Synthesis of nanosized BaSO4 and CaCO3 particles with a membrane reactor: effects of additives on particles

Nanosized BaSO(4) particles, about 15 nm in size, were synthesized successfully by a membrane reactor at the aids of additives, in which Na(2)SO(4) solutions were added into BaCl(2) solutions gradually through the micropores of ultrafiltration membranes to control the saturation ratio, subsequently the nucleation and growth rates. The effects of additives species, additives concentrations, and membranes molecular weight cut-off (MWCO) on the particle morphology, along with the formation processes of particles, were investigated. CaCO(3) nanoparticles of 30-60 nm in size were also prepared by the reactor. The results revealed that the addition of methyl alcohol, ethanol etc. favor the synthesis of nanoparticles with small size. The particles size decreases with the increase in ethanol concentrations. With the increase in membrane MWCO, the products tend from nanoparticles towards aggregates.     

Improvement in gas separation properties of a polymeric membrane through the incorporation of inorganic nano‐particles

The present work tries to introduce a high‐performance nano‐composite membrane by using polydimethylsiloxane (PDMS) as its main polymer matrix to meet some specific requirements in industrial gas separations. Different nano‐composite membranes were synthesized by incorporating various amounts of nano‐sized silica particles into the PDMS matrix. A uniform dispersion of nano‐particles in the host membranes was obtained. The nano‐composite membranes were characterized morphologically by scanning electron microscopy and atomic force microscopy. Separation properties, permeability, and ideal selectivity of C₃H₈, CH₄, and H₂ through the synthesized nano‐composite membranes with different nano‐particle contents (0.5, 1, 1.5, 2, 2.5, and 3 wt%) were investigated at different pressures (2, 3, 4, 5, 6, and 7 atm) and constant temperature (35°C). It was found out that a 2 wt% loading of nano‐particles into the PDMS matrix is optimal to obtain the best separation performance. Afterwards, sorption experiments for the synthesized nano‐composite membranes were carried out, and diffusion coefficients of the gases were calculated based on solution‐diffusion mechanism. Gas permeation and sorption experiments showed an increase in sorption and a decrease in diffusion coefficients of the gases through the nano‐composite membranes by adding nano‐particles into the host polymer matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication and Performance of a Low Operating Pressure Nanofiltration Poly（vinyl chloride） Hollow Fiber Membrane

A low operating pressure nanofiltration membrane is prepared by interfacial polymerization between m-phenylenediamine(MPDA) and trimesoyl chloride(TMC) using PVC hollow fiber membrane as supporting.A series of PVC nanofiltration membranes with different molecular weight cutoff(MWCO) can be obtained by controlling preparation conditions.Chemical and morphological characterization of the membrane surface was carried out by FTIR-ATR and SEM.MWCO was characterized by filtration experiments.The preparation conditions were investigated in detail.At the optimized conditions(40 min air-dried time,aqueous phase containing 0.5% MPDA,0.05% SDS and 0.6% acid absorbent,oil phase containing 0.3% TMC,and 1 min reaction time),under 0.3 MPa,water flux of the gained nanofiltration membrane reaches 17.8 L/m2·h,and the rejection rates of methyl orange and MgSO4 are more than 90% and 60%,respectively.     

Preparation and properties of Nafion/SiO2 composite membrane derived via in situ sol–gel reaction: size controlling and size effects of SiO2 nano‐particles

