Adsorption-desorption mechanism of phosphate by immobilized nano-sized magnetite layer: interface and bulk interactions

Phosphate adsorption mechanism by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon (nFe-GAC) was studied for both interface and bulk structures. X-ray Photoelectron Spectroscopy (XPS) analysis revealed phosphate bonding to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. Initially, phosphate was adsorbed by the active sites on the magnetite surface, after which it diffused into the interior of the nano-magnetite layer, as indicated by intraparticle diffusion model. This diffusion process continues regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake. Desorption, using NaOH solution, was found to be predominantly a surface reaction, at which hydroxyl ions replace the adsorbed phosphate ions only at the surface outer biding sites. Five successive fix-bed adsorption/regeneration cycles were successfully applied, without significant reduction in the nFe-GAC adsorption capacity and at high regeneration efficiency.     

二季戊四醇磷酸酯的合成、表征及阻燃性能测试

以磷酸和季戊四醇为原料,采用直接酯化法合成阻燃剂二季戊四醇磷酸酯,对样品进行了表征,并对合成工艺及其在聚烯烃中的阻燃性能进行了研究.确定最佳合成条件:二甲苯为带水剂;反应温度180-200℃;反应时间6-7h.将此阻燃剂与聚磷酸铵按40/60(质量比)复配添加到聚烯烃中,样品比重30%时阻燃级别可达UL94V-0级.     

Fixed bed phosphate adsorption by immobilized nano-magnetite matrix: experimental and a new modeling approach

Nano-sized magnetite impregnated charcoal granular activated carbon (nFe-GAC) was utilized for the removal of phosphate from aqueous solutions using a fixed bed column. The dynamic of the phosphate adsorption was analyzed using a new approach to the Thomas model based on a two-step differential sorption rate process. The initial adsorption was found to be external mass transfer controlled, while intra-particle diffusion was the predominant mechanism in the latter stage. Consequently, two kinetic coefficients were calculated for each breakthrough curve resulting in an excellent model prediction. By implementing this approach a transition point, at which diffusion becomes the predominant adsorption mechanism, can be accurately determined. The effect of varying parameters, such as feed flow rates, feed pH, initial phosphate concentrations and adsorbent bed height were examined and described using the modified Thomas model. Reaction rates increased with augmentation of the flow rates from 1 to 40 mL/min while the adsorption capacity and transition point decreased. Similar transition points were obtained for initial phosphate concentrations between 10 and 100 mg/L. The unique characteristics of the nFe-GAC were evident as it exhibited very high phosphate adsorption capacity, at a wide range of pH values (4–9) with negligible effect of competing ions and short critical bed depth.     

Phenols removal by immobilized tyrosinase reactor in on-line high performance liquid chromatography

The development of an immobilized enzyme reactor (IMER) based on tyrosinase immobilized on aminopropyl-controlled pore glass (AP-CPG) for the removal of phenols from model aqueous solutions was reported. To elucidate the influence of the substrate nature, the apparent (V'max, K'm) and the inherent (Vmax, Km) Michaelis-Menten constants were determined by Lineweaver-Burk method and the external diffusional contributions on measured enzyme activities were removed by a graphical method. The dephenolization process was realized by recycling the phenol solutions through the bioreactor connected to a chitosan trap in order to remove the colored quinone-type products of the tyrosinase reactions. The results indicated that a complete removal of phenol derivatives in the range of 150-300 min, with the exception of 60% removal for phenol reached in 400 min, was obtained. The observed sequence: cresol > 4-methylcathecol > catechol > 4-Cl-phenol phenol was in accordance to the V'max/K'm values.     

