Stripping voltammetric determination of Pb(II) and Cd(II) based on the multiwalled carbon nanotubes-Nafion-bismuth modified glassy carbon electrodes

In this work, a new method for the simultaneous determination of Pb(II) and Cd(II) on the multiwalled carbon nanotubes (MWNT)-Nafion-bismuth modified glassy carbon electrode (GCE) using square-wave anodic stripping voltammetry has been studied. Scanning electron microscopy was used to investigate the characteristics of the MWNT-Nafion-bismuth modified GCE.

Combining chemical reduction with an electrochemical technique for the simultaneous detection of Cr(VI), Pb(II) and Cd(II)

This work herein reports the approach for the simultaneous determination of heavy metal ions including cadmium (Cd(II)), lead (Pb(II)), and chromium (Cr(VI)) using a bismuth film electrode (BFE) by anodic stripping voltammertry (ASV). The BFE used was plated in situ. Due to the reduction of Cr(VI) with H2O2 in the acid medium, on one hand, the Cr(III) was produced and Cr(VI) was indirectly detected by monitoring the content of Cr(III) using square-wave ASV. On the other hand, Pb(II) was also released from the complex between Pb(II) and Cr(VI). Furthermore, the coexistence of the Cd(II) was also simultaneously detected with Pb(II) and Cr(VI) in this system as a result of the formation of an alloy with Bi. The detection limits of this method were 1.39 ppb for Cd(II), 2.47 ppb for Pb(II) and 5.27 ppb for Cr(VI) with a preconcentration time of 120 s under optimal conditions (S/N = 3), respectively. Furthermore, the sensitivity of this method can be improved by controlling the deposition time or by using a cation-exchange polymer (such as Nafion) modified electrode.

溶液中某些铅（II）、镉（II）混配配合物稳定性的研究

本文用pH电位滴定法测定了以Pb（II）、Cd（II）为中心离子，以氮杂芳香碱2,2'-联吡啶、邻二氮菲为第一配体，以“氧-氧”型和“氧-氮”型配位的丁二酸，邻苯二甲酸，4-硝荃苯二甲酸和甘氮酸、苯荃丙氨酸为第二配体，在温度为25 ℃，离子强度为0.1(KNO_3)条件下16个混配配合物体系的稳定常数及所有配体的酸解离常数和单配体配合物稳定常数。为了进一步探索混配配合物额外稳定性的根源，我们又测定了其中8个混配配合物在温度为15 ℃、35 ℃、45 ℃时的稳定常数，同时测定了各有关配体和单配体配合物在该温度范围内的酸解离常数和稳定常数。应用温度系数法求出了上述8个混配配合物各形成反应的热力学函数值。从各个方面讨论了这些混配配合物额外稳定性的原因，并提出了我们认为混配配合物额外稳定性的原因，并提出了我们认为混配配合物额外稳定性的合理表征。对一些混配配合物分子内可能存在配体间疏水缔合作用，通过~1H NMR的研究得到证实。

Sorption and desorption of lead (II) from wastewater by green algae Cladophora fascicularis

Biosorption is an effective method to remove heavy metals from wastewater. In this work, adsorption features of Cladophora fascicularis were investigated as a function of time, initial pH, initial Pb(II) concentrations, temperature and co-existing ions. Kinetics and equilibria were obtained from batch experiments. The biosorption kinetics followed the pseudo-second order model. Adsorption equilibria were well described by the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 198.5 mg/g at 298 K and pH 5.0. The adsorption processes were endothermic and the biosorption heat was 29.6 kJ/mol. Desorption experiments indicated that 0.01 mol/L Na(2)EDTA was an efficient desorbent for the recovery of Pb(II) from biomass. IR spectrum analysis suggested amido or hydroxy, C=O and C-O could combine intensively with Pb(II). (C) 2006 Elsevier B.V. All rights reserved.

