Role of anions for the reduction behavior of silver ions in polymer/silver salt complex membranes

The reduction of silver ions to silver nanoparticles is an essential issue in polymer/silver salt complex membranes for facilitated olefin transport, because it has a critical influence on the long-term stability of membrane performance. In this study, the role of anions for the formation of silver nanoparticles in polymer/silver salt complexes was investigated. This role was assessed for the complexes of poly(N-vinyl pyrrolidone) (PVP) with three silver salts including AgBF₄, AgCF₃SO₃, and AgNO₃. Especially, UV irradiation to the membranes was used to clearly investigate the reduction behavior of silver ions. Separation performance test, UV–vis spectroscopy and transmission electron microscopy (TEM) clearly show that the reduction rate of silver ions strongly depends on the counteranions of salt, and has the following order: AgBF₄ > AgCF₃SO₃ > AgNO₃. This behavior of the formation of silver nanoparticles in polymer/silver salt complex membranes is explained in terms of the interaction strength of silver ions with the carbonyl oxygens of polymer, and that of silver ions with counteranions. It is concluded that when the former interaction is strong and the latter one is weak, the reduction rate of silver ions to silver nanoparticles is fast, and vice versa. These interactions were characterized using FT-IR, FT-Raman spectroscopy, and theoretical ab initio calculation.     

Enhancement of thermal properties of Kevlar 29 coated by SiC and TiO2 nanoparticles and their binding energy analysis

In the fields of military research, aerospace, and vehicle technology, the thermal stability of Kevlar fiber is critical for improving its flame resistance. In this work, the pad mangle machine was used to improve the thermal properties of Kevlar 29 in order to expand the range of applications for thermal aspects. Silicon carbide and titanium oxide nanoparticles provide thermal stability on the fiber surface through intermolecular adhesion. Here, 5 wt% and 10 wt% of nanoparticles with various mass ratios (1:1) have been chosen. Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) analysis, and X-ray Photoelectron Spectroscopy (XPS) analysis have all been used to measure different thermal properties. The surface morphology of samples is represented by FESEM analysis, while the active organic groups are represented by FTIR analysis. The greater crystallization of epoxy and nanoparticles is linked to post-heat treatment of the material. The glass transition temperature of the coated samples shifted maximum from 559.13 °C to 580.51 °C, the end set temperature increased by 30.67 °C compared to the uncoated sample, and the residual weight changed from 29.77 percent to 4.06 percent, according to the findings (i.e., lightweight). When compared to the uncoated sample, the coated sample's enthalpy increased significantly (i.e., the samples can absorb more heat). The smaller the positive binding energy, the higher the activation energy, and hence the slower the chemical reaction, which is especially important in high-temperature applications. Finally, this research reveals a 4.5–5.2 percent increase in thermal characteristics.     

Transport phenomena in membranes

The realization that many elementary biological processes occur at membrane-like structures has led to renewed interest in the theory of molecular transport through membranes. Coupling phenomena in membranes, some of which are very complex, can now be rationally described with the aid of the thermodynamics of irreversible processes. The investigation of theoretical membrane models has proved a valuable complement to the thermodynamic method.     

Determination of metallo-cyanides by capillary electrophoresis after concentration on supported liquid membranes

A method for the determination of traces of metallo-cyanide complexes by capillary zone electrophoresis is described. The suitability of preconcentration procedures based on supported liquid membranes in a flow system is investigated. Methyltrioctylammonium chloride in dibutyl ether is used as the active component of the membrane liquid. Due to ion-pairing mechanisms enrichment factors ranging from 50 to 600 can be achieved for cyanide complexes of Fe(II), Fe(III), Ni, Co, Pd, Pt, Cr, Au and Ag. The final capillary electrophoretic separation of the metallo-cyanides is performed off-line with a phosphate-triethanolamine buffer at pH 8.5 as the carrier electrolyte. Its separation selectivity and compatibility with the preconcentration procedure are optimized by addition of hexamethonium bromide, sodium perchlorate and sodium cyanide. Detection limits in the low nmol range can be achieved by direct UV detection at 214 nm. An approach for the analysis of free and labile cyanide is discussed which involves the conversion of these species into the nickel cyanide complex. Applications in the fields of environmental monitoring and industrial process control are possible.     

