ESR studies on the interaction of calixarenes and free radicals

Electron spin resonance (ESR) measurements reveal that p-t-butylcalix[4]arene interacted with the radical generated by self-trapping of 2-methyl-2-nitrosopropane (MNP) as judged from the change in hyperfine coupling constants. The interaction can be ascribed to the inclusion of the radical in the calixarene, and the inclusion form is proposed. The further research indicates that the inclusion played a marked role in stabilizing short lifetime radicals, and obviously improved the efficiency of a spin trap, such as nitrosodurene (ND), in trapping the radicals.     

Investigation of electropolishing characteristics of tungsten in ecofriendly sodium hydroxide aqueous solution

In this study, an eco-friendly electrolyte for electropolishing tungsten and the minimum material removal depth on the electropolished tungsten surface are investigated using an electrochemical etching method. Using a concentrated acid electrolyte, the polarization curve and current density transient are observed. For a NaOH electrolyte, the effects of interelectrode gap and electrolyte concentration on electropolishing are investigated. The differences in electropolishing characteristics are compared among different electrolyte types. Microholes are etched on the electropolished tungsten surface to determine the minimum material removal depth on the tungsten surface. Experimental results indicate the color effect due to a change in the thickness of the oxide film on the tungsten surface after electropolishing with a concentrated acid electrolyte. The surface roughness decreases with the interelectrode gap width owing to the increased current density when using the NaOH electrolyte. However, the electropolishing effect is less prominent with a significantly smaller gap because the generated bubbles are unable to escape from the narrow working gap in time. A material removal depth of less than 10 nm is achieved on the tungsten surface in an area of diameter 300 lm, using the electrochemical etching method.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00309-y     

Isotherm and kinetic sorption of some lanthanides and iron from aqueous solution by aluminum silicotitante exchanger

Sorption of La³⁺, Eu³⁺, and Fe³⁺ onto new synthetic inorganic ion exchange material of aluminum silicotitante was investigated. The aluminum silicotitante (EX₁, EX₂, and EX₃) are synthetic with different concentration ratio (0.1:0.1:0.003, 0.1:0.1:0.1, and 0.1:0.1:0.1) at aging time 4, 4, and 1 day, respectively. The equilibrium kinetic for La³⁺, Eu³⁺, and Fe³⁺ onto EX₁, EX₂, and EX₃ materials takes about 120?min which is considered as a fast kinetic process. Sorption results were fitted using different kinetic models such as pseudo-first-order, pseudo-second order, and intraparticle diffusion models. The results indicated that the sorption of La³⁺, Eu³⁺, and Fe³⁺ onto EX₁, EX₂, and EX₃ materials is highly fit with the pseudo-second order model. Equilibrium data were described by the Langmuir, Freundlich isotherm models. The Langmuir isotherm model was fitted to the experimental data better than the Freundlich isotherm. The thermodynamics parameters (positive values of ΔH°, ΔS° and negative values of ΔG°) indicated the binding systems between the materials and adsorbate were endothermic, entropy gained and spontaneous in nature. The experimental data indicated that, aluminum silicotitante could be used as an efficient sorbent for La³⁺, Eu³⁺, and Fe³⁺. Maximum sorption % at equilibrium is 92.7, 99.0, and 78.5% for La³⁺, Eu³⁺, and Fe³⁺, respectively.     

Structural and ionization effects on the adsorption behaviors of some anilinic compounds from aqueous solution onto high-area carbon-cloth

The adsorption of anilinic compounds; aniline, p-toluidine, 1-napthylamine and sodium salt of diphenylamine-4-sulfonic acid from solutions in H₂O, in 1 M H₂SO₄ or in 0.1 M NaOH onto activated carbon-cloth was studied by in situ UV spectroscopy. A specially designed adsorption cell was used for this purpose. The adsorption processes were found to follow first-order kinetics and the rate constants were determined. The pH at the point of zero charge of the carbon-cloth surface was measured as 7.4. The highest rates and extents of adsorption were observed from H₂O solutions for aniline, p-toluidine and 1-napthylamine and from solution in 1 M H₂SO₄ for the sodium salt of diphenylamine-4-sulfonic acid. The adsorption behaviors of these four anilinic compounds in the three solutions (in H₂O, in 0.1 M NaOH and in 1 M H₂SO₄) were explained in terms of electrostatic and dispersion interactions between carbon-cloth surface and the anilinic species. The adsorption isotherm data for the anilinic compounds were derived at 30 °C and treated according to Langmuir and Freundlich models. The Freundlich model was found to represent the experimental isotherm data better than Langmuir model.     

