Metal-oxide water interface

Vasudevan, D. Dorley, P.J. Zhuang, X. (2001) Adsorption of hydroxy pyridines and quinolines at the metal oxide-water interface Role of tautomeric equilibrium. Environ. Sci. 

Brown Jr., G.E., Parks, G.A., Bargar, J.R., and Towle, S.E., Use of X-ray absorption spectroscopy to study reaction mechanisms at metal oxide-water interfaces, in Mineral-Water Interfacial Reactions Kinetics and Mechanisms, in Sparks, D.L. and Grundl, T.J., Eds., American Chemical Society, Columbus, OH, 1998, p.14. 

Interfacial phenomena at metal oxide/water interfaces are fundamental to various phenomena in ceramic suspensions, such as dispersion, coagulation, coating, and viscous flow. The behavior of suspensions depends in large part on the electrical forces acting between particles, which in turn are affected directly by surface electrochemical reactions. Therefore, this chapter first reviews fundamental concepts and knowledge pertaining to electrochemical processes at metal oxide powder (ceramic powder)/aqueous solution interfaces. Colloidal stability and powder dispersion and packing are then discussed in terms of surface electrochemical properties and the particle-particle interaction in a ceramic suspension. Finally, several recent examples of colloid interfacial methods applied to the fabrication of advanced ceramic composites are introduced. 

Use of X-ray Absorption Spectroscopy To Study Reaction Mechanisms at Metal Oxide-Water Interfaces... 

Davis, J.A. and Leckie, J.O., Surface ionization and complexation at the oxide/water interface, II surface properties of amorphous iron oxyhydroxide and adsorption of metal ions, J. Colloid Interface Sci. 67, 90-107, 1978. 

Oxide-water interfaces, in silica polymer-metal ion solutions, 22 460—461 Oxidimetric method, 25 145 Oxidization devices, 10 77-96 catalytic oxidization, 10 78—96 thermal oxidation, 20 77-78 Oxidized mercury, 23 181 Oxidized polyacrylonitrile fiber (OPF), 23 384... 

In surface precipitation cations (or anions) which adsorb to the surface of a mineral may form at high surface coverage a precipitate of the cation (anion) with the constituent ions of the mineral. Fig. 6.9 shows schematically the surface precipitation of a cation M2+ to hydrous ferric oxide. This model, suggested by Farley et al. (1985), allows for a continuum between surface complex formation and bulk solution precipitation of the sorbing ion, i.e., as the cation is complexed at the surface, a new hydroxide surface is formed. In the model cations at the solid (oxide) water interface are treated as surface species, while those not in contact with the solution phase are treated as solid species forming a solid solution (see Appendix 6.2). The formation of a solid solution implies isomorphic substitution. At low sorbate cation concentrations, surface complexation is the dominant mechanism. As the sorbate concentration increases, the surface complex concentration and the mole fraction of the surface precipitate both increase until the surface sites become saturated. Surface precipitation then becomes the dominant "sorption" (= metal ion incorporation) mechanism. As bulk solution precipitation is approached, the mol fraction of the surface precipitate becomes large. 

Davis, J. A., and J. O. Leckie (1978a), "Surface Ionization and Complexation at the Oxide/Water Interface. II. Surface Properties of Amorphous Iron Oxyhydroxide and Adsorption of Metal Ions," J. Colloid Interface Sci. 67, 90-107. 

Chemical relaxation methods can be used to determine mechanisms of reactions of ions at the mineral/water interface. In this paper, a review of chemical relaxation studies of adsorption/desorption kinetics of inorganic ions at the metal oxide/aqueous interface is presented. Plausible mechanisms based on the triple layer surface complexation model are discussed. Relaxation kinetic studies of the intercalation/ deintercalation of organic and inorganic ions in layered, cage-structured, and channel-structured minerals are also reviewed. In the intercalation studies, plausible mechanisms based on ion-exchange and adsorption/desorption reactions are presented steric and chemical properties of the solute and interlayered compounds are shown to influence the reaction rates. We also discuss the elementary reaction steps which are important in the stereoselective and reactive properties of interlayered compounds. 

