Electrochemical determination of trace amounts of lead (II) and cadmium (II) at a calix[6]arene modified carbon paste electrode

An electrochemical method for the simultaneous determination of lead(II) and Cadmium(II) with a calix[6]arene modified carbon paste electrode (CPE) has been developed. Pb²⁺ and Cd²⁺ were accumulated at the surface of the modified electrode via formation of chemical complexes with calix[6]arene, and reduced at 1.40 V. During the following anodic potential sweep, reduced lead and cadmium were oxidized, and two well-defined striping peaks appeared at about −0.60 V and −0.84 V. Compared with a bare carbon paste electrode, the calix[6]arene modified CPE greatly improves the sensitivity of determining lead and cadmium. The stripping peak currents change linearly with the concentration of Pb²⁺ 3.0×10⁻⁸–8.0×10⁻⁶ mol·L⁻¹ and with that of Cd²⁺ 6.0×10⁻⁸–1.0×10⁻⁵ mol ·L⁻¹. The detection limits of Pb²⁺ and Cd²⁺ are found to be 8.0×10⁻⁹ mol·L⁻¹ and 2.0×10⁻⁸ mol·L⁻¹, respectively. The modified carbon paste electrode was applied to determine trace levels of lead and cadmium in water samples. Comparing with that of atomic absorption spectrometry, the results suggests that the calix[6]arene modified CPE has great potential for the practical sample analysis. Foundation item: Supported by the National Natural Science Foundation of China (60171023) Biography: JI Xiao-bo (1980-), male, Master, research direction: electroanalytical chemistry.     

Photocatalytic degradation pathways and adsorption modes of H-acid in TiO2 suspensions

Effect of adsorption mode on photodegradation of H-acid in TiO2 suspension was studied using DFT calculation,UV-Vis spec-troscopy,FTIR,and ionic chromatography.At pH 2.5,H-acid was adsorbed on TiO2 surfaces by one dissociated sulfonic group.The adsorbed sulfonic group was attacked by surface ·OH,resulting in the production of SO42-and the cleavage of the naphtha-lene ring.At pH 5.0,H-acid was adsorbed on TiO2 surfaces by two sulfonic groups.The two adsorbed sulfonic groups were sim-ultaneously attacked by surface ·OH,leading to a faster initial production of SO42-and initial degradation rate of H-acid than those under pH 2.5.Microscopic adsorption structures may be more important than adsorption amount in controlling the photo-degradation pathways of organic pollutants.     

Partial oxidation of methane to syngas in a mixed-conducting oxygen permeable membrane reactor

Mixed-conducting oxygen permeable membranes represent a class of novel ceramic membranes, which exhibit mixed oxygen ionic and electronic conductivities. At high temperatures, oxygen can permeate through the membrane from the high to low oxygen pressure side under an oxygen concentration gradient. Theoretically, the permselectivity of oxygen is 100%. Recently, a novel mixed-conducting membrane—Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ has been developed, which shows extremely high oxygen permeability and promising stability. Furthermore, the reactor made with such membranes was successfully applied to the partial oxidation of methane to syngas reaction using air as the oxygen source, which realized the coupling of the separation of oxygen from air and the partial oxidation of membrane reaction in one process. At 850°C, methane conversion > 88%, CO selectivity > 97% and oxygen permeation rate of about 7.8 mL/(cm² · min) were obtained.     

Electrochemistry study on PEO-LiClO<Subscript>4</Subscript>-ZSM5 composite polymer electrolyte

Allsolid-statelithiumpolymerbatteriesmaybeoneofthebestchoicesforelectrochemicalpowersourceofthefuturecharacterizedbyitshighenergydensities,goodcyclability,reliabilityandsafety[1,2].PEO-LiXbasedpoly-merelectrolyteshadreceivedextensiveattention[4,5],foritspotentialcapabilitytobeusedascandidatematerialforthetraditionalliquidelectrolytes,sinceWrightetal.foundthatthecomplexofPEOandalkalinesaltshadtheabilityofionicconductivityin1973[3].ThegeneralconceptofthetransportofLi+inthepolymerelectrolytewa…     

A novel Pd/silicalite-1 composite membrane for hydrogen separation

A novel Pd/silicalite-1 composite membrane supported on the macroporous tubular stainless steel substrate was successfully fabricated by electroless plating at 303 K. The structure, morphology and gaseous permeability of the membrane were detected by X-ray diffractiometry （XRD）, scanning electron microscopy （SEM） and single-gas permeation test, respectively. Results confirm the formation of a thin, smooth, and continuous Pd/silicalite-1 composite membrane. The obtained composite membrane shows a high H2 permeance of 1.15×10^-6 mol. m^-2. s^-1. Pa^-1 with moderate H2 selectivity of 250 for H2/N2 at 773 K, at 0.1 MPa pressure drop, suggesting the potential application for H2 separation.     

