Oxides colloids

Manganese ions enzyme activators, 6,578 probes, 6,563 RNA polymerases activation, 6, 585 transport microbes, 6, 569 plants, 6, 572 Manganese oxide colloidal... 

A strategy to solve this problem is to separate the core formation process from the reduction of metal ions in the cores as shown in Scheme 1, and use solvent (EG) and simple ions (OH , etc.) as the stabilizers [11]. In the first step of this process, metal salts hydrolyzed in the alkaline solution of EG to give rise to metal hydroxide or oxide colloids, which were then reduced by EG at elevated temperature to produce colloidal metal nanoclusters in the... 

Xin and co-workers modified the alkaline EG synthesis method by heating the metal hydroxides or oxides colloidal particles in EG or EG/water mixture in the presence of carbon supports, for preparing various metal and alloy nanoclusters supported on carbon [20-24]. It was found that the ratio of water to EG in the reaction media was a key factor influencing the average size and size distribution of metal nanoparticles supported on the carbon supports. As shown in Table 2, in the preparation of multiwalled carbon nanotube-supported Pt catalysts... 

Generally, the absence of water favors the formation of stable metal nanocluster colloids, while its presence favors the formation of metal hydroxide or oxide colloids in the... 

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

X., Tohji, K., Jeyadevan, B., Shinoda,K., Ogawa, T., Arai, T., Hihara,T., and Sumiyama, K. (2002) Size- and shape-controls and electronic functions of nanometer-scale semiconductors and oxides. Colloids and Surfaces A Physicochemical and Engineering Aspects, 202 (2-3), 291-296. 

Nechaev, E. A., Nikolenko, N. V. (1986). Adsorption of chloride complexes of gold(III) on iron-oxides. Colloid Journal of the USSR, 48(6), 992-996. 

Simple electrolyte ions like Cl, Na+, SO , Mg2+ and Ca2+ destabilize the iron(Hl) oxide colloids by compressing the electric double layer, i.e., by balancing the surface charge of the hematite with "counter ions" in the diffuse part of the double... 

Other quite different assemblies can be formed, e.g., colloidal silica, metal oxides, colloidal metals, etc. They have many properties that are reminiscent of micelles, while also having specific features of their own. These systems will not be discussed. 

Oxide hydrosols synthesis relies on the destabilization of a true solution by a pH change. In order to prepare palladium oxide colloidal particles, two experimental routes can be carried out the neutralization of an acidic (basic) solution by an alkaline (acidic) solution, or thermohydrolysis of the palladium precursor solution. 

The formation of palladium oxide colloidal particles from an acidic palladium nitrate solution can be achieved by addition of an alkaline solution. The different steps, describing the chemistry involved in such a process are ... 

HRTEM images of surfactant-stabilized PtRuOsIr oxide colloids at different magnification, (Reprinted with permission from M. T. Reetz et al.. Journal of Physical Chemistry B, 107, 7414 (2003). Copyright 2007, American Chemical Society.)... 

Harvey, D.T. Linton, R.W. (1984) X-ray photoelectron spectroscopy (XPS) of adsorbed zinc on amorphous hydrous ferric oxide. Colloids Surfaces 11 81-96... 

Colloids. Colloids include particles with hydrophobic, hydrophilic and intermediate forms with a size range 1 - 400 nm. Both organic (including macromolecules) and inorganic (hydrolyzed silica and metal oxides) colloids occur in the marine environment (Sigleo and Helz, 1981). Their surfaces often contain suitable sites for interactions with trace metals (adsorption, complexation). In the marine environment all particles have a negative surface charge (Neihof and Loeb, 1972 Hunter and Liss, 1982). Increase of the electrolyte concentration decreases the stability of the colloidal particles. As a result the... 

Kretzschmar R., and H. Sticher. 1997. Transport of humic-coated iron oxide colloids in a sandy soil Influence of Ca2+ and trace metals. Environmental Science Technology 31 3497-3504. 

Equation 17.26 is directly involved in DOM photomineralization, and Equation 17.25 yields Fe2+. Complexation of Fe(III) by organic ligands is in competition with the precipitation of ferric oxide colloids [79], and the formation of ferrous iron on photolysis of Fe(III)-carboxylate complexes is an important factor in defining the bioavailability of iron in aquatic systems. Iron bioavailabihty, minimal for the oxides and maximal for Fe2+, is considerably enhanced by the formation of Fe(III)-organic complexes and their subsequent photolysis. Iron bioavailabihty plays a key role in phytoplankton productivity in oceans [80-82], while that of freshwater is mainly controlled by nitrogen and phosphoms. 

Finally, our recent research work has demonstrated that hazardous compounds can be formed in the presence of the nitrating agent N02, arising from nitrate photolysis or nitrite oxidation [88-91], and the chlorinating Cl2 " [92], Formation of the latter from OH and CD can only take place in acidic solution, but chloride oxidation is, for instance, possible upon charge-transfer processes in the presence of irradiated Fe(III) oxide colloids (represented as =Fe3+—OH in Equation 17.32) [93],... 

As far as chloride is concerned, we have found that it enhances the photodegradation of carbamazepine (an antiepileptic drug that is found at elevated concentration in surface waters) by Fe(III) oxide colloids at pH >5 [93], Under more acidic conditions the elevated efficiency of "OH photoproduction by Fe(III) monomeric species, stable at acidic pH, and the scavenging of "OH by chloride would cause CT to inhibit photodegradation. In contrast, at neutral to basic pH the Fe(III) oxide colloids would photooxidize chloride to Cl2" faster than they directly degrade carbamazepine, and further reaction between Cl2" and carbamazepine would account for the enhancement of the degradation rate by chloride. Additionally, chloride is not able to scavenge OH in neutral to basic solution. 

The described enhancement of carbamazepine photodegradation by Fe(III) oxide colloids could take place in deltas and estuaries, and our laboratory data suggest that the photochemical consequences of the chloride build-up could more than compensate the decrease of iron, due to colloid coagulation and sedimentation, which is usually observed in these environments. Interestingly, carbamazepine photodegradation on interaction between Fe(III) oxide colloids and chloride was more important than DOM-sensitized photolysis or direct photolysis, which are usually major photodegradation pathways for organic pollutants in surface waters [93]. 

Metal oxide colloids have been effectively coupled with multifunctional ligands containing carboxyl groups that bind to the surface of nanoparticles [46]. One can rationally design optimal photocatalysts by tailoring functional groups for selective adsorption of specific... 

Surface doping of oxide colloids and nanostructured electrodes with transition metal ions and complexes is of great interest for improving efficiency and selectivity of photocatalysts and photoelectrodes. Such surface ions as electron donors or acceptors play an important role as catalytic active centers, in charge transfer and in adsorption. There were many publications on this subject and we will try to bring forward the most... 

EPR studies of metal-doped Ti02 and other oxide colloids were used for structural and functional characterization of such materials. This information is spread in many original articles, and was partially collected in [21, 220-222]. Various paramagnetic ions such as Mo5+, W5+, Cr5+, Nb4+, Ta4+, Mn4+, Mn3+, Cr3+, Fe3+, Ce3+, Al3+, Pt3+, Ni3+, Ni2+, Ni+, Co2+, Cu2+, etc., were used as spin dopants. As in the previous paragraph, Table 8.9 contents the spin-Hamittonian parameters of metal centers in Ti02 (rutile - R, anatase - A, brookite - B), and the same data concerning other wide bandgap semiconductor oxides are collected in Table 8.10. 

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