Controlled formation of ag nanoparticles by means of long-chain sodium polyacrylates in dilute solution

A new tool is presented to control formation of Ag nanoparticles. Small amounts of silver ions were added to dilute solutions of long-chain sodium polyacrylates (NaPA). Four NaPA samples covering a molar mass regime of 97 kD < or = Mw < or = 650 kD have been used. With amounts of added Ag(+) as low as 1-2% of the COO(-) groups of the polyanionic chains, significant changes could already be induced in the NaPA coils with 650 kD. If the NaPA concentration was kept below 0.1 g/L, the coils with 650 kD exhibited a significant coil shrinking in stable solutions. At larger NaPA concentrations, addition of Ag+ initiates an aggregation of the polyacrylate coils toward compact structures. Coil shrinking and aggregation was revealed by means of time-resolved static light scattering. If exposed to UV-radiation, small Ag particles formed within the shrunken anionic polyacrylate coils. The Ag nanoparticles were identified by means of an enhanced light scattering and a characteristic plasmon absorption band around 410 nm. No such Ag particle formation could be observed even at 5 times larger concentrations of Ag(+) and NaPA if the two smallest polyacrylate samples have been used under otherwise equal conditions. This molar mass sensitive response of NaPA to Ag(+)-addition suggests an interesting phenomenon: if the coil size of the NaPa chains, which act as Ag(+) collectors, is large enough, local Ag(+) concentration in these coil-shaped Ag(+) containers exceeds a critical value, and irradiation with UV generates Ag nanoparticles.     

Detection of slightly soluble systems by means of organized media in flow-injection analysis

Species that are slightly soluble in water (reagents, analytes or reaction products can be used in hydrodynamic analytical systems by means of a judicious choice of an appropriate organized medium allowing one to operate in homogeneous media with the attendant advantages. In addition, these systems allow one to improve existing analytical methods and to develop new analytical procedures. Results obtained with two types of insoluble systems are presented: those provided by 1-(2-pyridylazo)-2-naphthol (PAN) and those originating from Arsenazo III in a strongly acid medium. Detection in these systems is possible by working with an organized medium. New methods for the determination of thorium, uranium and rare-earth elements are proposed.     

二苯胺磺酸钠还原法制备粒径可控的金纳米粒子

采用二苯胺磺酸钠还原四氯合金酸的方法,在室温条件下,用SDS(十二烷基硫酸钠)、SDBS(十二烷基苯磺酸钠)作表面活性剂,成功地合成了金纳米粒子.分别讨论了还原剂二苯胺磺酸钠、表面活性剂(SDS、SDBS)及四氯台金酸的浓度等对金纳米粒子的粒径和形貌的影响.通过控制反应条件,可以合成出平均粒径大约为10、14、30、36nm的金纳米粒子.利用透射电镜(TEN)、紫外-可见(UV-Vis)吸收光谱对金纳米粒子进行了表征.研究结果表明不同的SDS或SDBS/HAuCl4的摩尔比,对金纳米粒子的尺寸大小有影响.     

芘荧光探针法研究海藻酸钠与SDS的作用

采用芘荧光法研究了海藻酸钠(NaAlg)与十二烷基硫酸钠(SDS)在不同pH水溶液中的相互作用.以芘单体的荧光光谱第一峰与第三峰的荧光强度之比(I1/I3)及激基缔合物与单体荧光强度之比(IE/IM)来探测芘分子所处环境的极性.结果表明:NaAlg水溶液随pH值降低,出现了聚合物的疏水微区;pH从7降到5,NaAlg类似简单盐,对SDS的临界胶束浓度(CMC)有明显的影响;在pH 3时,海藻酸主链上有足够的疏水片段,使得SDS与海藻酸通过疏水性作用而聚集.NaCl对NaAlg /SDS体系的影响亦较明显.     

Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media

Colloidal dispersions of silver bromide (AgBr) in aqueous surfactant medium have been prepared using a surfactant-assisted synthesis approach with hexadecyltrimethylammonium bromide (CTAB). The surfactant acts both as source of bromide ion as well as the stabilizing agent. Upon progressive addition of silver nitrate to aqueous CTAB solution, stable AgBr dispersions were obtained. Formation of surfactant cation (CTA(+)) stabilized AgBr was confirmed by way of XRD, FTIR and NMR studies. Thermal behavior of the isolated nanoparticles was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), where the occurrence of phase transition in the surfactant-stabilized nanoparticles was observed. Kinetics of the particle growth was investigated by dynamic light scattering measurements, which predicted the formation of surfactant bilayered structures associated with the nanoparticles of AgBr. Band gap of the nanoparticles was determined by suitably analyzing the UV-visible spectral data, which concluded that the particles behaved like insulators. Morphology of the particles, studied by TEM measurements, was found to be spherical. Finally, enthalpy of formation of surfactant-stabilized AgBr, determined calorimetrically, was found to be dependent on the concentration of the precursors.     