Biosorption of Cu（Ⅱ） and Pb（Ⅱ） by Auricularia polytricha

For searching biological material for heavy metal removal of waste-water, using macrofungus Auricularia polytricha as biosorbent for Cu^2＋ and Pb^2＋ removal was investigated. After shaking and biosorbing Cu^2＋ and Pb^2＋ in solution by biosorbents, the filtrates were tested by AAS and the adsorbed quantity of Cu^2＋ and Pb^2＋ was calculated. The biosorbents were effective in removal of Cu^2＋ and Pb^2＋ on the biosorbents that showed a high- est value around pH 5-6. The biosorption rate of Cu^2＋ and Pb^2＋ on A. polytricha biomass decreased with increasing the initial concentration of Cu^2＋ and Pb^2＋ in the medium. The biosorption of Cu^2＋ and Pb^2＋ on the biomasses follows pseudo-second order kinetics. The determined maximum biosorption capacities presented by the fungus biomass were 3.34 and 13.03 mg·g^-1 dry weight for Cu^2＋ and Pb^2＋, respectively by the biosorption equilibrium with Langmuir adsorption isotherm. According to the whole data analysis in each experiment of studying Cu^2＋ and Pb^2＋ biosorption including condition factors and adsorption isotherm, the adsorbed capacity of Pb^2＋ by A. polytricha biomass was bigger than Cu^2＋. The biosorption by A. polytricha was most effective when pH 5-6. The biosorbents are suitable for low Cu^2＋ and Pb^2＋ concentration waste-water, especially for Pb^2＋ removal.     

Detection and response mechanism of CN− using Ag2S coated piezoelectric crystal sensor

A new method of determination of trace CN⁻ in water was proposed. A thin film of Ag₂S was electrochemically deposited on both sides of a silver coated piezoelectric crystal. The Ag₂S−Ag films can react with CN⁻ selectively, which causes the frequency shifts of the plezoelectric crystal. The frequency shifts are proportional to the concentration of CN⁻ in the range of 10⁻⁶≈10⁻³ g/L. XPS experiments indicated the sensing film was Ag₂S−Ag. A coordination complex Ag−CN⁻ was formed when Ag₂S−Ag film contacted with solution containing CN⁻ ion. A response mechanism was proposed based on the XPS data. Supported by National Natural Science Foundation of China Hu Jiming: born in Sept, 1952, Professor     

Summer monsoon and dust signals recorded in the Dasuopu firn core, central Himalayas

In September 1997, a 15-m firn core was recovered from an elevation of 7 000 m a. s.l. from the Dasuopu Glacier in the central Himalayas. The analysis of δ18O values and major ion (Ca2+ , Mg2+ , NH4+ , SO42- and NO3-) concentrations shows that average annual accumulation is 0.75 m (water equivalent) in the Dasuopu firn core. The seasonal variations of δ18O values and major ion concentrations in the core indicate that present summer monsoon and dust signals are recorded with high-resolution in the Dasuopu Glacier. δ18O in precipitation are controlled by amount effect in summer monsoon season, more negative δ18O is representative of summer monsoon signal in snow layers. Higher concentrations of Ca2+ , Mg2+ , SO42- and NO3-are dominated by spring dust storm imput derived from the arid and semi-arid desert regions in central Asia. Also EOF analysis verifies that high spring concentrations of major ions are consistent. Due to the possibly different sources, the secondary variations of NH4+ and NO3- are negatively relevant with that of Ca2+ and Mg2+ .     