A novel technique in controlling the size of SiO₂ nano‐particles in the preparation of Nafion/SiO₂ composite membranes via in situ sol–gel method, as well as the effects of nano‐particle size on membrane properties and cell performance, is reported in this paper. Nafion/SiO₂ composite membranes containing SiO₂ nano‐particles with four different diameters (5 ± 0.5, 7 ± 0.5, 10 ± 1, and 15 ± 2 nm) are fabricated by altering the reactant concentrations during in situ sol–gel reaction. Sequentially, size effects of SiO₂ nano‐particles on membrane properties and cell performance are investigated by SEM/EDAX, TEM, TGA, mechanical tensile, and single cell tests, etc. The results suggest that 10 nm is a critical diameter for SiO₂ incorporated into Nafion matrix, exhibiting desirable physico‐chemical properties for operation at elevated temperature and low humidity. At 110°C and 59% RH, the output voltage of the cell equipped with Nafion/SiO₂ (10 nm) obtains an output voltage of 0.625 V at 600 mA/cm², which is 50 mV higher than that of unmodified Nafion. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation of Fe3O4/chitosan/poly(acrylic acid) composite particles and its application in adsorbing copper ion (II)

Fe₃O₄/chitosan/poly(acrylic acid) (Fe₃O₄/CS/PAA) composite particles, which are reusable, biodegradable and of high adsorption capacity, have been prepared through polymerizing acrylic acid in chitosan and Fe₃O₄ nanoparticles aqueous solution. By varying in-feed mole ratio of carboxyl to amino group (n^c/n^a) and reactant concentration, the average diameter of Fe₃O₄/CS/PAA composite particles can be controlled to vary from 100 to 300 nm. FT-IR, XRD and TEM were used to characterize Fe₃O₄/CS/PAA composite particles. Results showed that Fe₃O₄ was indeed incorporated into CS/PAA particles. The composite particles showed high efficient to remove copper ions (II) in aqueous solution. Adsorption kinetic studies showed that the adsorption process followed a pseudo-second-order kinetic model and the equilibrium data agreed well with the Langmuir model. The saturated adsorption capacity obtained from the experimental was 193 mg/g in close to proximity to the data 200 mg/g calculated from Langmuir model. The saturated adsorption capacity still retained 100 mg/g after three cycles of adsorption–desorption of copper ions (II).     

Conformational change of adsorbed and desorbed bovine serum albumin on nano-sized magnetic particles

Adsorptions of bovine serum albumin (BSA) on nano-sized magnetic particles with and without the presence of carbodiimide were studied. Desorption of BSA from magnetic particles were carried out in either NaOH or Na₂HPO₄ solutions. The structures of native BSA, adsorbed BSA on magnetic particles, and desorbed BSA were studied by several methods, circular dichroism (CD), fluorescence spectroscopy and differential scanning calorimetry (DSC). The magnitude of conformational changes of protein was determined by calculating the α-helix content from the circular dichroism (CD) spectra and by evaluating fluorescence spectrum and DSC thermograms. Adsorbed BSA on magnetic particles shows no thermal transition with respect to the native BSA. The structural change of BSA when desorbed by Na₂HPO₄ solution is much smaller in comparison to that when desorbed by NaOH solution. Hence, this indicates that BSA could be desorbed from nano-sized magnetic particles using Na₂HPO₄ without much conformational change.     

Texture of spherical aluminum phosphate particles

Spherical aluminum phosphate particles with a mean particle diameter of 477±16 nm, produced from aging of a solution containing Al(NO₃)₃, Na₂HPO₄ and HNO₃ at 100°C for 19 h in 20-cm³ Teflon-lined screw-capped Pyrex test tube without agitation, were characterized by various means. It was revealed from x-ray diffraction measurement and transmission electron microscope observation that amorphous particles are formed by agglomeration of small primary particles. The particles exhibited a high selective adsorption of H₂O though they adsorbed small amount of N₂ and CO₂. This characteristic phenomenon was explained by rehydration of Al³⁺ ions by H₂O molecules that were penetrated into the particles.     

