Study on superabsorbent composite XVI. Synthesis, characterization and swelling behaviors of poly(sodium acrylate)/vermiculite superabsorbent composites

A series of superabsorbent composites were synthesized by copolymerization reaction of partially neutralized acrylic acid on unexpanded vermiculite (UVMT) micropowder using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator in aqueous solution. And the samples were further characterized by means of fourier-transform spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The effects of vermiculite content on water absorbency were studied. Swelling behaviors of the superabsorbent composites in various cationic salt solutions (NaCl, CaCl₂ and FeCl₃), anionic salt solutions (NaCl, Na₂SO₄ and Na₃PO₄) and pH solutions were also systematically investigated. Results obtained showed that the equilibrium water absorbency increased with increasing UVMT content and the concentration of 20 wt.% clay gave the best absorption (1232 g/g in distilled water and 89 g/g in 0.9 wt.% NaCl). Data achieved also suggested that the water absorbency in various saline solutions decreased with an increase in the ionic strengths of these solutions. And it was found that at a higher ionic strength (>1 × 10⁻³ M), the water absorbency in monovalent cationic solutions was higher than those in multivalent cationic solutions. However, at the same ionic strength (>1 × 10⁻³ M), the effect of three anionic salt solutions on the swelling has the following order: NaCl < Na₂SO₄ < Na₃PO₄.     

Determination of the swelling behavior of superabsorbent polymers by a tracer-assisted on-line spectroscopic measurement

This work reports on a method for the accurate determination of kinetic swelling behavior and properties of superabsorbent polymers by a tracer-assisted on-line spectroscopic measurement. Based on monitoring the spectral absorption of a tracer compound (blue dextran 2000) at 610 nm in a superabsorbent polymer containing solution, the swelling (water absorption) of the polymer during the process can be followed, from which the parameters in a kinetic equation can be obtained. The results showed that the data obtained by the present method has a good measurement precision and accuracy, in which the relative differences were less than 4.0% when comparing the data measured by a reference method (i.e., the tea bag method). Since the present method can perform an on-line measurement, it is much superior to the current tea bag method and therefore is very suitable to be used in the process related study for the swelling behavior of superabsorbent polymers in many applications.     

Study on superabsorbent composite. III. Swelling behaviors of polyacrylamide/attapulgite composite based on acidified attapulgite and organo-attapulgite

A novel kind of salt-resistant superabsorbent composite, polyacrylamide/attapulgite, from acrylamide (AM) and attapulgite (APT) was prepared by free-radical aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The organification of APT with hexadecyltrimethyl ammonium bromide (HDTMABr) was proved by FTIR and XRD. The effects of acidified APT (H⁺-APT), organo-APT (HDTMABr-APT) and the content of APT in the superabsorbent composite on the water absorbency and the initial swelling rate for the superabsorbent composite in distilled water and in various saline solutions were studied. The effects of incorporated HDTMABr-APT and H⁺-APT on the reswelling ability of the superabsorbent composites were investigated. The results indicate that the incorporation of APT had remarkable influence on the improvement of water absorbency and swelling rate of the composites. Comparing with the composite doped with H⁺-APT, the water absorbency for the composite doped with 10 wt% HDTMABr-APT was enhanced from 2140 g g⁻¹ to 2800 g g⁻¹ in distilled water and from 100 g g⁻¹ to 121 g g⁻¹ in 0.9 wt% NaCl solution, respectively. The water absorbency of the composites in various saline solutions decreased with the increasing concentration, especially for the multivalent cations. In addition, the reswelling ability of the superabsorbent composites is also improved evidently by adding a small amount of HDTMABr-APT into the composite, comparing with that of incorporated with H⁺-APT.     

Study on superabsorbent composite. IV. Effects of organification degree of attapulgite on swelling behaviors of polyacrylamide/organo-attapulgite composites

A novel kind of superabsorbent composite, polyacrylamide/organo-attapulgite, from acrylamide (AM) and attapulgite (APT) was prepared by aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. APT was organified with five different degree of hexadecyltrimethyl ammonium bromide (HDTMABr), and the organification degree of APT was proved by FTIR, TGA and XRD. The effects of organification degree of APT on water absorbency and swelling rate of the superabsorbent composite in distilled water and in various saline solutions were investigated in this study. The effect of organification degree on reswelling ability of the superabsorbent composites was also investigated. The results indicate that the organification degree of APT had remarkable influence on swelling behaviors of the superabsorbent composites. The superabsorbent composite acquired its highest water absorbency when the organification degree of APT is 8.02 wt.%.     

