Separation of vanadium and tungsten from synthetic and spent catalyst leach solutions using an ion-exchange resin

Vanadium and tungsten ion adsorption and desorption characteristics and separation conditions were investigated using a simple porous anion-exchange resin. Initially, systematic experimental research was performed using synthetic aqueous vanadium and tungsten solutions. To evaluate the vanadium and tungsten (50-500 mg L^-1) isotherm parameters, adsorption was performed at pH 7.0 using 0.5 g of ion-exchange resin at 303 K for 24 h. Well-known adsorption models such as Langmuir, Freundlich, and Temkin were used. Vanadium was desorbed from the resin using HCl and NaOH solutions. In contrast, tungsten was not desorbed by the HCl solution, which enabled the separation of the two ions. The desorption reaction reached equilibrium within 30 min of its start, yielding over 90% desorption. We investigated the adsorption mechanism and resin stability with the aid of spectroscopic and microscopic analysis, as well as adsorption results. The applicability and feasibility of the resin was tested via recovery of both metals from real spent catalysts. The applicability and reusability results indicated that the resin can be used for more than five cycles with an efficacy of over 90%.

The synthesis of W-O-W μ-oxo clusters by hydrolysis of tungsten aminoalkoxides and their structural characterisation

The tungsten aminoalkoxides W(O)(OPr(i))(3)L [L = dmae, OCH(2)CH(2)NMe(2) (1); bdmap, OCH(CH(2)NMe(2))(2) (2); tdmap, OC(CH(2)NMe(2))(3) (3)] have been synthesised. Controlled hydrolysis of 1-3 has allowed isolation of W(4)O(4)(μ-O)(6)(dmae)(4) (4), W(4)O(4)(μ-O)(4)(OPr(i))(4)(bdmap)(4) (5), W(6)O(6)(μ-O)(9)(tdmap)(6) (6), W(4)O(4)(μ-O)(6)(tdmap)(4) (7), W(4)O(4)(μ-O)(6)(tdmap)(4)·4H(2)O (7a), all of which have been characterised by X-ray crystallography. 4, 7, 7a each embody a W(4)O(6) core with adamantane structure, 5 incorporates a folded W(4)O(4) square and 6 has a trigonal prismatic W(6)O(9) at its heart. 7 decomposes in air at to give orthorhombic WO(3), while 1-3 decomposed under an autogenerated pressure (Reaction under Autogenic Pressure at Elevated Temperatures, RAPET) to form mixtures of carbon-coated WO(x) needles and carbon spherules.

One-pot fabrication and magnetic studies of Mn-doped TiO(2) nanocrystals with an encapsulating carbon layer

Mn-doped TiO(2) nanocrystals encapsulated in a carbon layer (Ti(1-x)Mn(x)O(2)@C) were synthesized by the one-pot RAPET (reaction under autogenic pressure at elevated temperature) technique. Manganese was doped into the body-centered tetragonal TiO(2) anatase phase to give a Mn:Ti atomic ratio of 1%, 5% and 10%. The surface modification by carbon was achieved in order to make the cubic/tetragonal nanocrystals non-toxic and biocompatible. Electron paramagnetic resonance (EPR) studies revealed a broad resonance (centered at g = 1.9977 due to the interacting spins in the oxide matrix) with increased dopant concentration and the resonance due to carbon. Manganese is mainly present as +II or +III oxidation states. The magnetic behavior was found to be very dependent on the manganese concentration with a ferromagnetic behavior of the 1% doped sample due to the coupling between carriers and manganese spins. A predominant paramagnetic behavior was observed for the higher Mn-doped samples. This study opens up a new dimension for the carbon encapsulation of room-temperature ferromagnetic diluted magnetic semiconductor (DMS) nanomaterials.

Core-shell nanorods of SnS-C and SnSe-C: synthesis and characterization

The straightforward, efficient, solventless, RAPET (reactions under autogenic pressure at elevated temperature) approach was explored for the fabrication of core-shell nanomaterials. Carbon-encapsulated SnS and SnSe nanorods were synthesized by a one-step thermal decomposition of tetramethyltin in the presence of either S or Se powder in a closed reactor at 700 degrees C for 40 min, under their autogenic pressure in an inert atmosphere. The powder X-ray diffraction measurements provided structural evidence for the formation of pure orthorhombic phases of SnS or SnSe particles. The Raman spectroscopy measurements ensured that the nature of the coated carbon was semigraphitic. The scanning electron micrographs verified the 1D morphology of the formed SnS and SnSe chalcogenides, and their stoichiometry was confirmed by EDAX measurements. The HR-TEM micrographs distinguished between core and shell morphologies. The nitrogen gas adsorption on the surface of core-shell nanostructures was determined by BET surface area analysis. The plausible mechanism for the creation of chalcogenide cores (SnS or SnSe) with a carbon shell was elucidated.

Synthesis of a Conducting SiO2−Carbon Composite from Commercial Silicone Grease and Its Conversion to Paramagnetic SiO2 Particles

The thermal decomposition of commercial silicone grease was carried out in a closed reactor (Swagelok) that was heated at 800 degrees C for 3 h, yielding a SiO2-carbon composite with a BET surface area of 369 m2/g. The bulk conductivity (5.72 x 10(-6) S x cm(-2)) of the SiO2-carbon composite was determined by impedance measurements. The as-prepared SiO2-carbon composite was further annealed at 500 degrees C in air for 2 h, which led to the formation of white paramagnetic silica particles (confirmed by ESR), possessing a surface area of 111 m2/g. The present synthetic technique requires unsophisticated equipment and a low-cost commercial precursor, and the reaction is carried out without a solvent, surfactant, or catalyst. The mechanism for the formation of a porous SiO2-carbon composite from the silicone grease is also presented.