This study contributes to the sustained effort to unravel the chemical structure of graphite oxide (GO) by proposing a model based on elemental analysis, transmission electron microscopy, X-ray diffraction, 13C magic-angle spinning NMR, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance investigations. The model exhibits a carbon network consisting of two kinds of regions (of trans linked cyclohexane chairs and ribbons of flat hexagons with CC double bonds) and functional groups such as tertiary OH, 1,3-ether, ketone, quinone, and phenol (aromatic diol). The latter species give clear explanation for the observed planar acidity of GO, which could not be interpreted by the previous models. The above methods also confirmed the evolution of the surface functional groups upon successive oxidation steps.

Structural and magnetic properties, methods of synthesis, and applications of seven iron-(III) oxide polymorphs, including rare beta, epsilon, amorphous, and high-pressure forms, are reviewed. Thermal transformations resulting in the formation of iron oxides are classified according to different parameters, and their mechanisms are discussed. 57 Fe Mo ¨ssbauer spectroscopy is presented as a powerful tool for the identification, distinction, and characterization of individual polymorphs. The advantages of Mo ¨ssbauer spectroscopy are demonstrated with two examples related to the study of the thermally induced solid-state reactions of Fe 2 (SO 4 ) 3 . Lead-InIron(III) oxide is not only a strategic industrial material but also a convenient compound for the general study of the polymorphism and the mutual polymorphous changes in nanoparticles. The existence of amorphous Fe 2 O 3 and four polymorphs (alpha, beta, gamma, and epsilon) has been established. Their discoveries as well as the majority of formation processes are connected with thermal transformations of iron-bearing materials in an oxidizing atmosphere. 57 Fe Mo ¨ssbauer spectroscopy is a unique method that allows one to distinguish and identify individual structural forms, amorphous and nanostructured Fe 2 O 3 particles, to analyze their magnetic properties and to study their formation mechanism during thermally induced solidstate reactions. In this review, thermal processes resulted in the Fe 2 O 3 formation are classified from different viewpoints and their mechanism is discussed. Applications, structural and magnetic properties, and methods of synthesis of all known forms of iron(III) oxide and their Mo ¨ssbauer characterization are also summarized. A detailed survey of the properties of rare forms (amorphous Fe 2 O 3 , β-Fe 2 O 3 , -Fe 2 O 3 , and highpressure Fe 2 O 3 ) is presented for the first time. With respect to the more known R-Fe 2 O 3 and γ-Fe 2 O 3 , the presented data spring from a series of previous works, including the excellent book by R. M. Cornell and U. Schwertmann. 1 Some unresolved problems, such as the relation between the properties of the original ferrogenous precursor and the structure of the formed iron-(III) oxide, or the experimental possibility to distinguish the amorphous Fe 2 O 3 from nanostructured γ-Fe 2 O 3 or R-Fe 2 O 3 particles are discussed. The value of Mo ¨ssbauer spectroscopy for the characterization of iron(III) oxides produced by thermal processes is demonstrated with two experimental examples taken from our work in the field. † Dedicated to R. L. Mo ¨ssbauer on the occasion of the 40 th jubilee of Nobel Prize presentation.

Hollow clay microspheres of high thermal stability were easily fabricated by the adsorption of colloidal clay layers onto the surfaces of a spherical anion exchange resin and calcination of the resulting resin-clay composite.