Surfaces functional groups

It follows that the method by which pH regulates charge and metal adsorption by a surface (S) can be described as a competitive process. For example, 

When —S—O- forms an inner-sphere complex with a heavy metal (M+), the reaction is expressed by 

Considering that -O-H may be a weaker complex than -O-M, formation of the latter would be relatively independent of pH. The latter complex would involve a strong bond (e.g., chemisorption). The same explanation applies to anion adsorption. For example, phosphate (P04) adsorption by oxides may take place in an outer- or inner-sphere mode of the monodentate or bidentate type (Fig. 4.7). 

A large attraction force between interlayer cations and adjacent siloxane cavities allows some cations with certain hydration energy to dehydrate. If the dehydrated cation radius is smaller than the inside diameter of the siloxane cavity, the mineral could collapse and an inner-sphere complex would form (e.g., K-vermiculite) (Fig, 4.3). When vermiculite contains a relatively strongly hydrated cation such as Ca2+ or 

Mg2+ (Table 4.1) its interlayer spacing would be approximately 5 A or 0.05 nm wide (1 A = 10-8 cm) (Fig. 4.9). When K+ replaces the interlayer Ca2+, or Mg2+, the low hydration energy of K+ and its good fit in the siloxane cavity would allow vermiculite to collapse and bring the 5-A (0.05 nm) interlayer gap to near 0 A. Thus, an inner-sphere complex would form and such K+ is often referred to as fixed K+ . Vermiculite is also known to form inner-sphere complexes with NH.  

---

Eig. 1. Schematics of (a) acid-cataly2ed and (b) base-cataly2ed siHca gels showing the differences in microstmcture and surface functional groups. 

Surface properties are generally considered to be controlled by the outermost 0.5—1.0 nm at a polymer film (344). A logical solution, therefore, is to use self-assembled monolayers (SAMs) as model polymer surfaces. To understand fully the breadth of surface interactions, a portfoHo of chemical functionahties is needed. SAMs are especially suited for the studies of interfacial phenomena owing to the fine control of surface functional group concentration. 

Adsorption and Surface Chemical Grafting. As with siHca and many other siHcate minerals, the surface of asbestos fibers exhibit a significant chemical reactivity. In particular, the highly polar surface of chrysotile fibers promotes adsorption (physi- or chemisorption) of various types of organic or inorganic substances (22). Moreover, specific chemical reactions can be performed with the surface functional groups (OH groups from bmcite or exposed siHca). 

Determination of surface functional groups, e.g., —OH, —C - C—, and >C = O, and identificadon of adsorbed molecules comes principally from comparison with vibrational spectra (infixed and Raman) of known molecules and compounds. Quick qualitative analysis is possible, e.g., stretching modes involving H appear for v(C—H) at 3000 cm and for v(0—H) at 3400 cm L In addition, the vibrational energy indicates the chemical state of the atoms involved, e.g., v(C=C) " 1500 cmT and v(C=0) " 1800 cm"L Further details concerning the structure of adsorbates... 

This process is probably accompanied by fixation at surface functional groups as well as crosslinking reactions. The simplicity of this approach makes it quite promising for a more general application. 

Broadening of the optimal pH range for reactive dye biosorption by chemical modification of surface functional groups of Corynebacterium glutamicum biomass... 

Several mechanisms have been proposed to explain the activation of carbon surfaces. These have Included the removal of surface contaminants that hinder electron transfer, an Increase In surface area due to ralcro-roughenlng or bulld-up of a thin porous layer, and an Increase In the concentrations of surface functional groups that mediate electron transfer. Electrode deactivation has been correlated with an unintentional Introduction of surface contaminants (15). Improved electrode responses have been observed to follow treatments which Increase the concentration of carbon-oxygen functional groups on the surface (7-8,16). In some cases, the latter were correlated with the presence of electrochemical surface waves (16-17). However, none of the above reports discuss other possible mechanisms of activation which could be responsible for the effects observed. 

Due to their well defined geometrical sizes, globular shapes, and uniform multiple surface functional groups, dendrimers are promising candidates for the construction of mono- or multi-layer films. 

At present, improved methods of dendrimer construction have made possible the commercial availability of these macromolecules with a variety of molecular weight ranges and surface functional groups. Instead of testing the limits... 

In this paper, we presented new information, which should help in optimising disordered carbon materials for anodes of lithium-ion batteries. We clearly proved that the irreversible capacity is essentially due to the presence of active sites at the surface of carbon, which cause the electrolyte decomposition. A perfect linear relationship was shown between the irreversible capacity and the active surface area, i.e. the area corresponding to the sites located at the edge planes. It definitely proves that the BET specific surface area, which represents the surface area of the basal planes, is not a relevant parameter to explain the irreversible capacity, even if some papers showed some correlation with this parameter for rather low BET surface area carbons. The electrolyte may be decomposed by surface functional groups or by dangling bonds. Coating by a thin layer of pyrolytic carbon allows these sites to be efficiently blocked, without reducing the value of reversible capacity. 

Tanahashi, M. and Matsuda, T. (1997) Surface functional group dependence on apatite formation on self-assembled monolayers in a simulated body fluid. Journal of Biomedical Materials Research, 34, 305-315. 

Fig. 2 TIRFM images of HUVEC adhesion behavior on SAMs with four different types of surface functional groups at the indicated times after first applying the cell suspension. Scale bar 200 pm [42]...

We examined protein adsorption to SAMs that carried four different functional groups [42] and mixed SAMs with different wettabilities [21], Large amounts of serum proteins adsorbed to all these SAMs, but the different surface functional groups greatly affected cell adhesion behavior (Figs. 2 and 3). Thus, the amount of adsorbed proteins did not correlate with the degree of cell adhesion to SAMs. 

Arima Y, Iwata H (2007) Effect of wettability and surface functional groups on protein adsorption and cell adhesion using well-defined mixed self-assembled monolayers. Biomaterials 28 3074-3082... 

In addition to the Ti, hydroxyl groups constitute a second class of surface functional groups on dehydrated samples that can be of importance in catalytic reactions. The presence of a large number of Si-OH groups on the surfaces of all the titanosilicates is apparent from the intense absorption in the 3200-3800 cm-1 region of the infrared spectra. The experimental evidence of surface... 

---