Efficient artificial mineralization route to decontaminate Arsenic(III) polluted water -the Tooeleite Way

Increasing exposure to arsenic (As) contaminated ground water is a great threat to humanity. Suitable technology for As immobilization and removal from water, especially for As(III) than As(V), is not available yet. However, it is known that As(III) is more toxic than As(V) and most groundwater aquifers, particularly the Gangetic basin in India, is alarmingly contaminated with it. In search of a viable solution here, we took a cue from the natural mineralization of Tooeleite, a mineral containing Fe(III) and As(III)ions, grown under acidic condition, in presence of SO42- ions. Complying to this natural process, we could grow and separate Tooeleite-like templates from Fe(III) and As(III) containing water at overall circumneutral pH and in absence of SO42- ions by using highly polar Zn-only ends of wurtzite ZnS nanorods as insoluble nano-acidic-surfaces. The central idea here is to exploit these insoluble nano-acidic-surfaces (called as INAS in the manuscript) as nucleation centres for Tooeleite growth while keeping the overall pH of the aqueous media neutral. Therefore, we propose a novel method of artificial mineralization of As(III) by mimicking a natural process at nanoscale

Theoretical Study of Small Iron–Oxyhydroxide Clusters and Formation of Ferrihydrite

Hydrolysis of iron compounds in water leads to the formation of Fe­(III) oyxhydroxide-based minerals like ferrihydrite, which act as natural scavengers of inorganic contaminants in the environment. Though studied widely, experimental identification of these oxyhydroxides remains very difficult due to their extreme reactivity. The present study theoretically investigates the formation of Fe­(III) oxyhydroxides starting from a single hydrated Fe­(III) ion, modeling the formation of larger clusters gradually. The structures, formation enthalpies, and free energies of dimers, trimers, tetramers, and even larger Fe­(III) oxyhydroxide clusters comprising of Fe₅, Fe₇, and Fe₁₃–Keggin ions in gaseous phase and in aqueous medium (using self-consistent reaction field method) are systematically studied using density functional theory. Spontaneous formation of certain multinuclear Fe­(III) oxyhydroxide clusters with clear structural signatures of ferrihydrite highlights their potential as prenucleation clusters in the course of mineralization

Adsorbed hypostrophene: can it roll on a surface by rearrangement of bonds?

Hypostrophene is well-known to undergo the degenerate Cope rearrangement. Our calculations show that hypostrophene chemisorbed on the Al(1 0 0) surface can undergo a similar rearrangement involving only single bonds, resulting in a net movement of the molecule on the surface. The activation energy is found to be 16.9 kcal/mol. The usual diffusional (sliding) motion is found to have activation energy about five times larger. Degenerate Cope rearrangement of free hypostrophene has a barrier of 25.3 kcal/mol and the metal decreases this value, even though the adsorbed molecule has no double bonds in it

Adsorbed hypostrophene:can it roll on a surface by rearrangement of bonds?

Hypostrophene is well-known to undergo the degenerate Cope rearrangement. Our calculations show that hypostrophene Chemisorbed on the Al(100) surface can undergo a similar rearrangement involving only single bonds, resulting in a net movement of the molecule on the surface. The activation energy is found to be 16.9 kcal/mol. The usual di€usional (sliding) motion is found to have activation energy about five times larger. Degenerate Cope rearrangement of free hypostrophene has a barrier of 25.3 kcal/mol and the metal decreases this value, even though the adsorbed molecule has no double bonds in it

Evaluation of the impact of different heat treatments on the toughness and tempering resustance for a Cr-Mo-V hot-work tool steel

High Pressure Die Casting (HPDC) has very high demands on toughness and tempering resistance of the tool. A typical hardening cycle for this purpose consists on austenitizing and quenching in a vacuum furnace followed by three temperings at 600°C. In this work the possibility of optimizing the toughness and tempering resistance in Uddeholm Dievar by adding an extra tempering at the beginning and/or the end of the tempering process is investigated. Extra temperings were performed at 300-400° and hardness levels, impact toughness and tempering resistance were evaluated. Microstructural investigations as well as thermodynamical calculations were also carried out. Results showed no feasible differences between the results of the here conducted tests and those from the common tempering procedures