Dielectric relaxation of PrFeO3 nanoparticles

PrFeO₃ (PFO) nanoceramic is synthesized by a sol-gel reaction technique. Thermogravimetric study of the as prepared gel is performed to get the lowest possible calcination temperature of PFO nanoparticles. The Rietveld refinement of the powder X-ray diffraction (XRD) pattern shows that the sample crystallizes in the orthorhombic (Pnma) phase at room temperature. The particle size of the sample is determined by scanning electron microscopy. The vibrational properties of the samples are studied by Raman spectroscopy at an excitation wavelength of 488 nm to substantiate the XRD results. Group-theoretical study is performed to assign the different vibrational modes of the sample in accordance with structural symmetry. Dielectric spectroscopy is applied to investigate the ac electrical properties of PFO at various temperatures between 313 and 473 K and in a frequency range of 42 Hz–1.1 MHz. The modified Cole-Cole equation is used to describe the experimental dielectric spectra. The frequency-dependent conductivity spectra are found to follow the power law. The temperature dependent dc conductivity is found to obey the Arrhenius law with an activation energy of 0.280 eV. An analysis of the real and imaginary parts of impedance is performed, assuming a distribution of relaxation times as confirmed by Cole-Cole plot.     

Produced water treatment by nanofiltration and reverse osmosis membranes

Produced water, water that is co-produced during oil and gas manufacturing, represents the largest source of oily wastewaters. Given high oil and gas prices, oil and gas production from non-conventional sources such as tar sands, oil shale and coal bed methane will continue to expand resulting in large quantities of impaired produced water. Treatment of this produced water could improve the economic viability of these oil and gas fields and lead to a new source of water for beneficial use.Two nanofiltration and one low-pressure reverse osmosis membrane have been tested using three produced waters from Colorado, USA. The membranes were analyzed before and after produced water filtration using field emission scanning electron microscopy (FESEM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, membrane–water contact angles have been measured. XPS data indicate adsorption of organic and inorganic species during filtration. FESEM and ATR-FTIR data support theses findings. Water contact angles indicate the effect of membrane hydrophilicity on fouling. Our results highlight the value of using multiple surface characterization methods with different depths of penetration in order to determine membrane fouling. Depending on the quality of the produced water and the water quality requirements for the beneficial uses being considered, nanofiltration may be a viable process for produced water treatment.     

Dissolution kinetics of oxidic nanoparticles: The observation of an unusual behaviour

The solubility of nanoparticles was measured in aqueous solution as a function of time, and oxides of aluminium, silicon, titanium, and zirconium were investigated. Our solubility results show a maximum at the beginning of the dissolution process, whereas over time, the solubility levels are shown to decrease. Depending on the special conditions the solubility maximum may exceed the long-time solubility of the nanoparticles by several orders of magnitude. This behaviour is called as kinetic size effect. The extent of the effect depends on the size, surface tension and mass of the particles exposed to dissolution. It will always be of practical interest if a larger quantity of nanoparticles is brought into contact with a solvent, even when the equilibrium solubility data appears negligible. A rigorous thermodynamic and kinetic analysis of a colloidal system, which includes nucleation, particle growth, Ostwald ripening, and dissolution of particles, shows at least a qualitative agreement between all the experimental results and model calculations.     

Conformational study of CdS nanoparticles prepared by ultrasonic waves

CdS nanoparticles of about 5 nm in size have been prepared with the aid of ultrasound irradiation to ethylenediamine solution of cadmium acetate dehydrate and elemental S in presence of 1-decanthiol under air and normal laboratory conditions. X-ray diffraction (XRD) and selected area electron diffraction (SAED) studies indicate that the products are nanocrystallites in hexagonal structure. High resolution transmission electron microscopy (HRTEM) image reveals that lattice fringes are clearly visible, conforming their crystallinity with lattice space of 0.27 nm corresponding to (1 0 2) plane of hexagonal CdS. Energy-dispersive X-ray analysis (EDAX) shows that the product are entirely pure and atomic percentage ratio of Cd to S is about 53:47. UV–vis absorption spectroscopy of the as prepared nanoparticles reveals an energy band gap of about 3.8 eV compared to 2.42 eV corresponding to its bulk value; a blue shift of about 1.38 eV, which is understood as quantum size effect due to confinement of electron and hole in a small volume.     

