Aqueous vanadium systems

Baes-Messmer diagram for the aqueous vanadium system. Standard redox potentials (in V) vs the normal hydrogen electrode (NHE) are given. The two parallel dashed lines running from the upper left to the lower right indicate the range of stability of water. Reproduced from C. F. Baes and R. E. Messmer, The Hydrolysis of Cations, pp. 197-210. Copyright (1976), with permission from John Wiley Sons, Ltd. 

Figure 7 presents the outdoor characteristics of the bipolar direct ohmic AlGaAs / Si/V +/ + photoelectrochemical cell under solar illumination. The system comprises the individual components illustrated in Fig. 5 and uses a HF containing aqueous vanadium electrolyte to improve photocurrent stability (0.35 M V(II)- -V(III), 4M HCl, 0.2 M HF). The photoelectrochemical characteristics of the cell were determined under 75-mW cm insolation. As shown under... 

The early research of RFB systems was mainly carried out in the United States and Japan. NASA built the first 1 kW true RFB system with an Fe/Cr redox couple in the 1970s [11]. In this system, an aqueous solution of ferric-ferrous is employed as the positive reactant redox couple, and the negative reactant is a solution of chromos-chromic couple, with hydrochloric acid as a supporting electrolyte in most cases. Because of the poor kinetics of the chromium redox reaction, a serious deterioration of RFBs was observed after a long period of time moreover, a relatively low open circuit potential was also obtained. These drawbacks limited its practical application. In the following years, several RFB systems were evaluated, but none of them was developed on a commercial scale until the bromine/polysulphide RFB and vanadium system was invented [4]. In this section, in addition to these two systems, we will also introduce new progress in tme RFB systems. 

Actual droplet formation is not necessary as long as the mobile phase can pass through the stationary phase without displacing it. As a matter of fact, both aqueous and nonaqueous biphasic systems have been used (51, 332). Recent results reveal that a variety of natural products such as saponins, saturated fatty acids, and biomacromolecules - the latter on a biphasic aqueous polymer system - can be separated (332). Because of its comparatively rapid and non-destructive action, CPC has recently been used in the isolation of the tunichromes, the rather sensitive phenolic peptides from the vanadium-collecting sea squirt Ascidia nigra (53, 54) and of W-cis- and trans-rciindA from a complex photoisomerization mixture (51). 

Kaliva M, Kyriakakis E, Gabriel C, Raptopoulou CP, Tarzis A, Tuchangues JP, Salifoglou A (2006) Synthesis isolation, spectroscopic and structural characterization of a new pH complex structural variant from the aqueous vanadium(V)-peroxy-citrate ternary system. Inorg Chim Acta 359 4535 548... 

Development of systems using vanadium(II) that fix nitrogen in an aqueous environment34... 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

In contrast Shilov and his group propose a very different mechanism (Scheme 20), which involves a bridging dinitrogen and four vanadium atoms, each acting as a one-electron reductant (contrasting to Schrau-zer s proposal that vanadium acts as a two-electron reductant). The hydrazine may then be reduced to ammonia. On theoretical grounds Shilov considers that dA metal ions would make the best dinitrogen reducers in these binuclear systems (44), and there is ample evidence to support the formulation of vanadium(II) dinuclear species in aqueous solution. However, Shilov postulates and finds vanadium(III) products, which Schrauzer ascribed to a conproportionation (289) as shown in Eq. (78). 

Andersson, I., S J. Angus-Dunne, O.W. Howarth, and L. Pettersson. 2000. Speciation in vanadium bioinorganic systems 6. Speciation study of aqueous peroxovanadates, including complexes with imidazole. J. Inorg. Biochem. 80 51-58. 

Elvingson, K., A.G. Baro, and L. Pettersson. 1996. Speciation in vanadium bioinorganic systems. 2. An NMR, ESR, and potentiometric study of the aqueous H+-vanadate-maltol system. Inorg. Chem. 35 3388-3393. 

Elvingson, K., M. Fritzsche, D. Rehder, and L. Pettersson. 1994. Speciation in vanadium bioinorganic systems. 1. A potentiometric and 51V NMR study of aqueous equilibria in the H+-vanadate(V)-L-a-alanyl-L-histidine system. Angew. Chem., Int. Ed. Engl. 48 878-885. 

Characteristics of biological systems, coupled with the rich chemistry of vanadium in aqueous solutions, make the study of effects of vanadium compounds in living systems difficult. The cell is divided into different organelles and vesicles by mem-... 

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