on pectin yield and pectin quality was investigated. It was established that the increase of Pw and time lead to increase in the pectin yield with 180-240 % in comparison with the control. Apparently, the microwave treatment leads to a considerable increase in the soluble form of pectin, characterized by increase in the jelly strenght and in the polyuronic content. 

Intensity of microwave treatment K Time of microwave heating min Yield of pectin, g per 200 g fresh material AUAC, % DE, % Molecul mass Mv Huggins constant Kh Intrinsic viscosity hi dl.g- Gel. strength °TB... 

Static headspace may also be carried out by substituting the heating step by a microwave treatment. In this procedure the material is immersed in a solvent that is transparent to microwaves relative to the sample in order to impart most, if not all, of the microwave energy to the sample [208]. Another configuration of MAP gas-phase extraction relates to dynamic headspace sampling. 

Igarashi H, Sugimura H, Maruyama K, et al. Alteration of immunoreactivity by hydrated autoclaving, microwave treatment, and simple heating of paraffin-embedded tissue sections. APMIS 1994 102 295-307. 

Traditional Heck arylation of the corresponding ethyl vinyl ether afforded high yields with most of the aryl bromides investigated (Eq. 11.11). Under continuous singlemode microwave treatment the transformations were complete within 10-12 min [25], Heck reactions without solvent in a domestic microwave oven have been examined by Diaz-Ortiz [26]. The reactions were conducted in closed vessels with reported temperatures of 150 °C. A study was performed in which reactions performed with microwave irradiation were compared with oil-bath-heated reactions with identical reaction times and temperatures. The isolated yields tended to substantially favor the microwave-heated reactions (Eq. 11.12). 

Carbon nanotubes have been decorated with metal nanoparticies of Au, Ag, Pt, Pd and Co employing different procedures such as the click reaction [107], microwave treatment [106], electroless plating [108] and laser irradiation of mixtures of the individual components [109]. Pt-carbon nanotube hybrids have been used as catalysts for the conversion of nitrobenzene to aniline [110]. Tessonier et al. report that MWNTs covered with Pd nanoparticies on the interior walls can be employed for... 

Rodriguez-Soto, J., Wamke, R., and Rouse, R. (1997) Endogenous avidin-bind-ing activity in paraffin-embedded tissue revealed after microwave treatment. Appl. Immunohistochem. 5, 59-62. 

In order to accelerate sample preparation, new extraction methodologies such as accelerated solvent extraction (ASE) and MAE, based on the use of elevated temperature and pressure to heat the mixture sample-solvent, have been recently developed and applied for PAH extraction from meat [695] and vegetables [696-698]. Garda Falcon et al. [699] used microwave treatment with hexane to accelerate PAH extraction from freeze-dried foods. The fat extracted in this way underwent microwave assisted saponification with ethanolic KOH. Hernandez-Borges et al. [700] combined microwave-assisted hydrolysis and extraction to isolate organic pollutants from mussels, while... 

Malafaya, R. B., Elvira, C., Gallardo, A., San Roman, J., Reis, R. L. (2001). Rorous starch-based drug delivery systems processed by a microwave treatment. J. Biomater. Sci. Polym. Ed., 72(11), 1227-1241. 

Additionally, the microwave treatment during the crystallization process at high temperature may cause the metastable mesophase to collapse into the denser or amorphous phase in synthetic mixture as well as provide the favorable condition for the formation of silicalite-1. A summary of parameters obtained by nitrogen sorption is shown in Table 2. In Table 2, pore diameters of major peaks ( ) for sample II-IV are increased from 2.5 to 2.87 nm as extending the microwave irradiation. It implied that the additional space created in the mesoporous channels, as a consequence of the pore size enlargement, that is filled by extra water [16]. 

Ferreira, C. S., Amato Neto, V., Gakiya, E., Bezerra, R. C., and Rodriguez Alarcon, R. S. (2003). Microwave treatment of human milk to prevent transmission of Chagas disease. Rev. Inst. Med. Trop. Sao Paulo 45(1), 41-42. 

Bauer, M., Schilling, N., and Spanel-Borowski, K. 2001. Limitation of microwave treatment for double immunolabeling with antibodies of the same species and isotype. Histochem. Cell Biol. 116(3) 221-222. 

Henke, R.-P., and Ayhan, N. 1994. Enhancement of hybridization efficiency in interphase cytogenetics on paraffin-embedded tissue sections by microwave treatment. Analyt. Cell. Pathol. 6 319-325. 

Igarashi, H., Sugimura, H., Maruyama, K., Kitayama, Y., Ohta, I., Suzuki, M., Tanaka, M., Dobashi, Y., and Kino, I. 1994. Alteration of immunoreactivity by hydrated autoclaving, microwave treatment, and simple heating of paraffin-embedded tissue sections. APMIS 102 295-307. 

Paukert, T. and Z. Sirotek. 1993. A study of the microwave treatment of water samples from the Elbe River, Bohemia, Czech Republic. Chem. Geol. 107 133-144. 

Microwave-assisted extractions (MAE) can be performed in open (focused MAE) or closed (pressurized MAE) flasks. This technique is commonly used for extractions from complex and difficult sample matrices, replacing time- and solvent-intensive Soxhlet extractions or hydrodistillations.46 MAE is also widely applied to environmental samples, for example, for extracting polycyclic aromatic hydrocarbons (PAH) from soil, methylmercury from sediments, and trace metals and pesticide residues from plant material47 48 The use of microwave treatment instead of hydrodistillation offers a solvent-free separation technique essential oils are heated and dry-distilled 46... 

Microwave treatment is widely used to prepare various refractory inorganic compounds and materials (double oxides, nitrides, carbides, semiconductors, glasses, ceramics, etc.) [705], as well as in organic processes [706,707] pyrolysis, esterification, and condensation reactions. Microwave syntheses of coordination and organometallic compounds, discussed in this chapter, are presented in a relatively small number of papers in the available literature. As is seen, the use of microwaves in coordination chemistry began not long ago and, due to the highly limited number of results, these works can be considered as a careful pioneer experimentation, in order to establish the suitability of this technique for synthetic coordination chemistry. 

A large class of coordination compounds, metal chelates, is represented in relation to microwave treatment by a relatively small number of reported data, mainly p-diketonates. Thus, volatile copper) II) acetylacetonate was used for the preparation of copper thin films in Ar — H2 atmosphere at ambient temperature by microwave plasma-enhanced chemical vapor deposition (CVD) [735a]. The formed pure copper films with a resistance of 2 3 pS2 cm were deposited on Si substrates. It is noted that oxygen atoms were never detected in the deposited material since Cu — O intramolecular bonds are totally broken by microwave plasma-assisted decomposition of the copper complex. Another acetylacetonate, Zr(acac)4, was prepared from its hydrate Zr(acac)4 10H2O by microwave dehydration of the latter [726]. It is shown [704] that microwave treatment is an effective dehydration technique for various compounds and materials. Use of microwave irradiation in the synthesis of some transition metal phthalocyanines is reported in Sec. 5.1.1. Their relatives - porphyrins - were also obtained in this way [735b]. 

According to the opinion of the authors of Ref. 32, the negative results of the experiments above do not mean that metal-free Pc could not be theoretically obtained from these precursors additional detailed studies (combination of different techniques, such as UV irradiation, microwave treatment, use of other inert solvents, electrolysis in the systems producing free radicals, etc.) are required for successful resolution of this problem. However, under the same conditions it is possible to obtain some transition metal complexes of the Pc due to the template effects (see below). 

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