Nanostructures hydroxides

G.J.C. Carpenter, Z.S. Wronski, NanocrystaUine NiO and NiO-Ni(OH) composite powders prepared by thermal and mechanical dehydroxylation of nickel hydroxide, Nanostructured Mater. 11(1) (1999) 67-80. 

G. J. C. Carpenter, Z. S. Wronski, Nanocrystalline NiO and NiO-Ni(OH)2 Composite Powders prepared by Thermal and Mechanical Dehydroxylation of Nickel Hydroxide, Nanostructured Mater., 1999,... 

Since ceria exhibits a cubic fluorite crystal structure, the noncubic nanostructures, such as NRs, NWs, and nanoplates, are fabricated under experimental conditions that are suitable to break dovm the symmetry. One general way is to exploit an appropriate intermediate, such as Ce(OH)3 or Ce(OH)C03. The rare earth hydroxide crystalline NRs/NWs/ NTs are obtained in basic solutions imder hydrothermal treatment, which is discussed in Section 2.3. If certain oxidant is present in the hydrothermal treatment, the ceria NCs could be obtained in a one pot manner. In this way, rod-like, wire-like, or tube-like nanoceria could be synthesized. If the hydrothermal treatment is carried out under oxygen free... 

Guillou et al., 1997 Kleinlogel and Gauckler, 2000 Purohit et al., 2001 Trovarelli et al., 1997). The method by annealing of cerium hydroxides or cerium hydroxyl carbonates with special nanostructures is used to obtain ceria nanostructure, which has been discussed above. 

Dry methods and postcalcination methods The industrial micron sized R2O3 powder is commonly made by thermal pyrolysis of rare earth carbonates or oxalates at a temperature of 600-1000 °C. The dry methods usually result in fine powders with a relatively wide size distribution. After the sintering, the surface OH and other solvent related species are generally removed, therefore, the powder may exhibit better luminescence efficiency and longer decay time. Nano-sized rare earth oxide products could be obtained from finely selected precursors like hydroxides gels, premade nanostructures, through heat treatment, spray pyrolysis, combustion, and sol-gel processes. 

In addition to the hydroxides, the hydroxyl carbonates could be used as intermediates before calcination is carried out. The urea mediated hydrothermal methods could well lead to the production of these nanostructures of rare earth hydroxyl carbonates. Recent examples include the Y203 Eu hollow spheres (Jia et al., 2009). 

There are also other ways to obtain rare earth hydroxide nanocrystals. The formation of rare earth hydroxide needles or nanotubes was observed as a corrosion product with LaNis in KOH (Maurel et al., 2000). Fang and Xu et al. reported that with medium pH values, that is, near the precipitation pH value of rare earth hydroxides, the hydration of medium rare earth (Tb, Dy, Y) oxides with a hydrothermal treatment will lead to rare earth hydroxide nanotubes (Fang et al., 2003a Xu et al., 2003 Figure 25). Lee and Byeon reported the hydration of LaOCl for the synthesis of La(OH)3 nanostructures (Lee and Byeon, 2006). 

Properties and applications of rare earth hydroxide nanostructures... 

However, hydroxides proved to be applicable intermediate for preparing various nanocrystals of rare earth oxide, oxysulphide, oxyfluoride, and other rare earth compounds. In this route, the crystallized R(OH)s nanocrystals instead of gels were obtained and collected, later a next step is performed to convert the R(0H)3 nanocrystals into other compounds, without destroying the morphology. The obtained new nanocrystals may or may not have a certain crystal growth direction related to the precursor. A selection of typical works on the conversion of rare earth hydroxide nanostructures are listed in Table 1. 

Intercalation materials, in which different nanostructured components are attached to the porous matrix. This is the case of metal and metal oxide nanoparticles generated into zeolites and mesoporous silicates or organic polymers intercalated between laminar hydroxides. 

Cao, M., He, X., Chen,). and Hu, C. (2007) Self assembled nickel hydroxide three dimensional nanostructures A nanomaterial for alkaline rechargeable batteries. Crystal Growth Design, 7, 170-174. 

Also not new are the phenomena seen in nanostructures—all sol-gel (e.g.. Chapter 13 all aerogels are nanocrystalline ) and life chemistry is nanostruc-tural, and chemists long have been able to prepare molecular clusters and nanocrystalline powers by vaporization or, better, by decomposition of precursors (typically hydroxides, carbonates, nitrates, acetates, citrates, and so on). Even the recent production of biphasic or polyphasic nanostructures from polymers had been preceded by the decomposition of mixed crystals [e.g., CaMg(Co3)2, dolomite, to CaO and MgO]. Carbon and SiC fibers (Nicalon ) are nanostructural. In this book, nanocrystalline cobalt from 1966 is mentioned (Chapter 18). Naturally, the nanostructural works of chemists could not be directly examined before the advent of electron microscopes, but more indirect... 

Fei, J., Cui, Y., Zhao, J., Gao, L., Yang, Y., Li, J. Large-scale preparation of 3D self-assembled iron hydroxide and oxide hierarchical nanostructures and their applications for water treatment. J. Mater. Chem., 21, 11742—11746. 

Yuan, A. B., M. Zhou, X. L. Wang, Z. H. Sun, and Y. Q. Wang. 2008. Synthesis and characterization of nanostructured manganese dioxide used as positive electrode material for electrochemical capacitor with lithium hydroxide electrolyte. Chinese Journal of Chemistry 26 65-69. 

The generation of hydroxide ions induces a localised increase in the pH values close of the cathode where the Ztf + and OH ions react together leading to the precipitation of the ZnO nanostructures on the cathode via the following electrochemical reaction. ... 

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