Fabrication and characterization of a novel TiO2 nanoparticle self-assembly membrane with improved fouling resistance

A novel TiO₂ nanoparticle self-assembly membrane was prepared based on ultrahigh molecular weight poly(styrene-alt-maleic anhydride)/poly(vinylidene fluoride) (SMA/PVDF) blend membrane. TiO₂ nanoparticle solution was beforehand prepared via the controlled hydrolysis of titanium tetraisopropoxide. The diameter (10 nm or less) and anatase crystal structure were analyzed using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The SMA/PVDF blend membranes prepared by the phase inversion method were immersed into the TiO₂ nanoparticle solution for a week to produce TiO₂ self-assembly membranes. The chemical compositions in membrane surface were analyzed by X-ray photoelectron spectroscopy (XPS). The membrane morphologies were measured by scanning electron microscopy (SEM). Finally, the membrane hydrophilicity, protein anti-fouling property and the molecular weight cutoff (MWCO) were characterized by water contact angle measurement, static protein absorption and filtration experiments, respectively. It is demonstrated that, in comparison to PVDF/SMA blend membrane, the permeability and anti-fouling ability of TiO₂ self-assembly membranes were significantly improved.     

Synthesis of SiO2/polystyrene hybrid particles via an esterification method

SiO₂/polystyrene (SiO₂/PS) hybrid particles are synthesized successfully by an esterification method under extremely mild conditions, for instance, ambient temperature, moisture, and atmospheric pressure. The resulting hybrid particles are characterized by XPS, FTIR, SEM, DLS, TGA, and DSC techniques. Results show that the resulting hybrid particles have core-shell structure with PS on the outside and SiO₂ in the core, and the particle size increases from 230 to 260 nm upon the PS grafting. The grafted PS accounts for about 32.2 wt.% of the total amount of hybrid particles. Meanwhile, PS segments attached on the SiO₂ particle surface have better thermal stability and higher glass transition temperature than those of the pristine carboxyl-terminated PS.     

Synthesis and characterization of bimetallic Ni-Cu particles

Bimetallic Ni-Cu particles were synthesized from either suspensions of nickel carbonate and copper carbonate, and solutions of nickel nitrate and copper nitrate in ethylene glycol which acts both as solvent and reducing agent. The nature and composition of the powders depend on both the reaction temperature and time, and the reactants. Using the carbonates, bimetallic Ni-Cu powders composed of a nickel-rich and a copper-rich solid solution were obtained after 39 h at 140°C. Increasing the reaction temperature to 190°C gives a Ni-Cu powder composed of a copper-rich solid solution and nickel. Particles obtained under these conditions, however, are polydisperse. The nitrate solution gave bimetallic Ni-Cu particles with a narrow size distribution of about 140 nm after 4 h of reaction at 196°C. These particles are made of a copper core and a nickel shell. The mechanism of bimetallic particle formation is controlled by the solubility of the reactants, the formation of intermediate metal glycolates and Cu₂O, and the required reduction temperature.     

Precipitation and recrystallization of uniform CuCl particles formed by aggregation of nanosize precursors

Uniform, spherical CuCl particles were obtained by mixing aqueous solutions of CuCl ₂ and ascorbic acid in the presence of polyvinylpyrrolidone (PVP) as dispersing agent. The size and the uniformity of the resulting particles depended on the volume ratio of the reactant solutions, their concentrations, the distribution of the stabilizers, and the mixing method. The single jet precipitation yielded large spheres of broad size distributions, while the particles obtained by the double jet technique were rather uniform in size. The final colloidal CuCl particles were formed by the aggregation of nanocrystals, initially generated in the system. Depending on the pH of the reaction mixture, these particles slowly change to large CuCl crystals on aging in the mother liquor.     

Preparation and characterization of calcium hydroxyapatite and balloon-like calcium phosphate particles from forced hydrolysis of Ca(OH)2–triphosphate solution