Magnetic porous polymer microspheres: Synthesis,characterization and adsorption performance for the removal of phenol

The magnetic poly(ethylene glycol dimethacrylate-n-vinylimidazole) (Fe₃O₄@poly (EGDMA@VIM)) microspheres were prepared by suspension polymerization method using magnetite Fe₃O₄ nano-powder and the porosity, morphology, chemical composition and structure of the magnetic polymer microspheres were characterized. The specific surface area and swelling ratio of the Fe₃O₄@poly(EGDMA@VIM) microspheres were found to be 278.6?m²·g^–1 and 48%, respectively. The Fe₃O₄@poly(EGDMA@VIM) microspheres were used as an adsorbent for phenol removal. The effects of the parameters such as adsorbent dosage, temperature, pH and initial concentration of phenol solutions on the adsorption were investigated. The experimental adsorption equilibrium data obtained were fitted with Langmuir, Freundlich and Dubinin-Radushkevich isotherms and the pseudo-first-order, pseudo-second-order and intra–particle diffusion kinetic models. The adsorption equilibrium data agreed well with the Freundlich isotherm and the pseudo-second-order kinetic model. The maximum capacity of the Fe₃O₄@poly(EGDMA@VIM) microspheres was calculated to be 33.83?mg·g^–1 at 298?K and natural pH from Langmuir isotherm. The Fe₃O₄@poly(EGDMA@VIM) microspheres were found to be reusable for removal of phenol after desorption for several times. The result indicated that the Fe₃O₄@poly(EGDMA@VIM) microspheres are potential candidate for removal of phenol in wastewaters.     

二季戊四醇磷酸酯三聚氰胺盐的合成及阻燃性能测试

以磷酸、季戊四醇、三聚氰胺为原料,通过酸醇直接酯化和烘焙中和两步反应合成膨胀型阻燃剂二季戊四醇磷酸酯三聚氰胺盐,并对烘焙中和反应条件及其在聚乙烯中的阻燃性能进行了研究.确定最佳合成条件:n (二季戊四醇磷酸酯):n (三聚氰胺)=1:1;反应温度130-140℃;反应时间3-4h.将此阻燃剂添加到聚乙烯中,样品重量35...     

Synthesis of nano‐sized magnetite mesoporous carbon for removal of Reactive Yellow dye from aqueous solutions

In this study, core‐shell structures of magnetite nanoparticles coated with CMK‐8 ordered mesoporous carbon (Fe₃O₄@SiO₂‐CMK‐8 NPs) have been successfully synthesized for the first time by carbonizing sucrose inside the pores of the Kit‐6 mesoporous silica. The nano‐sized mesoporous particles were characterized by X‐ray diffraction, Fourier transform‐infrared spectroscopy, scanning electron microscope, dynamic light scattering, vibrating‐sample magnetometer, Brunauer–Emmett–Teller (BET) and transmission electron microscopy instruments. The obtained nanocomposite was used for removal of Reactive Yellow 160 (RY 160) dye from aqueous samples. The N₂ adsorption–desorption method (at 77 K) confirmed the mesoporous structure of synthesized Fe₃O₄@SiO₂‐CMK‐8 NPs. Also, the surface area was calculated by the BET method and Langmuir plot as 276.84 m²/g and 352.32 m²/g, respectively. The surface area, volume and pore diameter of synthesized nanoparticles (NPs) were calculated from the pore size distribution curves using the Barrett–Joyner–Halenda formula (BJH). To obtain the optimum experimental variables, the effect of various experimental parameters on the dye removal efficiency was studied using Taguchi orthogonal array experimental design method. According to the experimental results, about 90.0% of RY 160 was removed from aqueous solutions at the adsorbent amount of 0.06 g, pH 3 and ionic strength = 0.05 m during 10 min. The pseudo‐second order kinetic model provided a very good fit for the RY 160 dye removal (R² = 0.999). The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were applied to describe the equilibrium isotherms, and the Langmuir isotherm showed the best fit to data with the maximum adsorption capacity of 62.893 mg/g. Furthermore, the Fe₃O₄@SiO₂‐CMK‐8 NPs could be simply recovered by external magnet, and exhibited recyclability and reusability for a subsequent six runs.     

