The effect of natural organic matter on the formation and solubility of M(OH)4 solid phases

In this study the formation of M(OH)₄ solid phases (e.g. Th(IV), Ce(IV) and Zr(IV)) has been investigated as a function of the natural organic matter (NOM) concentration in 0.1 M NaClO₄, in the pH range between 2 and 5, and under normal atmospheric conditions. M(OH)₄ has been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, XPS and solubility measurements. According to the experimental data M(OH)₄ is stable and is the solubility limiting solid phase even in the presence of increased humic acid concentration in solution. In contrast to MO₂(OH)₂ and M(OH)₃ solid phases, increasing humic acid concentration does not affect the crystallite size and the solubility product of M(OH)₄. The M(OH)₄ solubility is basically pH depended and governed by the presence of colloidal species. Regarding the effect of NOM on the solid phase formation of redox-sensitive M(IV) ions (e.g. Ce(IV)), it could be shown that the amount of the reduced metal-ion (e.g. Ce(III)) in the solid phase depends linearly from the NOM concentration in the test solutions.     

Raman and UV–vis spectroscopy studies on luteolin–Al(III) complexes

Luteolin is one of the most common flavonoids, but its ability to complex metal ions (e.g. aluminum) is still being discussed. This work presents the results of structural investigation of the luteolin–Al(III) complexes in methanol:water solutions and in the solid state. The analysis was carried out using UV–vis and FT-Raman spectroscopy accompanied by Factor Analysis, deconvolution and quantum-chemical calculations. It was found that in acidic solutions two complexes of luteolin–Al(III) of 1:1 and 1:2 ligand:metal ratio are formed, where luteolin is one- and twofold deprotonated, respectively. Additionally, a third complex precipitated from a basic solution of 1:2 stoichiometry with a threefold deprotonated ligand was obtained.     

Investigation of the Cr(VI) removal from aqueous solutions by stabilized iron-nanoparticles using 51Cr-tracer

Stabilized iron-nanoparticles were used for the Cr(VI)-removal from acidic and neutral aqueous solutions (pH 1, 3, 5 and 7). The chromium interaction with the iron-nanoparticles was studied by a batch technique under different experimental conditions (e.g. pH, temperature, contact time, solid to liquid ratio) using ⁵¹Cr as radiotracer and gamma-ray spectroscopy. The results showed that the Cr-removal was fast and the interaction kinetics could be described by a pseudo-second order rate equation. The maximum Cr-removal was observed from solutions of initial pH 3. The sorption showed a positive temperature and solid to liquid ratio dependence. The experimental results were modeled using the Langmuir, Freundlich and Dubinin–Radushkevich isotherm equations and compared with literature data obtained using other sorbents. X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the mechanism of the Cr-removal by the iron-nanoparticles. It was demonstrated that the dominated process based on the Cr(VI) reduction followed by the simultaneous oxidation of iron.     

Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications.     

The detection of biomarkers in evaporite matrices using a portable Raman instrument under Alpine conditions

The binding of rhodamine 6G and hydroxy propyl β-cyclodextrin (Hβ-CD) was investigated measuring fluorescence and absorption at pH 7.0. The solid inclusion complex of Rh6G and Hβ-CD has been studied by Ultraviolet (UV) spectroscopy, Fluorimetry, Fourier Transform Infrared (FTIR), (1)H Nuclear Magnetic Resonance ((1)HNMR) and in the Scanning Electron Microscope (SEM). Association constant K(g) and K(e) were determined by the enhancement of the fluorescence of rhodamine 6G in the presence of Hβ-CD. Fluorescence of Rh6G is generally enhanced, in complexes of Rh6G and β-Cyclodextrin in aqueous solutions. The free energy change for the ground state (ΔG(g)) and for the excited state (ΔG(e)) have also been determined. The experimental results indicated that the inclusion process is an exothermic and spontaneous.     

