Assisted hydrothermal oxidation

D. S. Ross, I. Jayaweera, D. Bomberger, On-site Disposal of Hazardous Waste via Assisted Hydrothermal Oxidation, Rev. High Pressure Sci. Technol., 7, 1386-1388 (1998). 

Shiju NR, Guliants W. Microwave-assisted hydrothermal synthesis of monophasic Mo-Y-Te-Nb-O mixed oxide catalyst for the selective ammoxidation of propane. Chem-PhysChem. 2007 8(11) 1615-1617. 

Microwave-assisted hydrothermal synthesis is a novel powder processing technology for the production of a variety of ceramic oxides and metal powders under closed-system conditions. Komameni et al. developed this hydrothermal process into which microwaves are introduced. " This closed-system technology not... 

Even more, for layered second-row transition metal oxides it was possible to obtain binder-free, nanobelt-Mo03/G film electrodes by using microwave-assisted hydrothermal methods. Irrespective of the large molecular weight of the oxide, the gravimetric capacity could reach 291 mA h at 100 mA g with retention of ca. 60% after 100 cycles [142]. An exciting achievement was also the flexible properties of the electrode that could finally lead to new applications in bendable batteries or the origami concept [143]. 

TiCl4 in oxygen [11], hydrolysis of titanium alkoxides in different conditions [12], photo-assisted sol-gel method from titanium tetrabutoxide [13], hydrothermal oxidation of metallic titanium powder [14], hydrothermal hydrolysis of titanium tetraethoxide [15], oxysulfate [16,17] and tetrabutylammonium [18], solvothermal synthesis from titanium butoxide in 2-butanol [19], crystallization of amorphous Ti02 in hydrothermal condition [20], vapor hydrolysis of titanium tetraisopropox-ide [21], destabilization of titanium lactate [22], decomposition of titania-hydrate [23], epoxide sol-gel process to aerogel of Ti02 [24], hydrolysis of aqueous solution of TiCl4 in the presence of polyethyleneglycol [25], and so forth. 

Marques et al. [49] used hydrothermal oxidation in HNO3 at elevated pressure (0.5 MPa) and temperature (120-200°C) to functionalize SWCNTs and to control both the type and amount of surface functional groups. Their results showed that the degree of surface functionalization is correlated with the HNO3 concentration by a first-order exponential function. Lebron-Colon et al. [53] used dye-assisted photo-oxidation to functionalize SWCNTs. Their stndy revealed that photo-oxidized SWCNT contain np to 40% more oxygen (11.3 at.%) bound to the tnbe snrface (chemisorption), as compared to H2S04-treated samples (6.7 at.%), primarily in the form of carboxylic, carboxylate, and ester groups. 

Grabowska et al. (2008) prepared a composite oxide ZnAl O by microwave-assisted hydrothermal treatment of a precursor mixture of lydroxides obtained by precipitation of aluminum and zinc nitrates. Various studies show that ZnAl O is nanosized and is a micro/mesoporous material with large a suifaee area (140 mVg). The gas phase catalytic methylation of 4-hydroxypyridine in the presence of the ZnAljO catalyst was performed in a continuous process at atmospherie pressure in the temperature range of 240-360 °C. A mixture of O- and N-alkylated products, namely 4-methoxypyridine and N-methyl-4-pyridone were obtained. The alkylation of 4-hydroxypyridine with methanol at 345 °C offered 87.6% selectivity towards N-methyl-4-pyiidone with about 89% 4-methoxypyridine conversioa... 

Iron oxide nanoparticles supported on almninosilicate catalysts were found to be efficient and easily recoverable materials in the aqueous selective oxidation of alcohols to their corresponding carbonyl compoimds using hydrogen peroxide under both conventional as well as microwave heating (Rajabi et al., 2013). A new and versatile approach to synthesize SnO nanociystals (ratile-type stmcture) using microwave-assisted hydrothermal method was reported by Mendes et al. (2012). They observed that there are substantial changes in optical absorbance of tin (IV) oxide nanoparticles. 

Various methods have been used to synthesize metal oxide nanopartides. The methods discussed here indude hydrothermal alteration, reflux, and microwave-assisted methods. 

Over the past few years, a large number of experimental approaches have been successfully used as routes to synthesize nanorods or nanowires based on titania, such as combining sol-gel processing with electrophoretic deposition,152 spin-on process,153 sol-gel template method,154-157 metalorganic chemical vapor deposition,158-159 anodic oxidative hydrolysis,160 sonochemical synthesis,161 inverse microemulsion method,162 molten salt-assisted and pyrolysis routes163 and hydrothermal synthesis.163-171 We will discuss more in detail the latter preparation, because the advantage of this technique is that nanorods can be obtained in relatively large amounts. 

The hydrothermal route has been used for synthesizing nanotubes and related structures of a variety of other inorganic materials as well. Thus, nanotubes of several metal oxides (eg., SiO, V2O5, ZnO ) have been produced hydrothermally. Nanotubes of oxides such as VJO, are also conveniently prepared from a suitable metal oxide precursor in the presence of an organic amine or a surfactant. Surfactant-assisted synthesis of CdSe and CdS nanotubes has been reported. Here the metal oxide reacts with the sulfidizing/selenidizing agent in the presence of a surfactant such as TritonX. ... 

In summary, self-organized transition metal oxide nanostructures were successfully synthesised by means of hydrothermal methods. In particular, the microwave-assisted method provides a fast and reliable technique to produce reasonable amounts of material. The nanosized morphology of the materials can influence the reaction behaviour so that higher capacities can be reached (TiOj) than in the bulk or metastable phases can be stabilised (LiCoOj). 

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