Synthesis of nanosized BaSO4 particles with a membrane reactor: effects of operating parameters on particles

Nanosized BaSO₄ particles were synthesized successfully by a membrane reactor, in which Na₂SO₄ solution permeated through the micropores of ultrafiltration (UF) membrane gradually into BaCl₂ solution to control the saturation ratio, nucleation and growth rates. The effects of membrane molecular weight cut-off (MWCO), temperature, transmembrane pressure and reactant concentration on the particles morphology were investigated. The results reveal that the products tend from nanoparticles towards aggregates with the increase in membrane MWCO and reactant concentrations. Higher temperature favors the synthesis of regular particles. Transmembrane pressure does not show significant influences on the particles under the experimental conditions.     

The effect of sodium dodecyl sulfate solutions as gelation media on the formation of PES membranes

Sodium dodecyl sulfate (SDS) aqueous solutions were used as gelation media in the preparation of polyethersulfone (PES) membranes. The casting solution composition was the same for all the tested membranes. The temperatures of gelation media were 4 and 20°C. The concentration of SDS was changed from 0 to 3.0 g/l at 4°C and 0 to 1.6 g/l at 20°C.The surface tension of the gelation media was measured by drop weight method and the electrical conductivities were also determined. The membranes were characterized by transport parameters obtained from separation experiments and roughness parameters, obtained by the atomic force microscopic (AFM) technique.The molecular weight cut-off (MWCO) values of the studied membranes were found to be between 9 000 and 88 000 Da for membranes gelled at 4°C, and between 28 000 and 85 000 Da for membranes gelled at 20°C. The pore sizes were found to be between 3.04 and 10.73 nm for the membranes gelled at 4°C and between 4.48 and 10.74 nm for membranes gelled at 20°C, respectively. In general, both MWCO and pore size decreased with an increase of SDS concentration in gelation media when the concentration was below critical micelle concentration (CMC) and increased with an increase with SDS concentration when the concentration was above CMC. Images of membrane surfaces, taken by AFM, showed that the size of nodules and depressions decreased with a decrease in pore size. The roughness of membranes increased with an increase in pore size and MWCO.     

Synthesis of spherical submicron-sized magnetite/silica nanocomposite particles

This paper describes a method for fabricating spherical submicron-sized silica particles that contained magnetite nanoparticles (magnetite/silica composite particles). The magnetite nanoparticles with a size of ca. 10 nm were prepared according to the Massart method, and were surface-modified with carboxyethylsilanetriol. The fabrication of magnetite/silica composite particles was performed in water/ethanol solution of tetraethoxyorthosilicate with ammonia catalyst in the presence of the surface-modified magnetite nanoparticles. The magnetite/silica composite particles with a size of ca. 100 nm were successfully prepared at 0.05 M TEOS, 15 M water, and 0.8 M ammonia with injection of the magnetite nanoparticle colloid at 2 min after the initiation of hydrolysis reaction of TEOS. Magnetite concentration in the composite particles could be raised to 17.3 wt.% by adjustment of the injected amount of the magnetite colloid, which brought about the saturation magnetization of 7.5 emu/g for the magnetite/silica composite particles.     

Formation mechanism of nanostructured Ag films from Ag2O particles using a sonoprocess

Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag₂O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag₂O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag⁺ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag⁺ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag⁺, Ag ₄ ²⁺ and Ag_n (n?≈?3). The Ag_n clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag₂O particles with ethanol under ultrasonication. The reactions of Ag⁺ ions in ethanol to form Ag nanomaterials (through the formation of Ag ₄ ²⁺ clusters) were also accelerated by ultrasonication.     

Properties of novel gel particles with projections and preparations of composite particles with gold nanoparticles

Mono-dispersed gel particles with projections were prepared by dispersion polymerization with ethyleneglycol dimethacrylate and a polyethyleneglycol (PEG) block macro azo initiator in H₂O/ethanol solutions. The effects of molecular weight of PEG blocks and polymerization conditions on the morphology and some properties were examined for the gel particles. The diameters and the extent of coagulation were different with the polymerization conditions. Relatively large specific areas and large swelling ratio with H₂O were obtained, and these values were related with the polymerization conditions. By mixing the gel particles with gold nanoparticles in solutions, composite particles were formed, which were composed of gold nanoparticles adsorbed on the gel particles. Interaction between gold nanoparticles and reactive azo groups remained in the gel particles concerned for the formation of the composite particles.     