X-Ray Spectra and Electronic Structure of 3C SiC and BN Based Solid Solutions

The local coherent potential approximation is used in the framework of multiple-scattering theory to calculate the electronic energy structure of solid solutions of silicon carbide Si_1-xCR_x and boron nitride BN_1-xR_x and B_1-xNR_x (x = 0-0.75, R = C, Al, Ti) in a diamond-like modification. The total and partial densities of states are calculated for each atom in the solid solutions. The crystal potential is evaluated in an MT approximation. The lattice parameter is determined by Vegard's rule. The electronic energy structures of the solid solutions are compared with each other and with binary analogs in the framework of one approximation. The calculated partial densities of states are compared with the experimental X-ray spectra of silicon in the compounds. The calculation of the partial charges of atoms at the top of the valence band showed that the charge transfer (0.35 e) from boron to nitrogen in binary 3C BN changes sign in B_0.75NC_0.25. In the latter system, nitrogen donates 0.19 e to boron, and carbon acts as a donor for the electronic configurations of boron and nitrogen. An electronic structure analysis of the solid solutions indicates that the quasicore resonance states inherent in the binary compounds are delocalized, probably because of the weakening of chemical binding in the solid solutions.     

Applications of inductively coupled plasma mass spectrometry and laser ablation inductively coupled plasma mass spectrometry in materials science

Inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) have been applied as the most important inorganic mass spectrometric techniques having multielemental capability for the characterization of solid samples in materials science. ICP-MS is used for the sensitive determination of trace and ultratrace elements in digested solutions of solid samples or of process chemicals (ultrapure water, acids and organic solutions) for the semiconductor industry with detection limits down to sub-picogram per liter levels. Whereas ICP-MS on solid samples (e.g. high-purity ceramics) sometimes requires time-consuming sample preparation for its application in materials science, and the risk of contamination is a serious drawback, a fast, direct determination of trace elements in solid materials without any sample preparation by LA-ICP-MS is possible. The detection limits for the direct analysis of solid samples by LA-ICP-MS have been determined for many elements down to the nanogram per gram range. A deterioration of detection limits was observed for elements where interferences with polyatomic ions occur. The inherent interference problem can often be solved by applying a double-focusing sector field mass spectrometer at higher mass resolution or by collision-induced reactions of polyatomic ions with a collision gas using an ICP-MS fitted with collision cell. The main problem of LA-ICP-MS is quantification if no suitable standard reference materials with a similar matrix composition are available. The calibration problem in LA-ICP-MS can be solved using on-line solution-based calibration, and different procedures, such as external calibration and standard addition, have been discussed with respect to their application in materials science. The application of isotope dilution in solution-based calibration for trace metal determination in small amounts of noble metals has been developed as a new calibration strategy. This review discusses new analytical developments and possible applications of ICP-MS and LA-ICP-MS for the quantitative determination of trace elements and in surface analysis for materials science.     

Monitoring surface metal oxide catalytic active sites with Raman spectroscopy

The molecular aspect of the Raman vibrational selection rules allows for the molecular structural and reactivity determinations of metal oxide catalytic active sites in all types of oxide catalyst systems (supported metal oxides, zeolites, layered hydroxides, polyoxometalates (POMs), bulk pure metal oxides, bulk mixed oxides and mixed oxide solid solutions). The molecular structural and reactivity determinations of metal oxide catalytic active sites are greatly facilitated by the use of isotopically labeled molecules. The ability of Raman spectroscopy to (1) operate in all phases (liquid, solid, gas and their mixtures), (2) operate over a very wide temperature (-273 to >1000 °C) and pressure (UHV to ?100 atm) range, and (3) provide molecular level information about metal oxides makes Raman spectroscopy the most informative characterization technique for understanding the molecular structure and surface chemistry of the catalytic active sites present in metal oxide heterogeneous catalysts. The recent use of hyphenated Raman spectroscopy instrumentation (e.g., Raman-IR, Raman-UV-vis, Raman-EPR) and the operando Raman spectroscopy methodology (e.g., Raman-MS and Raman-GC) is allowing for the establishment of direct structure-activity/selectivity relationships that will have a significant impact on catalysis science in this decade. Consequently, this critical review will show the growth in the use of Raman spectroscopy in heterogeneous catalysis research, for metal oxides as well as metals, is poised to continue to exponentially grow in the coming years (173 references).     

