Cetyltrimethylammonium bromide silver bromide complex as the capping agent of gold nanorods

A complex between cetyltrimethylammonium bromide (CTAB) surfactant and silver bromide (CTASB) is recognized by NMR and X-ray photoelectron spectroscopy (XPS) to be the entity at the surface of gold nanorods, resulting from an in situ formation in the classical scheme of synthesis. It can thus be introduced directly along with the initial reactants in place of silver(I) salt to produce a new effective synthesis of these objects. Complementary XPS and quartz crystal microbalance (QCM) measurements on macroscopic gold surfaces confirm a strong adsorption of CTASB that is higher than that of CTAB and any other CTAX surfactants. The role of CTASB as a rod inducing agent by surface complexation is stressed.     

十六烷基三甲基溴化铵/油酸钠混合体系蠕虫状胶束流变性研究

阴、阳离子表面活性剂之间强烈的相互作用利于形成自由弯曲的蠕虫状胶束。本文利用阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)和阴离子表面活性剂油酸钠(Na OA)制备了CTAB/Na OA蠕虫状胶束,研究了两表面活性剂的混合比和表面活性剂总浓度的变化对蠕虫状胶束体系稳态流变性及动态粘弹性的影响。结果表明,蠕虫状胶束在剪切过程中的解缠、拟网状结构的破坏以及最终沿剪切速度方向取向等是蠕虫状胶束产生剪切稀释特性的原因。两表面活性剂的混合比和表面活性剂总浓度的变化导致表面活性剂之间的静电作用、疏水作用发生较大的变化,最终引起体系内部表面活性剂聚集体形态的差异。体系内蠕虫状胶束长度、体系结构复杂程度、蠕虫状胶束形成的网络结构的致密度等都影响着体系的流变行为。在混合比R=3.6、总浓度CT=0.24mol/L时,体系中蠕虫状胶束最长,网络结构最为紧密,体系的零剪切粘度达到最大值。表面活性剂浓度一定时,混合比的提高有助于蠕虫状胶束的定向生长,弛豫时间τR和储能模量高频区平台模量G0提高,R=3.6时两者皆达到极大值,此后由于蠕虫状胶束的分枝化及(或)胶束破裂导致τR及G0下降。在表面活性剂混合比一定(R=3.6)时,表面活性剂浓度的提高利于蠕虫状胶束的增长或者分枝化,增加了胶束网络结构缠绕(融合)点的密度,导致G0逐渐增大。Cole-Cole图证实本文研究的蠕虫状胶束体系是符合Maxwell模型的线性粘弹性流体。     

Thorough tuning of the aspect ratio of gold nanorods using response surface methodology

In the present work a central composite design based on response surface methodology (RSM) is employed for fine tuning of the aspect ratios of seed-mediated synthesized gold nanorods (GNRs). The relations between the affecting parameters, including ratio of l-ascorbic acid to Au³⁺ ions, concentrations of silver nitrate, CTAB, and CTAB-capped gold seeds, were explored using a RSM model. It is observed that the effect of each parameter on the aspect ratio of developing nanorods highly depends on the value of the other parameters. The concentrations of silver ions, ascorbic acid and seeds are found to have a high contribution in controlling the aspect ratios of NRs. The optimized parameters led to a high yield synthesis of gold nanorods with an ideal aspect ratio ranging from 1 (spherical particle) to 4.9. In addition, corresponding tunable surface Plasmon absorption band has been extended to 880 nm. The resulted nanorods were characterized by UV–visible spectrometry and transmission electron microscopy.     