Visualisation of an ultrafiltration membrane by non-contact atomic force microscopy at single pore resolution

Non-contact atomic force microscopy (AFM) has been used to investigate the furface pore structure of a polyethersulfone ultrafitration membrane of specified molecular weight cut off (MWCO) 25 000 (ES625, PCI Membrane Systems). Excellent images at up to single pore resolution were obtained. This is the first time that AFM images of a membrane at such high resolution have been presented. Analysis of the images gave a mean pore size of 5.1 nm with a standard deviation of 1.1 nm. The results have been compared to previously published studies of membranes of comparable MWCO using contact AFM and electron microscopy. Non-contact AFM is a powerful means of studying the surface pore characteristics of ultrafiltration membranes.     

Fabrication and Characterization of Nanocomposite Flexible Membranes of PVA and Fe3O4

Composite polymer membranes of poly(vinyl alcohol) (PVA) and iron oxide (Fe₃O₄) nanoparticles were produced in this work. X-ray diffraction measurements demonstrated the formation of Fe₃O₄ nanoparticles of cubic structures. The nanoparticles were synthesized by a coprecipitation technique and added to PVA solutions with different concentrations. The solutions were then used to generate flexible membranes by a solution casting method. The size and shape of the nanoparticles were investigated using scanning electron microscopy (SEM). The average size of the nanoparticles was 20±9 nm. Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) were utilized to investigate the structure of the membranes, as well as their vibration modes. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated the thermal stability of the membranes and the crystallinity degree. Electrical characteristics of the thin membranes were examined using impedance spectroscopy as a function of the nanoparticles’ concentrations and temperatures. The resistivity of the fabricated flexible membranes was possible to adjust by controlled doping with suitable concentrations of nanoparticles. The activation energy decreased with the nanoparticles’ concentrations due to the increase in charge carriers’ concentrations. Therefore, the fabricated membranes may be applied for practical applications that involve the recycling of nanoparticles for multiple application cycles.     

Size control synthesis of sulfur doped titanium dioxide （anatase） nanoparticles, its optical property and its photo catalytic reactivity for CO2 ＋ H2O conversion and phenol degradation

Sulfur doped anatase TiO2 nanoparticles (3 nm−12 nm) were synthesized by the reaction of titanium tetrachloride, water and sulfuric acid with addition of 3M NaOH at room temperature. The electro-optical and photocatalytic properties of the synthesized sulfur doped TiO2 nanoparticles were studied along with Degussa commercial TiO2 particles (24 nm). The results show that band gap of TiO2 particles decreases from 3.31 to 3.25 eV and for that of commercial TiO2 to 3.2 eV when the particle sizes increased from 3 nm to 12 nm with increase in sulfur doping. The results of the photocatalytic activity under UV and sun radiation show maximum phenol conversion at the particle size of 4 nm at 4.80% S-doping. Similar results are obtained using UV energy for both phenol conversion and conversion of CO2+H2O in which formation of methanol, ethanol and proponal is observed. Production of methanol is also achieved on samples with a particle size of 8 and 12 nm and sulfur doping of 4.80% and 5.26%. For TiO2 particle of 4 nm without S doping, the production of methanol, ethanol and proponal was lower as compared to the S-doped particles. This is attributed to the combined electronic effect and band gap change, S dopant, specific surface area and the light source used.     

Fabrication of blend hydrophilic polyamide imide (Torlon®)-sulfonated poly (ether ether ketone) hollow fiber membranes for oily wastewater treatment

Blend hydrophilic polyamide imide (PAI)-sulfonated poly (ether ether keton) (SPEEK) hollow fiber membranes were fabricated for oil-water emulsion separation. The structure and performance of the membranes were examined by FESEM analysis, N₂ permeation, overall porosity, collapsing pressure, water contact angle, pure water flux, molecular weight cutoff (MWCO), and oil rejection tests. By studying ternary phase diagrams of polymer/solvent-additive/water system, the higher phase-inversion rate was confirmed for the solutions prepared at higher PAI/SPEEK ratio. A more open structure with larger finger-likes was observed by increasing PAI/SPEEK ratio. Mean pore size of 81 nm, overall porosity of 79% and water contact angle of 58° were obtained for the improved membrane prepared by PAI/SPEEK ratio of 85/15. Increasing SPEEK ratio resulted in lower mechanical stability in terms of collapsing pressure. Pure water flux of about 2.5 times of the plain PAI membrane was found for the improved membrane. MWCO of 460 kDa was found for the improved blend membrane. From oil rejection test, all the membranes demonstrated an oil rejection of over 95%. The improved membrane showed a lower rate of permeate flux reduction compared to the plain membrane which was related to the smaller fouling possibility. Less fouling resistance of the improved membrane was related to the higher flux recovery ratio (about 92%). For all the membranes, the dominant fouling mechanism was found to be the cake filtration. The improved PAI-SPEEK hollow fiber membranes was found to be practical for ultrafiltration of oily wastewaters.     