Synthesis and characterization of magnetite nanoparticles for photocatalysis of nitrobenzene

The present work shows the photocatalytic degradation of nitrobenzene (NB) using Fe₃O₄ magnetic nanoparticles (MNP) as a photocatalyst in the presence of UV light. The MNP were synthesized by an ultrasonic-assisted reverse co-precipitation (US-RP) method using FeSO₄, FeCl₃ and NH₄OH as precursors. The prepared nanoparticles were characterized by UV–vis spectroscopy, attenuated total reflectance Fourier transformed infrared spectroscopy (ATR FT-IR), Raman spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Dynamic light scattering (DLS), Zeta potential, Vibrating sample magnetometer (VSM) and Magnetic thermogravimetric analysis (MTGA). The successive decrement in the absorbance at 265 nm shows the effective decrease in NB concentration measured by UV–vis spectroscopy. The reaction intermediates detected by gas chromatography/mass spectrum (GC/MS) were 2-nitrophenol (2-NPh), 3-nitrophenol (3-NPh) and 4-nitrophenol (4-NPh). The prepared MNP showed an optimal NB degradation at an initial pH of 2 and 100 ppm of the photocatalyst.     

Synthesis and characterization of polystyrene-grafted magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticles were synthesized by chemical precipitation. To reduce the aggregation of Fe₃O₄ nanoparticles, an effective surface modification method was proposed by grafting polystyrene onto the Fe₃O₄ particles. The results of Fourier transform infrared spectra and elemental analysis showed that the polymer chains have been successfully grafted from the surface of the Fe₃O₄ nanoparticles and that the percentage of grafting can reach 73%. Transmission electron microscope showed that grafted polymer chains on nanoparticles could prevent the aggregation of Fe₃O₄ nanoparticles markedly in toluene and improve their compatibility with organic phase. Another finding was the grafting reaction did not alter the crystalline structure of the Fe₃O₄ nanoparticles according to the X-ray diffraction patterns, and the saturation magnetization of PS-Fe₃O₄ nanoparticles was found to be lower than bulk magnetite.     

超声陈化法制备纳米NaY分子筛及形成机理研究

Nano-sized NaY zeolite was synthesized from metakaolin in the hydrothermal synthesis system by using ultrasonic during aging time.The process of crystallizing NaY zeolite was studied by XRD、SEM、ICP OES ,and the formation mechanism of nano-sized NaY zeolite was researched,finally the conditions of synthesizing nano-sized zeolite NaY had been brought forward.     

Synthesis, testing, and characterization of a novel Nafion membrane with superior performance in photoassisted immobilized Fenton catalysis

A new type of Nafion/Fe structured membrane ensuring faster kinetics, higher efficiency, and mechanical properties has been prepared and will be compared in its performance with the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane during the abatement of model organic compounds. During the casting of the laboratory Nafion sample, the iron ions were introduced directly into the Nafion oligomer solution. This novel laboratory Nafion/Fe was tested as an immobilized catalyst in the degradation of several toxic pollutants showing a faster photoassisted degradation kinetics and a wider effective photocatalytic pH range compared to the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane. When carrying out Ar ion sputtering of the 50 topmost catalyst layers, evidence is presented by X-ray photoelectron spectroscopy that Fe ions are found in the inner Nafion layers and seem to be responsible for the immobilized photoassisted Fenton processes leading to the degradation of 4-chorophenol (4-CP) taken as a model organic pollutant for the degradation process reported in this study. In the laboratory sample, the iron oxy/hydroxy Nafion moiety undergoes a transition to a more stable Nafion/Fe species during 4-CP degradation as determined by X-ray diffraction. This more stable form shows a higher iron dispersion and crystallinity compared to the fresh sample and is stabilized by the Nafion matrix avoiding the formation of separate iron phases. By infrared absorption (Fourier transform infrared), evidence is presented for the band of akaganeite-like species at 870 cm(-1) on the laboratory Nafion/Fe sample. This band disappears after 4-CP degradation because of the formation of the more highly dispersed iron species. Sputtering experiments show a decrease of F-containing groups in the laboratory Nafion/Fe samples closer to the catalyst upper layer while the amounts of Fe, C, and in particular O species increase in the topmost layer(s). In particular, the oxygenated species develop in the Nafion/Fe up to approximately 50 A below the catalyst surface. These species remain stable during the long-term Nafion/Fe degradation of 4-CP. Dynamo-mechanical analysis performed on laboratory Nafion/ Fe membrane samples revealed that these membranes possessed a greater mechanical modulus and resistance than the commercial Dupont 117 Nafion membrane.     