Electrochemical determination of dipyridamole at a carbon paste electrode using cetyltrimethyl ammonium bromide as enhancing element

Electrochemical behaviors of dipyridamole (DIP) at a carbon paste electrode in the presence of cetyltrimethyl ammonium bromide (CTAB) were investigated by voltammetry, chronocoulometry and electrochemical impedance spectroscopy (EIS). The results indicated that the electrochemical responses of DIP are apparently improved by CTAB, due to the enhanced accumulation of dipyridamole at the carbon paste electrode surface. Electrochemical parameters for the oxidation of DIP were explored by chronocoulometry. Under optimal conditions, the oxidation peak current at 0.53 V was proportional to DIP concentration in the range of 0.03-12 microg mL-1, with a detection limit of 0.01 microg mL-1 for 120 s accumulation by different pulse voltammetry (DPV). This method was applied to the determination of DIP in the tablet samples. The results were satisfying compared with that obtained by standardized method of high performance liquid chromatography (HPLC).     

Development of a novel and robust microprecipitation approach using cetyltrimethyl ammonium bromide (CTAB) for preconcentration and speciation of mercury in waters prior to CVAAS determination

A novel and simple microprecipitation method was developed for the preconcentration of ultra-trace quantities of inorganic and methyl mercury species (iHg and MeHg) prior to their determination by cold vapour atomic absorption spectrometry (CVAAS). This method is based on the formation of anionic complexes of Hg²⁺ with KI followed by ion-associate complex with cetyltrimethyl ammonium bromide (CTAB) that forms a fluffy precipitate in perchloric acid medium. As a result, a fluffy coagulated mass separates and collects at the top of the liquid surface with clear phase separation without need of cooling or heating or centrifugation. The ion-association complex of iHg was then extracted into surfactant-rich phase (top layer) of CTAB-perchlorate precipitate while the uncomplexed MeHg remained in the aqueous phase (bottom layer). This condition also facilitates the removal of aqueous phase by simply draining out. The fluffy mass formed was dissolved in a mixture of HNO₃ and HCl which was subsequently treated with chloroform to separate the surfactant from the mixture. Then the aqueous phase containing the preconcentrated iHg was analysed for mercury by CVAAS. Key factors such as sample pH, concentration of KI and CTAB that affect the performance of the proposed microprecipitation method were thoroughly investigated. For the determination of total mercury, another fresh aliquot of water was initially adjusted to pH ~ 3.5 with perchloric acid and subjected to oxidation by using modified UV-irradiation set-up and then taken through the microprecipitation procedure. This method allows speciation of mercury with a preconcentration factor of 200 and the limits of detection (LOD) of mercury obtained for CVAAS in conjunction with the present preconcentration method was found to be 2.4 ng L^?1. Average recoveries obtained with the proposed approach were found to be in the range of 96–104% with RSD values < 5%. The interfering effects of various cations and anions were also investigated. The method was successfully applied for the determination of ultra-trace quantities of mercury species in real samples such as bottled water, tap water, lake water and ground waters.     

Stability of xylene-in-water emulsions in the presence of cetyltrimethyl ammonium bromide/cetyl alcohol mixtures

Interfacial tension (γ) measurements at the xylene/aqueous cetylrimethylammonium bromide (CTABr) solutions in the presence and absence of cetyl alcohol have shown that addition of cetyl alcohol reduces γ and increases the adsorption of CTA⁺ ions at the O/W interface. The same increase was observed in the presence of 0.5 and 1 mole l⁻¹ NaCl in the aqueous phase. Microelectrophoresis measurements at various CTABr concentrations in the presence and absence of cetyl alcohol showed a gradual increase of zeta potential (ξ) with increase of CTABr concentration, followed by a rapid increase in zeta potential and eventually ξ reached a limiting value which increased progressively with increase of the alcohol content in the mixture. These results confirm the increased adsorption of the cationic surfactant on addition of alcohol. This increase may be due to the more dense packing of the CTA⁺ ions as a result of the reduction of the repulsion between the head groups when the alcohol adsorbs between the surfactant ions.The rate of coalescence of xylene/water emulsions was measured by droplet counting (using optical microscopy) as a function of time. The rate constant K of coalescence was calculated from the slope of the tangent of the log N_t versus t curves. The results showed that addition of cetyl alcohol (10, 20, and 30 mole %) reduces the rate of coalescence significantly and, at 30 mole % cetyl alcohol, very stable emulsions were produced. Similar results were obtained in the presence of 1 mole l⁻¹ NaCl and 0.5 mole l⁻¹ CaCl₂. The enhanced stability is probably due to the formation of a coherent strong interfacial film which acts as a “barrier” preventing coalescence, possibly by virtue of its rheological properties, e.g. dilational viscoelasticity.     