Investigation of irradiated graphene oxide/ultra-high-molecular-weight polyethylene nanocomposites by ESR and FTIR spectroscopy

Graphene oxide/ultra-high-molecular-weight polyethylene (GO/UHMWPE) nanocomposite has a potential application for artificial joints. However, free radicals and antioxidative properties of irradiated GO/UHMWPE were not clearly clarified. In this paper, GO/UHMWPE nanocomposites were prepared and irradiated by gamma-irradiation with a dose of 100 kGy. Afterward, test samples were aged in air. Free radicals and molecular structures of test samples were investigated by electron spin resonance (ESR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy, respectively. These studies indicated that irradiation enhanced GO radical concentrations. And GO radicals were stable in air and even could not be quenched after accelerated aging. GO radicals were superimposed on free radicals of irradiated UHMWPE. Although GO showed free radical-scavenging capacity, the influence of GO on free radicals of irradiated UHMWPE was too weak to be observed in ESR spectroscopy. Free radicals concentrations of irradiated GO/UHMWPE nanocomposites were gradually decayed with aging time evolving in air. Observing the oxidation index values of test samples, it was proposed that irradiated GO/UHMWPE might show very weak antioxidative properties.     

Some observations on the liquid crystalline and gel behaviors of aqueous dispersions of a prodrug

BMS-830216 is a diprotic acid prodrug of two pK_a values (<2 and 6.8) with high apparent solubility at pH ≥ 7. At?～?pH 4 solutions of BMS-830216 appear to be surface active, in which their surface tension can be reduced from 72 to 65 dynes when its concentrations is above the critical aggregation concentration (CAC～0.2?mM). Additionally, at this pH, BMS-830216 tends to form liquid crystalline phases (at ≥ 2?mg/mL) in acetate buffer when using tris salt. Furthermore, after raising the concentration beyond 20?mg/g, formation of gel-like dispersions was noted. These gel-like dispersions exhibited a strong elastic strength, significantly impacting the dissolution behavior of the tris salt. Mechanistically, it is likely that BMS-830216 tris salt in solution first forms a lamellar phase followed by formation of a gel phase at higher concentrations (≥20?mg/mL). As indicated by SAXS, the lamellar phase formed seems to have two d-spacing values (～5?nm and ～10?nm (weak), which seems to correspond to two molecules connected tail by tail (5?nm). Further investigation is needed for phase identification, as their properties can affect the physical behavior of BMS-830216 in the development of pharmaceutical dosage forms.     

Rate studies on the adsorption of some dyestuffs and p-nitrophenol by chitosan and monocarboxymethylated(mcm)-chitosan from aqueous solution

In this study, the effect of temperature on the adsorption of some dyestuffs [orange II (O-II), crystal violet (CV) and reactive blue 5 (RB5)] and p-nitrophenol (PNP) by chitosan and of O-II and CV by modified chitosan [monocarboxymethylated(mcm)-chitosan] from aqueous solution was investigated. Kinetical data related to the adsorptions of each dyestuff and PNP by chitosan and of O-II and CV by mcm-chitosan were applied to Lagergren and Weber-Morris equations, and adsorption rate constants (kads) and pore diffusion rate constants (kp) were determined, respectively. In addition, Langmuir isotherm constants with experimental data related to the adsorptions of O-II and CV by chitosan and of CV by mcm-chitosan were applied to McKay et al. equation, and external mass transfer coefficients (kf) were also determined. Lastly, chitosan and mcm-chitosan were compared according to their dyestuffs and PNP uptake capabilities. It was seen that mcm-chitosan removed more O-II (99.2%) and RB5 (34.9%) but less CV (3.1%) and PNP (0.9%).     

