Adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide from simple (1-1) electrolyte solutions

The adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide (delta-MnO2) has been studied using two methods, viz., isotherms at constant pH in the presence of buffer solution and pH variation in the absence of buffer solution from a fixed metal ion concentration. While the adsorption isotherm experiments were carried out in 0.5 M NaCl only, pH variation or batch titration experiments were carried out in 0.5 M NaCl, 0.01 M NaCl, and 0.01 M KNO3 solutions. The complex nature of adsorption isotherms at constant pH values indicates that adsorption of all the cations is non-Langmuirian (Freundlich) and takes place on the highly heterogeneous oxide surface with different binding energies. The proton stoichiometry derived from isotherms at two close pH values varies between 0.3 and 0.8. The variation of fractional adsorption with pH indicates that the background electrolyte solution influences the adsorption of cations through either metal-like or ligand-like complexes with Cl-, the former showing a low adsorption tendency. The proton stoichiometry values derived from the Kurbatov-type plot varies not only with the electrolyte solution but also with the adsorbate/adsorbent ratio. The variation of fractional adsorption with pH can be modeled either with the formation of the SOM+ type or with a combination of SOM+ and SOMOH type complexes, depending upon the cation and electrolyte medium. The equilibrium constants obtained from Kurbatov-type plots are found to be most suitable in these model calculations. Adsorption calculated on the basis of ternary surface metal-chlorocomplex formation exhibits very low values.     

Adsorption of Co, Ni, Cu, and Zn on hydrous manganese dioxide from complex electrolyte solutions resembling sea water in major ion content

Adsorption of Co, Ni, Cu, and Zn onto a poorly crystalline hydrous manganese dioxide (delta-MnO2) has been studied in complex electrolyte solutions such as (a) 0.5 M NaCl+0.054 M MgCl2, (b) 0.5 M NaCl+0.028 M Na2SO4, and (c) artificial sea water prepared according to the standard literature method. These three solutions allow us to identify the specific effect of major cations, major anions, and the mixture of major cations and anions (including carbonate and bicarbonate) that is present in real sea water. The adsorption isotherm in major ion sea water at pH 7.25 indicates that while Co and Zn exhibit increases in adsorption with increase in concentration, Ni shows relatively poor adsorption, reaching a plateau at 0.075 mM concentration. The three trace metals (Co, Ni, and Zn) show Langmuirian behavior for adsorption at low concentration. It is generally observed that the fractional adsorption vs pH curve shifts to higher pH either in the presence of 0.054 M MgCl2 or in sea water. In the presence of 0.028 M Na2SO4 the fractional adsorption vs pH curve remains almost unchanged with respect to a 0.5 M NaCl solution. The competitive adsorption of one trace metal in the presence of other three in major ion sea water indicates that this phenomenon is more predominant with Ni and Zn than with Co and Cu.     

Surface electrochemical properties of mixed oxide ceramic membranes: Zeta-potential and surface charge density

The surface electrochemical properties of alumina based ceramic microfiltration membranes were studied by measuring electroosmotic rates and surface charge densities obtained from potentiometric titrations. The rate of electroosmosis, which determines the zeta-potential, was measured on the membrane itself, whereas the surface charge was titrated on a suspension obtained by crushing of the membrane. The zeta-potential was measured in the presence of salts including NaCl, CaCl₂ and Na₂SO₄, for a wide range of pH values (4–9) at ionic strengths of 0.01 and 0.001 M. The pH value of the isoelectric point (iep) show a specific adsorption of SO₄²⁻ and Ca²⁺ ions onto the membrane surface. The iep in NaCl solutions occurs at pH 4.7 ± 0.1. The low iep is due to the large amount of silicium oxide in the membrane. The surface charge density is relatively high with respect to the low values of zeta-potentials. The point of zero charge pH(pzc) determined from surface charge and pH profiles occurs at pH 8.2 ± 0.1 in NaCl solution. The pH(pzc) value was also determined by two ‘addition’ methods. Similar pH(pzc) values were obtained. The difference between the pH(pzc) and pH(iep) may be correlated to a loss of acidity that is due to using crushed-membrane powder to perform potentiometric measurements.     

