Interface complex metallic

Cowie M, McDonald R, Antonelli DM (1989) Interfaces in metal complex chemistry, International Symposium, Rennes, France, July 9-14, Abs. C 13... 

This illustrates that we are far from the point where we can develop robust and transferable semiempirical potentials for the general M/C interface. This task is fundamentally difficult because the bonding changes character at the interface, from metallic to ionic, and because of the structural complexity present. This probably requires explicit inclusion of quantum effects, at least at a low level. 

The various steps that characterize the transport of metal species through SLMs can be described with the help of Figure 31.4. Step 1 The metal species, after diffusing to the source-membrane interface, react with the metal carrier, ions are simultaneously released into the feed solution (counter-transport, acidic carrier) or ions accompany the metal ions into the membrane (cotransport, neutral, or basic carriers). Step 2 The metal-carrier complex diffuses across the membrane because its concentration gradient is negative. Step 3 At the membrane-receiver interface the metal-carrier complex releases metal ions into the aqueous phase, ions replace M ions into the membrane (counter-transport) or X ions are simultaneously released together with M ions into the strip solution (cotransport). Step 4 The uncomplexed carrier diffuses back across the membrane. 

Rubin, A. J., and D. L. Mi rci-r. 1981. Adsorption of free and complexed metals from solution by activated carbon. In Adsorption of inorganics at solid-liquid interfaces, ed M. A. Anderson and A. J. Rubin, pp. 295-325. Ann Arbor, Ml Ann Arbor Science. 

In the area of interfacial charging at the solid/liquid interface of metal oxide aqueous suspensions, the "surface complexation or site binding concept is commonly used [3-20]. This concept is characterised by consideration of specific ionic reactions with surface groups, rather than assuming simple binding of ions to the surface or their accumulation at the interface (adsorption). In the past decade several different models were introduced on the basis of the surface complexation model (SCM) they differ in the assumed structure of the electrical interfacial layer (EIL) and in the proposed mechanisms and stoichiometries of surface reactions leading to surface charge. 

Research on the metal speciation of the soil solution has been encouraged by the free metal ion hypothesis in environmental toxicology (Lund, 1990). This hypothesis states that the toxicity or bioavailability of a metal is related to the activity of the free aquo ion. This hypothesis is gaining popularity in studies of soil-plant relations (Parker et al., 1995). However, some evidence is now emerging that free metal ion hypothesis may not be valid in all situations (Tessier and Turner, 1995). Plant uptake of metals varies with the types of chelators present in solution at the same free metal activity. Furthermore, given the same chelate, total metal concentration in solution affects metal uptake by plants. Either kinetic limitations to dissociation of the complex or uptake of the intact complex could explain these observations (Laurie et al., 1991). The possible reactions of complexed metals at the soil-root interface and the potential uptake by plants of metal-organic complexes are depicted in Figure 1.8. 

The treated metal-bearing wastewater solution flows along the outside of several hoUow-fiber membranes. The particular ELM is pumped through the inside of the hoUow fibers (Fig. 8.4A). The diluent and the dissolved extractant (H L) fiUs the pores of the membrane support, while the stripping phase is dispersed further away from the interface. The metal ion to be extracted (M +) from the wastewater diffuses to the interface between the wastewater and the hoUow-fiber membrane. Here it reacts with the extractant and the metal-extractant complex, ML, is formed (Fig. 8.4B). To preserve the electroneutrality of the system, n of protons H " are transported into the treated wastewater. ML diffuses through the ELM matrix toward... 

For the DDQ-doped dodecathiophene/In diode a complex impedance analysis was performed (Figure 13.35). The two partly overlapping circles can be analyzed with an equivalent circuit model shown in the inset. Instead of pure capacitance, constant phase elements Q were used which are defined as Q = 1 /((ict))"C7) which represents the impedance of a pure capacitance for n=l. Impedance scans at different bias voltages, showed that the right-hand circle strongly depends on the bias voltage. It dominates at reverse bias and rapidly diminishes with increasing forward bias. This circle can thus be ascribed to the Schottky junction impedance. The left circle may be ascribed to the impedance of a resistive layer of about 30 nm thickness at the interface between metal and semiconductor. 

The most specific role of liquid-liquid interfaces that we found is a catalytic effect in the solvent extraction of metal ions and interfacial complexation kinetics. Shaking or stirring of a solvent-extraction system generates a wide interfacial area or a high specific interfacial area defined as the interfacial area divided by the bulk phase volume. Almost all extractants, and an auxiliary ligand in some cases, are more or less interfacially active, since they have both hydrophilic and hydrophobic groups. Interfacial adsorption of the extractant or an intermediate complex at the liquid liquid interface can very effectively facilitate the extraction rate. In this chapter, the catalytic role of the interface in metal complexation will be discussed. 

In this chapter, we have briefly reviewed the development of novel gold catalysts for WGS and PROX. These new catalysts are not those composed of gold and a pure oxide support. Instead, they usually contain relatively complex metal-support interfaces. These catalysts can be classified into three categories (1) a regular oxide support is modified by a metal oxide additive, followed by loading gold (2) a mixed... 

Fig. 1. Levels of complexity of a (liquid) metal interface (a) metal/ vacuum (b) metal surface with adsorbed molecules of solvent ...

It can be speculated that copper, and by analogy other trace metals, is retained in soluble forms and transported through the soil complexed by FA type organic molecules. However, at the soil root interface the metals may be transferred to small biochemical molecules of either plant or microbial origin. 

Corrosion Control. Sihca in water exposed to various metals leads to the formation of a surface less susceptible to corrosion. A likely explanation is the formation of metahosihcate complexes at the metal—water interface after an initial dismption of the metal oxide layer and formation of an active site. This modified surface is expected to be more resistant to subsequent corrosive action via lowered surface activity or reduced diffusion. 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

Electrolytic plating rates ate controUed by the current density at the metal—solution interface. The current distribution on a complex part is never uniform, and this can lead to large differences in plating rate and deposit thickness over the part surface. Uniform plating of blind holes, re-entrant cavities, and long projections is especiaUy difficult. 

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