UV‐Visible Spectroelectrochemical Detection of Side‐Reactions in the Hexacyanoferrate(III)/(II) Electrode Process

Hexacyanoferrate(III)/(II) system has been studied by UV‐visible long‐pathway spectroelectrochemistry. Three different methodologies, based on potentiodynamic techniques, have been successfully used in the thermodynamic characterization of the system. Formation of soluble Prussian Blue has been detected during the electrode process. The values of the formal potential (E^0′=0.200 V) and the electron stoichiometry of this side‐reaction (n=0.5) have been obtained.     

Americium(III) Adsorption on Polyethylene from very Dilute Aqueous Solutions

The Am(III) adsorption from very dilute aqueous solutions on polyethylene was studied as a function of the pH value, the composition of dissolved salts and the presence or absence of adsorbent SiO₂. It was found that the Am(III) adsorption on polyethylene is decreased with increasing H⁺ concentration and dissolved salt concentrations and in the presence of SiO₂ as an adsorbent. The mechanisms of Am(III) adsorption on polyethylene were discussed. Based on the observations in this paper, extreme care is necessary to minimize and correct the Am(III) adsorption on the container walls in order to improve the accuracy of Am(III) distribution coefficient (K _d) between a solid and an aqueous solution.     

Determination of Electrochemical Electron‐Transfer Reaction Standard Rate Constants at Nanoelectrodes: Standard Rate Constants for Ferrocenylmethyltrimethylammonium(III)/(II) and Hexacyanoferrate(III)/(II)

The most common approximation of electroneutrality is inappropriate for analyzing the voltammetric response of nanoelectrodes. Therefore, the microelectrode theory for extracting the standard rate constant k⁰ for electron transfer from steady‐state voltammograms is invalid for nanoelectrodes. Unlike previous approaches, we considered the influence of the interfacial potential distribution caused by the absence of electroneutrality. We estimated the magnitude of the error at low overpotential incurred as a result of ignoring the absence of electroneutrality and found that it was small. In this region, electrochemical reaction appears to be limited by the rate of electron transfer. Under these conditions, k⁰ can be obtained from steady‐state voltammogram data in a low overpotential region according to an approximate form of the Butler–Volmer equation. This procedure can greatly simplify analysis and calculation of the rate constant k⁰ at nanoelectrodes. Steady‐state voltammogram of equal‐concentration hexacyanoferrate(III)/(II) (Fe(CN) /Fe(CN) ) and ferrocenylmethyltrimethylammonium(III)/(II) (FcTMA²⁺/FcTMA⁺) redox couples were investigated at Pt? Ir nanoelectrodes in the presence of a support electrolyte. k⁰ for Fe(CN) /Fe(CN) and FcTMA²⁺/FcTMA⁺ at Pt? Ir nanoelectrodes were evaluated.     

Radiation Effect on Concentrated Potassium Hexacyanoferrate(II) Solutions

Neutron irradiation was carried out on 0.2, 0.4 and 0.7 M solutions of potassium hexacyanoferrate(II) at the pH range of 2-10. Fe(CN)₅^1? was found when pH<5; which is consistent with the oxidation potential consideration of the slow reaction between Fe(CN)₅^4? and OH. Fe(OH), was precipitated in the whole range of pH studied. Chemical and radiochemical yields were compared.     

Complexation of Chlorodiethylenetriaminegold(III) with Chloride Ions in Aqueous Solutions

The reaction of Au(Dien)Cl²⁺ (Dien is diethylenetriamine) with the chloride ion was studied spectrophotometrically in an aqueous solution at I = 1.0 mol/l and T = 20°C. The formation constant of pentacoordinated Au(Dien)Cl ₂ ⁺ was determined and its spectrum was calculated.     

Complexation of Arabinogalactan with Copper(II) Ions in Aqueous Solutions

Complexation of Cu(II) with arabinogalactan as influenced by solution pH was studied by spectrophotometry and the method of dialysis equilibrium. Copper ions form complexes with arabinogalactan in a wide pH range, pH 5.0-12.5. Arabinogalactan forms two complex species with the metal. The composition and formation constant of the complex formed at pH <10.8 were determined.     

