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.     

Stoeber二氧化硅溶胶中氨水的去除方法

通过pH值、电导率和二氧化硅解离量的测定，研究了Stfber二氧化硅溶胶的提纯过程．发现离心水洗很难完全去除体系中的氨水并且残留的氨水会影响二氧化硅粒子的化学稳定性．对二氧化硅溶胶进行酸处理后再提纯，可以大大加速提纯过程并消除氨水对二氧化硅粒子化学稳定性的影响。     

Stber二氧化硅溶胶中氨水的去除方法

通过pH值、电导率和二氧化硅解离量的测定,研究了St ber二氧化硅溶胶的提纯过程.发现离心水洗很难完全去除体系中的氨水并且残留的氨水会影响二氧化硅粒子的化学稳定性.对二氧化硅溶胶进行酸处理后再提纯,可以大大加速提纯过程并消除氨水对二氧化硅粒子化学稳定性的影响.     

A Systematic Study of the Use of DL-Tartaric Acid in the Synthesis of Silica Materials Obtained by the Sol-Gel Method

DL-tartaric acid was used as a template for the formation of silica nanotubes and spheres by the sol-gel method from tetraethylorthosilicate (TEOS) as silica source. The reactions were carried out in ethanol/water mixtures in the presence of aqueous ammonia, between 0°C and 75°C, using both stirred and non-stirred conditions. TEM and SEM images show that the yield and microstructure of the silica is influenced by the synthetic conditions (temperature, ammonia (aq) concentration, gelation time, solvent mixture). It was observed that the chiral form of the tartaric acid used and the diffusion of TEOS to the template determines the eventual silica structure.     

The interaction at the solid/liquid interface of 2,4-dichlorophenoxyacetic acid with silica modified by reaction with ammonia gas

A method for the attachment of ammonia to modified silica gel has been developed. In the first step, tetraethylorthosilicate and (3-glycidoxypropyl)trimethoxysilane were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified mesoporous silica. The epoxy group incorporated into the mesoporous silica was opened by ammonia gas thus introducing amine chelate groups covalently bound to the inorganic surface. The modified material contained 1.13+/-0.06 mmol of amine per gram of silica, exhibited a surface area of 831+/-29 m(2)g(-1) and a porous diameter of 1.95 nm. Infrared, 29Si and 13C NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. This ordered organic-inorganic hybrid presented a high capacity for the removal of the agrochemical 2,4-dichlorophenoxyacetic acid from water: the DeltaH and DeltaG values for the interaction were determined to be -110.61 and -9.37 kJ mol(-1), respectively.     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（ＴＥＯＳ）生长出单分散颗粒的简便方法。该方法仅在初始的悬浮液中滴加ＴＥＯＳ即可使种子正常生长，无须补充氨水以修正体系浓度的变化。最终的分散相浓度可达１０％（质量分数）。可选择生长的粒径范围在１微米以内并可精确控制。所得颗粒粒径分布偏差于Ｓｔｏｂｅｒ方法     

铜基催化剂的制备方法对草酸二乙酯加氢反应的影响

草酸二乙酯加氢性成乙二醇的反应过程中，所用的铜基催化剂是由Ｃｕ（ＮＯ３）２与硅溶胶凝法制得的。本文考察了该催化剂的ＴＰＲ特性，结果表明，随着催化剂中Ｃｕ／ＳｉＯ２值的增大，其ＴＰＲ主峰ＴＭ峰温有所升高，这意味着催化剂的还原温度随Ｃｕ／ＳｉＯ２值的增大而提高。用ＸＲＤ和ＸＰＳ等手段对该催化剂还原后铜的含量及价态进行了考察，表明用胶凝法制备的铜基催化剂，还原后存在Ｃｕ＾ｏ和Ｃｕ＾＋两种价态。结合活性评     

In situ investigation of the ionisation of silica in aqueous ammonia by using a high frequency dielectric method

The reaction of silica gel and St?ber beads of silica with ammonia was studied in aqueous medium using a high frequency dielectric method. Measurements of the complex impedance of silica pulps in both static and dynamic modes were found to be a new rapid, sensitive and non-destructive way for the in situ characterisation of the surface silica ionisation process in aqueous ammonia. The influence of various parameters (field frequency, ionic strength, ammonia concentration) was discussed. The apparent equilibrium constant for the following reaction (SiOH) + NH(3)<-->(SiO(-)NH(4)(+)) was found to be strongly affected by the degree of dissociation of both silica samples, so that the complete neutralisation was never observed. The porosity of the St?ber silica towards the NH(3) species was demonstrated experimentally through the formation of (SiO(-)NH(4)(+)) entities in the interior of the silica beads. The reversibility of the neutralisation reaction was applied to successive on-column analysis for which the hydrolysis of ammoniated silica was found to be catalysed by the presence of acids.     