Recent high-resolution glaciochemical record from a Dasuopu firn core of middle Himalayas

A 16.8 m firn core of middle Himalayas was recovered on the col of Dasuopu glacier in August 2006, being 7000 m above sea level. A total of 317 samples were measured for stable oxygen isotope ratios （6180） and major ion concentrations （Na＋, NH＋, K＋, Mg2＋, Ca2＋, Cl-, SO4^2-, and NO3^-. The firn core dating and seasonal partitioning were carried out based on the marked seasonal variations along the stable oxygen isotopes and crustal species （Ca2＋, Mg2＋） profiles. The multi-parameters and high-resolution glaciochemical data set of Dasuopu firn core recorded the detailed chemical characteristics of pre cipitation in high-elevation region, middle Himalayas, since 1991 A.D., which mainly originated from the crustal and anthropogenic sources, while the sea-salt contribution was minor. The seasonal variability of major ion concentrations was dominated by the seasonal alternation of the prevalent air mass, atmospheric circulation situation and precipitation regime. Linear regression analysis indicated that most of the variance in annual ionic fluxes can be explained by a linear dependence on snow accumulation rate.     

Determination of trace heavy metals in milk using an ionic liquid and bismuth oxide nanoparticles modified carbon paste electrode

A novel carbon composite electrode modified with bismuth oxide nanoparticles and the ionic liquid n-octylpyridinium hexafluorophosphate was fabricated and used to simultaneously determine cadmium and lead levels using square wave anodic stripping voltammetry.This electrode combines the unique advantages of nanomaterials and ionic liquid with the low cost and easy fabrication of the carbon composite electrode.Compared with the traditional binder based composite electrode,our electrode exhibited well-defined and separate stripping voltammetric peaks for cadmium and lead.Furthermore,the antifouling capacity of the bismuth film electrode was significantly improved by the ionic liquid.Under optimized conditions,the linear range of the composite electrode was from 3.0 to 30.0 μg L-1 for both metal ions with a detection limit of 0.15 μg L-1 for cadmium and 0.21 μg L-1 for lead.Trial milk sample analyses showed that the modified electrode was sensitive,reliable and effective for the determination of trace heavy metals,holding great promise for routine analysis applications.     

Application of Nanometer-Size Titanium Dioxide in Extreme-Trace V（Ⅴ） Analysis

0Introduction Vanadiumplaysanimportantroleinmodernindustry,es peciallyinsteelandchemicalindustry.Forinstance,itscompoundsarewidelyappliedintheproceduresofvitrioland petroleumchemicalmanufactureascatalyzers[14].Vanadium hasseveralvalences,butgenerallyitslowvalencesturnintohighoneseasilyinenvironment[5].BecauseV(Ⅴ)isthemost stableandpoisonousone,weoftenlayemphasisonitinenvi ronmentalpollutioncontrol.Vanadiumexistsinenvironmentalwaterwithextremelylowconcentration.Inseawateritscontentislessthan…     

Kinetic studies of the decomposition reaction of adducts of dinuclear Fe(Ⅱ)/O2

Kinetic studies of the decomposition reaction of dinuclear Fe(Ⅱ) adducts [Fe₂(N-Et-HPTB){O₂P(OPh)₂}](Cl- O₄)₂ (1) and [Fe₂(N-Et-HPTB) {O₂P(Ph)₂}] (ClO₄)₂ (2) with O₂ have been carried out at low temperature using UV-vis spectra. The decomposition reaction of Fe(Ⅱ)/O₂ adducts was first-order in the experimental conditions, and the activation parameters were obtained. ?H^¹ = 85.62 kJ·mol^-1, ?S¹ = 19.43 J·mol^-1·K^-1 for compound (1) and ?H^¹ = 97.97 kJ·mol^-1, ?S^¹ = 55.68 J·mol^-1·K^-1 for compound (2). These results are similar to those of dioxygen adducts of other metals complexes and natural enzymes such as methane mono- oxygenase (MMOH).     

