Papers by Keyword: Anion Exchange

Abstract: Solid-solution nanosheets (down to ~5 nm thick, in the form of flower like assemblies) of the (Y_0.95Eu_0.05)₂NO₃∙nH₂O were directly synthesized via chemical precipitation at the freezing temperature of ~4°C. In situ exchange of the interlayer NO₃^- with halogen anions produced a series of halogen derivatives (Y_0.95Eu_0.05)₂X∙nH₂O (X= F^-, Cl^-, Br^- and I^-) of the same layered structure and two-dimensional crystallite morphology. The basal spacing of the derivatives was discussed from the geometric size/spatial orientation of the anions and also from anion-host interaction via electrostatic attraction and hydrogen bonding. The thermal behavior and photoluminescence spectroscopies were found to be strongly related to the anion-host interactions.

Abstract: Ferric hydrosulfate minerals are commonly byproducts of biotic oxidation of Fe (II) in acid mine drainage and biohydrometallurgy like biogenic jarosite. In this study, adsorption of Cr (VI) on jarosite was a rapid process and the optimum pH for Cr (VI) adsorption was found at 7.0. The variation of Cr (VI) adsorbed on jarosite fitted the Langmuir adsorption isotherm models and the maximum adsorption capacity was 3.23 mg/g. It was evident that anion exchange mechanism was responsible for Cr (VI) adsorption on jarosite based on the sulfate leaching data and optimum pH experiments.

Abstract: Layered rare-earth hydroxide nanosheets (3-8 nm thick) of Y₂(OH)₅NO₃·nH₂O (NO₃^--LYH) were successfully synthesized in one step via chemical precipitation at ~4 °C and pH ~8, using yttrium nitrate and ammonium hydroxide as reagents. The interlayer NO₃^- was found to be free ions and can be completely replaced with SO₄^2- to yield Y₂(OH)₅(SO₄)_0.5·nH₂O (SO₄^2--LYH). Thermal decomposition behavior of the SO₄^2--LYH was studied in detail, and the phase and morphology evolutions upon calcination in the temperature range 500-1100 °C were also investigated. Characterizations via XRD, FE-SEM, TEM, and FT-IR found that anion exchange did not bring about any appreciable change to the 2-dimensional crystallite morphology but the basal spacing of the crystal structure shrank from ~0.884 to 0.840 nm owing to the indirect coordination of SO₄^2- to the Y³⁺ ions. DTA/TG and XRD analysis found that the NO₃^--LYH converts to Y₂O₃ at ~600 °C, but the SO₄^2--LYH decomposes to oxide at a higher temperature of ~1000 °C via monoclinic Y₂O₂SO₄ in the range of 800-900 °C. The resultant Y₂O₃ particles have an average size of ~60 nm.

Abstract: Hydrocalmite-like hydrate is one of calcium aluminate hydrated products. This hydrate has a layer structure and the principal layer, which is similar to calcium hydroxide define alternate with interlayer including divalent anions and water molecules. Their anions are able to react with outer anions by anion-exchange reaction. In this study, anion-exchange reaction between hydrocalmite-like hydrate including chloride anion (Ca₄Al₂(OH)₁₂·Cl₂·4H₂O, Cl-HC) and chromate anion (CrO₄^2-) is examined. CrO₄^2- is immobilized in various hydrated forms, which are varied with an increasing in the additive ratio of CaCrO₄ to Cl-HC. As the additive ratio of CaCrO₄ to Cl-HC is below 1.0 in molar, Ca₄Al₂(OH)₁₂·CrO₄·nH₂O (n=6 or 8, CrO₄-HC) is formed. In this case, the concentration of chromate ion in solution is less than 1.0 ×10^-3 mol·dm^-3 and over 99% of chromium immobilize in solid phase. However, when the additive ratio of CaCrO₄ is over 1.0, ettringite type hydrate including CrO₄^2- (Ca₆Al₂(OH)₁₂·3CrO₄ ·26H₂O) is generated and over 10 % of chromium is eluted from the solid phase.

Abstract: Takovite, a kind of hydrotalcite-like compounds (HTlcs), was used for boron removal from water. It was prepared by coprecipitation method and characterized by X-ray diffraction technique (XRD). The equilibrium time of boron sorption by takovite as well as its boron uptake capacities was determined by the reaction kinetic experiments and isotherm sorption experiments. The effects of experimental conditions on boron removal efficiency were also evaluated. Generally, the boron uptake by takovites increases with increasing initial boron concentration in solution. The isotherm sorption data match well with the Freundlich model, indicating that the anion exchange contributes a lot to solution deboronation. Moreover, at higher temperature, greater boron removal by takovite was observed. As compared to calcined takovite, uncalcined takovite has better performance in terms of boron uptake, since the structural restoration of calcined takovite didnt happen during its contact with boron-containing solution, which is quite different from the behavior of other HTlcs as reported.