Magnetically recoverable chiral catalysts immobilized on magnetite nanoparticles for asymmetric hydrogenation of aromatic ketones

Novel heterogenized asymmetric catalysts were synthesized by immobilizing preformed Ru catalysts on magnetite nanoparticles via the phosphonate functionality and were characterized by a variety of techniques, including TEM, magnetization, and XRD. These nanoparticle-supported chiral catalysts were used for enantioselective heterogeneous asymmetric hydrogenation of aromatic ketones with very high enantiomeric excess values of up to 98.0%. The immobilized catalysts were easily recycled by magnetic decantation and reused for up to 14 times without loss of activity and enantioselectivity. Orthogonal nature of the present catalyst immobilization approach should allow the design of other superparamagnetic nanoparticle-supported asymmetric catalysts for a wide range of organic transformations.     

Dye-ligand immobilized IPNs membrane for removal heavy metal ions

We have developed a novel approach to obtain high metal sorption capacity utilizing a membrane containing chitosan and an immobilized reactive dye (i.e. Reactive Yellow-2). The composite membrane was characterized by SEM, FT-IR, swelling test, and elemental analysis. The membrane has uniform small pores distribution and the pore dimensions are between 5 and 10 μm, and the HEMA:chitosan ratio was 50:1. The reactive dye immobilized composite membrane was used in the removal of heavy metal ions [i.e., Pb(II), Hg(II) and Cd(II)] from aqueous medium containing different amounts of these ions (5-600 mg l⁻¹) and at different pH values (2.0-7.0). The maximum adsorption capacities of heavy metal ions onto the composite membrane under non-competitive conditions were 64.3 mmol m⁻² for Pb(II), 52.7 mmol m⁻² for Hg(II), 39.6 mmol m⁻² for Cd(II) and the affinity order was Pb(II) > Hg(II)>Cd(II).     

Characterization of hemoglobin immobilized on gamma-zirconium phosphate

The fact that different γ-zirconium phosphate (γ-ZrP) preintercalation method induced varied degree and type of conformational change of the adsorption protein was confirmed by characterization techniques including circular dichroism (CD), fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) analysis. The results indicated that the association of hemoglobin with γ-ZrP preintercalated using butylamine was correlated with conformational change in the secondary structure of the protein. γ-ZrP which was preintercalated with tetra (n-butylammonium) hydroxide caused the conformational change of Hemoglobin in both the secondary structure and the tertiary structure. X-ray powder diffraction analysis was used to analyze the crystalline structure of the nanocomposites prepared by relamination. The adsorption isotherms of Hemoglobin on different matrices were set up and fitted with Langmuir and Freundlich equations.     

Synthesis and LPG sensing properties of nano-sized cadmium oxide

This paper reports the synthesis and liquid petroleum gas (LPG) sensing properties of nano-sized cadmium oxide (CdO). The nano-sized CdO powder was successfully synthesized by using a chemical co-precipitation method using cadmium acetate and the ammonium hydroxide, as starting materials and water as a carrier. The resulting nano-sized powder was characterized by X-ray diffraction (XRD) measurements and the transmission electron microscopy (TEM). The LPG sensing properties of the synthesized nano-sized CdO were investigated at different operating temperatures and LPG concentrations. It was found that the calcination temperature and the operating temperature significantly affect the sensitivity of the nano-sized CdO powder to the LPG. The sensitivity is found to be maximum when the calcination temperature was 400 °C. The sensitivity to 75 ppm of LPG is maximum at an operating temperature 450 °C and it was found to be ∼341%. The response and recovery times were found to be nearly 3-5 s and 8-10 s, respectively. The synthesized nano-sized CdO powder is able to detect up to 25 ppm for LPG with reasonable sensitivity at an operating temperature 450 °C and it can be reliably used to monitor the concentration of LPG over the range (25-75 ppm). The experimental results of the LPG sensing studies reveal that the nano-sized CdO powder synthesized by a simple co-precipitation method is a suitable material for the fabrication of the LPG sensor.     