Experimental and numerical study of cetyltrimethylammonium bromide (CTAB)-directed synthesis of goethite nanorods

This study demonstrates a facile surfactant-directed approach to prepare goethite (α-FeOOH) nanorods in aqueous solution at room temperature. The obtained α-FeOOH nanorods have a diameter of ～20 nm and length up to 300 nm. Various experimental parameters have been investigated, such as surfactants, solution pH, and reaction temperature. It is observed that the surfactant, cetyltrimethylammonium bromide (CTAB), plays a key role in the growth of goethite nanorods at ambient conditions. The final product can be purified using diluted hydrochloric acid (HCl) to remove particles of other shapes. Molecular dynamics (MD) method is used to understand the underlying principles governing particle growth through the analysis of the interaction energies between crystal surfaces and surfactant molecules. The simulation results indicate that CTAB can strongly interact with {100}, {010}, and {110} planes, which benefits the growth of nanorods along [001] direction. Such simulations can provide useful information for the synthesis and shape control of other metal oxide materials.     

Crystal overgrowth on gold nanorods: tuning the shape, facet, aspect ratio, and composition of the nanorods

Electrochemically prepared Au nanorods were used as seeds for the overgrowth of thin shells of gold, silver, and palladium by using a mild reducing agent, ascorbic acid, in the presence of surfactants at ambient condition. The unique crystal facets of the starting nanorods results in anisotropic crystal overgrowth. The overgrowth rates along different crystallographical directions can be further regulated by adding foreign ions or by using different metal reduction methods. This overgrowth study provides insights on how different metal ions could be reduced preferentially on different Au nanorod surfaces, so that the composition, aspect ratio, shape, and facet of the resulting nanostructures can be rationally tuned. These surfactant-stabilized bimetallic Au(core)M(shell) (M=Au, Ag, Pd) nanorod colloids might serve as better substrates in surface-enhanced Raman spectroscopy as well as exhibiting enhanced catalytic properties.     

Chromogenic reaction of bromopyrogallol red with tri- and hexavalent chromium in the presence of cetyltrimethyl ammonium bromide and its application in Cr speciation

The coordination reactions of bromopyrogallol red (BPR) with tri- and hexavalent chromium in the presence of cetyltrimethylammonium bromide (CTAB) have been studied by absorption spectrometry. Results show that the reactions of Cr(VI) and Cr(III) with BPR in the absence or presence of CTAB have different temperature dependences. The reaction mechanism of Cr(VI) is that Cr(VI) is first reduced by BPR to Cr(III) and then the Cr(III) produced reacts with BPR. Based on the study on the coordination reactions and the effects of surfactants upon them, a simple, rapid, sensitive and accurate method for Cr speciation has been developed. Over the range of 0–8 g Cr(VI) or 0–12g Cr(III) per 25ml final volume, the calibration curve is linear with a detection limit of 3.5 × 10^–7 mol/1 for Cr(VI) or 4.4 × 10^–7 mol/1 for Cr(III).     

One-step synthesis of gold and silver hydrosols using poly(N-vinyl-2-pyrrolidone) as a reducing agent

Synthesis of gold and silver hydrosols was carried out in a one-step process by reduction of aqueous solutions of metal salts using poly(N-vinyl-2-pyrrolidone) (PVP). Both kinds of metal nanoparticles were obtained without the addition of any other reducing agent, at low temperatures and using water as the synthesis solvent. Shape, size, and optical properties of the particles could be tuned by changing the employed PVP/metal salt ratio. It is proposed that PVP acts as the reducing agent suffering a partial degradation during the nanoparticles synthesis. Two possible mechanisms are proposed to explain the reduction step: direct hydrogen abstraction induced by the metal ion and/or reducing action of macroradicals formed during degradation of the polymer. Initial formation of the macroradicals might be associated with the metal-accelerated decomposition of low amounts of peroxides present in the commercial polymer.     

