Sorption Capacity and Selectivity Relative to Metal Ions for Oxidized Carbon Sorbents with Different Numbers of Oxygen-Containing Groups

We have determined the sorption capacity and selectivity for a broad range of metal ions (alkali, alkaline-earth, transition metal, noble metals, etc.) in two-component and multicomponent mixtures of oxidized carbon sorbents with different numbers of oxygen-containing surface functional groups. We discuss the reasons for the observed changes, their connection with the nature and number of oxygen-containing surface functional groups, and the possibilities for practical application.     

High-Performance Chelation Chromatography of Metal Ions on Sorbents with Grafted Iminodiacetic Acid

The chromatographic behavior of some alkaline-earth, transition, heavy, and rare-earth metals on a number of complexing sorbents containing surface iminodiacetic acid (IDA) functional groups is studied. The conditions under which metal retention is determined by complexation on the sorbent surface were established, and the main principles of a new variant of the liquid chromatography, i.e., high-performance chelation ion chromatography (HPCIC), are formulated. The efficiency and selectivity of separation of the metal ions are considered depending on the type of the IDA bonding, the sorbent matrix parameters, the eluent composition, and the temeprature of the chromatographic column. Under optimal conditions, the metal retention is shown to linearly correlate with the stability constants of the respective complexes in the double-logarithmic scale. The application of HPCIC to the analysis of multicomponent systems is considered.     

Metal complexes of 1-oxa-4,7,10-triazacyclododecane-N,N',N''-triacetic acid

The macrocyclic complexone 1-oxa-4,7,10-triazacyclododecane-N,N',N'-triacetic acid (cODTA) has been synthesized and its protona constants, stability constants of metal complexes and enthalpy changes for the formation of alkaline-earth complexes have been determined. Although it is not so powerful a complexing agent as the N-acetate derivative of the corresponding tetra-aza macrocycle, cDOTA, this is still one of the strongest complexones known, particularly towards the alkaline-earth metals. The complexes of the transition metals are also very stable and there is an inversion of the Irving-Williams order of stability for the complexes of cobalt and nickel.     

New copolymer gels based on <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylacrylamide and crown-containing allyl derivative of 1,8-naphthalimide as optical sensors for metal cations in an organic medium

New copolymer gels bases on N,N-dimethylacrylamide and a crown-containing allyl derivative of 1,8-naphthalimide showing intense visible fluorescence have been prepared. The effect of metal cations on the optical properties of the fluorescent monomer and its copolymer gels has been studied. These gels have been found to exhibit optical response selectivity with respect to binding of alkaline-earth metals in an acetonitrile medium.     

Chasing Multiple Bonding Interactions between Alkaline-Earth Metals and Main-Group Fragments

Formally dianionic ligands such as alkylidenes or organoimidos play a major role in the organometallic chemistry of transition metals and are an emerging topical area of f-element chemistry. The pursuit and development of main-group-metal congeners has been tackled sporadically but is clearly lacking behind. The pronounced ionic bonding in particular, prevailing in alkali and alkaline-earth (Ae) metal derivatives, proved cumbersome. Recent substantial progress in the respective field of divalent Ae chemistry has been triggered by the implementation of new synthesis strategies involving new Ae^II precursors and tailor-made ligands. The main emphasis of this Minireview will be on the synthesis and reactivity of well-defined Group 2 alkylidenes, organoimides, silylenes, and phosphandiides.     

Solid-state ion-selective electrodes as end-point detectors in compleximetric titrations : Part III. Selection of some experimental conditions for back-titrations in alkaline medium

The applicability of the copper(II) solid-state electrode in alkaline medium for compleximetric back-titrations of the alkaline-earth metals with EDTA and EGTA has been studied. Copper(II) is used as the back-titrant. Special attention is given to the use of ammonia and cyclohexylamine as the buffer substance.     

A cyclopendant complexon based on dibenzo-18-crown-6

A derivative of dibenzo-18-crown-6 containing dihydroxyphosphorylmethyl groups in the 4, 5, 4′, and 5′ positions of the benzene ring has been synthesized. Unlike dibenzo-18-crown-6, its phosphorylated derivative does not form stable complexes with cations of alkali and alkaline-earth metals. Complexes with transition metals are water-insoluble in most cases. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1789–1791. September, 1998.     