Pyrene-assisted synthesis of size-controlled gold nanoparticles in sodium dodecyl sulfate micelles

Gold nanoparticles prepared by chemical reduction in sodium dodecyl sulfate (SDS) solution are size-controlled with the addition of pyrene. Micellar electrokinetic capillary chromatography (MEKC) is applied to the system to examine the size and polydispersity of gold nanoparticles and to show that pyrene has the extraordinary effect in decreasing the size and narrowing the dispersity of gold nanoparticles. The MEKC electropherograms further suggest that pyrene could be oxidized by the aqueous Au(III) complexes first. All the reduced Au complexes were then solubilized in the pyrene-SDS micelles. The growth of gold nanoparticles beyond the embryonic stage was subsequently inhibited by the encapsulating SDS and electrophilic pyrene.     

Microemulsions as reaction media for the synthesis of Pt nanoparticles

For the synthesis of Pt nanoparticles we used water-in-oil droplet microemulsions as templates. The focus was on the correlation between the size of the microemulsion droplets and that of the resulting Pt particles. To study this correlation in a systematic way, all particles were synthesized at the water emulsification failure boundaries where the microemulsion droplets are spherical and where their size can easily be tuned by the amount of added water. The metallic particles were synthesized by mixing two microemulsions one of which contains the metal salt H(2)PtCl(6) and the other the reducing agent NaBH(4). The size and structure of the microemulsion droplets was studied via small-angle X-ray scattering, while the Pt particles were characterized by high-resolution transmission electron microscopy in combination with energy-dispersive X-ray spectroscopy and selected area electron diffraction. The clear correlation between droplet and particle size was further supported by accompanying Monte Carlo simulations.     

海藻酸钠脱除重金属研究进展

重金属污染已成为全球性的环境问题,脱除重金属是治理重金属污染的主要途径。海藻酸钠(SA)本身无毒、性质稳定、价格低廉,具有较强的胶凝性、成膜性和络合能力,既可作为脱除重金属的吸附材料,又可作为脱除重金属的固定化载体,在重金属脱除中具有广泛的应用。本文重点综述了SA凝胶球、SA复合膜、SA纳米复合材料、SA分子印迹脱除重金属,以及SA作为单一固定化载体和复合固定化载体脱除重金属进展情况。展望了SA脱除重金属的应用前景。     

非共价键交联海藻酸钠水凝胶的制备与性能

天然多糖海藻酸钠制备的水凝胶具有优越的生物相容性和生物组织相似性,作为生物医用材料在药物控制释放、组织工程支架、抗菌材料及创伤敷料等领域发挥着越来越大的作用。本文在介绍海藻酸钠物化性质的基础上,重点综述了非共价键交联(静电作用、氢键、范德华力、亲疏水作用等)海藻酸钠水凝胶的制备方法以及性能表征方法,最后讨论了制备方法及性能表征研究中的一些需要解决的问题。     

Problem solving by expert systems in analytical chemistry

Summary It is expected that artificial intelligence and more particularly, expert systems, will have a profound effect upon analytical chemistry. This paper provides an overview of this rapidly evolving field. General aspects of expert systems are dealt with first, such as knowledge representation, knowledge manipulation, dealing with uncertainty, and the application of software tools to facilitate the construction of expert systems. The accomplishments with respect to the application of expert systems to chemistry — particularly analytical chemistry — are discussed. Future directions of the research and applications are forecasted.

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Expert Systems zur Problemlösung in der analytischen Chemie

Zusammenfassung Es ist zu erwarten, daß künstliche Intelligenz und besonders expert systems einen großen Einfluß auf die analytische Chemie ausüben werden. In dieser Arbeit wird ein Überblick über dieses in schneller Entwicklung befindliche Gebiet gegeben. Zunächst werden die expert systems im allgemeinen behandelt (Darstellung und Handhabung von Wissen, Behandlung von Unsicherheiten, Anwendung von Software zur Konstruktion der expert systems). Anschließend werden Anwendungen in der Chemie — speziell der analytischen Chemie — diskutiert und zukünftige Entwicklungen aufgezeigt.

