Surface functional groups infrared spectroscopy

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]. 

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 application of infrared spectroscopy to the inorganic compounds started as a more frequent technique during the 60 s with Lawson. This author made a first attempt to compile the work done in the relatively new field-inorganic Infrared Spectroscopy since 1952 where 1171 references were reported. Farmer, in 1964, studied the silicates and Nakamoto in relation to the coordinated compounds prepared a helpful atlas of these compounds. Afremow (1966) presented for an important research of inorganic pigments and extenders in the mid-infrared region from 1500 cm-1 to 200 cm-1. The study of surface chemistry and the nature of surface functional groups was also advanced by Basila (1968). 

The acid and base values of the surface functional groups of the samples were determined by Boehm s titration method [50]. To determine the acid value, O.lg of the sample was added to 100 ml of 0.1 M NaOH solution and the mixture was shaken for 24 h. The solution was then filtered through a membrane filter (pore size = 0.24 pm, nylon) and titrated with 0.1 M HCl. Likewise, the base value was determined by the reverse titration of the acid value. The specific surface areas (Sbet. [51]) of the samples were determined by gas adsorption. Physical adsorption of gases was used to characterize the CBs support, and the adsorbate used was N2 at 77 K with automated adsorption apparatus (Micromeritics, ASAP 2400). Prior to adsorption measurements, the samples were outgassed at 298 K for 6 h to obtain a residual pressure of less than 10 torr in high vacuum. To analyze the functional groups of CBs, the treated CBs were subjected to infrared (IR) spectroscopy (FTS-165 spectrometer, Bio-Rad Co.). 

Thirdly, in order to improve the dispersion of platinum catalysts deposited on carbon materials, the effects of surface plasma treatment of carbon blacks (CBs) were investigated. The surface characteristics of the CBs were determined by fourier transformed-infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and Boehm s titration method. The electrochemical properties of the plasma-treated CBs-supported Pt (Pt/CBs) catalysts were analyzed by linear sweep voltammetry (LSV) experiments. From the results of FT-IR and acid-base values, N2-plasma treatment of the CBs at 300 W intensity led to a formation of a free radical on the CBs. The peak intensity increased with increase of the treatment time, due to the formation of new basic functional groups (such as C-N, C=N, -NHs, -NH, and =NH) by the free radical on the CBs. Accordingly, the basic values were enhanced by the basic functional groups. However, after a specific reaction time, Nz-plasma treatment could hardly influence on change of the surface functional groups of CBs, due to the disappearance of free radical. Consequently, it was found that optimal treatment time was 30 second for the best electro activity of Pt/CBs catalysts and the N2-plasma treated Pt/CBs possessed the better electrochemical properties than the pristine Pt/CBs. 

As indicated above, the penetration depth is on the order of a micrometer. That means that in ATR, absorption of infrared radiation mostly occurs within a distance 8 of the surface and ATR is not as surface sensitive as some other surface analysis techniques. However, ATR, like all forms of infrared spectroscopy, is very sensitive to functional groups and is a powerful technique for characterizing the surface regions of polymers. 

Infrared Spectroscopy can be used to gain important information about functional groups on surfaces of minerals, but quantitative determinations have been difficult. For complex materials, like coal, the spectra are still not resolved fully for example, there is great deal of uncertainty about the 1600cm-1 band which is the dominant feature of all coal spectra. Fourier-transform infrared spectroscopy, which is a considerable improvement in this technique, has recently been used to investigate low-temperature oxidation of coal (13). 

A variety of other carbon-o gen groups have been suggested, including lactones, anhydrides, peroxides, ethers, and esters (14-18). These surfaces oxides have been studied by functional group reactions (18), titration, and infrared spectroscopy (15,... 

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