冠醚修饰电极及其在分析化学中的应用

本论文较系统地研究了Naf:on聚合物薄膜冠醚修饰电极阳极溶出伏安法在分析中的应用。首次将Naf:on薄膜冠醚类化合物修饰电极应用于铊、银和铅三种离子的测定，得到了高灵敏度的分析方法亦用于实际样品测定。用涂层法制备了Naf:on聚合物薄膜冠醚（二环已基18－冠－6）化学修饰电极，用这种修饰电极测定金属离子的高灵敏度来源于将Naf:on对大阳离子的强离子交换能力、冠醚类化合物络合金属阳离子形成大阳离子的能力与溶出伏安法的高灵敏度三者的结合，冠醚化合物中性分子可与金属阳离子络合形成大络阳离子：M~(n+)＋qC=(MC_q)~(n+) Naf:on膜由于其具有的对大阳离子的强交换能力而将冠醚与和金属离子形成的大阳离子络合并吸附于电极表面，在溶出伏安法的富集过程中，电位置于是以令（MCq）~(n+)还原的位置以使（MCq）~(n+)还原：（MCq）~(n+)＋ne=M＋qC 析出的零价态的金属可在Naf:on膜内固定，同时又放出冠醚分子成为新的未被占据的络合吸附中心，继续捕获溶液中的阳离子从而起到富集作用。由于使用溶出伏安法排除电极表面络合吸附饱和的问题，从而使本方法灵敏度大大高于一般的使用化学修饰电极进行预富集的分析测定方法。提出了Naf:on薄膜冠醚修饰电极阳极溶出伏安法测定水溶液中Te(I)的方法，在电位为－1.30 Vvs.Ag/Ag ce处0.1高氯酸锂溶液中，用该修饰电极富集30分钟，检测下限可低至2×10~(-12)M（0.4 ppt）。溶液中Te(I)浓度在5×10(-12)M～1×10(-8)M范围内与溶出峰电流成良好的线性关系且通过原点，可以用标准加入法测定。常见共存元素Zn（II），Su（II），Cu（II），Fe（II），Co（II），Ni（II），In（III）等无干扰。Pb（II）与Cd（II）共存时对Te（I）有干扰，同1×10~(-3)M EDTA掩蔽可有消除干扰。测定了合成样品中的Te（I）含量，平行测定七组样品相对标准偏差4.2％。本文法是目前Te（I）的分析中最灵敏的电化学方法之一。提出了Naf:on薄膜冠醚修饰电极阳极溶出伏安法测定水溶液中Ag（I）的方法。在0.01MHNO_3 4～7×10~(-3)M Cl混合溶液中，检测电位在－0.30Vvs.SCE富集30分钟，检出下限可低至2×10~(-12)M，是迄今所见Ag（I）的分析中灵敏度最高的电分析方法。Ag（I）浓度在2×10~(-11)M～1×10~(-8)M范围内与溶出峰电流成良好的线性关系且通过原点。五到十倍量的Hg（II）和Au（II）有干扰。用本法测定了分析纯硝酸铵中的银含量为0.000048％，平行测定七组样品相对标准偏差为3.7％。提出用Naf:on薄膜冠醚修饰电极阳极溶出伏安法测定水样中铅的方法。在0.lMLiNO_3底液中，电位在－1.10Vvs.SCE富庥3分钟检测限达5×10~(-10)M，方法快速灵敏。Pb（II）浓度在1×10~(-9)～1×10~(-7)M范围内与溶出峰电流呈线性关系。1×10~(-6)以上Cu（II）存在使Pb（II）的峰电流时显增加。用本方法测定了自来水样中的铅含量，平行测定七组样品相对标准偏差8.0％。该修饰电极在K~+浓度为1×10~(-5)～1×10~(-7)M范围内对K~+有能斯特响应。本工作为铊、铅、银的痕量分析提供了高灵敏度的方法，为溶出伏安法摆脱汞污染的问题做出了贡献，为化学修饰电极用于分析化学领域提供了新的途径。

Flow-through room temperature phosphorescence optosensing for the determination of lead in sea water

The chelates formed between the heavy metal ion Pb(II) and the reagents 8-hydroxy-5-quinolinesulphonic acid, 8-hydroxy-7-quinolinesulphonic acid and 8-hydroxy-7-iodo-5-quinolinesulphonic acid exhibit strong room temperature phosphorescence (RTP) if retained on the surface of anion exchange resin beads. Based on the on-line formation, in a flow-injection system, of such RTP lead chelates and their transient immobilization on an anion exchange resin, three flow-through optosensing systems are investigated for lead in sea water. Optimum experimental conditions and the analytical performance characteristics of the three optosensors are discussed. Relative standard deviations (RSDs) of the order of 3% are typical at 100 ng ml−1 Pb(II) and the active sensing phases can easily be regenerated by passing 500 μl of 6 M hydrochloric acid. A lead(II) detection limit of 0.1 ng ml−1 (3×background SD, for 2 ml sample injection volumes) was achieved for the optosensor based on 8-hydroxy-7-quinolinesulphonic acid. Possible interferences present in sea water, including cations and anions which could affect the sensor response, are discussed in detail. Finally, the selected RTP flow-through optical sensor has been successfully tested for the determination of lead in sea water at a few ng ml−1.