     

Molecular mass distribution of sodium alginate by high-performance size-exclusion chromatography

A sensitive high-performance size-exclusion chromatography (HPSEC) method with simple UV detection was developed for the molecular mass analysis of sodium alginate. It was used to evaluate alginates of varying molecular mass and the results were compared with the viscosity measurements. This HPSEC method was sensitive to serve as the stability indicating method for alginate after storage under different conditions. The information of relative molecular mass distribution of alginate was provided with reference to pullulan molecular mass standards. The comparison of the HPSEC chromatograms of alginate, pullulan and dextran revealed the effect of chemical composition of a polysaccharide and its effect on apparent molecular mass distribution.     

Experimental study of ultrafiltration membrane fouling by sodium alginate and flux recovery by backwashing

Membrane fouling is the major limitation for a broader application of membrane technology. One of the main causes of membrane fouling in advanced wastewater reclamation and in membrane bioreactors (MBR) are the extracellular polymeric substances (EPS). Among the main constituents in EPS, polysaccharides are the most ubiquitous. This study aims at a better understanding of the fouling mechanisms of EPS and the efficiency of backwashing technique, which is applied in practice to restore membrane flux. For that purpose, the evolution of fouling by sodium alginate, a microbial polysaccharide, is studied in ultrafiltration. Fouling experiments are carried out in a single fiber apparatus, aiming at identifying the significance of distinct fouling mechanisms and their degree of reversibility by backwashing. An important parameter considered in the study is the concentration of calcium ions, which promote sodium alginate aggregation and influence the rate of flux decline, the reversibility of fouling and rejection. A rapid irreversible fouling takes place due to internal pore constriction, at the beginning of filtration, followed by cake development on the membrane surface. With increased calcium addition, cake development becomes the dominant mechanism throughout the filtration step. Furthermore, fouling reversibility is increased with the increase of calcium concentration. A unique behavior of sodium alginate solution in the absence of calcium is also noted, i.e. the formation of a labile layer on the membrane surface, which is affected by the small cross-flow that exists inside hollow fibers, even in the nominally dead-end mode of operation.     

Flame synthesis of calcium-, strontium-, barium fluoride nanoparticles and sodium chloride

Non-oxidic salts such as NaCl, CaF2, SrF2 and BaF2 were synthesised using a flame spray method; optional doping of such fluorides with rare earth elements suggests possible applications in optics.     

Polymer synthesis by means of germylene and stannylene

Divalent group 14 metal species, a germylene(la) and a stannylene(lb), behaved as a comonomer(reductant monomer) in the copolymerization with p-benzoquinone derivatives(oxidant monomer)(“oxidation-reduction copolymerization”) and as an initiator for anionic monomers. The copolymerization took place without initiator at a lower temperature to give an alternating copolymer. N-phenyl-p-quinoneimine also behaved as a reactive oxidant monomer toward la and lb. These species have been shown to induce the polymerization of anionically polymerizable monomers such as methyl methacrylate, methacrylonitrile, and 4-vinylpyridine. Based on the mechanistic examination of the polymerization, a new alternating copolymerization between la and 2-cyclohexene-l-one has been developed to produce a copolymer having a metal-enolate structure, which involves the oxidation-reduction process during the copolymerization.     

Different viscosity grade sodium alginate and modified sodium alginate membranes in pervaporation separation of water + acetic acid and water + isopropanol mixtures