The Mediation Effect of a Polyaniline-Coated Electrode on the Reduction of Iron (III) Ions

The mediation effect of polyaniline-coated platinum electrodes on the reduction of iron(III) ions was studied by the cyclic voltammetry and rotating disk electrode methods. The rate constants of the cross reaction between iron(III) ions and polyaniline (PA) were found to depend upon the amount of PA coated on the electrode. On the basis of the rate constants the PA-coated electrode mediates the reduction of iron(III) ion efficiently and behaves as well as a metallic electrode.     

The Solid State Electrochemistry of Dysprosium(III) Hexacyanoferrate(II)

A new electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, dysprosium hexacyanoferrate (DyHCF), was prepared chemically and characterized using techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), UV‐vis spectrometry and X‐ray photoelectron spectroscopy (XPS) etc. The cyclic voltammetric behavior of DyHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 217 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 M NaCl solution and the redox peak currents increased linearly with the square root of the scan rates.     

Sorption of Hexacyanoferrate(II,III) Anions on Nickel(II) Hydroxide

Fe(CN)₆ ^{3 -} and Fe(CN)₆ ^{4 -} anions are sorbed from aqueous solutions of their potassium and cesium salts on -Ni(OH)2 by the mechanism of anion exchange with hydroxy groups. Alkali metal cations (K⁺, Cs⁺) are also partly sorbed on nickel(II) hydroxide in the form of anionic complexes (K,Cs) _z Fe(CN)₆ ^{(n - z)-}, where n = 3 or 4 (0 < z < n). The chemical composition of the new phase appearing in contact of nickel(II) hydroxide with aqueous potassium and cesium hexacyanoferrates(II, III) was determined by X-ray phase analysis and IR spectroscopy.     

Cu(II) Hexacyanoferrate(III) Modified Carbon Paste Electrode; Application for Electrocatalytic Detection of Nitrite

Copper hexacyanoferrate (CuHCF) film‐modified carbon paste electrode (CPE) has been prepared from various electrolytic aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms showed the direct deposition of CuHCF films from the mixing of Cu²⁺ and Fe(CN)₆^3? ions and each time with one of the six cations: H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, and Al³⁺. The CuHCF film showed a single redox couple that exhibited a cation effect (Na⁺, K⁺, Mg²⁺, and NH₄⁺) and anion effect (Cl^?, NO₃^?, SO₄^2?, ClO₄^?, and BrO₃^?) in the cyclic voltammograms. Voltammetric studies have indicated that in presence of nitrite, the cathodic peak current of CuHCF increases, followed by a decrease in the corresponding anodic current. This indicated that nitrite was reduced by the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The process of reduction and its kinetics were investigated by using cyclic voltammetry, differential pulse voltammetry, chronoamperometry and chronocoulometry techniques. The electrocatalytic ability about 800 mV can be seen. The rate constant of the catalytic reduction of nitrite was found to be 7.9×10⁵ cm³ mol^?1 s^?1. Linearity range obtained was 5×10^?5?8.4×10^?3 by cyclic voltammetry and 8×10^?6?1.3×10^?3 and 4×10^?3?2×10^?2 by differential pulse voltammetry.     

Preparation of Graphene Oxide-Maghemite-Chitosan Composites for the Adsorption of Europium Ions from Aqueous Solutions