Determination of Co,Cr, Mn and Ni traces in fluorine containing materials for optical fibers using laser enhanced ionization techniques with flame and rod-flame atomizers

Two fluorine-containing materials (NH₄F and NaF) for optical fiber production have been analyzed with respect to their contents of Co, Cr, Mn and Ni using two different laser enhanced ionization (LEI) techniques, one using a rod-flame as an atomization-ionization system and one using a flame as the atomizer. One advantage of the rod-flame system is that it can separate the evaporation and atomization steps which thereby leads to a reduction of the influences of matrices. Another advantage is that it can be used for analysis of both solid and liquid samples. The NH₄F sample was analyzed as a solid and also as a solution (dissolved to 50 or 100 g/l in water). In the flame atomizer the NH₄F matrix created a non-selective ionization background giving detection limits in the order of tens of ng/g (concentrations in the solid sample). Using the rod-flame system, however, it was found that Cr, Mn, and Ni could be determined in the NH₄F sample down to a few ng/g by analysis of the sample solutions without any need for preconcentration procedures. Direct analysis of solid samples, without any sample preparation, could also be done using the rod-flame system with a ten-fold improvement in detectability. The detection limits for analysis of the solid samples were estimated to be the following: Co, 1 ng/g; Cr, 0.2 ng/g; Mn, 0.3 ng/g; and Ni, 0.08 ng/g. The NaF sample was more complicated to analyze. When using the flame, a significant ionization background was obtained even for solutions diluted down to 0.2 g/l. However, using the rod-flame system, analysis of the elemental content of the NaF sample could be performed. Detection limits in the range of tens of ng/g could be obtained from diluted solutions (≤20 g/l). It was found that the NH₄F and NaF material contained the following concentrations of impurities (HN₄F: Cr, 70 ± 5 ng/g; Mn, 88 ± 6 ng/g; and Ni, 56 ± 5 ng/g. NaF: Cr, 290 ± 70 ng/g; Mn, 40 ± 15 ng/g; and Ni 2200 ± 400 ng/g). For the case of Co, only an upper limit could be assessed (<1 ng/g for NH₄F and <70 ng/g for NaF).     

Unanticipated guest motion during a phase transition in a ferroelastic inclusion compound

Urea inclusion compounds (UICs) have been used as tools to understand ferroelastic domain switching and molecular recognition during crystal growth. Although the vast majority of UICs contain helical arrangements of host H-bonds, those containing guests with the formula X(CH(2))(6)Y (X, Y = Br, Cl, CN, NC) adopt an alternative P2(1)/n packing mode in which the host molecules exist as stacked loops of urea hexamers. Such structures may be further separated into two classes, ones distorted away from hexagonal symmetry along [100] (Br(CH(2))(6)Br, Br(CH(2))(6)Cl, and Cl(CH(2))(6)Cl) and those distorted along [001] (e.g. NC(CH(2))(6)CN). In each of these systems, guests exist as equilibrium mixtures of gauche conformers whose populations control the direction and magnitude of the observed distortion. Such UICs are potentially ferroelastic, but the n-glide requires that domains are not related by a simple rotation-translation mechanism as in the helical systems. Ferroelastic (degenerate) domain reorientation would necessitate a large-scale reorganization of the urea framework and rupture of numerous H-bonds. Coupled with distortions of 2 to 10%, this mechanism-based barrier to domain switching has precluded observation of this phenomenon. To prepare ferroelastic UICs with minimal distortions from hexagonal symmetry, attempts were made to form solid solutions of UICs containing guests from the two classes. This failed, however: solid solution formation of the stacked loop form is usually possible within a series (e.g. with Cl(CH(2))(6)Cl and Br(CH(2))(6)Br), but not between series (e.g. Cl(CH(2))(6)Cl and NC(CH(2))(6)CN). Crystals of Cl(CH(2))(6)CN/urea, in which a single guest contains substituents from each class, are distorted along [001] by only 0.5% from hexagonal symmetry at 298 K and exhibit ferroelastic domain reorientation at high forces. At -66 degrees C, Cl(CH(2))(6)CN/urea undergoes a topotactic phase transition that is unexpectedly nontopochemical. The structure of the low-temperature phase, including the orientation of the methylene chain, closely matches the structures of UICs distorted by 10% along [100] (e.g. Cl(CH(2))(6)Cl/urea). In this transition, small conformation changes of guests give rise to large-scale guest translations of approximately 5.5 A down the channel axis, even though an analogous gauche-to-gauche jump is well established in closely related materials that adopt either high- or low-temperature forms (e.g. NC(CH(2))(6)CN/urea, Cl(CH(2))(6)Cl/urea). The large guest displacement during this transition explains the difficulty in preparing solid solutions of the P2(1)/n form with guests of formula X(CH(2))(6)Y from two different series (e.g. Cl(CH(2))(6)Cl and NC(CH(2))(6)CN). This failure arises not from the different orientations of guest-induced strain, but from preferential occupation of different sites along the channel by the two types of guests. The subtlety of this process and of the interactions involved highlights the difficulty in using simple considerations of isomorphism to design new materials.     

