Covalent surfaces, desorption kinetics

There is some evidence that first-order desorption kinetics occur on many covalent surfaces. Desorption of H2 from polycrystalline Te [59] and /3-SiC... 

In the 1970s and 1980s both the clean and H-covered Si surfaces were characterized by diffraction and spectroscopic methods, but only in the last decade have there been reproducible studies of chemical kinetics and dynamics on well-characterized silicon surfaces. Despite the conceptual simplicity of hydrogen as an adsorbate, this system has turned out to be rich and complex, revealing new principles of surface chemistry that are not typical of reactions on metal surfaces. For example, the desorption of hydrogen, in which two adsorbed H atoms recombine to form H2, is approximately first order in H coverage on the Si(lOO) surface. This result is unexpected for an elementary reaction between two atoms, and recombi-native desorption on metals is typically second order. The fact that first-order desorption kinetics has now been observed on a number of covalent surfaces demonstrates its broader significance. 

Desorption kinetics for Ig immobilized on the surface of the nanocomposites was studied with the use of physiological solution as a model medium. It has been shown that the release of immunoglobulin immobilized at the surface of Fe304/ PAA and Fe304/ -APS nanocomposites via covalent binding is slow and to a lesser extent than in the case of nonspecific immobilization. The antibodies immobilized at the surface of Fe304/HA and Fe304/HA/Ag nanocomposites showed weak desorption in a model medium. 

The process of heterogeneous catalysis involves the adsorption of molecules of reactants onto the catalyst surface and after the reaction is performed, the products undergo desorption. The process of adsorption can involve either weak van der Waals interactions between the surface of the catalyst and the adsorbed species (physisorp-tion) or covalent bonds between surface atoms and the adsorbate (chemisorption). These reaction steps were explored previously when discussing the kinetics of catalytic processes. 

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