Subtle Interplay of Weak Intermolecular Interactions. Crystal Structures of Lead(II) Complexes with 4,4′‐Dimethyl‐2,2′‐bipyridine

Three adducts of the N,N′‐bidentate aromatic base 4,4′‐dimethyl‐2,2′‐bipyridine (dmbpy) of lead(II) salts, [Pb(dmbpy)₂(NO₃)₂] ( 1 ), [Pb(dmbpy)₂(ClO₄)₂] ( 2 ) and [Pb(dmbpy)(NCS)₂]_n ( 3 ) have been synthesized and characterized by elemental analysis, IR, ¹H‐NMR and ¹³C‐NMR spectroscopy and studied by thermal analysis as well as X‐ray crystallography. The single‐crystal structures of these complexes show that the 6s electrons of lead(II) constitute a stereochemically active lone pair (SALP). The coordination numbers of the Pb^II ions are eight and seven, respectively. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular interactions.     

A Novel Polymeric Lead(II)‐Azido Compound: Synthesis,Structural Characterization,and DFT Calculations of [Pb(dmp)(N3)2]n

A novel 1D Pb^II coordination polymer containing Pb₂‐(μ‐N₃)₂ unit [Pb(dmp)(N₃)₂]_n (dmp =  2,9‐dimethyl‐1,10‐phenanthroline) has been prepared and characterized. Single‐crystal X‐ray diffraction analyses show that the coordination number for Pb^II ions is six, PbN₆, with “stereochemically active” electron lone pairs and the coordination sphere being hemidirected. The single‐crystal X‐ray data show the chains interact with each other through the π–π stacking interactions, which create a 3D framework. The structure of title complex has been optimized by density functional theory. Structural parameters and IR spectra for the complex are in agreement with the crystal structure.     

Impacts of calcium-alginate density on equilibrium and kinetics of lead(II) sorption onto hydrogel beads

Chronic exposure to Pb²⁺ above the 15-μg/L US Environmental Protection Agency action level for drinking water has been shown to cause a host of health problems in humans. Thus, it is important to study new methods available for the treatment and removal of Pb²⁺ from drinking water and wastewater, where elevated levels of heavy metals are found. Alginate-based beads represent one such possible method for heavy metal removal. The impact of alginate density on the equilibrium and kinetics of Pb²⁺ sorption onto hydrogel beads was investigated using Ca-alginate beads ranging from 1% to 8% (w/v) and exposed to Pb²⁺ concentrations ranging from 100 to 1,000 mg/L. When Ca-alginate beads were characterized using Fourier transform infrared analysis, the carboxylic acid groups of the mannuronate and guluronate residues in alginate were the primary functional groups that interacted with Pb²⁺. Hydration of Ca-alginate beads was also examined and found to decrease as Ca-alginate density increased. A positive correlation was observed between Ca-alginate hydration and Pb²⁺ sorption. Sorption of Pb²⁺ was fast, reaching equilibrium after approximately 4 h, and is well described by the Langmuir adsorption isotherm. Maximum sorption capacities for 1%, 4%, and 8% beads were 500 ± 100, 360 ± 30, and 240 ± 20 mg/g (dry weight), respectively. The kinetics of sorption were best described by the pseudo-second-order Lagergren model, with rate constants determined as 3.2 ± 0.1 × 10⁻⁴, 1.0 ± 0.1 × 10⁻⁴, and 1.6 ± 0.1 × 10⁻⁴ g mg⁻¹ min⁻¹ for 1%, 4%, and 8% beads, respectively.     

On the inventory model with continuous and discrete lead time,backorders and lost sales

A well-established global supply chain system plays an important role in an enterprise’s strategic management, and an effective just-in-time system is a critical success factor for a global supply chain system. The advantages and benefits of just-in-time are associated with controlling the lead time. In this paper, we propose an approach to overcome the drawback of traditional methods for improving the continuous and discrete lead time with mixture of backorders and lost sales, by which only a local optimal solution can be obtained. In addition, the proposed model allows decision-makers to add suitable constraints to their model in accordance with their actual business environments. Finally, in order to demonstrate the accuracy and effectiveness of the suggested model, a real-life case, some numerical examples and sensitivity analysis are also included.     

