Surface functional groups analyses

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... 

D. E. Williams and J. P. Cannady, Analysis of polymer surface functional groups. Abstracts, 182nd ACS National Meeting, p. 1NDE-23 (1981). 

Figure 38. Temperature-programmed decomposition (0.25 K s 1) of oxygen surface functional groups from a graphite powder. The simultaneous mass-spectroscopic analysis reveals the irreversible character of this experiment in which the substrate surface is removed during desorption of the adsorbate.

What is striking in Table 2 is the extremely carbonized structure of T40. The functional group analysis of the derivatized carbon fiber surfaces is given in Table 3. 

It is obvious that the Boehm titration method is the most popular one for the determination of various types of acidic (and basic) surface functionalities in carbon materials. From 1966 until 2002, when Boehm himself published a critical assessment of the analysis of surface oxides on carbon [201], an exhaustive utilization of this method has been desaibed by many authors. They underlined its simplicity, but pointed out also the need for using other complementary methods such as potentiometric titration, tanperature-programmed desorption (TPD), spectroscopic methods (mainly XPS and FTIR), and thermodynamic approaches such as calorimetry. The case of TPD is of special interest, to identify oxygenated functionalities. However, the CO and CO2 peaks must certainly be deconvo-luted before the surface composition can be estimated. Thus, a quantitative TPD analysis of surface functional groups is sensitive to the deconvolution method and to experimental conditions. The results are generally discussed in relation to those of DRIFTS and XPS analysis, as can be seen from the references listed in Table 3.1. 

Further insight into the nature of the interaction between irreversibly adsorbed species and the filler surface can be gained from DRIFTS analysis of the filler sample taken from the FMC cell after completion of the adsorption - desorption cycle. DRIFTS is described in more detail in Section 3.5.4, but in summary, it is an infrared spectroscopic technique, that by virtue of a significant proportion of glancing angle reflections, affords enhanced resolution of filler surface functional groups. The authors have found this technique particularly useful when studying competitive adsorption of polymer stabilisers and carboxylic acids onto silica and metal hydroxides, respectively. 

A rational analysis of filler effects on structural, proton transport properties and electrochemical characteristics of composite perfluorosulfonic membranes for Direct Methanol Fuel Cells (DMFCs) was reported [7]. It has been observed that a proper tailoring of the surface acid-base properties of the inorganic filler for application in composite Nafion membranes allows appropriate DMFC operation at high temperatures and with reduced pressures [7]. An increase in both strength and amount of acidic surface functional groups in the fillers would enhance the water retention inside the composite membranes through an electrostatic interaction, in the presence of humidification constraints, in the same way as for the adsorption of hydroxyl ions in solution [7]. 

The different stages of the preparation of peptide surfaces can be confirmed with surface-sensitive physical and chemical analysis techniqnes. For gold-based SAMs, Mrksich and co-workers have introduced a matrix-assisted laser desorption ionisation time-of-ftight (MALDI-TOF) mass spectrometry-based analysis procedure with which they are able to identify the presence of various surface functional groups via their mass (Yeo Mrksich, 2006 Yeo et al., 2003). Although this method is applicable to SAMs, it is not strictly a surface sensitive technique, as the desorption process in MALDI is not confined to the uppermost layer of a material. 

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