Calcium phosphate particles were prepared by aging a solution of dissolved Ca(OH)₂ and sodium triphosphate (sodium tripolyphosphate, Natpp: Na₅P₃O₁₀) at 100–150 °C for 18 h in a Teflon-lined screw-capped Pyrex test tube. Large spherical and/or small aggregated spherical particles were precipitated with an extremely fast rate of reaction under 100 °C. The large spherical particles were amorphous and the small aggregated ones were α-CaNa₂P₂O₇^.4H₂O. The former amorphous ones crystallized to β-Ca₂P₂O₇ after being calcined above 600 °C. Calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, Hap), with rod-like and ellipsoidal or spherical aggregated shapes, was successfully produced using polyphosphates as a source of orthophosphate ions. Time resolved TEM measurement revealed that the crystallization of Hap particles takes place on the surface of tiny amorphous particles precipitated before aging. The tiny particles played the role of nuclei for Hap crystallization. The aging temperature drastically varied the particle shape under conditions for producing uniform amorphous spherical particles; solid spherical particles were produced with an aging temperature of up to 120 °C, whilst transparent balloon-like hollow spheres were precipitated at 125 °C. Finally, fully transparent balloon-like hollow spheres were produced with mere trace amounts of small rod-like particles after aging the solution above 127 °C. The time resolved TEM observation and ICP-AES measurements revealed that the balloon-like hollow spheres were produced by dissolving the interior of solid spherical particles after reinforcing their shell by the adsorption of unhydrolyzed tpp and/or pyrophosphate (pp) ions, which are the hydrolysis product of tpp. The balloon-like hollow spheres of calcium phosphate may have the potential use as drug delivery vehicles and have biocompatibility advantages.     

Femtosecond relaxation of photoexcited states in nanosized semiconductor particles of iron oxides

Relaxation of photoexcited states in nanosized semiconductor particles of iron oxides was studied by femtosecond laser photolysis techniques: (1) in an aqueous colloidal solution of -Fe₂O₃; (2) in Fe₂O₃ particles in the Nafion^® cation-exchange polymeric membrane; (3) in an aqueous colloid of -Fe₂O₃; and (4) in nanocrystals of ferrihydrite 5Fe₂O₃·9H₂O, which are contained in the protein shell of ferritine. The photoinduced excited states relax at the femtosecond and picosecond time scale. The spectra of photoinduced absorption of photoexcited states and the relaxation dynamics in the studied iron oxides weakly depend on the structure and surface environment of a nanoparticle.     

Stability of chromium dioxide particles in aqueous media

An investigation was carried out to characterize the dissolution behavior of stabilized and unstabilized CrO₂ particles in water, used in magnetic recording. Special attention was paid to the measurement of Cr(VI) concentration in the contact solution and to the elucidation of the effects of the stabilizing treatment by x-ray photoelectron spectroscopy (XPS). The experimental results indicate that both stabilized and unstabilized CrO₂ particles predominantly release hexavalent chromium when in contact with water. The solubility of freshly stabilized CrO₂ is considerably smaller than that of unstabilized CrO₂, but the difference in solubility diminishes with aged particles. The XPS study indicated that stabilization of CrO₂ particles with a bisulfite solution results in the formation of Cr₂O₃ or a Cr₂O₃-like product on the particle. However, it appears that Cr(III) oxide coating does not uniformly form on all particles.     

Application of micellar enhanced ultrafiltration for the removal of sunset yellow dye from aqueous media

In this article, we report the removal of a reactive dye, viz. sunset yellow, from the aqueous solution using micellar media of two cationic surfactants, viz. cetyltrimethylammonium bromide and ethyl hexadecyldimethyl ammonium bromide (. The values of rejection coefficient (R%) and permeate flux (J) have been calculated using membranes with different pore sizes, viz. 10,000 (10k) molecular weight cutoff (MWCO) and 30,000 (30k) MWCO at 1.5 bar transmembrane pressure. The membrane of 30k MWCO was found to be more suitable in order to retain the dye molecules incorporated in the micelles.     

Methyltriethoxysilane-derived sol-gel coatings doped with silver metal particles

Silica sol-gel films were prepared by dipping, starting from an acid catalyzed solution of methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS). Silver metal nanoparticles were produced in the silica layer by introducing in the sol-gel precursor solution AgNO₃ or AgClO₄·H₂O. The silver ions were thermally reduced in air at 800°C, giving an intense yellow coating film. The silver metal particles were observed by transmission electron microscopy and X-ray diffraction. The diameter of the silver particles was found to be about 10 nm. Absorption measurements in the UV-Vis were used to evaluate the volume fraction of silver colloids embedded in the silica layer.     