Studies on Synthetic Inorganic Ion Exchangers-III Quantitative Separations of Mg2+ -Pb2+, Zn2+ - Pb2+ Cu2+ - Pb2+, Al3+ - Pb2+, Zn2+ - Cd2+, and Mg2+ - Cd2+ on Lead Antimonate Columns

Abstract

A new inorganic ion exchanger, lead antimonate has been synthesized having an Pb:Sb ratio of 1:5 and cation exchange capacity of 1.46 mequiv./g. It is fairly stable in water and dilute solutions of acids, bases and salts. Ion distribution studies on twenty metal ions have been determined on this gel at pH 1,2,3 and 5. The following mixtures have been separated: Mg²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Cu²⁺ - Pb²⁺, Al³⁺ - Pb²⁺, Zn²⁺ - Cd²⁺ and Mg²⁺ - Cd²⁺. Mg²⁺ and Al³⁺ were removed with 0.4 M ammonium nitrate, Cu²⁺ and Zn²⁺ with 0.4 M ammonium nitrate + 0.1M nitric acid (1:1), Pb²⁺ with 0.5M nitric acid and Cd²⁺ with 0.25M nitric acid. A tentative structure of this material is proposed on the basis of chemical analysis, pH titrations, thermogravimetry and IR spectrophotometry.     

Effect of Mn2+, Co2+, Ni2+, and Cu2+ on horseradish peroxidase: activation,inhibition, and denaturation studies

The effects of transition metal ions (M2+) such as Mn2+, Co2+, Ni2+, and Cu2+ on the functional and structural stabilities of horseradish peroxidase (HRP) were investigated with respect to reversible chemical denaturation, Michaelis-Menten kinetics, chemical modification and time-dependent catalytic activity. Conformational Gibbs free energy (deltaGo(H2O)) as a structural stability criterion and transition concentrations of metal ions ([M2+] 1/2) were estimated using a two-state chemical denaturation model. Activation and inhibitory concentration ranges for each metal ion were specified by the steady-state enzyme kinetics. Results of a pH-profile method confirmed by chemical modification indicate that a histidine residue interacts in the activation concentration range, whereas carboxylic residues (Asp and Glu) contribute to interaction in the inhibitory concentration range. Incubation of the enzyme with the metal ion at activation concentration leads to long-term functional stability of peroxidase. Thus, such metal ions as potent effectors induced the enhancement of conformational and functional stabilities of horseradish peroxidase.     

Quantitation of protein binding to the capillary wall in acidic, isoelectric buffers and means for minimizing the phenomenon

Notwithstanding the use of acidic, amphoteric, isoelectric buffers with isoelectric points (pI) in the pH 2-3 range, adsorption of proteins to the naked silica wall can be non-negligible. Two such buffers have been tested: iminodiacetic acid (IDA; pI 2.23, apparent pH 3.2 in 7 M urea) and aspartic acid (pI 2.77, apparent pH 3.7 in 7 M urea). Three potential quenchers of such interactions have been tested: hydroxyethylcellulose (HEC; number average molecular mass, Mr 27,000), TEPA (tetraethylenepentamine) and a novel, quatemarized piperazine [N(methyl-N-omega-iodobutyl)-N'-methylpiperazine] (Q-Pip), either alone or in binary and ternary mixtures. Human alpha- and beta-globin chains have been used as test proteins in capillary electrophoresis separations. It has been found that mixtures of these compounds are the worst possible remedy. E.g., a ternary mixture comprising 0.5% HEC, 0.5 mM TEPA and 1 mM Q-Pip still leaves behind 4.5% adsorbed protein onto the silica surface in runs in IDA buffer and 7 M urea (pH 3.2). Conversely, 0.5 mM TEPA or 1 mM Q-Pip, when used alone, minimize adsorption down to only 1.8% and 0.5%, respectively. When the same globin chain separations are performed in Asp and 7 M urea (pH 3.7), the situation is much worse: 44% protein is adsorbed in a ternary mixture of 0.5% HEC, 1 mM Q-Pip and 0.5 mM TEPA. However, when used alone, 0.5 mM TEPA and 1 mM Q-Pip reduce globin adsorption to levels of 8% and 5%, respectively. TEPA and Q-Pip are found to be in all cases the best quenchers of protein interaction to naked fused-silica; in addition they exhibit the unique property of smoothing the base-line and giving reproducible runs. The best method for desorbing bound protein was found to be an electrophoretic step consisting in driving sodium dodecylsulphate micelles from the cathodic reservoir.     

