Adsorption of U (VI) ions from aqueous solution using silicon dioxide nanopowder

The adsorption kinetics for removal of uranium (V1) from aqueous solution using silicon dioxide nanopowder (nano-SiO₂) was investigated in batch and continuous techniques. Pseudo-first order and pseudo-second order were used to analyze the kinetics of batch experiments. In continuous technique the important parameters (initial concentration, flow rate and bed height) on the breakthrough curves were studied and the adsorption kinetics was analyzed using Thomas and Yoon and Nelson kinetic models. The comparison between the kinetic models was evaluated by the correlation coefficients (r²). The results indicated that the batch experiments fitted well with pseudo second-order kinetic model. The comparison of the experimental breakthrough curve to the breakthrough profile obtained from Thomas and Yoon and Nelson methods showed a satisfactory fit for silicon dioxide nanopowder.     

Nanocomposite particles with core-shell morphology II. An investigation into the affecting parameters on preparation of Fe3O4-poly (butyl acrylate-styrene) particles via miniemulsion polymerization

The encapsulation of inorganic particles with polymers is desirable for many applications in order to improve the stability of the encapsulated products and disperse ability in different media. Colloidal particles with magnetic properties have become increasingly important both technologically and for fundamental studies. This is due to their tunable anisotropic. In the absence of an applied magnetic field, the particles have isotropic sphere dispersion, whereas in an external magnetic field the particles form anisotropic structures. Here, latexes containing nanocomposite particles of styrene-butyl acrylate/Fe₃O₄ with core-shell structure were prepared through miniemulsion polymerization technique. Magnetic composite nanospheres with high magnetic content were synthesized through miniemulsion polymerization using a new process based on a three-steps preparation route including two miniemulsion processes: (1) preparing a dispersion of oleic acid coated magnetite particles in water; (2) mixing of modified magnetite particles with styrene/butyl acrylate in the presence of sodium dodecyl sulfate (SDS), sorbitane mono oleate (Span 80), hexadecane (HD) and (3) miniemulsification of the modified Fe₃O₄ into the monomer droplets to reach to complete encapsulation. Subsequent polymerization generated magnetic nanocomposite spheres. Hence, the copolymerization reaction was performed on the surface of such particles in order to obtain core-shell morphology for these nanoparticles, which were characterized by several techniques such as TEM, SEM, DLS, TGA, VSM and FT-IR. The magnetic copolymer particles with diameter of 120-170 nm were obtained. The effect of several parameters such as magnetite, surfactants and hydrophobe amounts on the stability, particle size and magnetization were investigated and also optimized.     

Removal of heavy metal ions from water by using poly(ethyleneglycol dimethacrylate-co-acrylamide) beads

Poly(ethyleneglycol dimethacrylate-co-acrylamide) (poly(EDGMA-co-AAm)) copolymer beads have been prepared for use in the separation Pb(II), Hg(II), and Cd(II), metal ions in aqueous solution by a batch equilibration technique. Adsorption capacity were increased with pH for Pb(II), Cd(II) and Hg(II) and then reached almost plateau value around 6.0. The high initial rate of metal ions uptake (<10 min) suggests that the adsorption occurs mainly at the bead surface. The metal uptake results show that poly(EGDMA-co-AAm) can be used for the adsorption of the following metals in the indicated order: Pb(II) > Cd(II) > Hg(II) expressed on a molar basis. However, when the uptake was expressed in terms of the amount of metal removed from solution was as follows: Pb(II) > Hg(II) > Cd(II). The beads still showed preference toward Pb(II) when this metal was in a mixture with Hg(II) and Cd(II). A linearized form of the Freundlich and the Langmuir isotherm model fits the experimental equilibrium concentration data of Hg(II) and Cd(II) better than isotherm type model of Pb(II). The recovery of the metal ions after adsorption and the regeneration of the adsorbent can be carried out by treatment of the loaded beads with either 0.5 M NaCl, or 1 M HNO₃.     