Molecular roller and rocker on surfaces

We present theoretical studies of a 'molecular roller' and a 'molecular rocker.' syn-tricyclooctadiene molecule chemisorbed on Al(100) can undergo a 'Cope like' rearrangement and behave like a molecular roller. The barrier height for the rolling motion is found to be 13.64 kcal/mol. We also present our results for a molecular rocker—semibullvalene molecule chemisorbed on Al(100) surface. We find that it can behave like a rocker with a barrier height of 21.57 kcal/mol for the rocking motion

(QCO)+(QCO)^{+} as the model for bonding in non-classical carbonyls: a force approach study

As a model for non-classical metal carbonyls, we investigate CO in presence of a unit positive charge placed at different distances along the bond axis. We use the force approach, to look into the nature of the individual molecular orbitals. We find that in free CO the HOMO(\sigma(3)) is antibinding. As the positive charge approaches form carbon side, \sigma(l) and degenerate 77 orbitals become more binding,while \sigma(2) and \sigma(3) become more antibinding. The overall effect is more binding resulting in a shorter C-O bond. If the charge approaches from oxygen side, then \sigma(l), \sigma(3) and degenerate piorbitals become less binding, while \sigma(2) becomes slightly more binding, resulting in a lengthening of C-O bond

(QCO)<SUP>+</SUP> as the model for bonding in non-classical carbonyls: a force approach study

As a model for non-classical metal carbonyls, we investigate CO in presence of a unit positive charge placed at different distances along the bond axis. We use the force approach, to look into the nature of the individual molecular orbitals. We find that in free CO the HOMO (σ (3)) is antibinding. As the positive charge approaches form carbon side, σ (1) and degenerate Π orbitals become more binding, while σ (2) and σ (3) become more antibinding. The overall effect is more binding resulting in a shorter C-O bond. If the charge approaches from oxygen side, then σ (1), σ (3) and degenerate Π orbitals become less binding, while σ (2) becomes slightly more binding, resulting in a lengthening of C-O bond

Fluxional hopping of Fe(CO)<SUB>3</SUB> in some of its complexes with dienes

We first present a theoretical study of the Cope rearrangement of syn-tricyclooctadiene molecule. We find that the barrier height for the rearrangement is about 24 kcal/mol. We also investigate the possibility of fluxionality in hypothetical tricarbonyliron complexes of hypostrophene, syn-tricyclooctadiene, semibullvalene and 1,5-hexadiene (boat) in which the double bonds of the ligands coordinate to the Fe(CO)3 moiety. The ligands can undergo Cope rearrangement in which the double bonds are shifted and this can be accompanied by the hopping of Fe(CO)3 unit so as to be coordinated by the newly formed double bonds. We find that the barrier height for this process, varies from 22 to 37 kcal/mol

Structural Rearrangement Followed by Entrapment of Subnanometer Building Blocks of Iron Oxyhydroxide in Aqueous Iron Chloride Solutions

Iron oxyhydroxide, a natural nanophase of iron found in the environment, plays a crucial role in regulating surface and groundwater composition. Recent research proposes that within the nonclassical prenucleation cluster growth model, subnanometer-sized clusters (olation clusters/Fe-13 delta-Keggin oxolation clusters) might act as the prenucleation clusters (PNCs) of ferrihydrite or iron oxyhydroxide solid phase. However, these clusters are difficult to characterize as they are only observable momentarily in low-pH, high-Fe concentration solutions before agglomerating into extended solids, keeping the controversy over the true nature of the PNCs alive. In this study, we introduce large quantities of zinc acetate salt (ZA) into iron chloride solutions at the olation-oxolation boundary (3.6 mM Fe3+ at pH similar to 2.6). Remarkably, this manipulation is found to alter the structural arrangement of these subnanometer clusters before blocking them in isolation for hours, even at pH 6, where extended iron oxyhydroxide phases typically precipitate. On the other hand, controlled addition of ZA allows partial unblocking, leading to anisotropic agglomeration into cylindrical rod-like structures. Experimental techniques such as synchrotron-based small-angle X-ray scattering, X-ray absorption spectroscopy, high-resolution transmission electron microscopy (TEM), and cryo-TEM, along with density functional theory (DFT) calculations, reveal the nature of the structural rearrangement and the crucial role of Zn2+ ions in cluster stabilization