镍电极开路电位测定微量硼氢根离子

实验采用循环伏安法，用镍电极代替铂铑等贵金属电极测定了碱性体系中不同硼氢根离子浓度下的开路电位，得出了研究电极的开路电位（-0．355～-0．280vs.SCE／V）与微量硼氢根离子浓度的对应关系，并用于监测电解偏硼酸钠制备硼氢化钠体系中微量硼氢根离子，同时计算了该方法的误差。结果表明，测量结果的相对标准偏差为2．2％；回收率为98．4％。该法简单、快速，可测定10^-5～10^-3mol／L范围的硼氢根离子浓度。     

脉冲磁场氯离子选择电极瞬时电位分析研究

研究了脉冲磁场下AgCl电极对Cl-的响应,提出脉冲磁场离子选择电极瞬时电位分析方法。该方法可以实现快速高精度的测量。在脉冲磁场作用下AgCl电极对Cl-试液响应的瞬时峰电位Vp不受平衡电位值的影响,有很好的再现性和准确性,多次测量所得的峰电位最大偏差小于5.0 mV,平均偏差小于2.23 mV,明显优于常规电位分析方法;氯离子浓度c(Cl-)在1×10-4~0.1 mol/L范围内Vp~lgc(Cl-)有很好的线性关系,且离子的瞬时活度大于常规分析方法的活度,用“离子氛”理论解释了电位的变化。用该法测量了氯碱电解液的Cl-的浓度,与化学分析方法比较得到一致的结果。     

Mechanism of interaction of molecular hydrogen with adsorbed oxygen on platinum electrodes under open circuit conditions

Transients of open-circuit potential observed at the reaction of hydrogen molecules with oxygen preliminarily adsorbed (O_ads) on the smooth polycrystalline (pc Pt) and platinized platinum (Pt/Pt) electrodes are measured under conditions of controlled stirring of solution (0.5 M H₂ SO₄). The dependence of the surface coverage with O_ads(θ_O) on the potential in the cause of the potential decay on pc Pt are determined. It is found that for Pt/Pt, the reaction kinetics is largely determined by diffusion of H₂. For pc Pt in the range of high θ_O, the Eley-Ridiel mechanism is realized. For medium θ_O, the regions where the reaction obeys the mechanisms of Eley-Ridiel, “conjugated reactions”, and diffusion control are observed to overlap (even at the most intense stirring possible). The rate of H₂ reaction with O_ads is substantially higher compared with analogous reactions of CO, HCOOH, and CH₃OH.     

Qualitative separation of the physical swelling effect on the recovery behavior of shape memory polymer

The physical swelling effect-induced shape recovery is studied in a thermo-responsive styrene-based shape memory polymer (SMP). Fourier transform-infrared (FTIR) test reveals no apparent change in the characteristic polar bonds of CO and O-H after immersing the SMP into toluene solvent. Based on the rubber elastic and relaxation theory, the decrease in internal energy is identified as the driving force for the shape recovery. Subsequently, the rubber elastic theory is further applied to investigate the swelling-induced free/constraint shape recovery in this SMP, and the free-energy function is utilized to analyze the swelling-induced homogenous/inhomogeneous deformation. This study provides a framework to study both the swelling effect-induced shape recovery and complex shape memory behavior in solvent-responsive SMPs.     

Effects of applied anodic potential and pH on the repassivation kinetics of pure aluminium in aqueous alkaline solution

The repassivation kinetics of pure aluminium have been explored in aqueous alkaline solutions as functions of applied anodic potential and pH by using an abrading electrode technique and a rotating disc electrode. The repassivation rate of the abraded bare surface of pure aluminium increased with increasing applied anodic potential in aqueous alkaline solutions, while it decreased with increasing pH. These results revealed that the growth rate of the passivating oxide film is enhanced by an applied electric field, but it is lowered due to the chemical attack by hydroxyl ions. A potentiostatic anodic current decay transient obtained from the abraded electrode surface showed a constant repassivation rate in neutral and weakly alkaline solutions. In contrast, in concentrated alkaline solutions it was observed to consist of three stages: a high repassivation rate in the initial stage due to a high formation rate of the oxide film on the abraded bare surface; a zero value of the repassivation rate in the second stage due to the dissolution of the oxide film by the attack of OH⁻; a high repassivation rate in the third stage due to a lowered dissolution rate of the oxide film. The dissolution rate of the passivating oxide film was observed to depend on the removal rate of aluminate ions from the oxide/solution interface. Received: 1 April 1998 / Accepted: 3 July 1998     

Usefulness of Hysteresis Curves for Studying Temperature Effects on Ises Responses

Abstract

A procedure for study of the effects of the temperature on the response of ion-selective electrodes in which isothermal hysteresis cum determined at several concentrations are used for obtaining the temperature variation parameters (isothermal slope and potential coefficients and isopotential points) is proposed. The procedure was tested against the classic procedure in which calibration curves are obtained at different temperatures. 'All -solid-state' Ag₂S and Ag₂S/Agl electrodes with sensors applied to silver- and copper-loaded epoxy supports (and commercial electrodes, for comparison) were used for this purpose. The values of the temperature parameters obtained by the two procedures (in the raw 10–60°C) are compared. This comparison show that the present procedure yields acceptable values of temperature parameters for cases like the studied where the hysteresis is not very produced.     