液相法控制合成文石和方解石

用简便的水热法制备出菱形、针状和树状的碳酸钙晶体,不需任何添加剂,也不需要对pH值进行控制.用XRD、SEM、FT-IR和TGA-DTA技术对产物的形貌、结构特征和热力学稳定性进行了表征.对实验条件的系统研究发现,通过控制反应物的浓度,即可简便地获得多种晶型和形貌的碳酸钙.     

掺铒铋基玻璃的荧光俘获和浓度猝灭效应研究

用高温熔融法制备了系列掺铒铋硼锗酸盐玻璃,测试分析了不同铒离子掺杂浓度下玻璃样品的吸收光谱和荧光光谱.结果显示,掺铒铋硼锗酸盐玻璃中存在着强烈的荧光俘获和浓度猝灭效应.随着铒离子掺杂浓度的增加,1.53 μm波段荧光谱展宽,1 560 nm波长处荧光次峰相对增强.对此用一个等效的四能级模型予以了定性分析.同时,随着铒离子掺杂浓度的增加,4I13/2能级荧光寿命和1.53 μm波段荧光强度呈现出先增加后减小趋势.依据Dexter能量转移理论,计算了该玻璃系统中铒离子发生浓度猝灭的临界距离R0及相互作用参数CEr-Er,并与其它玻璃基质进行了比较.     

Fabrication and characterization of molecular hybrid materials with lanthanides covalently bonded in silica via sol-gel process

Tetraethoxysilane (abbreviated as TEOS) and a kind of monomer (abbreviated as PMA-APES) derived from modifying phenylmalonic acid with double carboxylate groups (abbreviated as PMA) with (3-aminopropyl)triethoxysilane (abbreviated as APES) were used as the inorganic and organic compounds respectively. Coordination reaction between lanthanides and the two -CO groups of the monomer happened simultaneously. The resulting material exhibits strong red-colored fluorescence (Eu³⁺) and green-colored fluorescence (Tb³⁺), suggesting the intramolecular energy transfer caused by coordination effect of the organic counterpart. IR, NMR, UV/vis absorption, low-temperature phosphorescence and fluorescence spectroscopy were applied for characterization of the material and the above spectroscopic data revealed that the triplet state energy of organic ligand matches with the emissive energy level of europium and terbium ions and effective intramolecular energy transfer process in these molecular hybrid systems.     

Stability study of flutamide in solid state and in aqueous solution

A high-performance liquid chromatography (HPLC) assay has been developed for the determination of flutamide and its degradation products. Using this method, the influence of important formulation factors on the stability of flutamide has been estimated. The stability studies have been carried out in solid state as well as in aqueous solution. The results obtained have shown a good stability for flutamide in solid state. This drug remained practically unchanged after a four-month assay in adverse temperature and humidity conditions. On the other hand, the results obtained from the stability study in solution during 12 days have shown that flutamide in aqueous solution underwent a clear degradation at mean or high temperature (22°C, 37°C) and acidic pH conditions (1.1). With respect to the influence of ionic strength, it has been found that the presence of sodium chloride prevents the degradation of flutamide in aqueous solution. The second-order kinetics model provides the best fit for highly degraded solutions.     

Investigation of the effect of different electrodes and their connections on the removal efficiency of 4-nitrophenol from aqueous solution by electrocoagulation

