Electrostatic adsorption dependence

Forces of Adsorption. Adsorption may be classified as chemisorption or physical adsorption, depending on the nature of the surface forces. In physical adsorption the forces are relatively weak, involving mainly van der Waals (induced dipole—induced dipole) interactions, supplemented in many cases by electrostatic contributions from field gradient—dipole or —quadmpole interactions. By contrast, in chemisorption there is significant electron transfer, equivalent to the formation of a chemical bond between the sorbate and the soHd surface. Such interactions are both stronger and more specific than the forces of physical adsorption and are obviously limited to monolayer coverage. The differences in the general features of physical and chemisorption systems (Table 1) can be understood on the basis of this difference in the nature of the surface forces. 

The most frequent type of interaction between solid and species in solution would be electrostatic adsorption (ion exchange), due to the action of attractive coulomb forces between charged particles in solution and the solid surfaces. This process would also be concentration dependent. 

Depending on the size of the probe, either covalent (Figures 10 and 11) or electrostatic immobilization (Figure 12) may be preferred. In general, oligonucleotides and DNA fragments of approximately 20 to 70 bases are amino-modified and bound covalently to the chip surface. Complete or partially complementary DNA of up to 5000 nucleotide bases is bound to the chip by electrostatic adsorption. 

Au NPs functionalized with biomolecules can be synthesized using different methods, depending on factors inducing the interactions promoted between the nanoparticle and the biomolecule. These interactions can be classified as electrostatic adsorption, chemisorption and covalent binding and, finally, specific affinity interactions. Some examples are given in the following paragraphs (Scheme 3.23). 

Wang et al. [607] studied the adsorption of dissolved organics from industrial effluents onto a commercial activated carbon. As illustrated in Table 20, they place emphasis on the pK, pK, or isoelectric point of the adsorbate and state that the pH effect upon the effectiveness of carbon adsorption mainly depends upon the nature of the adsorbed substance. Based on their own work and analysis of the literature, they postulate that maximum adsorption of organic acids and bases occurs around their respective pK , or pKh value, even though they acknowledge, at least as the ionic organic compounds become more complex, that electrostatic adsorption forces between the adsorbent and the ionic adsorbate appear to govern. ... 

This chapter shows that a unified explanation can be given of the adsorption from dilute aqueous solutions of different organic solutes, from nonelectrolytes to electrolytes, polyelectrolytes, and bacteria. Thus, the adsorption process is a complex interplay between electrostatic and nonelectrostatic interactions. Electrostatic interactions depend on the solution pH and ionic strength. The former controls the charge on the carbon surface and on the adsorptive... 

In chemisorption, unshared electron pairs or p electrons from organic compounds interact with the metal orbitals to form a coordinate-type bond. The interaction proceeds in the presence of heteroatoms (P, Se, S, N, and O) that possess lone-pair of electrons and/or aromatic rings in the adsorbed molecules [16,17]. Chelate forms through a coordinate covalent bond by electron transfer from organic compounds to metal. The chemisorption has higher activation energy than electrostatic adsorption. It is a temperature-dependent phenomena, it occurs slowly, and is not reversible. 

For a particular polymer functionality, the adsorption depends on the nature and energetics of the adsorption sites that are present on the surface. The adsorption of polymers via electrostatics, chemical bonding and hydrophobic attraction is relatively well understood. 

Complete hydration of oxides represented by structures II and III of Scheme 1 results in new surface structures (IV, V. and VI) at the oxide/solution interface. The interfacial phenomena at the solid/solution boundary include electrostatic adsorption, ion exchange, and ligand binding of species from solution. However, in most instances the species that count as charge-determining (in aqueous media) are always and O H ions. As the concentration of these ions is pH-dependent in solution, the predominance of one or another of the surface structures IV, V, and VI is also pH-dependent. 

Some of the types of compounds that function through electrostatic adsorption may also function by chemisorption. Chemisorption is most evident with nitrogen or sulfur heterocyclics. Benzotriazole and polytriazole, both effective inhibitors of copper corrosion, are believed to operate through chemisorption, as does 0. IM butylamine, which is effective in inhibiting the corrosion of iron in concentrated perchloric acid. However, the effectiveness of a given compound depends on the mechanism and operating conditions. 

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