Ice/Water Interface: Zeta Potential, Point of Zero Charge, and Hydrophobicity

The ice/water interface is a common and important part of many biological, environmental, and technological systems. In contrast to its importance, the system has not been extensively studied and is not well understood. Therefore, in this paper the properties of the H₂O ice/water and D₂O ice/water interfaces were investigated. Although the zeta potential vs pH data points were significantly scattered, it was determined that the isoelectric point (iep) of D₂O ice particles in water at 3.5°C containing 10⁻³ M NaCl occurs at about pH 3.0. The negative values of the zeta potential, calculated from the electrophoretic mobility, seem to decrease with decreasing content of NaCl, while the iep shifts to a higher pH. The point of zero charge (pzc) of D₂O ice and H₂O ice, determined by changes in pH of 10⁻⁴ M NaCl aqueous solution at 0.5°C after the ice particle addition, was found to be very different from the iep and equal to pH 7.0 ± 0.5. The shift of the iep with NaCl concentration and the difference in the positions of the iep and pzc on the pH scale point to complex specific adsorption of ions at the interface. Interestingly, similar values of iep and pzc were found for very different systems, such as hydrophilic ice and highly hydrophobic hexadecane droplets in water. A comparison of the zeta potential vs pH curves for hydrophilic ice and hydrophobic materials that do not possess dissociative functional groups at the interface (diamond, air bubbles, bacteria, and hexadecane) indicated that all of them have an iep near pH 3.5. These results indicate that the zeta potential and surface charge data alone cannot be used to delineate the electrochemical properties of a given water/moiety interface because similar electrical properties do not necessary mean a similar structure of the interfacial region. A good example is the aliphatic hydrocarbon/water interface in comparison to the ice/water interface. Although the experiments were carried out with care, both the zeta potential, measured with a precise ZetaPlus meter, and ΔpH values (a measure of surface charge) vs pH were significantly scattered, and the origin of dissemination of the data points was not established. Differently charged ice particles and not fully equilibrium conditions at the ice/water interface may have been responsible for the dissemination of the data.     

巯基树脂对金属离子的吸附性能(Ⅱ)

研究了自合成的巯基树脂对重金属离子Ag 、Hg2 、Cr3 的吸附容量、吸附动力学、等温吸附过程等静态吸附性能,影响吸附的因素和吸附机理.结果表明,该树脂对上述3种离子吸附能力强,吸附量分别达6.56mmol/g、3.25mmol/g、2.10mmol/g.树脂对各重金属离子等温吸附在实验浓度范围内符合Langmuir或Freundlich方程.吸附机理研究表明,巯基与金属离子发生了离子交换和配位反应,化学吸附起支配作用;另外树脂对Ag 、Hg2 吸附过程中存在一定的氧化还原现象.     

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.     

Modeling the adsorption of free and heavy metal complex-bound EDTA onto red mud by a nonelectrostatic surface complexation model

The adsorption of free and divalent heavy metal (copper, cadmium, and lead) complex-bound EDTA from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a nonelectrostatic surface complexation approach in respect to adsorbate concentration and pH dependency of EDTA adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and its abundance in natural waters. The adsorption experiments were conducted for pure EDTA or metal-EDTA complexes alone, or in mixtures containing (EDTA+metal-EDTA). For all studied cases, the solid adsorbent phase concentrations of the adsorbed species were found by using the derived model equations with acceptable compatibility of experimental and theoretically generated adsorption isotherms. The model basically assumed two modes of metal bonding to the surface hydroxyls: ionic (outer-sphere) binding of the EDTA anion (H(2)Y(2-)) or anionic metal-EDTA complex (MY(2-)) to the cationic surface site ( approximately SOH(+)(2)), and outer-sphere binding of H(2)Y(2-) or MY(2-) to the neutral approximately SOH site, possibly via hydrogen-bonding. The model was useful for EDTA and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to pH相似文献   