This study investigates the influence of variables on the removal efficiency of solution containing 4-NP (4-nitrophenol) by D. C. electrocoagulation (EC). The efficiency of different electrode connections and materials (steel 310, Fe, Al, graphite and steel 304) for 4-NP removal is compared. Current density, time of electrolysis, interelectrode distance, supporting electrolyte concentration and stirring rate of the solution were the variables that mostly influenced the 4-NP removal. Initially, a simple electrochemical cell was prepared with an anode and a cathode. Then the effect of each variable was studied separately using aqueous 4-NP in a batch mode. For a solution of 20 mg/L 4-NP+300 mg/L NaCl with chemical oxygen demand (COD) of approximately 40 mg O2/L, almost up to 99% 4-NP and 65% COD were removed, when the pH was about 9, time of electrolysis was approximately 10 min, current density was 100 A m(-2), interelctrode distance was 15 mm and stirring rate was 400 rpm. In the second series of experiments, the efficiency of EC cells with monopolar electrodes in series and parallel connections and an EC cell with bipolar electrodes was compared with that of a simple electrochemical cell. The best results obtained when steel 310 and Fe are used as anodes and employing Al and graphite as anodes would not be satisfactory. Also findings show that the types of sacrificial electrodes are not very significant in the removal of 4-NP. In the real wastewater obtained from Tabriz petrochemical plant 52% removal could be achieved after 10 min with using steel 310 as anode and steel 304 as cathode.     

基于双特征参数解的直杆弹性动力后屈曲研究

利用差分方法求解动力后屈曲非线性方程解，研究了弹性直杆的2类轴向碰撞屈曲问题．将双特征参数解得出的含有小幅值参数的初始动力屈曲模态作为非线性后屈曲解的初始条件．理论计算的结果与文献中的实验数据达到了很好的一致，由此验证了双特征参数方法的正确性．研究结果还揭示了碰撞过程中屈曲变形扩展和发展的机理，以及轴向应力波和屈曲变形的相互作用规律．     

纳米二氧化钛粉体水基体系分散稳定性评价研究

以乙二醇为分散剂，设计了正交实验考察纳米二氧化钛粉体在水中的分散性能，采用重力沉降法、分光光度法、粘度法、Zeta电位测定法、粒径分析等方法评价其分散效果。比较不同的表征手段的优劣及其适用的条件，寻求一种科学、准确、简易的表征二氧化钛粉体分散稳定性的方法。实验结果表明，分光光度法操作简便，对实验仪器要求不高，能快速表征体系的分散稳定性：结合Zeta电位测定和粒径分析，可以得到纳米二氧化钛分散稳定性的可靠信息。最后提出了纳米粉体分散研究的一般方法。     

Adsorption characteristics of haloacetonitriles on functionalized silica-based porous materials in aqueous solution

The effect of the surface functional group on the removal and mechanism of dichloroacetonitrile (DCAN) adsorption over silica-based porous materials was evaluated in comparison with powdered activated carbon (PAC). Hexagonal mesoporous silicate (HMS) was synthesized and functionalized by three different types of organosilanes (3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane and n-octyldimethysilane). Adsorption kinetics and isotherm models were used to determine the adsorption mechanism. The selective adsorption of five haloacetonitriles (HANs) in the single and mixed solute systems was also studied. The experiments revealed that the surface functional groups of the adsorbents largely affected the DCAN adsorption capacities. 3-Mercaptopropyl-grafted HMS had a high DCAN adsorption capacity compared to PAC. The adsorption mechanism is believed to occur via an ion-dipole electrostatic interaction in which water interference is inevitable at low concentrations of DCAN. In addition, the adsorption of DCAN strongly depended on the pH of the solution as this related to the charge density of the adsorbents. The selective adsorption of the five HANs over PAC was not observed, while the molecular structure of different HANs obviously influenced the adsorption capacity and selectivity over 3-mercaptopropyl-grafted HMS.     

溴化锂溶液中添加活性炭颗粒对制冷机出力的影响

为改善吸收式制冷机的性能,基于活性炭的高吸附性,研究在溴化锂水溶液添加适量活性炭颗粒形成的悬浮液的传热传质性能,分析活性炭/溴化锂悬浮液替代溴化锂水溶液作为吸收剂的可行性。研究表明,悬浮液的粘度随活性炭浓度线性增长,以悬浮液作为吸收剂的制冷机的出力随透湿系数、悬浮液吸附平衡常数及换热表面积呈近似线性增长关系,并且,以活性炭/溴化锂悬浮液作吸收剂的制冷机出力较以纯溴化锂溶液作吸收剂的制冷机出力大。     