Synthesis of colloidal dispersions of rhodium nanoparticles under high temperatures and high pressures

Colloidal dispersions of rhodium (Rh) nanoparticles have been synthesized by the reduction of Rh ions (III) in high-temperature and high-pressure water, ethanol, or water-ethanol mixture under the existence of the protective polymer of poly(N-vinyl-2-pyrrolidone). The possibility of the regulation of the particle size and size distribution has been tested under several solvents at various temperatures and pressures. At 473 K and 25 MPa, particularly, concentrated colloidal dispersions of Rh particles of 2.5+/-0.5 nm were synthesized from the ionic solution of ethanol ([Rh]=15 mM) within a few seconds. Dilute colloidal dispersions of Rh particles were also synthesized from the dilute ionic solution ([Rh]=1.5 mM) with a diameter of 2.0+/-0.4 nm. From the water solution, Rh particles tended to form aggregates, especially for the lower concentration solution. In the case of solutions in water and ethanol mixture, the average diameter of Rh particles tended to be larger than in ethanol solution, and their distribution became broad.     

Effect of nanoparticle aggregation at low concentrations of TiO2 on the hydrophilicity, morphology, and fouling resistance of PES-TiO2 membranes

This paper reports the fabrication and characterization of polyethersulfone-TiO(2) (PES-TiO(2)) nanoparticle composite membranes made from synthesis casting solution consisting of various compositions of polymer solvents (DMF and EtOH) and TiO(2) additive. The results also revealed that the membrane permeation and rejection rates, pore size, and porosity were dependent on the TiO(2) and EtOH concentrations. Nanoparticles were characterized by zeta potential measurements, TEM observations, and measurement of particle size distributions. Zeta potential measurements in aqueous solution demonstrated that the TiO(2) particles size is dominated by electric double layer interactions. Addition of EtOH promotes the increase of the clusters size as consequence of a double effect: reduction of the dielectric constant of solution and the depletion of the suspension field determined by the action of the polymer chains. The observed effects as result of EtOH addition and increase of TiO(2) concentration were similar: both procedures provoked an increase of macrovoid dimensions. The modified membranes by TiO(2) incorporation showed a structural change from a sponge-like to a finger-like structure. Strong correlations were observed between the hydrophilicity and the permeability of manufactured membranes. The formation mechanism of TiO(2)-blended membranes was altered, in a similar way, as result of EtOH at different contents of nanoparticles. Fouling resistance of modified membranes was significantly improved showing that EtOH addition is a suitable procedure for the membrane performance improvement. The rejection potential of membranes is hardly affected by the nanoparticles and EtOH incorporation into the polymeric solution.     

Preparation of copper and zinc sulfide nanoparticles and their modification with cysteine

A new method for the preparation of copper and zinc sulfides nanoparticles in homogeneous aqueous solutions using cysteine as a surface modifier was proposed. The size of the particles obtained is 5–7 and 1.5–3 nm for copper and zinc sulfides, respectively, depending on the concentration of the reactants. Associates of the nanoparticles 10–30 nm in size are formed in the system with an increase in the total concentrations of the sulfides. Sols of the nanoparticles obtained in cysteine solutions are resistant to oxidation and coagulation within several weeks. The variation of the synthesis conditions makes it possible to obtain zinc sulfide particles with optical properties related to size effects.     

Soap-free synthesis of highly monodisperse magnetic polymer particles with amphoteric initiator

A method applying soap-free emulsion polymerization with an amphoteric initiator, 2,2′-azobis[N-(2-carboxyethyl)-2-2-methyl-propionamidine], is proposed for synthesis of highly monodisperse particles composed of magnetic nanoparticles (Fe₃O₄/γ–Fe₂O₃) and polystyrene. The magnetic nanoparticles were pretreated by surface modification for introducing double bonds onto the particles. In the polymerization, magnetic nanoparticles were continuously supplied to the system for a certain period after the initiation of polymerization at various pH. Dissociation degrees of ionizable groups in the initiator molecules were controlled through pH by changing NH₃ concentrations at a constant NH₄Cl concentration. Selection of suitable pH in the polymerization could produce polymer particles that perfectly incorporated the supplied magnetic nanoparticles. The magnetic polymer particles had a coefficient of variation of size distribution as low as 4.3% with an average diameter of 515 nm and a saturation magnetization of 7.3 emu/g-sample. Electrophoresis measurements indicated that the magnetic polymer particles had an isoelectric point of pH 4.1.     