Cu + Au alloy particles formed in the underpotential deposition region of copper in acid solutions

Cu + Au alloy particles electrodeposited on an amorphous carbon electrode at the underpotential region of Cu in both perchloric acid and sulfuric acid solutions were investigated by means of transmission electron microscopy. The fraction of Cu in the Cu + Au alloy particles grown in both acid solutions with a concentration of 1 mM Au ion increased while the underpotential deposition (UPD) potential was decreased. However, it was independent of the concentration of Cu ion in solution. It is inferred that the composition of the Cu + Au alloy particles is dependent on the UPD potential. The fraction of Cu in the Cu + Au alloy particles grown at around the reversible Nernst potential of Cu in 0.1 mM HAuCl₄ + 50 mM Cu(ClO₄)₂ containing perchloric acid solution was 505. This result suggests a layer-by-layer formation of the Cu + Au alloy particles. The fraction of Cu in the Cu + Au alloy particles formed in the presence of sulfate was lower than that in the perchloric acid solution as the UPD potential and the concentration of Cu ion were the same. This is attributed to an influence of coadsorbed sulfate ions.     

Effect of aerosol chemical vapor deposition on characteristics of MoS<Subscript>2</Subscript> particles

Influence exerted by the main technological parameters in the process in which nano- and microparticles of molybdenum disulfide are formed by the aerosol chemical vapor deposition method from a gas phase containing aerosol particles of (NH₄)₂MoS₄?C₃H₇NO solutions on the dimension characteristics, structure, and composition of the products being formed was studied. It was shown that the shape, size, and structure of the particles being formed are determined by the processes occurring in the first, streamwise, reactor zone. The temperature of this zone is the most important technological parameter. The concentration of ammonium thiomolybdate in solution makes it possible to gradually vary the size of disulfide particles in a wide range (from tens of nanometers to micrometers). In the conditions under study, the technological conditions have no effect on the chemical composition of the products being synthesized, which is always described by the formula MoS₂. The results obtained can be used in development of industrial apparatus and technology for synthesis of molybdenum disulfide nano- and microparticles to be used as the antifriction component of lubricating materials.     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4/poly(N‐isopropylacrylamide‐co‐methacrylic acid) two‐shell thermosensitive magnetic composite hollow latex particles

In this study, the poly(N‐isopropylacrylamide‐methylacrylate acid)/Fe₃O₄/poly(N‐isopropylacrylamide‐methylacrylate acid) (poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA)) two‐shell magnetic composite hollow latex particles were synthesized by four steps. The poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles were synthesized first. Then, the second step was to polymerize NIPAAm, MAA, and crosslinking agent in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly(NIPAAm‐MAA) core–shell latex particles. Then, the core–shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, the Fe₃O₄ nanoparticles were generated in the presence of poly(NIPAAm‐MAA) hollow polymer latex particles and formed the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles. The fourth step was to synthesize poly(NIPAAm‐MAA) in the presence of poly(NIPAAm‐MAA)/Fe₃O₄ latex particles to form the poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA) two‐shell magnetic composite hollow latex particles. The effect of various variables such as reactant concentration, monomer ratio, and pH value on the morphology and volume‐phase transition temperature of two‐shell magnetic composite hollow latex particles was studied. Moreover, the latex particles were used as carriers to load with caffeine, and the caffeine‐loading characteristics and caffeine release rate of latex particles were also studied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2880–2891     

Preparation and characterization of a composite PDMS membrane on CA support

Polydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C₃H₈, CO₂, CH₄, and H₂ in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C₃H₈, compared to the lighter ones, such as CO₂, CH₄, and H₂. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C₃H₈/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C₃H₈ over CO₂, CH₄, and H₂, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley & Sons, Ltd.