Role of cetyltrimethyl ammonium bromide, crystal violet and humic acid in the degradation of diclofenac under simulated sunlight irradiation

The photodegradation of diclofenac in the absence/presence of cetyltrimethyl ammonium bromide,crystal violet and humic acid under simulated sunlight has been studied.Under the study conditions,it is apparent that cetyltrimethyl ammonium bromide and crystal violet concentrations inhibit effects on the photodegradation of diclofenac.Humic acid has no distinct effect on the photodegradation of diclofenac.Crystal violet has an obvious antagonistic action for humic acid and a similar antagonistic action between cetyltrimethyl ammonium bromide and crystal violet.Cetyltrimethyl ammonium bromide and humic acid have synergistic effect.An antagonistic action is present between cetyltrimethyl ammonium bromide,crystal violet and humic acid.Moreover,a simple linear model which describes the obtained results is shown.     

Effects of urea and a nonionic surfactant on the micellization and counterion binding properties of cetyltrimethyl ammonium bromide and sodium dodecyl sulfate

Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm^–3 and 0.25 mol dm^–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm^–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below.     

Quaternary ammonium bromide surfactant adsorption on low-index surfaces of gold. 1. Au(111)

The coadsorption of the anionic and cationic components of a model quaternary ammonium bromide surfactant on Au(111) has been measured using the thermodynamics of an ideally polarized electrode. The results indicate that both bromide and trimethyloctylammonium (OTA(+)) ions are coadsorbed over a broad range of the electrical state of the gold surface. At negative polarizations, the Gibbs surface excess of the cationic surfactant is largely unperturbed by the presence of bromide ions in solution. However, when the Au(111) surface is weakly charged the existence of a low-coverage, gaslike phase of adsorbed halide induces an appreciable (~25%) enhancement of the interfacial concentration of the cationic surfactant ion. At more positive polarizations, the coadsorbed OTA(+)/Br(-) layer undergoes at least one phase transition which appears to be concomitant with the lifting of the Au(111) reconstruction and the formation of a densely packed bromide adlayer. In the absence of coadsorbed halide, the OTA(+) ions are completely desorbed from the Au(111) surface at the most positive electrode polarizations studied. However, with NaBr present in the electrolyte, a high surface excess of bromide species leads to the stabilization of adsorbed OTA(+) at such positive potentials (or equivalent charge densities).     

Adsorption behavior of hexadecyltrimethylammonium bromide (CTAB) to mica substrates as observed by atomic force microscopy

The study of the adsorption behavior of surfac-which makes people further study the adsorptiontants to interfaces is very important in colloid and in-mechanism at the molecular level.terface science[1]owing to the important applications In situ AFM measur…     

99mTc-labelled compounds prepared with tungsten(III) as the reducing agent

The application of K₃W₂Cl₉ as reducing agent in preparation of^99mTc-labelled compounds is described. Pertechnetate reduction was carried out in solutions of pH 2 and also of pH 5.5. DTPA, citrate, gluconate, HEDSPA and MDP were successfully labelled. Two types of labelled gluconate complexes were obtained. Complex I exhibited in rats an increased^99mTc affinity to kidneys (21%). Complex II exhibited an increased^99mTc affinity to bone (8.7%). Two types of labelled HEDSPA preparations were obtained: one yielded 29%^99mTc activity in bone, the other type exhibited only 13.4%. The results indicated the absence of mixed complexes.     