Narion/Poly(sodium 4-styrenesulfonate) mixed coating modified bismuth film electrode for the determination of trace metals by anodic stripping voltammetry

To improve the reproducibility, stability, and sensitivity of bismuth film electrode (BiFE), we studied the performances of a mixed coating of two cation-exchange polymers, Nafion (NA) and poly(sodium 4-styrenesulfonate) (PSS), modified glassy carbon BiFE (GC/NA-PSS/BiFE). The characteristics of GC/NA-PSS/BiFE were investigated by scanning electron microscopy and cyclic voltammetry. Various parameters were studied in terms of their effect on the anodic stripping voltarnmetry (ASV) signals. Under optimized conditions, the limits of detection were 71 ng L-1 for Cd(II) and 93 ng L-1 for Pb(II) with a 10 min preconcentration. The results exhibited that GC/NA-PSS/BiFE can be a reproducible and robust toot for monitor of trace metals by ASV rapidly and environmentally friendly, even in the presence of surface-active compounds.

Relativistic Continuum Random Phase Approximation and Applications II. Applications

The fully consistent relativistic continuum random phase approximation (RCRPA) has been constructed in the momentum representation in the first part of this paper. In this part we describe the numerical details for solving the Bethe-Salpeter equation. The numerical results are checked by the inverse energy weighted sum rules in the isoscalar giant monopole resonance, which are obtained from the constraint relativistic mean field theory and also calculated with the integration of the RCRPA strengths. Good agreement between the misachieved. We study the effects of the self-consistency violation, particularly the currents and Coulomb interaction to various collective multipole excitations. Using the fully consistent RCRPA method, we investigate the properties of isoscalar and isovector collective multipole excitations for some stable and exotic from light to heavy nuclei. The properties of the resonances, such as the centroid energies and strength distributions are compared with the experimental data as well as with results calculated in other models.

Energy conversion in shape memory alloy heat engine - Part II: Simulation

In this paper, a theoretical model proposed in Part I (Zhu et al., 2001a) is used to simulate the behavior of a twin crank NiTi SMA spring based heat engine, which has been experimentally studied by Iwanaga et al. (1988). The simulation results are compared favorably with the measurements. It is found that (1) output torque and heat efficiency decrease as rotation speed increase; (2) both output torque and output power increase with the increase of hot water temperature; (3) at high rotation speed, higher water temperature improves the heat efficiency. On the contrary, at low rotation speed, lower water temperature is more efficient; (4) the effects of initial spring length may not be monotonic as reported. According to the simulation, output torque, output power and heat efficiency increase with the decrease of spring length only in the low rotation speed case. At high rotation speed, the result might be on the contrary.

铁基抗高温磨损激光熔覆涂层强韧设计和研究II:Fe-Cr-C-W-Ni激光熔覆层的微观组织及性能

本文以对热工模具进行失效分析的基础上，利用激光熔覆技术，在５ＣｒＭｎＭｏ基础上设计并制备强韧兼备的抗高温磨损涂层。

Studies on the phase diagram of the surfactant/1-pentanol water ternary system II: The liquid crystalline phase

The phase behavior of liquid crystalline in the ternary system of dodecyl dimethyl ammonium hydroxyl propyl sulfonate(DDAHPS)/1-pentanol(C5H11OH)/water deuteron (D2O) has been investigated by polarizing optical microscopy, H-2 NMR spectroscopy methods. The results indicate that two kinds of liquid crystals (the lamellar, and the hexagonal) exist in the liquid crystalline phase region. In this paper, we also use the polarized Raman spectroscopy method to measure the values of the order/disorder parameters and the values of the environment polarity parameters for the samples selected from the liquid crystalline phase region, and compare these two parameters of the samples with those of solid state DDAHPS and liquid state pentan-1-ol.

Mode I and Mode II Crack Tip Asymptotic Fields with Strain Gradient Effects

The strain gradient effect becomes significant when the size of fracture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dominant strain field is irrotational. For mode I plane stress crack tip asymptotic field, the stress asymptotic field and the couple stress asymptotic field can not exist simultaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode II plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode II plane stress and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode I and mode II, because the present theory is based only on the rotational gradient of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.