Amin-functionalized magnetic-silica core-shell nanoparticles for removal of Hg2+ from aqueous solution

Magnetic nanoparticles with monodisperse shape and size were prepared by a simple method and covered by silica. The prepared core-shell Fe₃O₄@silica nanoparticles were functionalized by amino groups and characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FT-IR) techniques. The synthesized nanoparticles were employed as an adsorbent for removal of Hg²⁺ from aqueous solutions, and the adsorption phenomena were studied from both equilibrium and kinetic point of views. The adsorption equilibriums were analyzed using different isotherm models and correlation coefficients were determined for each isotherm. The experimental data were fitted to the Langmuir–Freundlich isotherm better than other isotherms. The adsorption kinetics was tested for the pseudo-first-order, pseudo-second-order and Elovich kinetic models at different initial concentrations of the adsorbate. The pseudo-second-order kinetic model describes the kinetics of the adsorption process for amino functionalized adsorbents. The maximum adsorption occurred at pH 5.7 and the adsorption capacity for Fe₃O₄@silica-NH₂ toward Hg²⁺ was as high as 126.7 mg/g which was near four times more than unmodified silica adsorbent.     

Removal of zinc metal ion (Zn) from its aqueous solution by kaolin clay mineral: A kinetic and equilibrium study

A laboratory batch study has been performed to study the effect of various physic-chemical factors such as initial metal ion concentration, solution pH, and amount of adsorbent, contact time and temperature on the adsorption characteristics of zinc (Zn²⁺) metal ions onto kaolin. It has been found that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn²⁺) on kaolin is a two steps process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intra-particle diffusion in the interior of the adsorbent which has also been confirmed by intra-particle diffusion model. The equilibrium time is found to be in the order of 60 min. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetics among pseudo-first-order and intra-particle diffusion model. The different kinetic parameters including rate constant are determined at different initial metal ion concentration, solution pH, amount of adsorbent and temperature respectively. The equilibrium adsorption results are analyzed by both Langmuir and Freundlich models to determine the mechanistic parameters associated with the adsorption process. The value of separation factor, R_L from Langmuir equation also gives an indication of favorable adsorption. Finally thermodynamic parameters are determined at three different temperatures and it has been found that the adsorption process is exothermic due to negative ΔH° accompanied by decrease in entropy change and Gibbs free energy change (ΔG°).     

磁性Fe3O4@SiO2@ZrO2对水中磷酸盐的吸附研究

合成了以Fe₃O₄为核,以SiO₂为壳的磁性纳米微粒（Fe₃O₄@SiO₂）,并采用沉淀沉积法将ZrO₂包覆到材料表面。通过XRD、TEM、XPS和N₂吸附/脱附等手段对材料进行表征,结果表明材料Fe₃O₄@SiO₂@ZrO₂上沉积了氧化锆纳米颗粒,具有超顺磁性,可在外加磁场作用下实现从水中快速分离。同时系统研究了材料对水中磷酸盐的吸附行为,结果表明沉积ZrO₂使得材料对磷酸盐表现出良好的吸附性能,并且随着沉积量的增大吸附量增加。吸附等温线可用Freundlich方程拟合。吸附动力学可用拟二级动力学模型拟合,吸附速率随初始浓度增加而减缓。磷酸盐吸附量随溶液pH值的增大而减小,但几乎不受离子强度影响。     

Development of Fe3O4-poly(l-lactide) magnetic microparticles in supercritical CO2

The Fe₃O₄-poly(l-lactide) (Fe₃O₄-PLLA) magnetic microparticles were successfully prepared in a process of solution-enhanced dispersion by supercritical CO₂ (SEDS), and their morphology, particle size, magnetic mass content, surface atom distribution and magnetic properties were characterized. Indomethacin (Indo) was used as a drug model to produce drug-polymer magnetic composite microparticles. The resulting Fe₃O₄-PLLA microparticles with mean size of 803 nm had good magnetic property and a saturation magnetization of 24.99 emu/g. The X-ray photoelectron spectroscopy (XPS) test indicated that most of the Fe₃O₄ were encapsulated by PLLA, which indicated that the Fe₃O₄-PLLA magnetic microparticles had a core–shell structure. After further loading with drug, the Indo-Fe₃O₄-PLLA microparticles had a bigger mean size of 901 nm, and the Fourier transform infrared spectrometer (FTIR) analysis demonstrated that the SEDS process was a typical physical coating process to produce drug-polymer magnetic composite microparticles, which is favorable for drugs since there is no change in chemistry. The in vitro cytotoxicity test showed that the Fe₃O₄-PLLA magnetic microparticles had no cytotoxicity and were biocompatible, which means there is potential for biomedical application.     