Wetting effect of aqueous binary mixed solutions of cationic and nonionic surfactants

Wetting of low-energy solid surfaces (polymers, hydrophobized glass) with aqueous solutions of binary mixtures of cationic and nonionic surfactants was investigated at molar fractions of the cationic surfactant of 0.2, 0.5, and 0.8. In a narrow concentration range, the non-additive effect of wetting was observed: wetting of the solid surfaces with solutions of the mixtures is better than that would be expected from the additive behavior of the components. The magnitude of the effect depends on the surface energy of the solid substrate, total surfactant concentration in a mixture, and molar fraction of the cationic component. The wetting effect of surfactant mixtures with respect to low-energy solid surfaces can be predicted using the surface tension isotherms.     

Americium and samarium determination in aqueous solutions after separation by cation-exchange

The concentration of trivalent americium and samarium in aqueous samples has been determined by means of alpha-radiometry and UV–Vis photometry, respectively, after chemical separation and pre-concentration of the elements by cation-exchange using Chelex-100 resin. Method calibration was performed using americium (²⁴¹Am) and samarium standard solutions and resulted in a high chemical recovery for cation-exchange. Regarding, the effect of physicochemical parameters (e.g. pH, salinity, competitive cations and colloidal species) on the separation recovery of the trivalent elements from aqueous solutions by cation-exchange has also been investigated. The investigation was performed to evaluate the applicability of cation-exchange as separation and pre-concentration method prior to the quantitative analysis of trivalent f-elements in water samples, and has shown that the method could be successfully applied to waters with relatively low dissolved solid content.     

Cellulose conversion to polyols on supported Ru catalysts in aqueous basic solution

It is of great significance and challenge to achieve direct conversion of cellulose to specific polyols, e.g., ethylene glycol and propylene glycol. For such selective conversion, a novel one-pot approach was studied by combination of alkaline hydrolysis and hydrogenation on supported Ru catalysts. A wide range of bases including solid bases, e.g., Ca(OH)₂ and La₂O₃, and phosphate buffers were examined in the cellulose reaction in water, and the cellulose conversions and polyol products depended largely on the basicity or pH values in the aqueous solutions. Ethylene glycol, 1,2-propanediol, and especially 1,2,5-pentanetriol were obtained with selectivities of 15%, 14% and 22%, respectively, at 38% cellulose conversion at pH 8 in phosphate buffer solution. These preliminary results provide potentials for efficient conversion of cellulose to targeted polyols by using the advantages of bases.     

Preparation of transition metal complexes of strongly basic ligands by thermal decomposition

The usual stoichiometry of metal salicylates, 2-oxy-3-naphtholates, anthranilates and salicylaldoximates is M²⁺(HL⁻)₂.xH₂O. Heating such a solid in an inert atmosphere causes proton transfer between the two HL⁻-ligands and the following reaction takes place: M(HL)₂(s) → ML(s) + H₂L(g). The new complex ML(s) (e.g. zincsalicylate) reacts with solid or dissolved monoprotic ligands HL' (e.g. 8-hydroxyquinoline) to form the mixed complex (e.g. zinc-salicylate-oxyquinolate) in excellent yield.     