Enzymatic Determination of Ammonia in Lake Water Using a Semi-Automatic Analyser

Abstract

An enzymatic method was developed for the determination of ammonia concentrations in lake water. Lake water samples containing ammonia were mixed with a glutamate dehydrogenase (GIDH), reduced nicotinamide adenine dinucleotide phosphate (NADPH) and 2-oxoglutarate. The decrease in the absorbance intensity caused by the disappearance of NADPH by this reaction was measured at 340 nm. There was a linear relationship (r = 0.9997) between peak height and ammonia concentration over the range 0–29 μM. The detection limit was 0.29 μM for a sample volume of 250 μl. Interference of amino acids and urea at concentrations of 50 mg l^?1 was negligible. Good agreement was found between the enzymatic method and indophenol blue colorimetry.     

PVP改性氧化硅溶胶的微结构和流变性

以正硅酸乙酯为前驱体,聚乙烯吡咯烷酮（PVP）为聚合物改性添加剂,在碱性条件下制备氧化硅溶胶,通过小角X射线散射测量了改性溶胶的微结构参数,辅以动态光散射观测溶胶颗粒生长,研究了聚合物量、碱催化剂量和水量对溶胶颗粒度、分形特征以及流变性的影响规律.由于PVP链中强极性的分子内酰胺基团和氧化硅颗粒表面的羟基形成氢键,致使溶胶颗粒被聚合物链包裹,严重阻碍了溶胶颗粒的生长,使凝胶时间延长,流变性发生变化,同时对溶胶颗粒的微结构产生影响.     

Preparation of large monodispersed spherical silica particles using seed particle growth

To obtain large-sized, monodispersed spherical particles of silica by sol precipitation, a seed particle growth method was attempted. The formation of secondary particles during seed particle growth causing a multimodal distribution of particle size was suppressed via fine adjustment of the reaction conditions, such as TEOS, ammonia, and water concentrations, as well as operational conditions such as feeding time and agitation speed. Among the reaction conditions, an increase of TEOS concentration promoted secondary particle formation, resulting in bimodal particle distribution. However, secondary particle formation was depressed with increasing ammonia and water concentrations. In addition, long feeding time (low feed flow rate) and rigorous agitation significantly reduced secondary particle formation because they contributed to the slow generation of supersaturation and rapid seed particle growth, respectively.     

A facile two-step etching method to fabricate porous hollow silica particles

We report here the fabrication of hollow silica particles with mesopores larger than 10 nm on their wall via a facile two-step etching method. Different from the conventional template method, the new method uses the silica particles as starting materials, which were synthesized using the well-known Stöber method. In the hollow silica preparation, first, we gently etch the silica particles with a NaOH solution without using template molecules to make them porous. Then, we coat the porous silica particles with poly-dimethyldiallylammonium chloride (PDDA) and treat the PDDA-coated porous silica with an ammonia solution to form the hollow silica nanospheres. In this study, we found that the NaOH dosage and ammonia concentration have significant impact on the morphology of the final products. Adsorption was also studied and results show that the hollow nanospheres can effectively uptake protein-based biomolecules (hemoglobin).     

Isolation of gentamicin C compounds from culture filtrates of Micromonospora purpurea

A liquid chromatographic method was developed for the isolation of gentamicin C compounds from commercial fermentation products in order to monitor health hazards (oto- and nephrotoxicity). Chromatography was carried out on silica gel 60 (15-40 microns) with a medium-pressure chromatographic system, employing methanol-25% ammonia solution (85:15, v/v) and methanol-chloroform-25% ammonia solution (20:10:5, v/v) as mobile phases. The eluted fractions were neutralized with 1.0 M hydrochloric acid, concentrated in vacuo and desalted by gel filtration. It was possible to demonstrate by 1H NMR spectroscopy and high-performance liquid and thin-layer chromatography that the separated fractions contained components C1, C1a and C2 in purities of more than 95%.     

由硅酸酯合成单分散二氧化硅中碳的化学形态

单分散二氧化硅是指尺寸分布十分狭窄的二氧化硅颗粒．单分散颗粒在科学研究及工业应用中得到了广泛的应用［1］．单分散二氧化硅由正硅酸有机酯在氨催化下于醇溶液中水解缩合得到．硅酸酯的水解和缩合反应可用如下反应描述．总的反应式为：nSi（OR）4＋2nH20→nSiO2＋4nROH1956年Kolbe［2］发现正硅酸乙酯（TEOS）在碱催化下于乙醇溶剂中水解反应有时会形成均一颗粒二氧化硅以来，许多学者对这一反应体系进行了较为广泛的研究，提出了双分子缩合成核机理、单分子叠加生长机理、表面反应控制生长机理、扩散控制生长机理和微晶核团聚生…     