Synthesis and structure of Cu5(BTA)6(TTA)4 · 5DMF, a copper-nitrogen cluster containing η Π3-benzotriazolate

The title cluster compound—Cu₅(BTA)₆(TTA)₄·5DMF was prepared using thenyltrifluoroacetone and benzotriazolate ligands. The crystal structure indicates that a tetrahedral array of Cu(1), Cu(2), Cu(3) and Cu(4) ions surrounding a central Cu(5) ion are held together by bridging tridentate BTA^- and terminated by TTA^- bond cap. The three nitrogen atoms of a BTA^- bond three different copper ions to form a η³-benzotriazolate. The central Cu ion has a distorted octahedral structure and the surrounding Cu ions are 5 coordinated forming distorted tetragonal structures. The distances between the surrounding Cu(Ⅱ) ions and the central Cu(Ⅱ) ion are in the range of 0.3561—0.3755 nm and those between the surrounding Cu(Ⅱ) ions are in the range of 0.5785—0.6301 nm.     

Potential release of hydrogen fluoride from domestic coal in endemic fluorosis area in Guizhou,China

Almost half of the total rural area of Guizhou Province and many regions within the 11 adjacent provinces in southwestern China have a long history(at least 70 years) of endemic fluorosis,including dental fluorosis and osteofluorosis along with its associated deformities and disabilities.Over decades of research,this specific type of endemic fluorosis has been defined as coal-burning fluorosis,which is distinct from drinking-water fluorosis.It is generally acknowledged that indoor burning and combustion of high-fluorine coal leads to food contamination,and fluorine then enters the human body.However,the exact chemical form of fluorine during its release and transfer to the body is still unknown.In the present study,21 domestic coal samples from outcrop and semi-outcrop coal collected in five villages with fluorosis were analyzed by time-of-flight secondary ion mass spectrometry(TOF-SIMS).The total mass fraction of sulfur in the samples ranged from 0.24%-5.58% and total fluorine content ranged 90.2-149.2 mg/kg.H3O+,H2SO4+ and HSO4-were detected in the samples by TOF-SIMS,which indicated that sulfuric acid hydrate(H2SO4.H2O) was present in the samples.F-was detected in all of these,which suggested the samples contain ionic fluorine compounds.Under certain circumstances,such as heating or burning,the prevalence and coexistence of the acid(H2SO4.H2O) and base(F-) would lead to a neutralization reaction producing volatile hydrogen fluoride(HF,bp = 19.5℃).This would be the chemical form of fluorine released from the coal.Further studies using HF and SO2 test tubes on headspace gas over coal samples heated to 200℃ in the laboratory and on headspace gas over stoves or chimney tops at rural residences confirmed the release of HF.     

Mineralogical and sink-float studies of Jajarm low-grade bauxite

Jajarm’s bauxite deposits are mainly diasporic, and they have a low mass ratio of Al₂O₃/SiO₂. It is necessary to increase the run-of-mine mass ratio before feeding the material to the Bayer process. Chemical analysis indicated that the low-grade bauxite sample from Jajarm contained 43.9wt% Al₂O₃ and 13.35wt% SiO₂, resulting in a mass ratio of 3.29. According to mineralogical studies, the presence of aluminosilicate minerals such as kaolinite, illite, and quartz was the main reason for the decrease of the mass ratio. Microscopic observations revealed that, with the size reduction from -1000+710 to -38 μm, the liberation degree of diaspore increased from 10% to 60%, and that of aluminosilicates increased from 20% to 85%. Heavy liquids with the densities of 2.8, 3.0, 3.2, and 3.4 g/cm3 were used to evaluate the heavy media separation in three sizes, i.e., -3350+710, -710+212, and -212+125 μm. Laboratory studies confirm that the density of 3.2 g/cm3 can produce the concentrates (in sunk fractions) with recoveries of 89.09%, 91.24%, and 84.68% with the Al₂O₃/SiO₂ mass ratios of 5.03, 5.16, and 5.15 for the -3350+710, -710+212, and -212+125 μm sizes, respectively.     

Ionic liquids containing the urea moiety for recognition of halides and complex anions

A series of novel imidazolium based ionic liquids containing the urea moiety were designed and synthesized for anion recognition. 1-Ethylurea-3-methylimidazolium acetate ([Eumim]OAc) was used as the receptor for the halides and complex anions (BF4-, PF6-, BPh4-). 1H NMR spectra showed that the urea protons and imidazolium C(2) proton of the receptor ([Eumim]OAc) moved upfield on addition of various anions. A Job plot showed that the [Eumim]OAc receptor formed a 1:1 complex with BPh4-. X-ray diffraction analysis and the molecular modeling study revealed that the conformations of [Eumim]OAc and [Eumim]BPh4 were different. The conformational change of the cation was caused by anion exchange, and may provide an alternative to current methods for recognition of anions.     