Abstract: A new magnetic Fe₃O₄/MO-intercalated-LDH composite has been synthesized by combination of Fe₃O₄, layered double hydroxide (LDH) and methyl orange (MO). Fe₃O₄/Zn₂CrLDH and Fe₃O₄/MO-intercalated-LDH were obtained via two-step microwave hydrothermal and anion exchange method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometer (VSM) were conducted to characterize the as-prepared samples. The latter exhibited that basal spacing of Zn₂Cr-LDH is 1.18 nm. The value of saturation magnetization (M_s) is 20.5 emu/g. In addition, the amounts of adsorbed MO reached 1.54 mmol/g. Therefore, the material shows several advantages for the removal of pollutants.

Abstract: Three commercial resins (NDA150, NDA88 and NDA77) with different physicochemical properties were selected to investigate the adsorption behavior and primary factors controlling the adsorption of oxytetracycline (OTC) onto the resins. The adsorption kinetics of OTC onto all resins were fitted well to pseudo-second-order model. NDA150 had the largest adsorption capacity due to its higher surface area and larger total pore volume. Moreover, all of the three resins exhibited nearly the same equilibrium time because of their nearly the same particle size. The suitable pH for the effective adsorption of NDA150 and NDA77 is from 4 to 7, while the ideal pH for NDA88 is 10. OTC adsorption on all of the three resins increased with the increasing ionic concentration.

Abstract: The aim of this work was focused on developing a hydrotalcite by chemistry coprecipitation, which one was tested with one agricultural herbicide used in the region of the "Bajío" of the state of Guanajuato in Mexico. The clay was synthesized by a method by chemical precipitation at vacuum, and it was exposed to an herbicide for cultures control. The results showed that the hydrotalcitestructure and the toxic basicity, define their absorption in the hydrotalcite, performance fulfilling a function of soil recuperation.

Abstract: Hirudin is the most potent natural inhibitor of thrombin and a powerful anticoagulant. Large-scale production of recombinant hirudin is desirable for therapy. In this study, the gene encoding hirudin variant III was redesigned and synthesized by using Bacillus subtilis preferred codons, and the recombinant hirudin variant III (rHV3) was overexpressed in B. subtilis DB403 with strong anticoagulation activity for the first time. The hirudin activity from the supernatant of culture with optimized expression conditions could reach 210 ATU/ml. The protein in culture supernatant was precipitated by trichloroacetic acid, then desalted by ultrafiltration and purified by anion exchange chromatography. Strong anion Q F.F. performed better than weak anion DEAE F.F. The proper pH and conductivity was determined at pH 8 and 6 ms/cm, respectively. The maximum applied sample was 240 ATU/ml to medium of strong anion Q F.F. This optimized procedure was employed in strong anion exchange HiPrep 16/10Q with the 90% recovery rate and 70.2% purity. After gel filtration, the purity of rHV3 checked by HPLC could reach 95.1%, and the recovery rate was 93% for this step. The purified recombinant rHV3 showed a single band in SDS-PAGE. The rHV3 was stable at 100 °C and acidity condition, but was unstable under the condition of both heating and alkalinity. In conclusion, theses studies suggests that B.subtilis might be useful for the production of biologically active medicine peptides in secretion facilitating purification procedures, and that this isolation method was suitable for scale-up purification process at a low cost.

Abstract: The magnetic copolymer was prepared by polymerization of glycidyl methacrylate (GMA) and divinylbenzene (DVB) in the presence of OA-modified magnetic nano-particles. The magnetic strong-base anion exchange resin (MAER) was formed by quaternization of magnetic copolymer. Transmission electron microscope (TEM) and scanning electron microscope (SEM) were used for observation of prepared magnetic nano-particle and MAER, respectively. FT-IR spectrometer was used to characterize the magnetic nano-particle and MAER. To explore the potential application of MAER for natural organic matter (NOM) removal, completely-mixed (CMC) mode was used for humic acid (HA) adsorption. It was found that the HA removal for CMC mode with MAER resin was 10~20% higher than conventional process before breakthrough.