The adsorption of Eu(III) on composites synthesised from graphene oxide (GO), maghemite (MGH), and chitosan (CS) has been studied using different approaches. The physicochemical and morphological characteristics of the composites GO-MGH, GO-CS, GO-MGH-CS I, II, and III were determined by XRD, Mössbauer spectroscopy, FTIR, Raman spectroscopy, and TEM. According to the results of batch experiments, the maximum experimental adsorption capacity was 52, 54, 25, 103, and 102 mg/g for GO-MGH, GO-CS, GO-MGH-CS I, II, and III, respectively. The data obtained are in better agreement with the Langmuir, pseudo-second-order, and pseudo-first-order models only for GO-MGH. Thus, the adsorption of Eu(III) on the composites was a favourable, monolayer, and occurred at homogeneous sites. The nature of adsorption is chemical and, in the case of GO-MGH, physical. Tests of the composites in natural waters showed a high removal efficiency for Eu(III), Pu(IV), and Am(III), ranging from 74 to 100%. The ANFIS model has quite good predictive ability, as shown by the values for R², MSE, SSE, and ARE. The GO-MGH-CS composites with the high adsorption capacity could be promising candidates for the removal of Eu(III) and the pre-concentration of Pu(IV) and Am(III) from natural waters.     

亚砜类非离子型表面活性剂在固/液界面上的吸附(III)碳黑/水溶液界面上的吸附

研究了癸基甲基亚砜在水溶液/炭黑界面上的吸附及温度、加盐(Nacl)、加酸(HCl)对吸附的影响.吸附等温线呈完整的双平台形式. 第一平台吸附量～6 μmol·m~(-2); 第二平台吸附量,即极限吸附量, 为42—48 μmol·m~(-2). 随着吸附增加, 炭黑/水溶液接触角下降, 润湿性, 悬浮性改善.应用两阶段吸附模型和吸附等温线通用公式可以对实验结果作定性和定量的解释. 提供了吸附热力学数据. 指示吸附第二阶段是与体相中表面活性剂胶团化作用相似的熵驱动过程。     

Removal of Chromium(III) and Cadmium(II) Heavy Metal Ions from Aqueous Solutions Using Treated Date Seeds: An Eco-Friendly Method

The aim of the research was to prepare low-cost adsorbents, including raw date pits and chemically treated date pits, and to apply these materials to investigate the adsorption behavior of Cr(III) and Cd(II) ions from wastewater. The prepared materials were characterized using SEM, FT-IR and BET surface analysis techniques for investigating the surface morphology, particle size, pore size and surface functionalities of the materials. A series of adsorption processes was conducted in a batch system and optimized by investigating various parameters such as solution pH, contact time, initial metal concentrations and adsorbent dosage. The optimum pH for achieving maximum adsorption capacity was found to be approximately 7.8. The determination of metal ions was conducted using atomic adsorption spectrometry. The experimental results were fitted using isotherm Langmuir and Freundlich equations, and maximum monolayer adsorption capacities for Cr(III) and Cd(II) at 323 K were 1428.5 and 1302.0 mg/g (treated majdool date pits adsorbent) and 1228.5 and 1182.0 mg/g (treated sagai date pits adsorbent), respectively. It was found that the adsorption capacity of H₂O₂-treated date pits was higher than that of untreated DP. Recovery studies showed maximal metal elution with 0.1 M HCl for all the adsorbents. An 83.3–88.2% and 81.8–86.8% drop in Cr(III) and Cd(II) adsorption, respectively, were found after the five regeneration cycles. The results showed that the Langmuir model gave slightly better results than the Freundlich model for the untreated and treated date pits. Hence, the results demonstrated that the prepared materials could be a low-cost and eco-friendly choice for the remediation of Cr(III) and Cd(II) contaminants from an aqueous solution.     

Thermodynamic and Kinetic Studies for the Adsorption of Fe(III) and Ni(II) Ions From Aqueous Solution Using Natural Bentonite

