Equilibrium Sorption of Hexavalent Chromium from Aqueous Solution Using Iron(III)-Loaded Chitosan-Magnetite Nanocomposites As Novel Sorbent

This work describes magnetic separation of hexavalent chromium by iron(III)-loaded chitosan-magnetite nanocomposites. The Cr(VI) uptake data, studied at 25°C and 45°C, was well fitted into the Freundlich isotherm. The values of constant K_F and 1/n were found to be 1.515, 1.266 and 1.006 (mg g^?1) (l mg^?1)^1/n and 0.76, 0.77, and 0.71, respectively. The Dubinin-Kaganer-Radushkevich isotherm was applied to determine mean sorption energy E. The value of E was found to be in the 8.977 to 9.90 kJ mol^?1 range, thus indicating the chemical nature of the sorption process. The kinetics of Cr(VI) uptake was best interpreted by the Power function model. The intraparticle diffusion of sorbate was confirmed by the Bangham equation, and various thermodynamic parameters were also evaluated. Finally, a plausible mechanism has been suggested to understand the sorption process. The intraparticle diffusion was found to occur and later on confirmed by the Bangham equation. Finally, a plausible mechanism has been suggested for the observed Cr(VI) uptake on this newly developed sorbent. The various thermodynamic parameters were also evaluated.     

Solubility Study of the MH Buffer Assemblage in HCl Solutions at 300℃ and 500 bar

Using a gold cell hydrothermal apparatus the solubility of the MH (magnetite + hematite)buffer assemblage in HCl aqueous solutions was determined at 300℃ and 500 bar. The activity of ions in hydrothermal solutions was estimated, and the experiment data were treated by ridge regression and iteration to fit to all possible Fe speciation schemes. The result showed that the dominant Fe species in solutions was FeOH~+ under the run conditions. The equilibrium constant for the dissolution reaction was obtained, K=57.161. △G_5~0,FeOH~+ value of -260.3 kJ/mol at 300℃ and 500 bar was calculated. Fe basically exists as Fe-OH species in hydrothermal solution under geologically reasonable conditions of pH and chloride concentration.     

Structural and Electrical Properties of Iron-Containing Aluminosilicate Gel-Derived Pellets

Aluminosilicate pellets containing 10 mol% of Fe₂O₃, prepared by the sol-gel method, have been investigated. Electrical conductivity, dielectric constant, X-ray diffraction, scanning electron microscopy and electron paramagnetic resonance have been used to characterize the evolution of the samples with the heat-treatment temperature and atmospheric conditions. Results show that iron is present in the air heat-treated samples as Fe³⁺, goethite and hematite particles. Metallic iron and magnetite were identified in the samples heat-treated under reducing conditions. The d.c. conductivity decreases with increasing heat-treatment temperature of the samples indicating a variation, with the temperature, of the electrical free charges. However, in the case of the dielectric constant the samples heat-treated in air and under reducing conditions do not present the same behaviour. This variation was related with the microstructural evolution of the samples.     

Adsorption of surfactants on superfine magnetite

Superfine magnetite particles were obtained by chemical condensation. Their size can be varied by the magnetic field application and a change in the crystallization temperature. The X-ray diffraction and adsorption data suggested an increase in the crystallite size and a decrease in the value of limiting adsorption and specific area of magnetite with an increase in the temperature and magnetic field intensity. The nature of surfactants and solvents has a substantial effect on the adsorption process. The IR spectroscopic and equilibrium adsorption data showed that oleic acid has the highest affinity to the surface among the surfactants studied (stearic, oleic, and linoleic acids and sodium oleate). On going from carbon tetrachloride to hexane, the value of limiting adsorption of oleic acid decreases.     

Synthesis and characterization of water-soluble magnetite nanocrystals via one-step sol-gel pathway

Water-soluble magnetite nanocrystals have been prepared by one-step non-alkoxide sol-gel method.The magnetic properties of magnetite nanocrystals obtained are size dependent.The experimental results also reveal that 2-pyrrolidone not only serves as solvent,but also involves surface coordination which renders the magnetite nanoparticles water-soluble and colloidal solution stable.Although the current synthetic approach is a small modification to the non-alkoxide sol-gel method,it allows us to directly obtain...     