Different viscosity grade sodium alginate (NaAlg) membranes and modified sodium alginate membranes prepared by solution casting method and crosslinked with glutaraldehyde in methanol:water (75:25) mixture were used in pervaporation (PV) separation of water+acetic acid (HAc) and water+isopropanol mixtures at 30 °C for feed mixtures containing 10–50 mass% of water. Equilibrium swelling experiments were performed at 30 °C in order to study the stability of membrane in the fluid environment. Membranes prepared from low viscosity grade sodium alginate showed the highest separation selectivity of 15.7 for 10 mass% of water in the feed mixture, whereas membranes prepared with high viscosity grade sodium alginate exhibited a selectivity of 14.4 with a slightly higher flux than that observed for the low viscosity grade sodium alginate membrane. In an effort to increase the PV performance, low viscosity grade sodium alginate was modified by adding 10 mass% of polyethylene glycol (PEG) with varying amounts of poly(vinyl alcohol) (PVA) from 5 to 20 mass%. The modified membranes containing 10 mass% PEG and 5 mass% PVA showed an increase in selectivity up to 40.3 with almost no change in flux. By increasing the amount of PVA from 10 to 20 mass% and keeping 10 mass% of PEG, separation selectivity decreased systematically, but flux increased with increasing PVA content. The modified sodium alginate membrane with 5% PVA was further studied for the PV separation of water+isopropanol mixture for which highest selectivity of 3591 was observed. Temperature effect on pervaporation separation was studied for all the membranes; with increasing temperature, flux increased while selectivity decreased. Calculated Arrhenius parameters for permeation and diffusion processes varied depending upon the nature of the membrane.     

Enhancing foam stability in porous media by applying nanoparticles

Several new foaming agent formulations (surfactants and polymers) in the presence of multi-walled carbon nanotube (MWCNT) were developed in 3% salinity (NaCl, 2.4?wt%, CaCl₂, 0.6?wt%). The dispersion stability of the MWCNT and the viscosity of the solutions were examined as a prerequisite for reservoir applications. Foam was generated in situ and one-dimensional flow-through tests were performed by co-injecting air and foaming solution either in the presence of MWCNT or at particle-free condition. The pressure drop (Δp) across the sand-pack and the nanoparticles breakthrough were closely monitored. The fluid injection rate, gas fraction, and the effect of MWCNT on foams in porous media were investigated.

Our results reveal that foams stabilized by the selected nanoparticles are capable of generating stronger foams leading to higher apparent Δp. The Δp profile varies with gas fraction, which largely affects the foam texture and quality. Also, the viscosity of foaming agent solutions influences Δp values. Adding MWCNT to the foaming agent solutions appears beneficial to the flooding as surfactants adsorption onto nanoparticle surfaces, which facilitates surfactants partitioning to the G/L interface.

Addition of nanoparticles in the developed foam formulations leads to the formation of high-quality stronger foams in porous media, which could potentially improve the sweep efficiency and increase the oil recovery.     

Peptide synthesis by means of immobilized enzymes

-Chymotrypsin covalently bound to silica, enzacryl AA, and enzacryl AH catalyzes peptide bond formation between N-protected dipeptide methyl esters and H-Leu-NH₂ with results similar to those with the free enzyme. The influence of water-miscible and water-immiscible cosolvents, of the supports, and of the structure of the substrates is shown to be of importance for the ease of the chymotrypsin-medicated coupling reactions. The best yields were obtained using biphasic aqueous-organic solvent mixtures, silica-bound chymotrypsin, and substrates with leucine in the P₂-position. The yields of the syntheses are discussed in terms of the reactivity of substrates with similar structure in enzymatic hydrolyses. All the immobilized chymotrypsin preparations could be re-utilized successfully for further couplings. Abbreviations: IUPAC/IUB rules for peptides are followed, see Eur. J. Biochem.27, 201 (1972); Glt=4-carboxybutyrul (glutaryl),-Nan=4-nitroanilide. All amino acids except glycine are of L-configuration.     

Direct electrochemistry of hemoglobin immobilized in the sodium alginate and SiO2 nanoparticles bionanocomposite film on a carbon ionic liquid electrode

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using a room temperature ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) as binder. By using the CILE as basal electrode, the hemoglobin (Hb) molecule was immobilized on the surface of CILE with a sodium alginate (SA) hydrogel and SiO₂ nanoparticles organic-inorganic composite material. The direct electrochemical behaviors of Hb in the bionanocomposite film were further studied in a pH 7.0 Britton-Robinson (B-R) buffer solution. A pair of well-defined quasi-reversible cyclic voltammetric peaks of Hb was obtained on SA/nano-SiO₂/Hb/CILE with the formal potential (E^0’) at -0.355 V (vs. SCE), which was the characteristic of heme Fe(III)/Fe(II) redox couples. The formal potential of Hb Fe(III)/Fe(II) couple shifted negatively with increasing pH of solution with a slope of -45.2 mV/pH, which indicated that a one electron transfer accompanied with one proton transportation. The immobilized Hb showed good electrocatalytic manner to the reduction of trichloroacetic acid (TCA).