Colloidal silver nanoparticles stabilized by a water-soluble triosmium cluster

Silver nanoparticles stabilized by the water soluble triosmium cluster Os₃(μ-H)(CO)₁₀S(CH₂)₁₀COO]Na were prepared by both photochemical and chemical reduction of silver nitrate. The silver nanoparticles were characterized by UV-Vis spectroscopy and high resolution TEM. The particles obtained by chemical reduction showed remarkable stability.     

Electrically conducting electrospun silk membranes fabricated by adsorption of carbon nanotubes

We present a simple method of obtaining electrically conducting electrospun silk non-woven membranes consisting of nanofibers with multi-walled carbon nanotubes (MWCNTs) adsorbed on their surface. Nanofibrous membranes with fibroin diameters of 460 ± 40 nm were formed from aqueous Bombyx mori fibroin solution by electrospinning. The MWCNTs adhered well to the surface of the highly porous silk nanofibrous membranes when Triton X-100 was used as the surfactant for the dispersion of the MWCNTs in aqueous media. The electrical conductivity of the membranes was 2.4 × 10⁻⁴ S/cm due to the presence of the MWCNTs on their surface. In addition, the strong interaction between the MWCNTs and nanofibers keeps them from separating each other, even after ultrasonication. The combination of the high conductivity of the membranes and the simple process used to fabricate them could lead to significant advances in the development of new materials, such as electromagnetic interference shielding or electrostatic dissipation membranes.     

Preparation and characterization of nanoparticles formed by chitosan-caseinate interactions

Intermacromolecular complexation between chitosan and sodium caseinate in aqueous solutions was studied as a function of pH (3–6.5), using absorbance measurements (at 600 nm), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The chitosan–caseinate complexes formed were stable and soluble in the pH range 4.8–6.0. In this pH range, the biopolymers had opposite charges. At higher concentrations of chitosan (0.15 wt%), the soluble complexes associated to form larger particles. DLS data showed that, between pH 4.8 and 6.0, the particles formed by the complexation of chitosan and caseinate had sizes between 250 and 350 nm and these nanoparticles were visualized using negative staining TEM. Above pH 6.0, the nanoparticles associated to form larger particles, causing phase separation. Addition of NaCl increased the particle size. The pH dependence of the zeta potential of the mixture solutions was appreciably different from that of the pure protein and pure chitosan solutions.     

Microporous membranes obtained from polypropylene blend films by stretching

Blends of two linear polypropylenes (PP, having different molecular weights) were prepared to develop microporous membranes through melt extrusion followed by stretching. The role of high molecular weight chains on the row-nucleated lamellar crystallization was investigated. The orientation of crystalline and amorphous phases was measured by wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). Long period spacing was obtained using small angle X-ray scattering (SAXS). The effects of annealing temperature and applied elongation during annealing on the crystallinity of the films were studied using differential scanning calorimetry (DSC). It was found that annealing at 140 °C contributed significantly to the perfection of the crystalline phase. Scanning electron microscopy (SEM) images of the membrane surface showed more pore density and uniform pore size as the amount of high molecular weight component increased. The addition of the high M_w PP improved the water vapor transmission rate (WVTR) of the membranes, indicating increased interconnectivity of the pores, which was also confirmed from cross-section SEM micrographs of the membranes. The surface area and pore dimensions of the microporous membranes were measured using the BET nitrogen absorption technique and mercury porosimetry, respectively. The influences of temperature and amount of stretching during cold and hot stretching on WVTR were also explored. Tensile properties in the machine and transverse directions (MD and TD, respectively) as well as puncture resistance in the normal direction (ND) were evaluated. As the high M_w PP was added, a slight reduction in the mechanical properties along MD and TD and no changes in ND were observed.     