Adsorption of poly(N-isopropylacrylamide-co-4-vinylpyridine) onto core-shell poly(styrene-co-methylacrylic acid) microspheres

Adsorption of the thermoresponsive copolymer of poly(N-isopropylacrylamide-co-4-vinylpyridine) (PNIPAM-co-P4VP) onto the core-shell microspheres of poly(styrene-co-methylacrylic acid) (PS-co-PMAA) is studied. The core-shell PS-co-PMAA microspheres are synthesized by one-stage soap-free polymerization in water. The copolymer of PNIPAM-co-P4VP is synthesized by free radical polymerization of N-isopropylacrylamide and 4-vinylpyridine in the mixture of DMF and water using K₂S₂O₈ as initiator. Adsorption of PNIPAM-co-P4VP onto the core-shell PS-co-PMAA microspheres results in formation of the composite microspheres of PS/PMAA-P4VP/PNIPAM. The driven force to adsorb the copolymer of P4VP-co-PNIPAM onto the core-shell PS-co-PMAA microspheres is ascribed to hydrogen-bonding and electrostatic affinity between the P4VP and PMAA segments. The resultant composite microspheres of PS/PMAA-P4VP/PNIPAM with surface chains of PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 33 °C.     

Synthesis and characterization of monodisperse spherical SiO2@RE2O3 (RE=rare earth elements) and SiO2@Gd2O3:Ln (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles with core-shell structure

Spherical SiO₂ particles have been coated with rare earth oxide layers by a Pechini sol-gel process, leading to the formation of core-shell structured SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence spectra as well as lifetimes were used to characterize the resulting SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺, Er³⁺, Ho³⁺) samples. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 380 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (40 nm for two deposition cycles). Under the excitation of ultraviolet, the Ln³⁺ ion mainly shows its characteristic emissions in the core-shell particles from Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, Er³⁺, Ho³⁺) shells.     

Highly efficient removal of Cr(VI) from wastewater via adsorption with novel magnetic Fe3O4@C@MgAl-layered double-hydroxide

Novel magnetic Fe₃O₄@C@MgAl-layered double-hydroxide (LDH) nanoparticles have been successfully prepared by the chemical self-assembly methods. The properties of surface functional groups, crystal structure, magnetism and surface morphology of magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravity-differential thermal gravity (TG-DTG), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The adsorption studies of the novel adsorbent in removing heavy metals Cr (VI) from waste water showed that the maximum absorption amount of Cr(VI) was 152.0 mg/g at 40℃ and pH 6.0. The excellent adsorption capacity of the Fe₃O₄@C@MgAl-LDH nano-absorbents plus their easy separation, environmentally friendly composition and reusability makes them more suitable adsorbents for the removal of metal ions from waste water.     

Electrorheological properties and structure of (BaTiO(C2O4)2/NH2CONH2)

The core-shell structural (BaTiO(C₂O₄)₂/NH₂CONH₂) samples of giant electrorheological (ER) activity have been synthesized by a sol-gel method and studied by TEM, X-ray diffraction and IR spectroscopy. From the analysis of the X-ray diffraction, it is found that the component of samples is (BaTiO(C₂O₄)₂/NH₂CONH₂) with a different content of urea. The observations of the TEM morphology show that (BaTiO(C₂O₄)₂/NH₂CONH₂) particles are spheral with a size of around 80 nm and a surface coating with 5-10 nm thickness consisting of urea. The samples show an increasing tend of ER effect as the addition of urea increasing. Moreover, by IR spectroscopy study, it is revealed that some peaks of CO band and C-O band vibrations of BaTiO(C₂O₄)₂ are split into two peaks after urea added. The extent of the splits increase with the increase of urea content, which is resulted by the interaction between the chemical bonds of urea and oxalate of BaTiO(C₂O₄)₂. It is evident that the giant ER activity of the sample has a close relationship with the interfacial polarization between the core and the shell of (BaTiO(C₂O₄)₂/NH₂CONH₂).     

Preparation and ion chromatographic properties of a new core-shell chromatographic support Al2O3/SiO2-10

A new stationary phase Al₂O₃/SiO₂-10 was prepared and characterized by XPS, XRD, SEM and surface analysis. The anion exchanger properties of this new stationary phase were investigated by the separation of inorganic anions in ion chromatography (IC). pH of the mobile phase, concentration and strength of the Lewis base of the elute, and the organic modifier of the mobile phase strongly affect the separation of inorganic anions, and anion exchange selectivities of the analyte on the new support are significantly different from quaternary ammonium styrene based anion exchangers. The result of separation of inorganic anions shows that the new stationary phase provides excellent column efficiency, well-defined chromatographic peaks and favorable retention times.     