Label-free selective sensing of Pb2+ lead(II) sensors based on the aggregation of a pyrene fluorescent probe

In the present work, we report a label-free fluorescence turn-on approach for the sensitive and selective sensing of Pb²⁺. Pyrene with one positive charge was used as the fluorescent probe, and thrombin aptamer (TBA), which was a G-rich oligonucleotide, was employed to form G-quadruplex with lead(II). When TBA and Pb²⁺ were mixed with lead(II) in an aqueous solution, it was folded into a stable G-quadruplex. Subsequently, a single-stranded nucleic acid-specific nuclease S1 was added. The G-quadruplex stabilized by Pb²⁺ lead(II) had markedly a significant resistant ability to nuclease S1 digestion. However, in the absence of Pb²⁺ lead(II), no quadruplex or less stable quadruplex was formed and TBA was digested by nuclease S1 in 3 min under the optimized experimental conditions. Finally, pyrene probe was mixed with oligonucleotide in Pb²⁺ lead(II). Electrostatic interactions between oligonucleotide (a polyanion) and the probe induced the aggregation of the probe, which in turn produced strong emission of the strong pyrene excimer emission. The intensity of the induced excimer emission was directly proportional to the amount of Pb²⁺ added. Our approach shows good selectivity and sensitivity for the detection of Pb²⁺ with a limit of detection limit as low as 800 nmol/L.     

镍渣表面理化特性及对Pb2+、Cu2+的吸附研究

利用多种表征手段对镍渣的组成和表面特性进行分析,证实了镍渣具备吸附废水中重金属的能力。本实验所采用的水淬二次镍渣中含有含量较高的SiO₂、Al₂O₃、CaO、MgO等活性成分,且具备由不同聚合度的Si-O四面体、Al-O四面体或Al-O八面体组成的岛状、链状或网状骨架结构,能够通过离子交换和专性吸附去除溶液中的重金属离子。此外,镍渣粉体表面的碱中心可以为金属阳离子提供有效的吸附位点,且表面在pH=4~12的范围内均带负电,这些都有利于金属阳离子的吸附。镍渣粉体对模拟废液中的Pb²⁺、Cu²⁺吸附实验结果显示,其对废液中的Pb²⁺、Cu²⁺均表现出较好的吸附效果,且对Pb²⁺表现出更好的选择性吸附效果。     

The comparison of Cu（ll） adsorption capability of baker＇s yeast,nano-titania and their composite adsorbent

The anatase nano-TiO2 powder, with crystal size between 40 and 80 nm, was prepared by the liquid phase hydrolysis of TiCI4. At the same time, the nano-TiO2 was utilized with the baker＇s yeast biomass as a composite adsorbent to adsorb the Cu ions in the artificial aqueous solution. The investigation showed that the composite adsorbent had a fine adsorption efficiency. The TiO2 in the composite adsorbent could cooperate well with baker＇s yeast to improve the adsorbing capability of Cu^2＋ under the following experimental conditions as well： a quantity of composite adsorbent of 5 g·L^-1, pH≥4.0, an adsorption time of 40 min and an initial concentration of Cu ions of 10 mg·L^-1. In addition, the results of measurements, obtained with a scanning electron microscope, an infrared spectrophotometer and a Zeta potential analyzer, revealed that the baker＇s yeast and nano-TiO2 produced the composite adsorbent through coordination and hydrogen bonds in particular, etc. The stability of the composite adsorbent and the amount of titania loaded were largely dependent on the concentration of hydrogen ion in the solution.     

天然沸石的改性及其吸附Pb~(2+);Cu~(2+)的研究

以天然沸石为原料,结合废水处理应用中对吸附材料的要求,采用酸、碱、盐对沸石进行了改性;并利用改性沸石进行了去除溶液中Pb2+,Cu2+的方法、效果、影响因素和吸附机理的研究.结果表明,NaOH改性的沸石对Pb2+,Cu2+的吸附能力大幅度提高;随着初始浓度的增加,沸石的吸附容量也增加;改性沸石对Pb2+,Cu2+的吸附很快,在较短的时间内即可达到平衡;溶液的pH值越高越有利于沸石吸附Pb2+,Cu2+.