Potentiality of Graphene Oxide and Polyoxometalate as Radionuclides Adsorbent to Restore the Environment after Fukushima Disaster: A Mini Review

This paper discusses the promising candidate of excellent materials, graphene oxide (GO) and polyoxometalates (POMs), for radionuclide adsorbent. In this perspective, the unique properties of GO and POMs make them ideal candidates for developing new composites having the ability to adsorb radionuclides, and several essential things are reviewed. First, the anchoring mechanism to deposit POM on the GO surface area by (i) carboxylation method, (ii) covalent bonding, and (iii) impregnation method. Second, the radionuclides removal mechanism is described in several systems: (i) coagulation, (ii) electrostatic interaction, (iii) ion trapping, and (iv) H+-exchange. Third, the experimental condition that employed to enlarge the sorption capacity such as (i) pH adjustment, (ii) employing multiple oxidations, and (iii) cation charge. A thorough understanding of the POM-anchored GO material can pave the way for future research on similar materials. It can also help in understanding the nature of the interactive collaboration present between GO and POM.

Nepheline solid solution compositions: stoichiometry revisited, reviewed, clarified and rationalised

Molecular formulae used to recalculate nepheline analyses generally have different numbers of oxygens (e.g. NaAlSiO4 (Ne), KAlSiO4, (Ks), CaAl2Si2O8 (An) and SiO2 (Q)). A 32 oxygen cell has 16 T cations and 8 cavity sites, but ideal nepheline stoichiometry is not necessarily followed. Ca end-member □CaCaAl2Si2O4 (CaNe) and excess silica end-member □SiSi2O4 (Q’) calculation requires inclusion of both vacancy species as cavity cation values. Q’ parameter calculations can involve different assumptions and four parameters are described: Qxs; QSi; Q(Si–Al); and Qcavity; these should have closely similar values for high-quality, stoichiometric analyses. Representative published compositions are recalculated to assess whether authors followed ideal nepheline stoichiometry. Phenocrysts from peralkaline rocks and nephelinites typically exhibit Al deficiencies reflected in negative Δ(Al – cavity cation) parameters (ΔAlcc), negative ‘normative’ corundum (Al2O3, Cn), and anomalously low or negative Qxs parameters; for such rock types Q(Si–Al) provides a better estimate of excess silica contents. A ΔT-site (cation charge) parameter (ΔTcharge), is closely coupled to ΔAlcc and end-member NaAlSiO4 has a ΔAlcc/ΔTcharge ratio of 1.4296; the derivation of this value is controlled by strict stuffed-tridymite, unit-cell constraints. Natural nephelines all contain excess silica with a mean ΔAlcc/ΔTcharge of ~1.134 reflecting their Si/Al ratio being > 1. Nepheline analyses with relatively low Al and Si and high Na (also Ca) contents are common; this might reflect the presence of small amounts (up to ~5%) of cancrinite as an alteration phase or perhaps even in solid solution. The compositions of alteration lamellae of Ca-rich cancrinite in altered nepheline phenocrysts in phonolites from the Marangudzi alkaline complex, Zimbabwe, are used to define diagnostic parameters for recognising such non-stoichiometry. These alteration lamellae formed hydrothermally from Ca-rich and K-poor fluids. An EXCEL file is provided to help researchers to standardise calculation of nepheline end-member molecular proportions.

Crystal Chemistry of High-Temperature Borates

In recent years borate-based crystals has attracted substantial interest among the research community. The overall importance of this family of materials is reflected in miscellaneous articles and several reviews that have been published over the years. Crystalline borate materials exhibit numerous interesting physical properties, which make them promising for further practical applications. Diversity of functional characteristics results from their high structural flexibility caused in the linkage of planar/non–planar BO3 groups and BO4 tetrahedra, which can occur as isolated or condensed structural units. This report is a brief review on crystal chemistry and structure features of anhydrous/high-temperature borates. Polymorphism of boron-oxygen radicals has been considered basing on cations’ nature and synthesis conditions. Analysis of the laws governing borates structures and general principles of their systematics was discussed. As a result, an alternative classification of anhydrous compounds has been considered. It is based on four orders of their subdivision: (1) by the variety of anion formers, (2) by the cation charge, (3) by the N = NM:NB, i.e., ratio of metal atoms number to the ratio of boron atoms number (N-factor) value indicating the borate structural type (if it is known), (4) by the cation type and size.

Salt effects on the dilute solution properties of bototo gum (Cochlospermum vitifolium)

<p><span style="line-height: 113%; font-family: 'Times New Roman',serif; font-size: 10pt; mso-fareast-font-family: 'Times New Roman'; mso-font-kerning: 14.0pt; mso-contextual-alternates: yes; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Salt effects on the dilute solution properties of bototo gum (<em>Cochlospermum vitifolium</em>) were investigated. There were measured the intrinsic viscosities of the polymer under study in water, in NaCl (at different concentrations) and in NaCl, CaCl₂ and AlCl₃, at the same ionic strength (I = 1), using an Ubbelohde viscometer at 25°C. The Huggins intersection model (R²) is more appropriate to determine the intrinsic viscosity than the Kraemer's equation. This parameter tends to reduce with the increase in the salt concentration and the cation charge. The molecules of <em>C. vitifolium</em> gum exudate in water (solvent Φ) tend to adopt a “random coil” conformation, of great volume and radius, which exist in two regimes: diluted and semi-diluted; in the presence of salts, the coils exist only in a diluted regime where they are separate each other. The macromolecules in water have probably an extended ellipsoid shape but in presence of salts, they change to another more compact, probably spherical, with radii and smaller volumes. The knowledge of the behavior of <em>C. vitifolium</em> gum molecules in dilute solutions is an important criterion for its rational use in various industries</span></p>