Study on the chemisorption kinetics of Methylene Blue using SERS technique

SERS technique was used to study the chemisorption kinetics of Methylene Blue (MB) on the HNO3-etched silver surface. The adsorption kinetic parameters were deduced from different vibrational modes at a low concentration of 3.5×10-6 mol/L, and it showed that MB adsorbed uniformly (monolayerly) on silver surface. However, the adsorptive behavior turned anomalous at relatively higher concentrations and a possible explanation was suggested. In addition, the influence of Cl- ions on the adsorption states of MB was investigated, and it was shown that MB molecules, adsorbed on the silver surface, tended to transform from the "lying-down" state to the "end- on"4 state after Cl- ions were added.     

运用离子选择性电极研究氟离子与蛋白质的相互作用

摘要 在醋酸-醋酸钠缓冲溶液中（pH = 5.68）, 运用氟离子选择性电极研究了288 K～308 K时F–与牛血清蛋白（BSA）、牛血红蛋白（BHb）和卵清蛋白(OVA)的相互作用。F–和三种蛋白质相互作用体系的实验数据通过Klotz方程进行处理,得到了很好的线性关系,根据拟合的直线得到了F–在三种蛋白分子上的束缚位点数以及相应的束缚常数。结果表明,F–在BSA和BHb分子上的束缚位点数随着温度的升高而增大,而在OVA分子上的束缚位点数随着温度的升高而减小。另外,F–与BSA和BHb作用的束缚常数随着温度的升高,先减小后增大;而与OVA的束缚常数则表现出相反的规律,即先增大后减小。根据蛋白质分子二级结构的差别,对上述现象进行了合理的解释。运用热力学方程计算出了不同温度下每个束缚过程的热力学函数（△G,△H,△S）,说明F–和蛋白质分子之间主要依靠静电作用力相结合。     

电位法测定谷胱甘肽转移酶活性的研究

谷胱甘肽转移酶(GSTs)是生物体内一种重要的解毒酶,催化异源物与谷胱甘肽结合,有多种方法测定其活性,但都基于大分子产物。本实验基于H.Habig方法,探讨用氯离子选择电极,根据反应体系中Cl-浓度的变化来测定谷胱甘肽转移酶的活性。研究结果表明,利用透析膜包裹电极可以消除底物谷胱甘肽(GSH)对电极的干扰,生物反应体系中可能存在的离子、小分子(如Br-I、-、H2O2和Vc)对电极没有影响。此方法重现性良好,相对标准偏差为3.54%。     

Effect of the solvent on the kinetics of thermal decomposition of acetylcyclohexylsulfonyl peroxide

The kinetics of the decomposition of acetylcyclohexylsulfonyl peroxide (ACSP) in CCl₄, benzene, toluene, ethylbenzene, cumene, acetonitrile, ethanol, and 2-propanol in an atmosphere of O₂ were studied at 40–70 °C. The rate constants (k ₀) and activation parameters of the monomolecular decomposition of ACSP were determined. A linear dependence between logA ₀ and activation energyE ₀ (compensation effect) was established. The dependence ofk ₀ on the nature of a solvent is described by the four-parameter Koppel-Palm equation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 935–937, May 1997.     

Electrode polarization effects on interfacial kinetics of ionic liquid at graphite surface: An extended lagrangian-based constant potential molecular dynamics simulation study

Computational models including electrode polarization can be essential to study electrode/electrolyte interfacial phenomena more realistically. We present here a constant-potential classical molecular dynamics simulation method based on the extended Lagrangian formulation where the fluctuating electrode atomic charges are treated as independent dynamical variables. The method is applied to a graphite/ionic liquid system for the validation and the interfacial kinetics study. While the correct adiabatic dynamics is achieved with a sufficiently small fictitious mass of charge, static properties have been shown to be almost insensitive to the fictitious mass. As for the kinetics study, electrical double layer (EDL) relaxation and ion desorption from the electrode surface are considered. We found that the polarization slows EDL relaxation greatly whereas it has little impact on the ion desorption kinetics. The findings suggest that the polarization is essential to estimate the kinetics in nonequilibrium processes, not in equilibrium. © 2019 Wiley Periodicals, Inc.     