Synthesis,magnetic and ethanol gas sensing properties of semiconducting magnetite nanoparticles

The superparamagnetic magnetite (Fe₃O₄) nanoparticles with an average size of 7 nm were synthesized using a rapid and facile microwave hydrothermal technique. The structure of the magnetite nanoparticles was characterized by X-ray diffraction (X-ray), field effect scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The prepared Fe₃O₄ was shown to have a cubic phase of pure magnetite. Magnetization hysteresis loop shows that the synthesized magnetite exhibits no hysteretic features with a superparamagnetic behavior. The ethanol gas sensing properties of the synthesized magnetite were investigated, and it was found that the responsibility time is less than 10 s with good reproducibility for ethanol sensor. Accordingly, it is evaluated that the magnetite nanoparticles can be effectively used as a solid state ethanol sensor in industrial commercial product applications.     

Synthesis of carbon-coated, porous and water-dispersive Fe3O4 nanocapsules and their excellent performance for heavy metal removal applications

Porous Fe(3)O(4)@C nanocapsules with a diameter of about 120 nm (about 50 nm cavity) were synthesized by combining a sacrificial template method with solvothermal treatment. The N(2) adsorption-desorption isotherms reveals their mesoporous structure and large BET surface area (159.8 m(2) g(-1)). The magnetic investigation indicates their superparamagnetic nature and high saturation magnetization (55.93 emu g(-1)). The nanocapsules also exhibit negative zeta potential (-27.59 mV) and possess carboxyl groups on the outer carbon layer, which keeps them highly dispersive in aqueous solution and provides a chelating function for metal ions. The heavy metals removal test demonstrates the excellent affinity of nanocapsules, the high efficiency for different metals (>90%), 79 mg g(-1) adsorption capacity for Pb(2+) and ultrafast removal process (Pb(2+), 99.57% within 1 minute). Protected by a porous carbon layer, the nanocapsules display excellent acidic resistance and adsorption properties even in an acidic solution (pH = 3). Moreover, the metal ions can be easily adsorbed and desorbed through manipulating the pH value for adsorbent regeneration and heavy metal recycling.     

Synthesis of magnetite hydrosols in inert atmosphere

A setup is described for magnetite hydrosol synthesis in inert atmosphere via coprecipitation of bi- and trivalent iron salts in the presence of a base with the formation of nanoparticles having desired sizes and chemical composition. The size of nanoparticles is estimated based on analysis of light-scattering and transmission-electron-microscopy data. The chemical composition of magnetite nanoparticles is monitored by Raman spectroscopy.     

Dynamic modeling of an immobilized cell reactor

A mathematical model has been developed to describe the dynamic aerobic reaction occurring in a semibatch type of mixed flow reactor, containing cells immobilized in gel beads. This modeling is an extension of that developed in our previous study, for an immobilized cell reactor involving ethanol fermentation. In contrast to anaerobic reactions such as ethanol fermentation, (wherein the influent substrate concentration can be set at any desired level), aeration becomes necessary to provide additional substrate (oxygen) for most aerobic reactions occurring in immobilized cell reactors. Tobacco cell cultivation was chosen as a representative aerobic reaction, and the effect of aeration was assessed in terms of the volumetric coefficient of oxygen from gas to liquid phases.     

Synthesis and surface treatment of magnetite nanoparticles for tuning hydrophobicity and colloidal stability

Post-synthetic surface modification of magnetite nanoparticles synthesized by a modified co-precipitation process was carried out with triethoxy-terminated perfluoropolyether (PFPE) oligomers. The chemisorption of PFPE oligomers on the surface of magnetites was confirmed by ATR-FTIR and TGA analyses. The efficiency of surface modification of the oligomer to prevent the aggregation of magnetite nanoparticles was studied with the dynamic light scattering technique by measuring the hydrodynamic diameter and polydispersity index of the surface treated nanoparticles, together with their zeta potential. Aggregation kinetics profiles were constructed for surface treated nanoparticles. The obtained data was compared with magnetite nanoparticles treated with critic acid, to assess the efficiency of the surface modification with the PFPE oligomers. The comparison showed that the bifunctional PFPE oligomer treated nanoparticles are characterized by improved colloidal stability and hydrophobicity.