Gustavo Morari Do Nascimento

By Gustavo M. Do Nascimento

Part of the book: Nanofibers

By Gustavo M. Do Nascimento

A wide range of spectroscopic techniques employ higher-energy electromagnetic radiation, ranging from vacuum UV (≈10−40 eV, 125−31 nm), including soft X-rays (40−1500 eV, 31−0.8 nm), and going to hard X-rays (1500−105 eV, 0.8−0.01 nm) for elucidating molecular structures of chemical and biological interest. A typical X-ray absorption (XAS) spectrum has a large absorption near the edge followed by serial oscillations that gradually fade away. This set of oscillations extends over a wide energy range and can be divided into two regions: the absorption near the edge is called XANES (X-ray absorption near-edge structure) and the second region is the so-called EXAFS (extended X-ray absorption fine structure). The XAS data enables the determination of crystallographic parameters and also the signal intensity contains information of the oxidation state and the chemical bond in the solid. For instance, theoretical calculations were essential to verify the differences between the oxygen and silicon sites in clays. Experimental and theoretical EXAFS studies of clays with Cu(II) show that Cu(II) has interchangeable octahedral, tetragonal, and square planar coordinations in the clay interlayer, depending on Cu(II) loading and degree of hydration. XANES data of intercalated poly(aniline) show new bands at 398.8 eV and 405−406 eV, which were assigned to new chromophoric segments formed within the galleries of the Montmorillonite clay. Hence, in this chapter, this amazing new area will be reviewed concerning the state-of-the-art results of characterization of their structural features. Previous and new results of the X-ray absorption spectroscopy of clays and polymer–clay materials obtained by our group will be considered. The main goal of this work is to contribute to the rationalization of some important results obtained in the open area of clays and clay materials characterization.

Part of the book: Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals

By Gustavo M. Do Nascimento

Part of the book: Raman Spectroscopy

By Gustavo M. Do Nascimento

Part of the book: Nanomaterials

By Gustavo Morari do Nascimento

Raman spectroscopy is employed to study a myriad of complex materials due to the coupling of different resonances process and microscopic resources. For instance, vibrational and electronic aspects of carbon allotropes can be deeply investigated by resonance Raman spectroscopy. By selecting the appropriate laser line, it is possible to monitor different aspects of the samples, such as the behavior of metallic or semiconducting tubes and the graphene with different layers or chemical modifications. In this chapter, the potentialities of Raman technique will be exemplified in some examples obtained in our group about the characterization of carbon nanotubes and graphene. For instance, the doping process of nanotubes, carbon tube interactions with molecular magnets, and inhomogeneity of graphene samples will be discussed.

Part of the book: Modern Spectroscopic Techniques and Applications

By Gustavo Morari do Nascimento

In the recent years the synthesis and characterization of nanomaterials has been one of the most efficacious way to produce new materials with improved or completely new properties. The polymer-clay nanocomposites are one of the most interesting nanomaterials with the possibility to create a myriad of new materials with many applications. Lamellar materials are classified as two-dimensional (2D), because there are formed by platelets piled up in one crystallographic direction, as the graphite and clays. The synthesis of controlled dimensional nanostructures as well as the characterization of the intrinsic and potentially peculiar properties of these nanostructures are central themes in nanoscience. The study of different nanostructures has great potential to test and understand fundamental concepts about the role of particle dimensionality on their physicochemical properties. Among the various materials studied in the literature, undoubtedly, polymer-clay materials, especially conducting polymers with smectite clays, such as montmorillonites (MMT) are of particular note. Our group have paid many efforts in the characterization of nanomaterials by using powerful spectroscopic techniques to study both the guest and host in case of inclusion compounds, nanofibers, carbon allotropes or many phases present in polymer-clay nanocomposites. There are two central questions that it was possible to address in this study: (i) the molecular structure of the polymer is drastically changed inside the interlayer cavity of clay and (ii) by using the appropriate synthetic or heating route is possible to change the molecular structure of the confined polymer. In the follow lines, it is briefly told the main aspects of resonance Raman and X-ray absorption spectroscopies in the study of polymer-clay nanocomposites.

Part of the book: Clay Science and Technology