Geological and radioactivity studies accompanied by uranium recovery: Um Bogma Formation,southwestern Sinai,Egypt

Journal of Radioanalytical and Nuclear Chemistry - High radioactive anomalies were recorded in the variegated claystones at the middle member of Um Bogma Formation, the eU-content reaches...     

Charge transport in boron-doped nano MOSFETs: Towards single-dopant electronics

We investigate the hole transport in p-channel field-effect transistors doped with boron, at low temperatures (6-28 K). In transistors with a relatively large dimension, we observe the acceptor-mediated hopping and carrier freezeout, both of which are strongly influenced by the gate bias. In nanoscale transistors, these features turn into single-charge tunneling, i.e., the trapping/detrapping of single holes by/from individual acceptors. The statistics of the appearance of the modulation in a few ten samples indicates that the number of acceptors is small, or even just one, indicating that what we have observed is single-charge-transistor operation by a single-acceptor quantum dot.     

Mechanosynthesis,magnetic and Mössbauer characterization of pure and Ti4+-doped cubic phase BiFeO3 nanocrystalline particles

The mechanosynthesis of cubic γ-phase pure BiFeO₃ and Ti⁴⁺-doped BiFeO₃ nanocrystalline particles and their preliminary characterization with magnetic measurements and Mössbauer spectroscopy are reported. The BiFeO₃ nanoparticles (5–40 nm) were prepared by heating a 48 h pre-milled 1:1 molar mixture of α-Bi₂O₃ and α-Fe₂O₃ at 400 °C for (1 h). Doping α-Fe₂O₃ in the initial mixture of reactants with Ti⁴⁺ was found to lead to the formation of Ti⁴⁺-doped BiFeO₃ nanoparticles by milling the reactants for 32 h. The magnetization of the BiFeO₃ nanoparticles is found to be tripled under a maximum external field of 1.35 T and their magnetic hardness increases by ～15 times relative to those of the corresponding bulk. The Ti⁴⁺-doped BiFeO₃ nanoparticles exhibit higher magnetization relative to the pure ones. These observations are related to the spiral modulated spin structure of the compound. The Mössbauer data show ～12 % of the BiFeO₃ nanocrystalline particles to be superparamagnetic having blocking temperatures of less than 78 K. The quadrupole shift values of the magnetic spectral component favor the cubic structural symmetry. These observations were mainly associated with possible collective magnetic excitations as well as transverse relaxation of canted surface spins. The Ti-doped BiFeO₃ nanoparticles gave statistically-poor Mössbauer spectra with no signs of a superparamagnetic behavior.     

First principle calculation of accurate native defect levels in CaF<Subscript>2</Subscript>

We report on the first principle density functional calculation of the charge transition levels of native defects (vacancies and interstitials) in CaF₂ structure. The transition level was defined as the Fermi level where two charge states of given defect have the same formation energy. The common error in the band gap inherited to semiclocal density functional has been accounted for by incorporating the hybrid density functional method, leading to correct placement of the transition levels within the band gap. The band gap size from hybrid calculation has been validated using the full potential, Linearized Augmented Planewave method with the Modified-Becke-Johnson exchange potential. Prior to level calculations, we ensured that an agreement between the formation energies from small (95–97 atoms) and large (323–325 atoms) supercells was achieved after applying the Makov-Payne correction method. Our calculated transition level for the anion vacancy was 2.97 eV below the conduction band, agreeing with the experimental optical absorption band at 3.3 eV associated with the electron transition from the ground state F-center to the conduction band in CaF₂.     

Enhancement of Cerium Sorption onto Urea-Functionalized Magnetite Chitosan Microparticles by Sorbent Sulfonation—Application to Ore Leachate

The recovery of strategic metals such as rare earth elements (REEs) requires the development of new sorbents with high sorption capacities and selectivity. The bi-functionality of sorbents showed a remarkable capacity for the enhancement of binding properties. This work compares the sorption properties of magnetic chitosan (MC, prepared by dispersion of hydrothermally precipitated magnetite microparticles (synthesized through Fe(II)/Fe(III) precursors) into chitosan solution and crosslinking with glutaraldehyde) with those of the urea derivative (MC-UR) and its sulfonated derivative (MC-UR/S) for cerium (as an example of REEs). The sorbents were characterized by FTIR, TGA, elemental analysis, SEM-EDX, TEM, VSM, and titration. In a second step, the effect of pH (optimum at pH 5), the uptake kinetics (fitted by the pseudo-first-order rate equation), the sorption isotherms (modeled by the Langmuir equation) are investigated. The successive modifications of magnetic chitosan increases the maximum sorption capacity from 0.28 to 0.845 and 1.25 mmol Ce g⁻¹ (MC, MC-UR, and MC-UR/S, respectively). The bi-functionalization strongly increases the selectivity of the sorbent for Ce(III) through multi-component equimolar solutions (especially at pH 4). The functionalization notably increases the stability at recycling (for at least 5 cycles), using 0.2 M HCl for the complete desorption of cerium from the loaded sorbent. The bi-functionalized sorbent was successfully tested for the recovery of cerium from pre-treated acidic leachates, recovered from low-grade cerium-bearing Egyptian ore.     

Biotechnological recovery of uranium (VI) from Abu Zeneima spent ore residue using green lixiviant

Journal of Radioanalytical and Nuclear Chemistry - Promising green leaching technique was used by Humic acid (HA) for removing uranium from Abu Zeneima spent residue for environmental safety and...     

Hydrolysis Behaviour of Some Heterocyclic Nitrogen Azomethines

Kinetics of base hydrolysis of some new heterocyclic azomethines derived from aminotriazol and aromatic aldehydes were investigated in the presence of NaOH in 60% (wt/wt) water-ethanol medium. The base hydrolysis of these Schiff bases is strictly first-order with respect to OH^? and Schiff. The rate-determining step is suggested to be the attack of the hydroxide ion on the free base. Effect of the molecular structure of both aldehydes and amines and the nature of organic hydroxylic solvent on the hydrolysis rate was investigated and discussed.