Cobalt oxide nanoparticles

In contrast with the Schiff base salen, salicylaldehyde oxime (79) (salox) complexes of Co have received comparatively little attention, but a series of bis-bidentate divalent complexes of the form iraiis-Co(sa 1 ox)2( D M SO)2 have been reported.343 The heterocyclic bidentate oxime violurate (lH,3H-pyrimidine-2,4,5,6-tetrone 5-oximate, Hvi) (80) and its /V-methyl (mvi) and /V,/V -dimethyl (dmvi) derivatives form high-spin divalent [Co(vi)]+ and Co(vi)2 complexes, whereas [Co(vi)3] is low spin.344 The mixed-ligand Co(dmvi)2(phen) complex is also low spin. The crystal structure of m-Co(pxo)2Br2 (pxo = 2-acetylpyridine-l-oxide oxime) is isostructural with the Ni11 relative.345 The dichloro complex also adopts a cis configuration. The tridentate dioximes 2,6-diformyl-4-methylphenol dioxime and 2,6-diacetyl-4-methylphenol dioxime (Hdampo) form binuclear complexes of the type (81a) and (81b) respectively.346 Cobalt oxide nanoparticles were prepared by... 

Figure 1. SEM images of different electrodeposited metal oxide nanoparticles Ti02 nanotube arrays grown on Ti substrate(a) cobalt oxide nanoparticles onto glassy carbon electrode (b) nickel oxide nanoparticles(c) and zinc oxide nanoparticles Reproduced from references [ 138],[ 102],[ 137] and [135] with permission from Elsevier.

Figure 33. (A) CV response of GC electrode modified with CoOx Nanoparticles in pH 12 solutions at v = 20 mVs 1 (B) SEM image of the electrodeposited CoOx on GC electrode. Reprinted from Analytica Chimica Acta, 594, A. Salimi, R. Hallaj, H. Mamkhezri, S. Soltanian, Nanomolar detection of hydrogen peroxide on glassy carbon electrode modified with electrodeposited cobalt oxide nanoparticles,26,Copyrights(2007) and J. Electroanalytical Chemistry, 619-620, A. Salimi, R.Hallaj, H. MamKhezri, S.M.T. Hosaini, Electrochemical properties and electrocatalytic activity of FAD immobilized onto cobalt oxide nanoparticles Application to nitrite detection,33, Copyrights (2008) with permission from Elsevier.

However, the application of cobalt- oxide nanomaterials for immobilization of biomolecelus and biosensor fabrication is rare. Recently we used electrodeposited cobalt-oxide nanoparticles for immobilization of hemoglobin [67], The UV-visible spectrophotometric analysis and voltammetric studied indicates the immobilization of Hb onto cobalt-oxide nanoparticles (Figure 35). 

Figure 35. UV-visible spectra of catalase in PBS (pH 7) phosphate buffer solution (curve A) and Hb-CoOx film on ITO electrode (curveB).(B) CVs of glassy carbon electrode modified with cobalt oxide nanoparticles (a) and Glassy carbon electrode modified with cobalt oxide nanoparticles and Hb (b), electrolyte is PBS (pH7), scan rate is 100 mVs Reprinted from Biophysical Chemistry, 62, A.Salimi, R. Hallaj, S. Soltanian, Immobilization of hemoglobin on electrodeposited cobalt-oxide nanoparticles Direct voltammetry and electrocatalytic activity,124,125, Copyrights(2007) with permission from Elsevier.

Similar to other proteins and enzymes containing the heme group, the immobilized hemoglobin onto cobalt-oxide nanoparticles have ability to electrocatalytic reduction of H202 and 02 based on the following equations ... 

Due to high biocompability and large surface are of cobalt oxide nanoparticles it can be used for immobilization of other biomolecules. Flavin adenine FAD is a flavoprotein coenzyme that plays an important biological role in many oxidoreductase processes and biochemical reactions. The immobilized FAD onto different electrode surfaces provides a basis for fabrication of sensors, biosensors, enzymatic reactors and biomedical devices. The electrocatalytic oxidation of NADH on the surface of graphite electrode modified with immobilization of FAD was investigated [276], Recently we used cyclic voltammetry as simple technique for cobalt-oxide nanoparticles formation and immobilization flavin adenine dinucleotide (FAD) [277], Repeated cyclic voltammograms of GC/ CoOx nanoparticles modified electrode in buffer solution containing FAD is shown in Fig.37A. 

A similar electrochemistry can be observed for CoZSM-5 materials in contact with 0.10 M HCl, as depicted in Figure 8.23. The as-synthesized material incorporates Co + centers into the framework of ZSM-5 zeolite, displaying a sharp reduction peak at -e0.40 V vs. AgCl/Ag. Upon calcination and steam activation, extra-framework cobalt ions and cobalt oxide nanoparticles are formed, yielding signals at -e0.20 and -0.50 V. Similar features were obtained in phosphate buffer, as shown in Figure 8.24. Here, cobalt oxide species show a prominent reduction peak due to the reductive dissolution of cobalt oxide forms. 

Ito, T., Zhting, Q., Stuto, F. Synthesis of perovskite-type lanthanum cobalt oxide nanoparticles by metins of mechanochemical treatment. Powder Technol. 143-144, 170-173 (2004)... 

In situ structural studies can also provide considerable insight into material properties and formation pathways. Koziej and co-workers have employed X-ray absorption spectroscopy (XAS) and diffraction for this purpose and have studied the formation of cobalt and cobalt oxide nanoparticles from a benzyl alcohol route.Here, the importance of the reaction temperature on the reactivity of the cobalt isopropoxide starting material with benzyl alcohol was noted. The first report of cobalt nanoparticles from a benzyl alcohol route via the reduction of Co " was established for reaction temperatures of 180 °C. Meanwhile, lower reaction temperatures (80 °C) lead to oxidation and afford cubic C03O4 nanoparticles. The in situ studies have been carried out on samples prepared at 140 °C in an effort to understand the mechanism behind such a complex reaction scheme. It was found that at this temperature both processes occur simultaneously reduction to Co° and oxidation to C03O4, followed by reduction to CoO. Studying the assembly of nanoparticles in detail can also provide an insight into how these processes could be potentially manipulated. 

Athar T, et al. Wet synthesis of monodisperse cobalt oxide nanoparticles. J Sohd State Chem (submitted). 

Ahmed J, Yuan Y, Zhou L, Kim S (2012) Carbon supported cobalt oxide nanoparticles-iron phthalocyanine as alternative cathode catalyst for oxygen reduction in microbial fuel cells. J Power Sources 208 170-175... 

Ionic liquid assisted vanadium pentoxide, zinc oxide and cobalt oxide nanoparticles... 

Figure 2.3 Illustration of an asymmetric silica nanocoil catalyzed with a cubic cobalt oxide nanoparticle. Note the edges of a marquise-like cross-section.

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