纳米碳纤维表面修饰及其在水溶液中的分散

为了研究纳米碳纤维(CNFs)在水溶液中的分散情况,对其进行高温纯化处理,以甲基纤维素(MC)为分散剂,制备分散良好的CNFs悬浮液.采用差热分析(DTA)和热重分析(TGA)研究了高温处理对CNFs的影响,通过测定悬浮液的紫外可见光吸光度、等温吸附曲线、zeta电位及表面张力等方法研究了MC对CNFs分散性能的影响,并讨论分析了MC对CNFs的分散机理.结果表明:MC的加入使CNFs悬浮液的zeta电位由-15.4 mV升至0,表面张力由38.87 mN/m降至36.54 mN/m;等温吸附曲线表明MC在CNFs的表面为"单阶段吸附",当MC的质量浓度达到0.4 g/L时,MC在CNFs表面饱和吸附;当CNFs达到最佳分散状态时,MC与CNFs的质量比为2∶1.     

Breakage and coalescence of drops in turbulent stirred dispersions

The various existing models for predicting the maximum stable drop diameterd _max in turbulent stirred dispersions have been reviewed. Variations in the basic framework dictated by additional complexities such as the presence of drag reducing agents in the continuous phase, or viscoelasticity of the dispersed phase have been outlined. Drop breakage in the presence of surfactants in the continuous phase has also been analysed. Finally, the various approaches to obtaining expressions for the breakage and coalescence frequencies, needed to solve the population balance equation for the number density function of the dispersed phase droplets, have been discussed.     

Solubility of core materials in aqueous polymeric solution effect on microencapsulation of curcumin

Curcumin, the main active constituent of turmeric herb (Curcuma longa L.) have been reported to possess many medicinal values. The application of curcumin in dermatological preparations is limited by their intense yellow color property, which stains the fabric and skin. The objectives of this study were to reduce the color staining effect and enhance the stability of curcumin via microencapsulation using gelatin simple coacervation method. As for curcumin, ethanol and acetone were used as coacervating solvents. Curcumin was dispersed in ethanol while dissolved in acetone. Irrespective of the types of coacervating solvents used, microencapsulation resolved the color-staining problem and enhanced the flow properties and photo-stability of curcumin. Nevertheless, it was found that more spherical curcumin microcapsules with higher yield, higher curcumin loading, and higher entrapment efficiency were obtained with acetone than ethanol. The in vitro release of curcumin after microencapsulation was slightly prolonged. Further evaluation of the effects of solubility of core materials in coacervating solvent or polymeric aqueous solution using six different drug compounds, namely, ketoconazole, ketoprofen, magnesium stearate, pseudoephedrine HCl, diclofenac sodium, and paracetamol, suggested that the solubility of core materials in aqueous polymeric solution determined the successful formation of microcapsules. Microcapsules could only be formed if the core materials were not dissolved in the aqueous polymeric solution while the core materials could either be dissolved or dispersed in the coacervating solvent. In summary, microencapsulation not only circumvents the color-staining problem but also improved the stability and flowability of curcumin. The solubility of core material in aqueous polymeric solution plays a pivotal role in determining the successful formation of microcapsules.     

Investigation of reliability measurements with ramped and constant voltage stress on mos gate oxides

MOS gate oxide capacitors over a wide range of oxide thicknesses (10·9–28nm) were stressed using constant voltage, ramped voltage stress and combined ramped/constant voltage stress measurements. The reliability measurements were performed with different bias conditions in order to assess the effect of the measurement conditions on the gate oxide lifetimes. A unipolar pulsed ramp was applied during the ramped voltage stress. It will be verified that this ramp yields identical breakdown distributions to the commonly used staircase ramp. Times to breakdown from ramped and constant voltage stress were directly compared. It was found that for thick oxides the times to breakdown of the ramped stress were greater than those of the constant stress. The measurement results of the combined ramped/constant voltage stress indicate that it is a valuable tool for monitoring extrinsic and intrinsic breakdown properties. The observations made in this work imply that the time to breakdown at a constant voltage is strongly dependent on the peak current injected into the oxide and, therefore, on a pre-stress before the constant stress voltage.