Influence of the preparation method on the textural properties of zirconia

Summary New composite sorbents &quot;chlorides of alkaline-earth metals confined to porous alumina&quot; were synthesized and tested for ammonia abatement in a fixed-bed flow adsorber at 25-300°C. It was found that the matrix modification with the salts leads to an increase in its dynamic sorption capacity in the row BaCl₂ < CaCl₂ < MgCl₂. This can be caused by a salt-ammonia interaction that results in the formation of ammonia complexes. The dynamic capacity was found to strongly decrease with temperature. The maximal sorption capacity was detected for a sorbent based on MgCl₂. It equals 58.6 and 11.6 mg/g at T = 25 and 300°C, respectively, or 3.2 and 0.6 mole of ammonia per 1 mole of the salt. The data obtained can be used for the analysis of the dynamic behavior of the new sorbents in flow systems for the ammonia removal from gas mixtures, which can be of high interest for gas separation, chemical engineering and catalysis.     

The Valence Orbitals of the Alkaline-Earth Atoms

Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca₆H₉[N(SiMe₃)₂]₃(pmdta)₃ (pmdta=N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n−1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies.     

Simultaneous determination of uranium and thorium with Arsenazo III by second-derivative spectrophotometry

A derivative spectrophotometric method has been developed for the simultaneous determination of microgram quantities of uranium and thorium with Arsenazo III in hydrochloric acid medium. The second-derivative absorbances of the uranium and thorium Arsenazo III complexes at 679.5 and 684.4 nm are used for their quantification. Uranium and thorium, both in the range 0.1-0.7 mug/ml have been determined simultaneously with good precision. The procedure does not require separation of uranium and thorium, and allows the determination of both metals in the presence of alkaline-earth metals and zirconium, but lanthanides interfere.     

Dumbbells of Five-Connected Silicon Atoms and Superconductivity in the Binary Silicides MSi(3) (M = Ca, Y, Lu)

The new metastable binary silicides MSi(3) (M = Ca, Y, Lu) have been synthesized by high-pressure, high-temperature reactions at pressures between 12(2) and 15(2) GPa and temperatures from 900(100) to 1400(150) K. The atomic patterns comprise intricate silicon layers of condensed molecule-like Si(2) dimers. The alkaline-earth element adopts the oxidation state +2, while the rare-earth and transition metals realize +3. All of the compounds exhibit BCS-type superconductivity with weak electron-phonon coupling below critical temperatures of up to 7 K.     

Thermal decomposition study of sewage sludge and of organicwaste used in the sorption of metals

The conventional treatments of effluents containing heavy metals produce significant quantities of byproducts with recalcitrant characteristics, making necessary looking after alternative techniques in order to avoid the production of new contaminated residues. Sorption process of chromium and zinc in vertical columns loaded with sewage sludge and organic solid waste has been studied in this work. The data from the TG curves of the two sorbents presented significant differences when they were submitted to the metal uptake, being noticed the displacement of the thermal events towards lower temperatures for both types of sorbents studied. As it was expected, for both sorbents, an increase in the mass of samples has been observed at the completion of the thermal tests upon metal uptake. Therefore, these facts demonstrate that during the biosorption process a physico-chemical interaction took place between sorbents and metals, as it was evidenced by the more than 100 K increase in the decomposition temperatures as well as the variation of the ΔH values of the samples.     

A selective sorbent for concentrating noble metals

New chelating sorbents have been synthesized by aminating chloromethylated styrenedivinylbenzene macroporous copolymers with 3(5)-methylpyrazole. The sorption of noble metals from acid solutions and the selectivity has been studied. The sorbents are of interest for selective concentration and extraction of the noble metals.     

Preparation and Ion-Exchange Properties of Mixed Zirconium(IV) Phosphate-Phosphonate Sorbents

Composite sorbents based on Zr(IV) phosphate-hydroxyethylidenediphosphonate with different phosphate-phosphonate ratio were prepared. These sorbents were characterized by elemental analysis, X-ray diffraction, and IR spectroscopy, and their ion-exchange sorption capacity for several transition metals and strontium was studied. The sorption capacity of these sorbents increases with increasing pH.     

Metal-free, aerobic dioxygenation of alkenes using simple hydroxamic acid derivatives

The dioxygenation of alkenes using molecular oxygen and a simple hydroxamic acid derivative has been achieved. The reaction system consists of readily prepared methyl N-hydroxy-N-phenylcarbamate and molecular oxygen with a radical initiator, offering an alternative to common dioxygenation processes catalyzed by precious transition metals. This transformation capitalizes on the unique reactivity profile of hydroxamic acid derivatives in radical-mediated alkene addition processes.     