Sorbic acid as friendly curing agent for enhanced properties of ethylene propylene diene monomer rubber using gamma radiation

Sorbic acid (SA) is available in the market for low-cost and eco-friendly. It is known for using as a preservative. SA was used as a modifier together with gamma radiation to improve the properties of ethylene propylene diene monomer rubber (EPDM). The effect of SA concentration and gamma irradiation dose on the mechanical and physico-chemical properties of EPDM was investigated. The results indicated that the properties of EPDM rubber blended with SA were improved compared to untreated EPDM sample. The highest improvement was achieved by using SA concentrations of 10 phr (part per hundred part of rubber) a dose of 100 kGy of gamma irradiation. These findings were demonstrated by scanning electron microscopy (SEM), x-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA).     

Assessment of 4-(dimethylamino)pyridine as a capping agent for gold nanoparticles

Gold nanoparticles stabilized with 4-(dimethylamino)pyridine (DMAP) were prepared by ligand exchange and phase transfer (toluene/water) of functionalized gold nanoparticles. DMAP-protected gold nanoparticles are water-soluble, positively charged, and fairly monodisperse (6.2 +/- 0.9 nm). To understand the scope of this interesting system, the details of the binding of DMAP to gold nanoparticles were investigated. The adsorption of DMAP onto gold surfaces was studied by electrochemistry and surface plasmon resonance. It is concluded that of the three most likely binding modes, the one involving the pyridine nitrogen binding to the gold surface, as suggested previously (Gittins, D. I.; Caruso, F. Angew. Chem., Int. Ed. 2001, 40, 3001), is consistent with experimental data. Other 4-substituted pyridines were also assessed as capping agents. The solubility in toluene and basicity of the incoming ligand, as well as the ability to form charged nanoparticles, determine whether ligand exchange and subsequent phase transfer of the nanoparticles occur. The solubility and stability of the DMAP-protected gold nanoparticles were studied as a function of pH using UV-visible spectroscopy and transmission electron microscopy (TEM). These nanoparticles are soluble and stable over a wide pH range (5.0-12.8). It was found that excess DMAP is necessary for both the preparation and the stability of the DMAP-protected gold nanoparticles.     

Copolymerization of propylene oxide and CO2 using achiral salophen Co(III) penta-florobenzoate as catalyst and tetrabutyl ammonium bromide as co-catalyst

Copolymerization of racemic propylene oxide with carbon dioxide is investigated in the presence of economically inexpensive and effective achiral salophenCo(III)X [salophen = N,N'-bis(3,5-di-tert-butylsalicylidene)-phenylenediimine, X = pentaflorobenzoate] catalyst and tetrabutyl ammonium bromide as co-catalyst. Effects of different variables like monomer to catalyst ratio, catalyst/co-catalyst ratio, temperature, pressure of CO₂ on molecular weight, yield and selectivity of poly(propylene carbonate) [PPC] have been investigated. The maximum M_w of 25.8 g/mol has been obtained at 15 bar and 50°C. All the samples were found to have excellent polydispersity near to 1.     

Lamellar phases in mixtures of low molecular weight alkanols and cetyltrimethylammonium bromide (CTAB)

Partial phase diagrams showing the domains of existence of a transparent, viscous, lamellar-structured (D)-phase that transforms reversibly into fluid single phase solutions at high temperature are presented for the system: cetyltrimethylammonium bromide (CTAB), two low molecular weight alcohols, and water with and without additives. At constant temperature and with a fixed amount of surfactant, the size and location of this phase in the phase diagram depends upon three composition variables: i) the ratio of concentrations of medium chain alcohol to long chain alcohol (R), ii) the ratio of concentrations of medium chain alcohol to surfactant (R), and iii) the concentrations of small amounts (up to 10 % by weight) of additives such as ethylene glycol, propylene glycol, and dimethylformamide, as well as NaBr. Small-angle x-ray scattering measurements of these mixtures reveal a lamellar structure. The observed lamellar repeat distances range from 60 A to 290 Å and depend upon the ratiosR andR and the concentration of the additives. The mechanical and structural properties of theseD-phases can be tuned by adjustingR andR. TheD-phase-to-isotropic transition temperature can be varied from near room temperature to above 80 °C by adjustingR andR.