Effect of ionic strength on the formal potential of the glass electrode in various saline media

We examined the variation with ionic strength (I, adjusted with KCl, KNO₃, KBr, NaCl or NaClO₄) of the formal potential (E_const) for glass electrodes exhibiting a Nernstian response (i.e. E_cell=E_const−s log [H⁺]). For this purpose, we investigated the different factors included in the formal potential, so we obtained reported values for the liquid junction potential as a function of ionic strength and determined the logarithm of the activity coefficient for the proton in various saline media, using Pitzer equations.     

Wittig-Horner反应的动力学研究

Ｗｉｔｔｉｇ Ｈｏｒｎｅｒ反应是Ｗｉｔｔｉｇ反应的一种改进 ,二者可以互相补充 ,但Ｗｉｔｔｉｇ Ｈｏｒｎｅｒ反应还具有某些独特的优点[1] 。Ｗｉｔｔｉｇ Ｈｏｒｎｅｒ反应用于合成的研究有较多的报道 ,但对于该反应的理论研究却不多见[2 ] 。因此 ,我们合成了α 萘甲基磷酸二丁酯 ,并进行了它同一系列取代苯甲醛反应的动力学研究。在磷酸酯及醇钠恒定过量的条件下 ,测定了几种取代苯甲醛反应的假一级速率常数值。但实际上反应属于三级 ,对磷酸酯、乙醇钠和苯甲醛各为一级。因为当改变各反应组份的浓度时 ,速率发生改变。一般Ｗｉｔｔ…     

Study on kinetics of the pyrolysis process of aluminum sulfate

Abstract

Using high aluminum gangue as a raw material, aluminum sulfate 18 hydrate was made by the sulfuric acid leaching method under certain conditions. The product was characterized using X-ray diffraction (XRD) analysis of the phases, x-ray-fluorescence (XRF) analysis of the aluminum and sulfur content and thermogravimetric analysis of the crystallized water [Al₂(SO₄)₃·18H₂O]. Change characteristics of the crystal form and morphology during pyrolysis of octadecahydrate aluminum sulfate were studied by thermogravimetric Analysis (TGA), differential scanning calorimetry (DSC), differential thermogravimetry (DTG), XRD and scanning electron microscope (SEM). The theoretical basis for the preparation of metallurgical alumina from octadecahydrate aluminum sulfate was provided. According to the characteristics of the crystal structure change, the pyrolysis process of octadecahydrate aluminum sulfate can be separated into three stages. The first stage (dehydration stage 87–250?°C) had a weight loss rate of 40.5% and a loss of 15 water molecules; the weight loss rate of the second stage (dehydration stage 280–414?°C) was 8.1% with three water molecules lost; the weight loss rate of the third stage (decomposition stage 770–900?°C) was 36.1%, where three SO₃ molecules were lost. The pyrolysis products were mainly Al₂O₃. The activation energies of the three reaction stages were calculated using the Coats-Redfern method as 90.02?kJ/mol, 205.74?kJ/mol and 284.40?kJ/mol, respectively.     

Enhancement of electron transfer kinetics on a polyaniline-modified electrode in the presence of anionic dopants

The electrocatalytic redox behavior of 1,4-naphthoquinone (NQ) has been studied on a polyaniline-modified platinum electrode (PANI) using cyclic voltammetry and rotating disc electrode (RDE) as diagnostic techniques. The modified electrode was prepared by electropolymerization of aniline in different acidic solutions. The PANI showed electrocatalytic activity toward the redox behavior of NQ. This process includes the participation of PANI to the redox reaction of NQ via the surface catalysis phenomena. The cyclic voltammograms of NQ in HCl on the PANI-Cl-modified electrode showed an overlapped oxidation peak, the peak potential of which did not change with increasing scan rate. The influence of other anions including and as dopant was also studied and compared with Cl⁻. The use of HClO₄ as a supporting electrolyte resulted in well-separated redox peaks. The RDE voltammogram was used to obtain a quantitative assessment of reaction rate at the PANI-modified electrode. It was found that PANI acts as an electrocatalyst for NQ reduction with decreasing ΔE _p and increasing k°.     

纳晶稀土复合氧化物Dy~1~-~xSr~xCoO~3~-~yⅡ: 固相烧结动力学研究

研究了纳晶氧化物Dy~1~-~xSr~xCoO~3~-~y(x=0.6)的等温烧结动力学,计算了烧结激活能, 结果表明: 在烧结初期, 致密化机制主要为蒸发-凝聚传质; 在烧结中期, 致密化机制转为晶界控制。烧结过程的激活能为5.255×10^4J·mol^-^1。较小的激活能体现了纳米粒子的尺寸效应。快速运动的晶界, 导致晶界与气孔的运动速度不匹配, 造成纳晶氧化物密度低, 最终形成纳米海绵态网络结构。