In this study, the adsorption behavior of natural bentonite with respect to Fe(III) and Ni(II) has been studied in order to consider its application to purity metal finishing wastewaters. During the adsorption process, batch technique is used, and the effects of pH, bentoite amount, temperature, heavy metal concentration, bentonite treatment (calcinations of natural bentonite at 700°C, washing by deionized water to remove the excess salt from bentonite surface), and agitation time on adsorption efficiency are studied. The washed and calcined bentonite samples were labeled by WB and CB, respectively. The pH-dependence of Fe(III) and Ni(II) sorption on the bentonite is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. It was determined that adsorption of Fe(III) and Ni(II) is well fitted by the second order reaction kinetic. Furthermore, the sorption rate of Fe(III) was higher than the sorption rate of Ni(II). Adsorption of Fe(III) and Ni(II) on NB appeared to follow Langmuir isotherm. In addition, calculated and experimental adsorbed amounts of Fe(III) by the unit NB mass are very higher than Ni(II). The paper also discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Also the adsorption capacity of bentonite for Fe(III) Ni(II) and increases with increased bentonite dose. According to the equilibrium studies, the selectivity sequence can be given as Fe(III) > Ni(II). The adsorbed amount of Fe(III) and Ni(II) on washed bentonite (WB) were very higher compared to NB and CB. Our results show that bentonite could especially WB be considered as a potential adsorbent for Fe(III) and Ni(II) removal from aqueous solutions.     

Redox conversions in crystalline compounds based on macrocyclic complexes of nickel(II)/(III) and aromatic carboxylates

It is shown that conversion of nickel(II) complexes, in the composition of crystalline compounds of various structures, into nickel(III) leads to the preparation of new redox-active metal-organic skeletons. The structure of the chromophore of the metal ion and the chemical properties of the compounds formed by this process (thermal stability, reactivity) depend to an important extent on the nature of the construction blocks which makes possible the creation of new materials with controlled properties.     

The Mercury(II) Catalyzed Ligand Exchange Between Hexacyanoferrate(II) and Pyrazine in Aqueous Medium

The kinetic and mechanistic studies of Hg^II catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by pyrazine (Pz) were monitored by following the appearance of the yellow complex [Fe(CN)₅Pz]³⁻ at 440 nm corresponding to metal ligand charge transfer (MLCT) transitions at temp=25.0±0.1 °C, pH=2.5±0.02 and ionic strength, I=0.1 m (KNO₃). The effect of pH, ionic strength and the concentrations of [Fe(CN)₆]⁴⁻ and Pz on the rate of reaction were also studied and explained. To investigate the dependency of catalytic activity of Hg^II, the initial rates were determined at several concentrations of Hg^II, keeping the concentration of other reactants constant. The kinetic observations suggest that the substitution follows an interchange dissociative (I_d) mechanism and proceeds via formation of a solvent-bound intermediate. The repetitive spectral scan is also provided as evidence for the exchange of cyanide ions by pyrazine in [Fe(CN)₆]⁴⁻. Activation parameters have also been evaluated and provided support for the proposed mechanistic scheme.     

孔结构对活性炭吸附水溶液中铅离子的影响

选取三种表面化学性质相近的活性炭(AC),通过等温吸附实验考察活性炭对水溶液中铅离子的吸附性能,利用扫描电子显微镜(SEM)观察活性炭的表面微观形貌,通过低温(77 K)液氮吸附测定活性炭的比表面积和孔容,并分别以密度泛函理论(DFT)和Barrett-Joyner-Halenda (BJH)法计算微孔和中孔的孔径分布.结果表明:选用的三种活性炭AC1、AC2、AC3在比表面积和总孔容上呈依次下降的趋势,但表面开放孔均匀分布的AC2,具有最高的饱和吸附量,孔结构类似颗粒堆积孔的AC3,具有与表面开放孔分布集中的AC1相近的饱和吸附量;通过对孔结构与吸附量的关联分析可知,在活性炭吸附铅离子的过程中, 0.4-0.6 nm的孔是有效吸附孔, 10.5-20.6 nm、20.6-55.6 nm、5.2-10.5 nm三个区间的孔则会对吸附产生阻碍作用.     

Complexation of Cobalt(II) with Thiocyanate Ions in Aqueous Solutions of Nonionogenic Surfactants

The formation of tetrahedral cobalt(II) thiocyanate complexes in aqueous solutions of nonionogenic surfactants was studied using electronic spectroscopy. The equilibrium constants were calculated in the framework of different schemes of complexation reactions. The influence of such factors as the oxyethylene chain length and the size of the alkyl substituent of the surfactant on the stability of the complexes was examined.