Preparation of ultrathin membranes by layer-by-layer deposition of layered double hydroxide (LDH) and polystyrene sulfonate (PSS)

Nanofilms were prepared by consecutively alternating adsorption of Mg–Al (2:1) layered double hydroxide (LDH) and polysodium 4-styrenesulfonate (PSS). The charge density of oppositely charged materials strongly affect film properties like thickness and ordering. The specific charge of the colloid particles (LDH) and macromolecules was determined with the particle charge detector. The sequential build-up of the thin films was followed by spectrophotometry and X-ray diffraction. The surface morphology of the multilayers was characterized by atomic force microscopy. The influence of the charge density of the applied materials and of the mass ratio of LDH/PSS on the film thickness were studied.     

Preparation of ultrathin membranes by layer-by-layer (LBL) deposition of oppositely charged inorganic colloids

Nanofilms were prepared by alternating deposition of Mg–Al (2:1) NO ₃ ⁻ layered double hydroxide (LDH), hectorite and silica particles present study. The charge density of the oppositely charged materials strongly affect film properties like thickness and ordering. The specific charge of the colloidal particles was measured with the particle charge detector. The sequential build up of the thin films was followed by spectrophotometry and X-ray diffraction (XRD). The surface morphology of the formed multilayers was characterized and film thickness determination was performed by atomic force microscopy. The influence of the charge density of hectorite and silica particles on the LDH/hectorite, LDH/silica film thickness was studied. The results reveal that the LDH concentration has a significant effect on the film thickness while the hectorite and silica concentration were not important. Films prepared from the different types of negatively charged inorganic particles in the same concentration range (0.25–1.0%) have similar thickness because of the much higher surface charge relative to the LDH lamellae.     

Mechanism and kinetics of the enzymatic hydrolysis of polyester nanoparticles by lipases

The degradation of several aliphatic and aromatic polyesters with lipases from Candida cylindracea (CcL) and Pseudomonas species (PsL) was investigated applying nanoparticles of the polymers. Nanoparticles (diameters 50 nm to 250 nm) of a particle concentration up to 6 mg/ml could be prepared by a precipitation technique without adding any stabilizing agents in the aqueous solutions. Using a titration system to monitor ester cleavage, enzymatic degradation experiments could be performed in the time scale of some minutes. A kinetic model is proposed which is based on a surface erosion process dependent on molar ester bond density and enzyme loading. Experimental evidence provided that degradation of the particles occurs uniformly at the surface after a Langmuir type adsorption of the enzyme. Rate constants and the maximal enzyme loadings of enzyme were estimated from the kinetic model for different polyesters and the rate constants correlate well with the length of the diacid component of the polyester. Comparison of degradation rates of polyester films and nanoparticles revealed that nanoparticles of aliphatic polyesters are in the amorphous state. Hence, differences of the rate constants reflect the direct influence of the polymer structure on the enzymatic hydrolysis not overlaid by effects of crystallinity.     

Synthesis and characterization of Co3O4 nanoparticles by a simple method

Using solid complex molecular precursor [bis(salicylaldehyde)ethylenediiminecobalt(II)], [Co(salen)], a simple and surfactant-free method to synthesize Co₃O₄ nanoparticles was proposed. Cubic-phase Co₃O₄ nanoparticles of size 30–50-nm could be produced by thermal treatment of the Co(salen) in the air at 500 °C for 5 h. The as-prepared samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical absorption spectrum indicates that the direct band gaps of Co₃O₄ nanoparticles are 1.53 and 2.02 eV. The optical property test indicates that the absorption peak of the nanoparticles shifts towards short wavelengths, and the blue shift phenomenon might be ascribed to the quantum effect. The hysteresis loops of the obtained samples reveal their ferromagnetic behavior, an enhanced coercivity (H_c) and a decreased saturation magnetization (M_s) as compared to their respective bulk materials.     