Temperature effect on the zeta potential and fluoride adsorption at the alpha-Al2O3/aqueous solution interface

The effect of temperature and pH on the zeta potential of alpha-Al2O3 and adsorption of fluoride ions at the alpha-Al2O3/aqueous solution interface has been investigated through electrophoretic mobility measurements and adsorption studies, to delineate mechanisms involved in the removal of fluoride ions from water using alumina as adsorbent. When the temperature increases from 10 to 40 degrees C, the pH of the point of zero charge (pH(pzc)) shifts to smaller values, indicating proton desorption from the alumina surface. The pH(pzc) increases linearly with 1/T, which allowed estimation of the standard enthalpy change for the surface-deprotonation process. Fluoride ion adsorption follows a Langmuir-type adsorption isotherm and is affected by the electric charge at the alpha-Al2O3/aqueous solution interface and the surface density of hydroxyl groups. Such adsorption occurs through an exchange between fluoride ions and surface-hydroxyl groups and it depends on temperature, pH, and initial fluoride ion concentration. At 25 and 40 degrees C, maximum fluoride adsorption density takes place between pH 5 and 6. Increasing the temperature from 25 to 40 degrees C lowers the adsorption density of fluoride.     

Qualitative analysis of Cu2+, Co2+, and Ni2+ cations using thin-layer chromatography

The M(DEDTC)2 (M = Cu, Co, or Ni) and M(PyDTC)2 (M = Cu or Co) complexes prepared by reactions of sodium diethyldithiocarbamate and ammonium pyrollidinedithiocarbamate with metal (II) nitrates are examined for qualitative analysis and separation using thin-layer chromatography systems. These complexes and their mixtures are spotted to the activated thin layers of silica gel 60GF254 (Si-60GF254) with a 250-microm thickness. Pure toluene and a toluene-cyclohexane mixture (3:1, v/v) are used as mobile phases for running of the complexes. These chromatographic systems are successfully used for qualitative analysis of corresponding metal cations and separation of components in both M(DEDTC)2 and M(PyDTC)2 complex mixtures.     

H3PO4改性PS-EDTA树脂对水相中Cu2+、Zn2+和Cd2+的吸附性能研究

大孔氯甲基化聚苯乙烯小球先后与乙二胺、2-氯乙酸反应得EDTA型螯合树脂(PS-EDTA),再用磷酸在室温处理得PS-EDTA/P树脂。PS-EDTA/P树脂被用于水相中Cu2+、Zn2+和Cd2+的吸附净化处理,探讨了溶液的pH值、初始金属离子浓度、时间、温度等因素对吸附性能的影响,并研究了其对重金属离子的吸附动力学和热力学。结果表明,PS-EDTA/P树脂对Cu2+和Zn2+的吸附符合Langmuir等温式、对Cd2+的吸附符合Freundlich等温式,准二级吸附动力学方程能够很好地描述3种金属离子在树脂上的吸附动力学行为。同时,PS-EDTA/P树脂对重金属吸附的热力学参数表明,PS-EDTA/P树脂对Cu2+、Zn2+和Cd2+的吸附是一个自发的、吸热的过程。已吸附Cu2+、Zn2+和Cd2+的树脂可以用0.1mol/L HCl解吸,解吸后的树脂对Cu2+、Zn2+和Cd2+仍具有较高的吸附量。     

Simultaneous uptake of Ni2+, NH4+ and PO4(3-) by amorphous CaO-Al2O3-SiO2 compounds

