Determination of thermodynamic parameters for cloud point extraction of Arsenazo-III and Magdala Red dyes using mixed micelles: An essential requirement for high performance

A simple and low cost method for extraction and preconcentration of Arsenazo-III (ARS-III) and Magdala Red (MR) was developed by an efficient cloud point extraction (CPE) method using mixed micelles of Triton X–114 (TX–114) and cetyltrimethyl ammonium bromide (CTAB). Various parameters, such as pH/concentration of H₂SO₄, surfactant concentrations (TX-114 and CTAB), equilibrium temperature and time have been studied to maximise efficiency. Thermodynamic quantities like change in Gibbs free energy (ΔG⁰), change in enthalpy (ΔH⁰) and change in entropy (ΔS⁰) were calculated. The results show that the CPE of ARS-III and MR dye is feasible, spontaneous, and endothermic in the temperature range of (50–80) °C indicating good recoveries for the developed method. The effect of temperature, surfactant concentration and dye concentration on various thermodynamic quantities was investigated and it was found that ΔG⁰ values increased with temperature but decreased with surfactant and dye concentration. ΔH⁰ and ΔS⁰ values increased as surfactant concentration increased and decreased as dye concentration decreased. The recoveries were found to be the range from 90.02 – 101.03 % for ARS-III and 86.07–99.46 % for MR dyes which proves that the method is highly efficient.     

Linear and non linear rheology of a wormlike micellar system in presence of sodium tosylate

In this experimental work, we investigate the influence of an organic counterion, sodium tosylate, on the rheological properties of an aqueous solution of CTAB at the concentration of 0.05M. With this system we can clearly see shear thickening for small salt concentrations C _s and only shear thinning behavior at higher C _s characterized by a linear evolution of η=f(γ) in a log-log representation. In these evolutions it is only in a very small domain of concentrations of the salt (near C _s =0.035M) that we can observe a nearly constant plateau of the shear stress against shear rate. The values of σ₀ (characterizing the stress plateau), G ₀ (the plateau modulus) and τ_R (the relaxation time) obtained by dynamical rheological measurements, allow to compare experimental results obtained to predicted values of the theory of Cates corresponding to the occurrence of shear induced banding structures. Received: 22 July 1997 Accepted: 3 February 1998     

Temperature and flow-induced viscosity transitions for CTAB surfactant solutions

We report in this work new results concerning the temperature dependence of the non-Newtonian viscosity of semi-diluted aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr). Two structural transitions are responsible for the unusual flow curves obtained. The first transition induced by the shear flow corresponds to an induced liquid crystalline phase of the nematic type; the second corresponds to the disappearing of this phase with increase of the temperature.     

Intrinsic Crosslinking and Gel-Breaking Rheokinetics of CMHEC/CTAB Systems

The intrinsic rheokinetics of carboxymethyl hydroxyethyl cellulose and cetyltrimethyl ammonium bromide (CMHEC/CTAB) synergistic fracturing fluid in static crosslinking and gel-breaking processes were studied in this work. Microrheological properties including solid–liquid balance (SLB) and elasticity index (EI) during the static crosslinking and gel-breaking processes were obtained. The effects of temperature on the crosslinking process, concentration of gel-breaker (ammonium persulfate), and temperature on the gel-breaking process were investigated. The novel intrinsic crosslinking and gel-breaking rheokinetics equations were established, respectively. The results show that the crosslinking process can be divided into two stages, and the intrinsic crosslinking rheokinetics equation can well describe EI curves during the static crosslinking process at different temperatures. The EI curves during the gel-breaking process can be well described by the intrinsic gel-breaking rheokinetics equation. The parameters for these two rheokinetics equations are well-defined and reasonable.     

WS2纳米棒的合成及其摩擦学性能

以十六烷基三甲基溴化铵(CTAB)作为表面活性剂,利用水热合成法在180℃条件下成功制备出WS2纳米棒。用XRD、SEM、TEM和HRTEM对WS2纳米棒的结构进行表征和分析,并提出了可能的生长机理。将WS2作为润滑油添加剂加到基础油中,用CETR UMT-2摩擦磨损仪测试其摩擦学性能。结果表明:WS2纳米棒作为润滑油添加剂表现出良好的摩擦性能。     

Catalytic effect of CTAB on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70 × 10⁻³ mol dm⁻³ resulted in an increase in the pseudo-first-order rate constant (k_ψ) by a factor of ca. 3. Quantitative kinetic analysis of k_ψ − [CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants K_S (268 mol⁻¹ dm³ for Gly-Tyr) and K_N (64 mol⁻¹ dm³ for ninhydrin).     

