Eigen kinetics in surface complexation of aqueous metal ions
1Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 24, 2008
Summary
The release of water from metal ion hydration shells is the key step limiting chemisorption rates at surfaces. This finding aids in predicting metal ion sorption in soil and environmental science.
Area of Science:
- Soil chemistry
- Bioenvironmental science
- Surface chemistry
Background:
- Chemisorption of aqueous metal ions at surfaces is crucial in soil and bioenvironmental science.
- Understanding the rate-limiting steps is essential for accurate modeling.
Purpose of the Study:
- To quantitatively demonstrate the rate-limiting step in inner-sphere surface complexation of aqueous metal ions.
- To develop a predictive model for metal ion sorption rates.
Main Methods:
- Analysis of the role of hydration shell water release in surface complexation.
- Utilizing tabulated dehydration rate constants for metal ions.
- Applying Boltzmann statistics to define outer-sphere complex stability.
Main Results:
- Demonstrated that water release from the inner hydration shell is the rate-limiting step.
- Identified the reactive intermediate as an outer-sphere complex.
- Established a quantitative scheme for predicting sorption rates.
Conclusions:
- The rate of aqueous metal ion sorption is primarily controlled by the kinetics of water molecule detachment from the inner hydration shell.
- The developed model enables prediction of metal ion sorption rates on various surfaces.
- This research advances the understanding of fundamental processes in environmental geochemistry.
Related Concept Videos
01:23Complexation Equilibria: Overview
Complexation reactions take place when dative or coordinate covalent bonds form between metal ions and ligands. The compounds formed in these reactions are called coordination compounds. The number of bonds formed between the metal ion and the ligands is called its coordination number. Generally, most metal ions in an aqueous solution are solvated by water molecules and thus exist as aqua complexes.
The equilibrium constant of the complexation reaction is represented as the formation constant...
The equilibrium constant of the complexation reaction is represented as the formation constant...
03:45Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
01:09Complexation Equilibria: Factors Influencing Stability of Complexes
In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
01:19Complexation Equilibria: The Chelate Effect
In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...
00:56Extraction: Advanced Methods
Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...
02:51Metal-Ligand Bonds
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...