Simultaneous uptake of Ni2+, NH4+, and PO4(3-) by amorphous CaO-Al2O3-SiO2 (C-A-S) compounds was investigated using batch and column methods. Fifteen different C-A-S samples with systematically varied chemical compositions were prepared by coprecipitation from ethanol-water solutions containing Ca(NO3)2.4H2O, Al(NO3)3.9H2O, and Si(OC2H5)4, using NH4OH as the precipitating agent. The resulting precipitates were dried and heated at various temperatures to produce the C-A-S samples, which were then characterized by XRD, FTIR, solid state MAS NMR, DTA-TG, and N2 adsorption. All the C-A-S samples prepared at 600-900 degrees C were amorphous, apart from the CaO-rich samples. Simultaneous uptake of Ni2+, NH4+, and PO4(3-) was determined by a batch method using a solution with an initial concentration of 2 mM. In these experiments, the uptake abilities of the C-A-S samples for Ni2+ and PO4(3-) were high, but were relatively low for NH4+. The uptake abilities for Ni2+ and PO4(3-) increased but that for NH4+ decreased as the silica content in the C-A-S decreased, suggesting that similar uptake mechanisms (ion substitution and/or precipitation) are operating for Ni2+ and PO4(3-), but the uptake mechanism for NH4+ is different (physical adsorption). The column experiments indicate that the order of uptake ability of C-A-S for the three ions is NH4+ < PO4(3-) < Ni2+. Although the silica content of the C-A-S does not have the expected influence on the uptake of these three ions, for NH4+ it plays an important role in the formation of the amorphous phase and also in the suppression of Ca2+ and/or Al3+ release from the C-A-S during the uptake experiments. The optimum uptake properties of the C-A-S can thus be controlled by adjusting the chemical compositions and heating conditions under which the samples are prepared.     

高锰酸钾-鲁米诺反应体系中碱土金属离子Mg2+,Ca2+,Sr2+,Ba2+化学发光行为研究

将被认为没有化学发光活性的第二主族(碱土金属)离子Mg^2 ,Ca^2 ,Sr^2 ,Ba^2 溶液注入到已充分反应的高锰酸钾与鲁米诺混合液中时,又发生了新的化学发光反应,并检测到强的化学发光信号．在对有关反应的动力学性质、化学发光光谱、紫外可见光谱及其它一系列实验研究的基础上,提出了可能的化学发光反应机理．同时,优化了反应条件,评价了这一反应用于Mg^2 ,Ca^2 ,Sr^2 ,Ba^2 分析的可行性．     

Simultaneous determination of Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ by using second-derivative spectrophotometry method

A new method of simultaneous determination of Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ is proposed here by using the second-derivative spectrophotometry method. In pH=10.35 Borax-NaOH buffer, using meso-tetra (3-methoxyl-4-hydroxylphenyl) porphyrin ([T-(3-MO-4-HP)P]) as chromomeric reagent, micelle solution was formed after Tween-80 surfactant was added into the solution containing Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ ions. The original absorption spectrum of the above complexes was obtained after heating in the boiling water for 25 min. The second-derivative absorption peaks of five metal-porphyrin complexes can be separated from the original absorption spectrum by using chemometric tool. In this way, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ ions can be determined simultaneously. Under the optimal conditions, the linear ranges of the calibration curve were 0-0.60, 0-0.60, 0-0.40, 0-0.80 and 0-0.48 μg mL(-1) for Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+, respectively. The molar absorptivity of these color systems were 1.38×10(5), 1.01×10(5), 3.24×10(5), 1.07×10(5) and 1.29×10(5)Lmol(-1)cm(-1). The method developed in this paper has advantages in selectivity, sensitivity, operation and can effectively resolve spectra overlapping problem. This method has been applied to determine the real samples with satisfactory results.     

Liquid-liquid extraction of Th4+ and UO 2 2+ by LIX-26 and its mixtures

Solvent extractions of thorium(IV) and uranium(VI) by a commercially available chelating extractant LIX-26 (an alkylated 8-hydroxyquinoline) or 8-hydroxyquinoline, benzoic or salicylic acid, dipentyl sulphoxide (DPSO) and their mixtures with butanol as modifier in benzene/methylisobutyl ketone (MIBK) as the diluent have been studied. Extraction of uranium(VI) by 10% LIX-26 and 10% butanol in benzene becomes quantitative at pH 5.0. The pH 0.5 values for the extraction of thorium(IV) and uranium(VI) are 4.95 and 3.35, respectively. Quantitative extraction of thorium(IV) by the mixture of 0.1 M oxine and 0.1 M salicylic acid in methylisobutyl ketone was observed at pH 5.0. The influence of concentration of various anions on the extraction of Th⁴⁺ by mixtures of LIX-26 and benzoic acid has been studied. Studies on extraction of thorium(IV) and uranium(VI) by mixtures of LIX-26 (HQ) and DPSO show that the extracted species are possibly of the type [ThQ₂/DPSO/₂/SCN/₂] and [UO₂Q₂/DPSO/], respectively.     