Yb/Er掺杂Y2O3纳米核壳颗粒的荧光性能及体内标定研究

为改善无机Y2O3上转换纳米粒子(UCNPs)的荧光性能,且同步实现其在生物体内的成像标定,通过共沉淀法及梯度合成工艺,制备出各组不同壳层厚度的Y2O3:Yb³⁺,Er³⁺@Y2O3:Yb³⁺ UCNPs。利用透射电子显微镜(TEM)扫描、X射线衍射(XRD)、上转换荧光(UCL)光谱、UCL寿命等对样品的形貌、结构及荧光性能进行了表征。结果表明：利用共沉淀法制得小尺寸Y2O3:Yb³⁺,Er³⁺@Y2O3:Yb³⁺纳米核壳颗粒,平均粒径范围在25.57~26.24 nm之间。通过调整Yb³⁺浓度和水浴时间优化合成工艺,获得高发射强度、长荧光寿命方案(80% Yb掺杂,8 h水浴)。高红绿比的荧光发射特征,决定其在小动物体内荧光标定检测时更宜采用红色信道。     

Removal of Cu(II), Cd(II) and Cr(III) ions from aqueous solution by dam silt

The removal of heavy metals, such as Cu(II), Cd(II) and Cr(III) from aqueous solution was studied using Chorfa silt material (Mascara, Algeria). The main constituents of silt sediment are quartz, calcite and mixture of clays. The experimental data were described using Freundlich, Langmuir, Dubinin–Radushkevich (D–R) and Langmuir–Freundlich models. The adsorbed amounts of chromium and copper ions were very high (95% and 94% of the total concentration of the metal ions), whereas cadmium ion was adsorbed in smaller (55%) amounts. The Langmuir–Freundlich isotherm model was the best to describe the experimental data. The maximum sorption capacity was found to be 26.30, 11.76 and 0.35 mg/g for Cr³⁺, Cu²⁺ and Cd²⁺, respectively. The results of mean sorption energy, E (kJ/mol) calculated from D–R equation, confirmed that the adsorption of copper, chromium and cadmium on silt is physical in nature.     

Removal of Th(IV) ions from aqueous solution using bi-functionalized algae-yeast biosorbent

Composites could be more effective adsorbents than inorganic and organic components individually. In the present study, the red macro marine algae, Jania Rubens and yeast, Saccharomyces cerevisiae immobilized on silica gel were used as a constituent of bi-functionalized biosorbent to remove thorium ions from aqueous solution. Optimum biosorption conditions were determined as a function of pH, initial Th(IV) concentration, contact time, temperature, volume/mass ratio and co-ion effect. The morphological analysis of the biocomposite was performed by the scanning electron microscopy and functional groups in the biosorbent were determined by FT-IR spectroscopy. In order to find the adsorption characteristics, Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherms were applied to the adsorption data. The data were well described by Langmuir adsorption isotherms while the fit of Freundlich adsorption isotherms and Dubinin–Radushkevich equation to adsorption data was poor. Using the equilibrium constant value obtained at different temperature, the thermodynamics properties of the biosorption (ΔG°, ΔH° and ΔS°) were also determined. The results show that biosorption of Th(IV) ions onto biocomposite was exothermic nature, spontaneous and more favorable at lower temperature under examined conditions.     

A facile two-step modifying process for preparation of poly(SStNa)-grafted Fe3O4/SiO2 particles

This article reports the synthesis of the poly(sodium 4-styrenesulfonate)-grafted Fe₃O₄/SiO₂ particles via two steps. The first step involved magnetite nanoparticles (Fe₃O₄) homogeneously incorporated into silica spheres using the modified Stöber method. Second, the modified silica-coated Fe₃O₄ nanoparticles were covered with the outer shell of anionic polyelectrolyte by surface-initiated atom transfer radical polymerization. The resulted composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive microscopy (EDS), Fourier transform-infrared (FT-IR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and vibration sample magnetometer (VSM). The XRD results indicated that the surface modified Fe₃O₄ nanoparticles did not lead to phase change compared with the pure Fe₃O₄. TEM studies revealed nanoparticles remained monodisperse. The detection of sulfur and sodium signals was a convincing evidence that sodium 4-styrenesulfonate was grafted onto the surface of the magnetic silica in XPS analysis. Finally, super-paramagnetic properties of the composite particles, and the ease of modifying the surfaces may make the composites of important use in mild separation, enzyme immobilization, etc.     