Application of nano-scale zero-valent iron adsorbed on magnetite nanoparticles for removal of carbon tetrachloride: Products and degradation pathway

Nano-scale zero-valent iron (nZVI) attached to Fe₃O₄ nanoparticles (Fe⁰@Fe₃O₄), which has better dispersibility and a larger specific surface area than the nanoparticles alone, were prepared and applied to the reductive dechlorination of carbon tetrachloride (CT). CT removal efficiencies by Fe⁰@Fe₃O₄ composites with different ratios of the two components were compared. Under optimum conditions, when the Fe⁰/Fe₃O₄ ratio was 1:2, almost no CT was detected after 50 min and it took only about 30 min to reach a removal efficiency of 90%, compared with 120 min for an Fe⁰/Fe₃O₄ ratio of 1:4. An increase in the amount of nZVI in the catalyst effectively improved the removal of CT and accelerated the reaction rate. Chloroform was the main product. Compared with Fe₃O₄ alone, a significant increase in the solution concentrations of ferrous and ferric ions occurred in the Fe⁰@Fe₃O₄ system: both Fe²⁺ and Fe³⁺ reached their maximum concentrations at 60 min and then tended to decline over the next 60 min. The increase in Fe²⁺ concentration was attributed to the reaction between nZVI and CT, which produces ferrous ions when electrons transfer from Fe⁰ to organic chlorides. Synergistic effects between the composite constituents promoted the relative rates of mass transfer to reactive sites and Fe²⁺ generated in solution facilitated the reduction of chlorinated organic pollutants by magnetite. Thus, Fe⁰@Fe₃O₄ nanoparticles effectively achieved reductive dechlorination of CT and provide an improved nZVI catalyst for the remediation of chlorinated organic compounds.     

Cobalt supported on dendronized magnetic nanoparticles: A new highly efficient and recyclable catalyst for the Mizoroki–Heck cross‐coupling reaction

Polyamidoamine (PAMAM) is one of the most interesting types of hyperbranched polymers that carry a large number of amino groups on its surface. PAMAM has gained significant attention from synthetic organic chemists due to its structural characteristics, controllable structure, inner porosity, and ability to trap a wide range of ions and molecules. So, in this work, the PAMAM dendrimer was synthesized, grafted onto the surface of magnetite nanoparticles, and the resulting hybrid nanoparticles were then employed as suitable host for immobilizing cobalt nanoparticles. The newly developed catalyst was well characterized by Fourier transform‐infrared, X‐ray diffraction, thermogravimetric analysis, field emission‐scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, element mapping and energy‐dispersive X‐ray analysis. The efficiency of the as‐prepared nanocatalyst was evaluated for the Mizoroki–Heck cross‐coupling reactions. The MNP@PAMAM‐Co represented perfect catalytic efficiency and high selectivity for the Mizoroki–Heck cross‐coupling reaction compared with previously reported catalysts. The catalyst separation from the reaction mixture was easily achieved with the assistance of an external magnetic field, and its recycling was also investigated for five consecutive runs. Hot filtration confirmed no leaching of the active metal during the Heck coupling.     

Synthesis and characterization of 4‐AMTT‐Pd(II) complex over Fe3O4@SiO2 as supported nanocatalyst for Suzuki‐Miyaura and Mizoroki‐heck cross‐coupling reactions in water

Immobilization of Pd(II) nanoparticles on silica‐coated modified magnetite particles has been readily achieved via a surface modification of Fe₃O₄ particles with 4‐amino‐5‐methyl‐4‐H‐1,2,4‐triazole‐3‐thiol (4‐AMTT) as a ligand. This magnetite nanocatalyst was characterized by various analyses such as FT‐IR, SEM/EDX, ICP‐AES, VSM, TEM, XRD, XPS and TGA. This nanocatalyst showed admirable catalytic activity for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions under mild conditions in water, and could be simply separated by an outer magnet and reused for several times.     

Butane‐1‐sulfonic acid immobilized on magnetic Fe3O4@SiO2 nanoparticles: A novel and heterogeneous catalyst for the one‐pot synthesis of barbituric acid and pyrano[2,3‐d] pyrimidine derivatives in aqueous media

Butane‐1‐sulfonic acid immobilized on magnetic Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂‐Sultone) was easily prepared via direct ring opening of 1,4‐butanesultone with nanomagnetic Fe₃O₄@SiO₂. The prepared reagent was characterized and used for the efficient promotion of the synthesis of barbituric acid and pyrano[2,3‐d] pyrimidine derivatives. All reactions were performed under mild and completely heterogeneous reaction conditions affording products in good to high yields. The catalyst is easily isolated from the reaction mixture by magnetic decantation and can be reused at least eight times without significant loss in activity.