TiO_2光催化/膜分离耦合过程降解偶氮染料废水

以钛酸丁酯为前驱体,采用酸性溶胶法在低温下(<100oC)制备了纳米级TiO2粉末,X射线衍射分析表明,样品为锐钛矿型,晶粒尺寸为3.6nm.以250W紫外灯为光源,在自制悬浮式光催化膜反应器中进行降解活性艳红X-3B有机染料废水实验,采用尼龙6(N6)和混合纤维素(CN-CA)两类微滤膜对TiO2颗粒进行截留分离.综合考察了影响光催化和膜分离效率的因素.结果表明,反应起始pH值和催化剂用量对光催化膜反应器运行性能影响很大,该耦合体系的最佳pH值为4,染料和催化剂最佳浓度比为2:1,0.45和0.22μm的CN-CA膜对TiO2颗粒截留率可达96.5%以上.     

Synthesis and characterization of asymmetric polyethersulfone membranes: effects of concentration and polarity of nonsolvent additives on morphology and performance of the membranes

In this study, effects of methanol, ethanol and 1‐propanol as variable nonsolvent additives (NSAs) on the morphology and performance of flat sheet asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from PES/Polyvinylpyrrolidone (PVP)/N‐methyl‐2‐pyrrolidone (NMP) system via phase inversion. The obtained results indicate that with the addition of NSAs to the casting solution, the membrane morphology changes slowly from macrovoids to an asymmetric structure with finger‐like pores. By increasing the NSAs concentrations in the casting solution and decreasing their polarities, the membrane structure changes from finger‐like pores to sponge. The AFM and SEM images reveal that addition of NSA to the casting solution decreases the pore size of the prepared membranes and reduces the pure water flux and BSA solution flux, while increasing the protein rejection. Surface analysis of the membranes showed that mean pore size and surface porosity of the prepared membranes with NSAs in the casting solution are smaller compared with those of the membrane prepared with no NSA. Pure water flux and BSA solution flux through the membranes decrease and BSA rejection increases with increase in the concentration of NSAs and decrease in their polarity. Finally, it can be concluded that the T_g values of the PES membranes increase by addition of NSAs to the casting solution. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoinduced dissolution and redeposition of Au nanoparticles supported on TiO2

Au particles (mean size ca. 3 nm) supported on TiO(2) particles were irradiated by UV light (>300 nm) in aqueous solutions at 278 K. Photo-induced dissolution of Au nanoparticles followed by redeposition occurred in aqueous solutions containing halogen ions. The dissolution of Au nanoparticles yielded a Au(III) complex with a halogen ion; subsequent reduction of the Au(III) complex caused precipitation of larger Au particles on TiO(2).     

探索利用无机结合肽PT2(DRTSTWR)制备纳米铂晶体

实验中首先利用固定化于PET(聚对苯二甲酸己二醇酯)膜上无机结合肽PT2 (DRTSTWR)制备出铂微晶体. 然后用游离的PT2与PtCl₄在室温和pH中性环境中反应24 h, 所得产物用TEM观察, 其多数为1～2 nm呈方形和球形晶体, 经EDX分析显示晶体的元素组成中Pt远大于Cl的含量, 显然晶体不可能是PtCl₄或PtCl₂; 样品的XPS谱图中出现了结合能值为71.0 eV峰(Pt_4f标准值71.1 eV), 确认晶体为铂纳晶, 由此推断无机结合肽PT2在无细胞状态下能够作为模板仿生合成铂晶体. 继而在反应体系中加入不同浓度的壳聚糖和聚丙烯酸钠, 观察到纳米粒子的粒径和形貌随表面活性剂的加入发生了改变. 加入5倍的壳聚糖制备的铂晶体的直径在12～15.5 nm之间, 晶体排布似乎有成线状的趋势. 加入5倍的聚丙烯酸钠制备的铂晶体, 形貌更加规整, 以球形颗粒为主, 粒子直径在6～8 nm之间.     

Cds纳米微粒的聚四氟乙烯多孔膜法制备及其表面修饰

硫化镉;Cds纳米微粒的聚四氟乙烯多孔膜法制备及其表面修饰;纳米粒;多孔膜;表面修饰;聚四氟乙烯     

Synthesis and characterization of magnetic and non-magnetic core-shell polyepoxide micrometer-sized particles of narrow size distribution

Core polystyrene microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Uniform polyglycidyl methacrylate/polystyrene core-shell micrometer-sized particles were prepared by emulsion polymerization at 73 degrees C of glycidyl methacrylate in the presence of the core polystyrene microspheres. Core-shell particles with different properties (size, surface morphology and composition) have been prepared by changing various parameters belonging to the above seeded emulsion polymerization process, e.g., volumes of the monomer glycidyl methacrylate and the crosslinker monomer ethylene glycol dimethacrylate. Magnetic Fe(3)O(4)/polyglycidyl methacrylate/polystyrene micrometer-sized particles were prepared by coating the former core-shell particles with magnetite nanoparticles via a nucleation and growth mechanism. Characterization of the various particles has been accomplished by routine methods such as light microscopy, SEM, FTIR, BET and magnetic measurements.