Characterization surface functional groups

Perrone et al. (2001) modelled Ni(II) adsorp-tion to synthetic carbonate fluoroapatite (CaI0 ((P04)5(C03))(0H,F). The solid phase had a pHIEP of 6.3 and a ZPC of 6.4 with an SSA of 8.8m2/g, an estimated sorption site density of 3.1 sites/nm2. They conducted 8-day isotherms in closed vessels at Ni concentrations of 5 x 10-10 to 1 x 10 8 M, constant I (0.05, 0.1 or 0.5 M), constant solid phase concentrations of 10 g/dm3 at pH values of 4 to 12. As Ni sorption occurred, no significant release of Ca was seen. Sorption was reversible. Rather than precisely characterize surface functional groups, they elected to describe their sorbent surfaces using acid-base reactions for the average behaviour of all sites involved in protonation and deprotonation. Potentiametric titration data were used to estimate the constants with the FTTEQL computer code ... 

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

Soil particles were found to have a capacity for ligand binding of 2 1(H mol g-1 these surface functional groups are characterized by an apparent "mono-protic" acidity constant... 

Although we have used for exemplification largely the surfaces of hydrous oxides, the concepts given apply to all surfaces. As has been pointed out, most hydrous surfaces are characterized by functional groups that acquire charge by chemical interaction with H+, OH, metal ions and by ligands. (For the moment we ignore redox reactions.)... 

Suitable characterization techniques for surface functional groups are temperature-programmed desorption (TPD), acid/base titration [29], infrared spectroscopy, or X-ray photoemission spectroscopy, whereas structural properties are typically monitored by nitrogen physisorption, electron microscopy, or Raman spectroscopy. The application of these methods in the field of nanocarbon research is reviewed elsewhere [5,32]. 

Because surface functional groups influence the adsorption properties and the reactivity of activated carbons, many methods, including heat treatment, oxidation, animation, and impregnation with various inorganic compounds, have been developed in order to modify activated carbons [183], These modifications can alter the surface reactivity, as well the structural and chemical properties of the carbon, which can be characterized using various methods, as described in detail elsewhere [176],... 

This study is devoted to the investigation of porous methacrylate polymeric systems filled with chemically modified fumed silicas. IR and 13C NMR spectroscopies combined with AFM was applied to characterize changes in the material structure, and also the effect of surface functional groups of inorganic particles on the polymer-filler interaction. 

A comparison of the data in Fig. 2 (Plate A, filled circles) and Fig. 5 (Plate B, open symbols) reveals that the performance of the heat-treated wood-based carbon, even under some preloading conditions, is similar to single solute TCE uptake by coal-based activated carbons in the absence of preloading [9]. The observed effect may result from some combination of optimum surface acidity, optimal type of surface functional group, and/or pore structure effects. The WVB carbon has a mesoporous pore structure, which has been observed to minimize the impacts of preloading in preliminary comparative experiments designed to isolate this effect (data not shown). Future work will employ carbon surface characterization techniques that will allow identification of functional groups and more accurate correlation with surface reactivity. 

For the accurate characterization of the adsorption phenomena, it is necessary to obtain accurate information on pore stmctures. However, most of ordinary microporous carbons and mesoporous carbons are obtained with amorphous stmctures that are characterized by irregular arrangements of non-uniform pores. X-ray (or electron) diffraction (XRD) techniques are not useful for such carbons because there are no well-defined stmctural factors to correlate with the adsorption behavior. Moreover, porous carbons exhibit wide varieties of the surface functional groups and the thickness of the pore walls, depending on the details of the synthesis conditions. The lack of distinct XRD lines makes it difficult to distinguish stmctural differences between samples which causes many works to depend empirically on specific samples. 

NMR spectroscopy has proven to be the most effective technique for characterizing carbon functional groups in HMW DOM. The i C-NMR spectrum of HMW DOM collected at 15 m in the North Pacific Ocean surface is given in Figure 6(a). Nearly identical spectra have been collected from the Atlantic Ocean, as well as from some lakes and rivers (McKnight et al., 1997 Repeta et al., 2002). All C-NMR spectra display a rather simple pattern of broad resonance from carboxyl (CO-(OH or NH) 175 ppm), alkene/ aromatic (C=C 140 ppm), anomeric (O-C-O 100 ppm), alcoholic (H-C-OH 70 ppm), and... 

High quality IR spectra of different carbon surfaces were obtained by photo-thermal beam deflection spectroscopy (IR-PBDS) [123,124]. This technique was developed with the intention of providing an IR technique that could be used to study the surface properties of materials that are difficult or impossible to examine by conventional means. Recently, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been successfully applied to study the effect of different pretreatments on the surface functional groups of carbon materials [101,125-128]. Several studies aiming to improve the characterization of the carbon electrode surface and the electrode-electrolyte interface have been carried out using various in situ IR techniques [14,128-132]. The development of in situ spec-troelectrochemical methods has made it possible to detect changes in the surface oxides in electrolyte solutions during electrochemical actions. 

The material is organized into 15 chapters written by recognized experts in their fields. It has been decided to cover in depth new and hot topics as well as those that have not yet been the subject of extensive reviews. In the first three chapters the properties of carbon materials relevant to catalysis are discussed, with a special emphasis given to the description of carbon surface features, in particular to surface functional groups and their characterization methods, and to the theoretical investigation of molecular interactions on carbon surfaces. This provides a fundamental background for an understanding of the material covered in subsequent chapters. 

A more obvious but perhaps underappreciated problem with surface roughness is the existence of defect sites on a surface, i.e., sites that would not be exposed on a perfectly smooth surface. This type of defect is separate from classical defects like stacking faults, subgrain boundaries and dislocations, and is due just to non-uniform expression of the substrate structure in an uneven surface (Fig. 9) such as could occur with the local development of vicinal faces. As surface characterization methods are generally poor except in the case of a small suite of oxides and silicates, this effect has probably not been fully considered to date. For example, it is possible to imagine a low roughness (hkl) surface that is entirely terminated by small faces with other (hkl) orientations, so that the exposed surface functional groups differ both in density and orientation from what is expected. 

A third classifying quantity relates to the surface structure of silicas, which is characterized by the coordination of surface silicon atoms the resulting functional groups their density, topology, and distribution the degree of hydroxylation the hydration-dehydration behavior the acidic and basic properties of surface functional groups and their adsorption behavior and chemical reactivity. The pattern of the surface structure in terms of these properties is discussed in the section Current View of the Silica Surface. The following section reviews the methods by which reliable information on these properties is obtained. 

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