季铵盐改性四钛酸钾晶须及其吸附性能

通过季铵盐改性四钛酸钾晶须,应用X射线衍射分析、红外光谱,紫外-可见漫反射光谱对改性前后的四钛酸钾晶须进行表征,并初步研究了不同季铵盐改性的四钛酸钾晶须对苯酚吸附性能的研究。实验结果表明,改性前后的四钛酸钾晶须在紫外光区均有较强的光吸收,而在可见光区其吸收则较弱。改性前后四钛酸钾晶须的结构没有改变,季铵盐能够进入层状化合物的层板间,使改性后的层间距稍微增大。与改性前相比,改性后的四钛酸钾晶须对苯酚的吸附量和吸附率有了明显的提高。     

Improved simultaneous adsorption of Cu(II) and Cr(VI) of organic modified metakaolin-based geopolymer

In this paper, a metakaolin-based mesoporous geopolymer (GP-CTAB) was used as adsorbent for Cu(II) and Cr(VI) through a novel and simple synthetic route using cetyltrimethylammonium bromide (CTAB) as an organic modifier. The application of GP-CTAB for the simultaneous removal of metal anions and cations in aqueous solution was studied for the first time. The results of X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Brunauer, Emmett and Teller (BET), and Barrett, Joyner, and Halenda (BJH) methods indicate that GP-CTAB is still geopolymer even in the presence of quaternary ammonium salt cations. The material was tested to simultaneously adsorb Cu(II) and Cr(VI) from an aqueous solution. The results show that GP-CTAB can adsorb anions simultaneously without sacrificing the adsorption properties of heavy metal cations, which is superior to conventional geopolymers. The maximum theoretical adsorption capacity of GP-CTAB for Cu(II) and Cr(VI) was 108.2 mg/g and 95.3 mg/g in the binary system, respectively. It was also found that the presence of Cu(II) in the solution promoted the adsorption of Cr(VI). Given this characteristic of GP-CTAB, it has shown great application prospects in the prevention and control of heavy metal pollution.     

组合改性Y型分子筛的加氢裂化性能

采用水热、草酸脱铝及表面活性剂存在下的水热晶化相结合的组合法对Y型分子筛进行了改性, 考察了表面活性剂十六烷基三甲基溴化铵（CTAB）存在下的CTAB加入量对Y型分子筛相对结晶度（Xc）、晶胞常数（a₀）、硅铝比、比表面积、孔结构及加氢裂化性能的影响, 并利用NH₃-TPD对改性Y型分子筛进行了酸性表征。结果表明, 少量的CTAB就可以使Y型分子筛的相对结晶度从37.9%提高到68.3%, 硅铝比从7.72增大到9.32, a0从2.4534nm减小到2.4485nm, 介孔的孔体积从0.157mL/g提高到0.180mL/g以上,且总酸酸量降低。VGO的加氢裂化反应结果表明,CTAB存在下改性Y型分子筛的加氢裂化活性和中间馏分油收率比工业催化剂分别高2.42%和4.20%。     

Thermal degradation of CTAB in as-synthesized MCM-41

Thermal evacuation of a surfactant template from pure siliceous MCM-41 and MCM-41 containing aluminium in hydrogen flow was investigated. Micelle templated MCM-41 were prepared using hexadecyltrimethylammonium bromide (CTAB). The products of thermal surfactant degradation outside and inside pores were identified at various temperatures using ¹³C solid-state nuclear magnetic resonance (NMR) spectroscopy, gas chromatography coupled with mass spectrometer (GC-MS) and temperature programmed desorption coupled with mass spectrometer (TPD-MS). The GC-MS and ¹³C MAS NMR results obtained from this study provide an insight into the mechanism of surfactant transformation during MCM-41 synthesis on molecular level.