苯基荧光酮—溴化十六烷基三甲铵—十二烷基苯碘酸钠增溶吸光光度法测定微量锗

用苯基荧光酮－溴化十六烷基三甲铵一十二烷基苯磺酸钠增溶吸光光度法测定酸性水相中微量锗,选择505nm为工作波长,并对表面活性剂用量,显色时间,显色剂用量和酸度的影响进行了讨论,加入十二烷基苯磺酸钠溶解了固体样品消化后易出现的红色絮状物,取得较好效果。     

Electrical conductivity in solid solutions and in two-phase regions of the silver halide-bivalent metal (cadmium,cobalt, zinc) halide systems

Electrical conductivity of solid systems AgX-MX₂ (where M=Cd, Co, Zn and X=Cl, Br) were measured in a large range of temperature and compositions. Activation energies and conductivity values vs. composition are presented and discussed in relation to phase equilibria in the respective systems. Maximum of the conductivity value and stabilization of the activation energy have been found for silver halides doped heavily with divalent cation e.g. in the systems forming solid solutions on the silver halide side. Disorder in AgBr on the approach to melting, expected to be higher than in AgCl, has been shown by means of original DSC curves presented for both halides.     

The effect of hydrogen on amorphization of iron-tungsten alloys produced by electrochemical synthesis

It is shown that the transition from common crystal form (iron-based solid solutions) to the nanocrystalline form occurs at a hydrogen content exceeding 2–3 cube centimeters (at standard conditions) per 1 g of alloy. Therewith, the current density and potential of deposition can vary and depend on the solution composition and other conditions. It is proposed that the transition occurs as an explosive process: in a thin juvenile alloy layer containing a certain limiting amount of hydrogen, high stresses arise; as a result, the concentration of defects increases accelerating hydrogen incorporation. The relevant calculations are performed and the dimensionless constant of hydrogen codeposition is determined (within the framework of the model developed). An alternative supposition is that iron hydroxide precipitating in the near-electrode layer, which also enters into the alloy composition, plays an important role in these processes.     

Steps in Precipitation Reactions

The combined application of various methods of investigation (e.g. nephelometry, conductivity measurements, electron microscopy, isotope exchange, BET surface area determinations, paper chromatograhy, coprecipitation) lead to a refined insight into the course of precipitation reactions. The formation of a new solid phase within a solution can, in the case of ionic crystals, be formally described as proceeding via a number of steps – nucleation, growth, ripening, and recrystallization (aging) – which overlap in time. The precipitation of hydroxides is a more complex process since additional chemical reactions (e.g. hydrolysis, condensation reactions) take place within the newly formed solid phase.     

Direct liquid ablation: a new calibration strategy for laser ablation-ICP-MS microanalysis of solids and liquids

Trace elements in microliter quantities of aqueous solutions were analysed by direct liquid ablation using an 193 nm excimer with an inductively coupled plasma mass spectrometer (ICP-MS). Fractionation resulting from splashing and evaporation can be minimised by covering the liquid surface with a thin plastic film, through which a 20 μm hole is drilled with the laser. Particle-size distribution and oxide formation in the plasma resulting from the direct liquid ablation are similar to those generated by solid ablation. The ICP-MS response in cps/ppm is approximately 100 × higher for the direct ablation, but is proportional to the response from solid ablation, within an accuracy < 15% for most trace elements in NIST 610 and NIST 612 glass standards. A matrix load up to 2.5 wt.-% NaCl in the solution does not affect the proportionality of trace element responses. Thus, direct liquid ablation is not only suited for analysing small volumes of complex aqueous solutions (e.g., the quantitative microanalysis of fluid inclusions in minerals), but also provides a new approach for calibrating laser ablation ICP-MS microanalysis of solids. Received: 2 December 1996 / Revised: 3 March 1997 / Accepted: March 1997