Electron transfer reactions of metal ion complexes in homogeneous solution are understood in considerable detail, in part because spectroscopic methods and other techniques can be used to monitor reactant, intermediate, and product concentrations. Unfavorable characteristics of oxide/water interfaces often restrict or complicate the application of these techniques as a result, fewer direct measurements have been made at oxide/water interfaces. Available evidence indicates that metal ion complexes and metal oxide surface sites share many chemical characteristics, but differ in several important respects. These similarities and differences are used in the following discussions to construct a molecular description of reductive dissolution reactions. 

R.O. James, T.W. Healy, Adsorption of hydrolyzable metal ions at the oxide — water interface. II. Charge reversal of Si02 and Ti02 colloids by adsorbed Co(II), La(III), and Th(IV) as model systems, J. Colloid Interface Sd. 40 (1972) 53-64. 

In systems containing two or more adsorbates, either competitive or synergistic effects may operate. The commonest synergistic effect is that of ternary adsorption (11.5.4). Competitive behaviour may involve competition for the same surface sites, indirect effects due to the change in the electrostatic properties of the oxide/water interface and in some cases, formation of non sorbing, metal-ligand complexes in solution. 

Jambor, J.L. Dutrizac, J.E. (1998) Occurrence and constitution of natural and synthetic fer-rihydrite, a widespread iron oxyhydroxide. Chem. Rev. 98 2549-2585 James, R.O. ElealyT.W. (1972) Adsorption of hydrolyzable metal ions at the oxide-water interface. Ill A thermodynamic model of adsorption. J. Colloid Interface Sci. 40 65-81 James, R.O. Parks, G.A. (1982) Characterization of aqueous colloids by their electrical double layer and intrinsic surface chemical properties. Surface Colloid Sci. 12 119-126... 

Vasudevan, D., and A. T. Stone, Adsorption of catechols, 2-aminophenols, and 1,2-phenylenediamines at the metal (hydr)oxide-water interface Effects of ring substituents on the adsorption onto Ti02 , Environ. Sci. Technol., 30, 1604-1613 (1996). 

The adsorption of organic ligands onto metal oxides and the parameters that have the greatest effect on adsorption were also studied (Stone et al., 1993). The extent of adsorption was measured by determining the loss of the compound of interest from solution. The physical and chemical forces that control adsorption into two general categories were classified as either specific or nonspecific adsorptions. Specific adsorption involves the physical and chemical interaction of the adsorbent and adsorbate. Under specific adsorption, the chemical nature of the sites influences the adsorptive capacity. Nonspecific adsorption does not depend on the chemical nature of the sites but on characteristics such as surface charge density (Stone et al., 1993). The interactions of specific adsorption can be explained in two ways. The first approach uses activity coefficients to relate the electrochemical activity at the oxide/water interface to its electrochemical activity in bulk solution (Stone et al., 1993). This approach is useful in situations... 

Conceptual models of electron transfer (ET) mechanisms at Fe°-oxide-water interface (A) ET from bare iron metal exposed by pitting of the oxide layer (B) ET from conduction bands in the oxide layer (C) ET from adsorbed or lattice Fe(II) surface sites. (From Scherer, M.M. et al., CRC Crit. Rev. Environ. Sci. Technol., 30(3), 363 11, 2000. With permission.)... 

In this paper we examine the assumptions of our previous modeling approach and present new model calculations which consider alternative assumptions. In addition, we discuss the physicochemical factors which affect the formation of surface complexes at the oxide/water interface, in particular the effect of decreasing dielectric strength of the solvent. Finally, to demonstrate the general applicability of the model we present modeling results for a complex electrolyte system, where adsorption of a metal-ligand complex must be considered. 

Adsorption of Metal Ions. Significant advances have been made in recent years in the development of phenomenological models to describe trace metal adsorption at the oxide/water interface. In particular, the concepts of surface ionization and complexation introduced by Stumm, Schindler, and co-workers (, JJ., 12, 13) have aided in the understanding of complex adsorption phenomena. 

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