Only within the past decade has the potential of metal biosorption by biomass materials been well established. For economic reasons, of particular interest are abundant biomass types generated as a waste byproduct of large-scale industrial fermentations or certain metal-binding algae found in large quantities in the sea. These biomass types serve as a basis for newly developed metal biosorption processes foreseen particularly as a very competitive means for the detoxification of metal-bearing industrial effluents. The assessment of the metal-binding capacity of some new biosorbents is discussed. Lead and cadmium, for instance, have been effectively removed from very dilute solutions by the dried biomass of some ubiquitous species of brown marine algae such as Ascophyllum and Sargassum, which accumulate more than 30% of biomass dry weight in the metal. Mycelia of the industrial steroid-transforming fungi Rhizopus and Absidia are excellent biosorbents for lead, cadmium, copper, zinc, and uranium and also bind other heavy metals up to 25% of the biomass dry weight. Biosorption isotherm curves, derived from equilibrium batch sorption experiments, are used in the evaluation of metal uptake by different biosorbents. Further studies are focusing on the assessment of biosorbent performance in dynamic continuous-flow sorption systems. In the course of this work, new methodologies are being developed that are aimed at mathematical modeling of biosorption systems and their effective optimization. Elucidation of mechanisms active in metal biosorption is essential for successful exploitation of the phenomenon and for regeneration of biosorbent materials in multiple reuse cycles. The complex nature of biosorbent materials makes this task particularly challenging. Discussion focuses on the composition of marine algae polysaccharide structures, which seem instrumental in metal uptake and binding. The state of the art in the field of biosorption is reviewed in this article, with many references to recent reviews and key individual contributions.

Biosorption of Heavy Metals

The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.

The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties

Discovery of a Weyl Fermion Semimetal and Topological Fermi Arcs

A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, tantalum arsenide (TaAs). Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl fermion nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science.

https://science.sciencemag.org/content/sci/early/2015/07/15/science.aaa9297.full.pdf

Discovery of a Weyl fermion semimetal and topological Fermi arcs

Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

/pdf/the-effect-of-divalent-metals-on-the-properties-of-alginate-ihksjav3ds.pdf

The Effect of Divalent Metals on the Properties of Alginate Solutions. II. Comparison of Different Metal Ions.

/pdf/the-effect-of-divalent-metals-on-the-properties-of-alginate-5a2tqgzvpc.pdf

The Effect of Divalent Metals on the Properties of Alginate Solutions. I. Calcium Ions.

/pdf/the-molecular-structure-of-gaseous-dibenzene-chromium-c6h6-5a5nzwyjsh.pdf

The Molecular Structure of Gaseous Dibenzene Chromium (C6H6)2Cr.

/pdf/redetermined-crystal-structures-of-nite2-pdte2-pts2-ptse2-chv3i8vw39.pdf

Redetermined Crystal Structures of NiTe2, PdTe2, PtS2, PtSe2, and PtTe2.

/pdf/on-the-arsenides-and-antimonides-of-tantalum-40uchnbfci.pdf

Anders Westerdahl

Papers

The Effect of Divalent Metals on the Properties of Alginate Solutions. II. Comparison of Different Metal Ions.

The Effect of Divalent Metals on the Properties of Alginate Solutions. I. Calcium Ions.

The Molecular Structure of Gaseous Dibenzene Chromium (C6H6)2Cr.

Redetermined Crystal Structures of NiTe2, PdTe2, PtS2, PtSe2, and PtTe2.

On the arsenides and antimonides of tantalum