基于过渡金属二硫族化物析氢催化的研究进展

解决全球气候变化和能源危机的有效途径之一是用氢能源(H₂)代替传统的化石能源. 析氢反应(Electrochemical hydrogen evolution reaction, HER) 被认为是绿色环保的可持续产氢途径, 通常电解过程需要催化剂以降低电化学电位, 提高能量利用效率. 目前最先进的催化剂仍然依赖于贵金属, 但是研究表明, 过渡金属二硫族化物(Transition metal dichalcogenides, TMDs)同样具有优异的催化活性, 与贵金属相比, TMDs产量大、 价格低、 催化活性好、 便于调控和修饰, 有望替代贵金属在催化领域的应用. 基于此, 本文讨论了近年来TMDs在析氢方面的研究情况以及TMDs材料的性能调控, 包含原子工程、 相工程和异质结. 并总结和展望了TMDs催化材料的挑战与机遇.     

CC bond formation in diiron complexes

The growing effort to design new sustainable synthetic methodologies, based on readily available and environmentally friendly transition metals, has boosted research on iron complexes. This review article focuses on C?C-bond-forming reactions occurring at bridging ligands in diiron complexes, aimed at evidencing distinctive aspects and advantages associated with the presence of two adjacent iron centres. A number of diiron-mediated C?C-bond-forming reactions reported in the literature, including nucleophilic and electrophilic additions and insertion and cycloaddition reactions, have been accumulated over the years, which, together with more recent developments, indicate that diiron complexes might provide promising alternatives to precious metals in the challenging field of metal-promoted C?C bond formation.     

Recent advances in the determination of the platinum group elements and gold

Accurate determinations of the platinum group elements (PGEs) and gold, known as the precious metals, have always been difficult tasks. The metals are often present at trace levels in sample types of complex composition. This situation has improved recently due to developments of instrumental methods and their applications to analyses of the precious metals in a variety of matrices. Attention has been given to determinations of traces of precious metals in biological, clinical and environmental samples. Foremost in importance is inductively coupled plasma mass spectrometry (ICP-MS) which has provided a sensitive means of simultaneous determination of traces of PGEs and gold. Important extensions and improvements in atomic absorption spectrometry (AAS), nuclear and electrochemical methods have been reported also. More research on sample treatments, especially fire assays, applied to PGEs has been carried out. Chlorination has proven to be a viable alternative to fire assays for preconcentration of PGEs and gold in analyses of geological materials. In addition, the recent availability of some additional reference materials will be of great assistance in research work on precious metals.     

Role of macrocyclic effect in complex formation of palladium(II) with ligands anchored on a solid support

The method for grafting dithiacrown ether and its linear analogue to the silica surface using preliminary prepared organosilicon derivative is developed. The importance of the acylation step in the process of grafting is underlined. The acylation is required to prevent sorption of platinum metals complex anions by the anion exchange mechanism, the probability of which increases due to protonation of the spacer in an acidic medium. The interaction of palladium(II) with anchored ligands in hydrochloric acid media was studied in details. The comparative study of two sorbents revealed that the macrocyclic effect plays a negligible role in binding of palladi um(II) ions. Therefore, linear ligands are preferred for the development of sorbents for molecular recognition of platinum metals ions.     

Determination of ruthenium and tin on electrochemical anodes by energy-dispersive X-ray fluorescence

"Dimensionally Stable Anodes" (DSA)(R) have gained wide acceptance in electrochemical production of chlorine and caustic soda. The DSAs are usually composed of electrocatalytic layers of precious and non-precious metal oxides produced by thermal decomposition of salts on a valve-metal substrate (e.g., titanium). They have long lifetimes (some years) in commercial service, and accelerated aging is used in testing them. In these tests the cell potential is stable for most of the anode life. Failure of an anode is characterized by a rapid increase in potential to beyond the point of practical operation of the cell. Non-destructive X-ray techniques have been utilized to investigate the mechanism involved. It has been established that the precious metal content has been reduced by 50-60% when the anodes fail. Although present DSA coatings are more than adequate for commercial applications, there is continuing interest in improving them. The materials for DSA formulation include the precious metals iridium, ruthenium and rhodium, the non-precious metals tin, antimony and manganese, and the valve metals titanium and tantalum.