凝胶法制备条件对载体硅胶孔结构的影响

以水玻璃、硫酸为原料采用凝胶法制备了烯烃环氧化催化剂载体硅胶,为探讨制备条件对硅胶孔结构的影响,采用物理吸附仪对不同条件下制备的硅胶进行了表征,结果表明:溶胶pH值、老化温度和老化时间、氨水pH值对硅胶孔结构影响显著,当溶胶pH值为1.5,在80℃下用pH 10.5的氨水浸泡老化凝胶2 h,所得硅胶的比表面积在300 m2.g-1左右,孔径和孔容分别在9.71 nm和0.92 cm3.g-1以上,以此硅胶为载体制得的非均相催化剂Ti/SiO2对于氯丙烯和环己基过氧化氢的环氧化反应具有明显的催化活性。     

Determination of NH(3) in pyrolysis gases by ammonia selective electrode

The suitability of ion-selective electrode for the determination of ammonia in pyrolysis gases of fossil fuels was studied. The ammonia was absorbed into acidic solution and two kinds of determination methods were carried out. The ammonia was either measured directly from the acid solution, or ammonia was first released into the gas phase and then determined (air gap method) by the ammonia selective electrode. The electrode functioned well in both cases, but the linear calibration range was rather narrow, slightly more than one tenfold. The quantitative detection limit in the water phase was 5 x 10(-6)M (0.085 ppm) NH(3) and in gas phase operation solutions above 5 x 10(-4)M (8.5 ppm) NH(3) it was possible to measure quantitatively. The applications were carried out with Finnish energy peat samples and a coal sample.     

Silica coating of silver nanoparticles using a modified Stober method

Silver nanoparticles prepared through a borohydride-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stober method. Various amine catalysts were used for initialization of a sol-gel reaction of TEOS with no need for a prior surface modification. Use of dimethylamine (DMA) as a catalyst was found to be necessary to obtain a proper coating. The silica shell thickness was varied from 28 to 76 nm for TEOS concentrations of 1-15 mM at 11.1 M water and 0.8 M DMA. The optical spectra of the core-shell silver-silica composite particles show a qualitative agreement with predictions by Mie theory.     

Preparation and characterization of silica aquasols

Aquasols containing silica nanoparticles with diameters of 75 to 95 nm were obtained directly by hydrolysis of 2 wt.% tetraethoxysilane (TEOS) in water in the presence of a non-ionic surfactant. The reaction was catalyzed by hydrochloric acid, ammonia, or sodium hydroxide. The particle size, which mainly depends on the concentration of TEOS in water, was determined by dynamic light scattering (DLS). Whereas the catalysts have almost no influence on the particle size, they very strongly affect the morphology of the silica particles formed. The dried SiO(2) particles obtained via the HCl-catalyzed reaction have film-forming properties and show no measurable BET surface area. SiO(2) particles prepared with ammonia as catalyst form nanoporous films on glass, and the BET surface area of the freeze-dried particles is 540 m(2)/g. Using sodium hydroxide as catalyst results in some agglomeration of uniform spherical particles with a BET surface area of 237 m(2)/g. (29)Si MAS NMR investigations of the freeze-dried particles provide information about the degree of condensation and the ratio of "free" hydroxyl groups. The silica aquasols described have a surprisingly high hydrophilizing effect on hydrophobic fibers (PP, PET). Silica nanoparticles of comparable diameters, prepared by the "St?ber method", dispersed in alcohol do not show any hydrophilizing properties worth to mention.     

反相微乳液法制备纳米SiO2的研究

在壬基酚聚氧乙烯5醚(NP-5)/环己烷/氨水的反相微乳液体系中，进行正硅酸乙酯(TEOS)的水解、缩合反应，得到粒径在30～50 nm的单分散纳米SiO₂胶体。红外光谱法(FTIR)及透射电子显微镜(TEM)观察证明了纳米SiO₂粒子的生成。反相微乳液体系相图的研究表明，水相为氨水比纯水有较窄的W/O型微乳区。氨水微乳液是碱催化TEOS水解、缩合制备纳米SiO₂粒子的适宜体系。当体系中TEOS的浓度增大时，粒子的粒径随之增大。降低NP-5     

Synthesis and characterization of amino-functionalized silica nanoparticles

Monodispersed raw silica nanoparticles (RSNPs) with the particle size of 40 nm were successfully fabricated by condensation reaction of tetraethylorthosilicate in methanol with high concentration ammonia (1.2 M). The RSNPs were treated with the coupling agent 3-aminopropyltrimethoxysilane (APTMS) for grafting amine groups on the surface to obtain the amino-functionalized silica nanoparticles (ASNPs). The chemical structure and surface morphology of RSNPs and ASNPs were characterized by Fourier-transform infrared spectra, solid-state NMR spectra and scanning electron microscopy. In addition, a method to quantify the grafted amine groups on the surface of ASNPs was developed by using the ninhydrin assay. The ninhydrin analysis showed that 60 mol % of the APTMS molecules were immobilized on the surface, that is, 4.4 amine groups per nm2 of surface area were bonded on nonporous ASNPs. The weight loss of particles obtained from thermogravimetry analysis indicated the amount of grafted amine groups and was used as a reference to compare with the value determined from ninhydrin method.