Paper surfaces functionalized by nanoparticles

Nanomaterials with unique electronic, optical and catalytic properties have recently been at the forefront of research due to their tremendous range of applications. Taking gold, silver and titania nanoparticles as examples, we have reviewed the current research works on paper functionalized by these nanoparticles. The functionalization of paper with only a very small concentration of nanoparticles is able to produce devices with excellent photocatalytic, antibacterial, anti-counterfeiting, Surface Enhanced Raman Scattering (SERS) and Surface Plasmon Resonance (SPR) performances. This review presents a brief overview of the properties of gold, silver and titania nanoparticles which contribute to the major applications of nanoparticles-functionalized paper. Different preparation methods of the nanoparticles-functionalized paper are reviewed, focusing on their ability to control the morphology and structure of paper as well as the spatial location and adsorption state of nanoparticles which are critical in achieving their optimum applications. In addition, main applications of the nanoparticles-functionalized papers are highlighted and their critical challenges are discussed, followed by perspectives on the future direction in this research field. Whilst a few studies to date have characterized the distribution of nanoparticles on paper substrates, none have yet optimized paper as a nanoparticles' substrate. There remains a strong need to improve understanding on the optimum adsorption state of nanoparticles on paper and the heterogeneity effects of paper on the properties of these nanoparticles.     

J-complexes of retinol formed within the nanoparticles prepared from microemulsions

Retinol nanoparticles have been obtained by direct precipitation of retinol in the inner water cores of AOT/heptane/water microemulsions. The retinol dissolved in chloroform was injected into the microemulsion. The diameter of the so-obtained nanoparticles was measured using transmission electron microscope pictures where the revelation was made thanks to adsorbed iodine on the nanoparticles. The size is ca 6.0 nm, and it is not dependent either on the size of the water droplets or the concentration of the retinol molecules. This phenomenon is explained by the thermodynamic stabilization of the nanoparticles at a certain size. UV-visible spectra of the nanoparticles show a new band the maximum of which has a bathochromic shift with respect to the absorption band of the retinol monomers. If the bathochromic shift is plotted as a function of the line width, a linear correlation is obtained, the line width is decreasing with increasing shift. This behavior is interpreted as being due to an excitonic transition of a J-complex. Quantum chemical calculations have been carried out to confirm the presence of J-complexes. Taking into account the various possible geometries, the results confirm the presence of J-complexes composed of three head-to-tail molecules on the average.     

Small angle X-ray scattering study of surface modified tin oxide nanoparticles prepared by sol-gel route

The surface properties of SnO₂ nanoparticles were modified by grafting ionic (Tiron®_, (OH)₂C₆H₂(SO₃Na)₂·H₂O) or non-ionic (Catechol®_, C₆H₄-1,2-(OH)₂) capping molecules during aqueous sol-gel processing to improve the redispersibility of powdered xerogel. The effect of the amount of grafted organic molecules on the redispersibility of powders in aqueous solution at several basic pH values was studied. The nanostructural features of the colloidal suspensions were analyzed by small angle X-ray scattering (SAXS) measurements. Irrespective of the nature and amount of grafted molecules, complete redispersion was obtained in aqueous solution at pH = 13. The redispersion at pH = 11 results in a mixture of dispersed primary particles and aggregates. The proportion of well dispersed nanoparticles and aggregates (and their average size) can be tuned by the quantity of grafted ionic molecules.     

转铁蛋白修饰聚乳酸纳米微粒表面的99mTC标记及体内分布

以转铁蛋白溶液为外水相,聚乳酸丙酮溶液为油相,纳米沉淀法制备了表面结合转铁蛋白的聚乳酸纳米微粒,以二氯亚锡为还原剂,直接法和CDPTA螯合法对纳米微粒进行99mTc放射性标记,以C6胶质瘤细胞实验考察了标记对纳米微粒表面转铁蛋白活性的影响,结果表明直接法标记率较高,大于80.1%,对转铁蛋白活性有影响。CDPTA螯合法标记法较低(72.3%),对转铁蛋白活性影响较小。以脑部荷胶质瘤大鼠为动物模型,鼠尾静脉注射放射性标记纳米微粒,SPECT示踪和γ计数器检测显示:以转铁蛋白表面修饰的聚乳酸纳米微粒经静脉注射后主要分布于肝、脾,与正常鼠相比,荷胶质瘤大鼠对纳米微粒的摄取率有所提高。