Synthesis of SiO2/Y2O3:Eu core-shell materials and hollow spheres

The SiO₂/Y₂O₃:Eu core-shell materials and hollow spheres were first synthesized by a template-mediated method. X-ray diffraction patterns indicated that the broadened diffraction peaks result from nanocrystals of Y₂O₃:Eu shells and hollow spheres. X-ray photoelectron spectra showed that the Y₂O₃:Eu shells are linked with silica cores by Si-O-Y chemical bond. SEM and TEM observations showed that the size of SiO₂/Y₂O₃:Eu core-shell structure is in the range of 140-180 nm, and the thickness of Y₂O₃:Eu hollow spherical shell is about 20-40 nm. The photoluminescence spectra of SiO₂/Y₂O₃:Eu core-shell materials and Y₂O₃:Eu hollow spheres have better red luminescent properties, and the broadened emission bands came from the size effects of nanocrystals composed of Y₂O₃:Eu shell.     

Synthesis and characteristic of the Fe3O4@SiO2@Eu(DBM)3·2H2O/SiO2 luminomagnetic microspheres with core-shell structure

The core-shell structured luminomagnetic microsphere composed of a Fe₃O₄ magnetic core and a continuous SiO₂ nanoshell doped with Eu(DBM)₃·2H₂O fluorescent molecules was fabricated by a modified Stöber method combined with a layer-by-layer assembly technique. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), confocal microscopy, photoluminescence (PL), and superconducting quantum interface device (SQUID) were employed to characterize the Fe₃O₄@SiO₂@Eu(DBM)₃·2H₂O/SiO₂ microspheres. The experimental results show that the microshpere has a typical diameter of ca. 500 nm consisting of the magnetic core with about 340 nm in diameter and silica shell doped with europium complex with an average thickness of about 80 nm. It possesses magnetism with a saturation magnetization of 25.84 emu/g and negligible coercivity and remanence at room temperature and exhibits strong red emission peak originating from electric-dipole transition ⁵D₀ → ⁷F₂ (611 nm) of Eu³⁺ ions. The luminomagnetic microspheres can be uptaken by HeLa cells and there is no adverse cell reaction. These results suggest that the luminomagnetic microspheres with magnetic resonance response and fluorescence probe property may be useful in biomedical imaging and diagnostic applications.     

Fabrication and luminescent properties of the core-shell structured YNbO4:Eu/Tb@SiO2 spherical particles

The core-shell structured YNbO₄:Eu³⁺/Tb³⁺@SiO₂ particles were realized by coating the YNbO₄:Eu³⁺/Tb³⁺ phosphors onto the surface of spherical silica via a sol-gel process. The obtained materials were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra. The results indicate that 600 °C annealed samples consist of amorphous silica core and crystalline YNbO₄:Re shell, having perfect spherical morphology with uniform size distribution. Upon excitation by UV or electron beam, these phosphors show the characteristic ⁵D₀-⁷F_1-4 emission lines of Eu³⁺ and the characteristic ⁵D₄-⁷F_3-6 emission lines of Tb³⁺. The PL intensities of Eu³⁺ can be tuned by altering the annealing temperature and the coating number of YNbO₄:Eu³⁺ layers.     

过渡金属修饰Fe2O3/Al2O3氧载体的Redox性能研究

采用冷冻干燥法分别制备了经Cu、Co、Mn、Ni修饰的Fe₂O₃/Al₂O₃氧载体。利用化学吸附仪,通过程序升温还原(H₂-TPR)和程序升温氧化(TPO)来研究经不同过渡金属修饰的Fe₂O₃/Al₂O₃与H₂和O₂的反应性能。实验发现,在Fe₂O₃/Al₂O₃中加入Cu、Co、Ni以后,氧载体与H₂的反应性都有提高,但是当在Fe₂O₃/Al₂O₃中加入Mn以后,氧载体的反应性和载氧能力反而下降。经Cu修饰的Fe₂O₃/Al₂O₃与H₂的反应性最高,且具有很好的反应稳定性,适合用于化学链燃烧。