反相高效液相色谱法同时测定镉、铅、铜和锌

 研究了meso-四（对羟基苯基）卟啉为柱前衍生化试剂与Cd2+,Pb2+,Cu2+和Zn2+离子的配合反应条件及配合物在C18色谱柱上的分离条件,建立了反相高效液相色谱快速分离光度检测Cd2+,Pb2+,Cu2+和Zn2+的新方法。配合物和试剂在15 min内出峰完毕。4种离子的检出限为: Cd2+0.02 ng,Pb2+0.02 ng, Cu2+0.02 ng,Zn2+0.12 ng;线性范围为:Cd2+0.8 μg/L～150 μg/L,Pb2+0.8 μg/L～300 μg/L,Cu2+0.8 μg/L～500 μg/L,Zn2+5.0 μg/L～1 000 μg/L;方法的日内相对标准偏差为:2.8%～4.8%,测定低、中、高3个浓度的日间相对标准偏差为3.7%～9.7%。     

Modeling of Copper(II), Cadmium(II), and Lead(II) Adsorption on Red Mud from Metal-EDTA Mixture Solutions

The adsorption of toxic heavy metal cations, i.e., Cu(II), Cd(II), and Pb(II), from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a modified surface complexation approach in respect to pH and complexant dependency of heavy metal adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and abundance in natural waters. The adsorption experiments were conducted for metal salts (nitrates), metal-EDTA complexes alone, or in mixtures containing (metal+metal-EDTA). The adsorption equilibrium constants for the metal ions and metal-EDTA complexes were calculated. For all studied cases, the solid adsorbent phase concentrations of the adsorbed metal and metal-EDTA complexes were found by using the derived model equations with excellent compatibility of experimental and theoretically generated adsorption isotherms. The model was useful for metal and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to a certain pH. Thus adsorption of every single species (M(2+) or MY(2-)) or of possible mixtures (M(2+)+MY(2-)) at natural pH or after NaOH titration could be calculated by the use of simple quadratic model equations, once the initial concentrations of the corresponding species, i.e., [M(2+)](0) or [MY(2-)](0), were known. The compatibility of theoretical and experimental data pairs of adsorbed species concentrations was verified by means of nonlinear regression analysis. The findings of this study can be further developed so as to serve environmental risk assessment concerning the expansion of a heavy metal contaminant plume with groundwater move ment in soil consisting of hydrated-oxide type minerals. Copyright 2000 Academic Press.     

M+(12-crown-4) supramolecular cations (M+ = Na+, K+, Rb+, and NH4+) within Ni(2-thioxo-1,3-dithiole-4,5-dithiolate)2 molecular conductor

Monovalent cations (M+ = Na+, K+, Rb+, and NH4+) and 12-crown-4 were assembled to new supramolecular cation (SC+) structures of the M+(12-crown-4)n (n = 1 and 2), which were incorporated into the electrically conducting Ni(dmit)2 salts (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate). The Na+, K+, and Rb+ salts are isostructural with a stoichiometry of the M+(12-crown-4)2[Ni(dmit)2]4, while the NH4+ salt has a stoichiometry of NH4+(12-crown-4)[Ni(dmit)2]3(CH3CN)2. The electrical conductivities of the Na+, K+, Rb+, and NH4+ salts at room temperature are 7.87, 4.46, 0.78, and 0.14 S cm-1, respectively, with a semiconducting temperature dependence. The SC+ structures of the Na+, K+, and Rb+ salts have an ion-capturing sandwich-type cavity of M+(12-crown-4)2, in which the M+ ion is coordinated by eight oxygen atoms of the two 12-crown-4 molecules. On the other hand, the NH4+ ion is coordinated by four oxygen atoms of the 12-crown-4 molecule. Judging from the M(+)-O distances, thermal parameters of oxygen atoms, and vibration spectra, the thermal fluctuation of the Na+(12-crown-4)2 structure is larger than those of K+(12-crown-4)2 and Rb+(12-crown-4)2. The SC+ unit with the larger alkali metal cation gave a stress to the Ni(dmit)2 column, and the SC+ structure changed the pi-pi overlap mode and electrically conducting behavior.