原子吸收光谱法连续测定锌粉中的微量铁、铅和镍

盐酸及硝酸溶解试样 ,原子吸收光谱法测定锌粉中的铁、铅和镍含量 ,具有酸用量少、污染小、试样溶解完全的优点。加标回收率为 86 .7%— 10 0 .0 % ,相对标准偏差为 1.7%— 2 .1%。该方法操作简便、快速、准确。     

硅油-碳糊电极上微分脉冲伏安法测定痕量铅

研究了铅在盐酸体系中硅油-碳糊电极上的电化学行为,考察了酸度、富集时间、共存干扰离子的影响,在0.03—8.0μmol/L浓度范围内,铅离子的浓度对阳极峰电流呈很好的线性关系,回归方程为:iP(μA)=-3.568 17.75C(μmol/L),r=0.99987,SD=0.9216,检测限为:0.0085μmol/L(1.7ppb),用于实际湖水样品测定,结果令人满意。     

微波消解、石墨炉原子吸收光谱法测定土壤中的铅

采用微波消解系统处理土壤样品,可以大大减少消化试剂的用量及样品的处理时间。石墨炉原子吸收光谱法测定土壤中的铅,以磷酸二氢铵和硝酸镁作混合基体改进剂,可提高灰化温度,消除基体干扰。方法简便,快速,准确度高。铅的测定结果相对标准偏差为0.44%—5.2%;检出限为0.25mg/kg。     

Highly amorphous PbO2 as an electrode in hybrid electrochemical capacitors

This paper presents a synthesis and characterizes highly amorphous lead dioxide and its use in hybrid electrochemical capacitor C/PbO₂. Highly amorphous lead dioxide with a small amount of β-PbO₂ was synthesized by galvanostatic deposition from acetate solution. The hybrid supercapacitor was constructed with PbO₂ as the positive electrode whereas activated carbon as the negative electrode. The morphology of materials was examined by scanning electron microscopy and their structure was characterized by means of an X-ray diffraction technique. The electrochemical performance of hybrid electrochemical capacitor with synthesized PbO₂ was studied by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. To indicate that the amorphous form of lead dioxide was predominant, results were compared to highly crystalline β-PbO₂. The hybrid electrochemical capacitor with synthesized material exhibits a much greater specific capacitance, higher specific energy and power than the highly crystalline one. The specific capacitance values obtained for the supercapacitor rose more than twice in favour of amorphous PbO₂. Also, long cycling did not influence any of the electrochemical properties of this hybrid electrochemical capacitor, which makes it an interesting energy storage device.     

PbADC and PbADC·H2O: Two Coordination Polymers with Acetylenedicarboxylate (ADC2–) as Bridging Ligand

Single crystals of PbADC ( 1 ) and PbADC · H₂O ( 2 ) formed at the phase boundary of an aqueous silica gel containing acetylenedicarboxylic acid (HOOC–C≡C–COOH, H₂ADC) and an aqueous solution containing Pb(NO₃)₂. By choosing different concentrations of Pb(NO₃)₂, compounds 1 and 2 were obtained as phase pure products. Additionally, 1 was obtained by grinding Pb(CH₃COO)₂ · 3H₂O with H₂ADC resulting in a polycrystalline sample. The crystal structures of 1 (I4₁/amd, Z = 4; SrADC type structure) and 2 (P2₁/c, Z = 4, new structure type) were solved and refined from X‐ray single crystal data. Compound 1 exhibits a three‐dimensional framework structure: lead cations with a diamond‐like arrangement are interconnected by bridging ADC^2– ligands. In 2 double‐layers are formed by lead cations, bridging ADC^2– anions, and water molecules. These layers are held together by hydrogen bonds through water molecules and oxygen atoms of the ADC^2– ligands. Suspending 1 for 24 h in water at ambient conditions leads to the formation of 2 , which can be converted to 1 again by careful dehydration at approx. 400 K in vacuo. This reversible reaction can be structurally interpreted as a topochemical reaction, which transforms a 3D coordination network into a 2D network structure and vice versa, as both crystal structures show noticeable structural similarities.     

Quenching of the OH and nitrogen molecular emission by methane addition in an Ar capacitively coupled plasma to remove spectral interference in lead determination by atomic fluorescence spectrometry

A new method is proposed to remove the spectral interference on elements in atomic fluorescence spectrometry by quenching of the molecular emission of the OH radical (A²Σ⁺ → X²Π) and N₂ second positive system (C³Π_u → B³Σ_g) in the background spectrum of medium power Ar plasmas. The experiments were carried out in a radiofrequency capacitively coupled plasma (275 W, 27.12 MHz) by CH₄ addition. The quenching is the result of the high affinity of OH radical for a hydrogen atom from the CH₄ molecule and the collisions of the second kind between nitrogen excited molecules and CH₄, respectively. The decrease of the emission of N₂ second positive system in the presence of CH₄ is also the result of the deactivation of the metastable argon atoms that could excite the nitrogen molecules. For flow rates of 0.7 l min^− 1 Ar with addition of 7.5 ml min^− 1 CH₄, the molecular emission of OH and N₂ was completely removed from the plasma jet spectrum at viewing heights above 60 mm. The molecular emission associated to CH and CH₂ species was not observed in the emission spectrum of Ar/CH₄ plasma in the ultraviolet range. The method was experimented for the determination of Pb at 283.31 nm by atomic fluorescence spectrometry with electrodeless discharge lamp and a multichannel microspectrometer. The detection limit was 35 ng ml^− 1, 2–3 times better than in atomic emission spectrometry using the same plasma source, and similar to that in hollow cathode lamp microwave plasma torch atomic fluorescence spectrometry.