Solid-state characterization techniques

Decatungstate, in the form of a lipophilic tetrabutilamonium salt ((n-C4H9N)4 W10O32), has been homogeneously dispersed in porous membranes made of PVDF (PVDF-W10). Solid-state characterization techniques confirmed that catalyst structure and spectroscopic properties of decatungstate have been preserved once immobilized within the membranes [42-44]. 

The majority of characterization techniques discussed thus far have been surface-related, with some capable of analyzing sub-surface depths through in situ ion etching. This final section will focus briefly on a selection of common bulk techniques that may be used to characterize as-synthesized materials such as polymers, ceramics, etc. More details on these and other techniques not discussed herein may be found in the Further Reading section at the end of this chapter. In particular, these additional resources, as well as countless others online, will highlight solid-state characterization techniques such as ... 

The insolubility of polybutadiyne necessitated the use of solid state characterization techniques and the tailoring of sample preparation to a particular characterization experiment. 

Solid-state characterization techniques have been used to verify that the heterogenization procedure did not damage the catalyst. Fourier transform-infrared (FT-IR) spectra give useful indication about the structure of the catalyst heterogenized in the membrane. FT-IR spectra confirmed that the catalyst stmetore is preserved within the polymeric membrane (Fig. 27.1). The infrared spectrum of the catalytic membranes show the characteristic bands of Wio units (595, 803, 895, 958 cm ), as well as those typical of the employed alkylam-monium cation (2870 cm ). 

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

Bugay DE. Characterization of the solid-state spectroscopic techniques. Adv Drug Delivery Rev 2001 48 43-65. 

This chapter focuses on the application of solid-state NMR techniques for the characterization of oxidation catalysts. Initially, a brief introduction to these techniques is provided (Section 5.2), within which methods suitable for the study of both bulk structure (Section 5.2.1) and surface characteristics (Section 5.2.2), are described. Examples of the application of these techniques are then provided in Section 5.3, for bulk oxides, and Section 5.4, for surface properties. Finally, Section 5.5 provides an outlook as to future directions in this area. 

Study of the modification of solid surfaces requires, preferably, surface sensitive methods. Spectroscopic techniques, for example X-ray photoelectron spectroscopy (XPS) and FTIR spectroscopy are excellent tools for gathering information on the chemical surface composition and the kind and number of functional surface groups. The fact that the carbon and nitrogen containing organic phase is only introduced during the adsorption procedure and locally fixed on the outside of the particles allows the use of established methods for polymer and solid-state characterization, particularly NMR and solid-state NMR spectroscopy (e.g. 13C CP MAS NMR). 

Various spectroscopic techniques have been applied to the characterization of carbocations as stable ions in solution and in the solid state. The techniques that have found most application in the study of hypercoordinate carbocations were developed primarily to be capable of distinguishing trivalent cations undergoing rapid degenerate rearrangements from bona fide hypercoordinate ions. In recent years, theoretical studies have become also very useful in the study of hypercoordinate carbocations. Furthermore, many properties such as chemical shifts ( H, etc.) and vibrational spectra can be accurately computed. 

The following discussion focuses exclusively on what are termed small molecules in the industry, namely compounds with a molecular mass on the order of one 1000 Da or less. The study of proteins, polymers, and other such macromolecules by NMR warrants an entirely different approach that is beyond the scope of this book. Similarly, we will restrict our discussion to liquid-state NMR spectroscopy, since the quantity of sample available for the characterization of a degradant or impurity is typically far below reasonable amounts needed for most solid-state NMR techniques. The overall characterization strategy we will use for NMR is shown in Figure 25. 

Simultaneous thermogravimetric and differential thermal analysis (TG/DTA) is a useful technique for the solid-state characterization of pharmaceutical materials. Such characterization includes the determinations of loss on drying, phase transition temperatures, thermal stability, and whether or not water is bound or unbound. TG/DTA combines the measurement of a change in mass of a sample as a function of temperature (TG) with the temperature difference of a sample compared with an inert reference material as a function of temperature (DTA). 

High resolution solid-state NMR techniques are powerful means for characterizing the network polymer of polymer gel systems. They give useful information on the network polymer. The function of this chapter is to review the researches on synthesized polymer gels by high resolution solid-state NMR techniques. The research on polymer gels composed of natural materials, such as proteins and polysaccharides, are reviewed in other chapters. 

Only a brief description of selected techniques for solid-state characterization has been given above. Many other techniques are available. It is imperative that... 

For reference, Threlfall (1995) has produced an excellent review of the analysis of organic polymorphs. Spectral methods (IR, Raman and solid-state NMR) for the characterization of polymorphs and solvates have been reviewed by Brittain (1997). The basis of some of the techniques used in solid-state characterization has been discussed earlier in this chapter in the section on salt selection. A few examples are given here to show the utilization of these techniques. Characterization of pharmaceutical solvates by combined TGA and infrared anaylsis has been described by Rodriguez and Bugey (1997). 

This chapter does not cover the most common aspects of the solid-state NMR techniques employed in the study of heterogeneous catalysts such techniques are described in Chapter 4. Since this chapter emphasizes the surface characterization of silica and alumina systems and silica aluminas by NMR methods, only those technical aspects highly relevant to surface characterization and not otherwise emphasized in this volume are explicitly discussed here. NMR studies of zeolites and clays are treated in separate chapters, and the bulk structures of silica and alumina systems are covered by Eckert. Unavoidably this chapter is also concerned with dynamics at the surface, although the amount of detailed work on that subject to date is limited. With the increasing availability of variable-temperature solid-state NMR equipment, however, one can expect that attention devoted to dynamics at surfaces will increase markedly during the next few years. 

Zintl also found that the most convenient way to produce the solutions of the anionic clusters in liquid ammonia is to extract alkali metal/post-transition element alloys in the solvent. However, detailed solid-state characterization of the clusters is very difficult using this technique, since poorly crystalline and often pyrophoric solids are obtained once the solvent is evaporated. These troublesome solids are alkali-metal ammoniates of cluster ions, " of which only [Li(NH3)4]3-[Li2(NH3)2Sb5] -2NH3 seem to have been completely structurally characterized, Furthermore, the ammoniates most often slowly revert back to the alloy upon further loss of ammonia. The last step involves transfer of electrons from the strongly reducing cluster anion back to the alkali-metal ion and thus represents a major synthetic obstacle. 

In the present work, the practice of the most commonly encountered techniques performed for the solid-state characterization of polymorphic or solvate properties will be reviewed. No attempt will be made to summarize every recorded use of these methodologies for such work, but selected examples will be used to illustrate the scope of information that can be extracted from the implementation of each technique. 

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