Determination of neodymium isotopes as burnup indicator of highly irradiated (U,Pu)O2 lmfbr fuel

A new counting method was developed to determine²²⁶Ra in environmental samples by separating the equilibrated²²²Rn into a liquid scintillator. The integral counting method, which was originally developed for isolated individual radionuclides, was extended to the mixture of²²²Rn and its daughters in equilibrium. The optimum measurement conditions were established by examining the energy spectrum, counting time and quenching effect. An absolute counting was practiced by extrapolating the integral counting rate-bias voltage curve with the highest gain to zero bias. The detection limit thus obtained was 3 to 4·10⁻¹³ Ci.     

Isotopic composition of inorganic carbon as an indicator of benzoate degradation by pseudomonas putida: temperature, growth rate and pH effects

Degradation experiments of benzoate by Pseudomonas putida resulted in enzymatic carbon isotope fractionations. However, isotopic temperature effects between experiments at 20 and 30 degrees C were minor. Averages of the last three values of the CO(2) isotopic composition (delta(13)C(CO2(g))) were more negative than the initial benzoate delta(13)C value (-26.2 per thousand Vienna Pee Dee Belenite (VPDB)) by 3.8, 3.4 and 3.2 per thousand at 20, 25 and 30 degrees C, respectively. Although the maximum isotopic temperature difference found was only 0.6 per thousand, more extreme temperature variations may cause larger isotope effects. In order to understand the isotope effects on the total inorganic carbon (TIC), a better measure is to calculate the proportions of the inorganic carbon species (CO(2)(g), CO(2)(aq) and HCO(3)(-)) and to determine their cumulative delta(13)C(TIC). In all three experiments delta(13)C(TIC) was more positive than the initial isotopic composition of the benzoate at a pH of 7. This suggests an uptake of (12)C in the biomass in order to match the carbon balance of these closed system experiments.     

Colchiceine as an extractive indicator in the determination of copper(II)

Colchiceine, a new extractive indicator, is satisfactorily used in the determination of copper(II). A highly sensitive greenish yellow complex is formed with copper, which is extractable into chloroform. The results are comparable in sensitivity and selectivity with those of its precursors.     

The use of stable isotopes for Cr(VI) determination in silty-clay soil solution

In assessing the environmental hazard of Cr(VI) present in soil, exchangeable Cr(VI) is important, since it can be easily washed out from the upper part of the soil into subsurface soil, surface and ground water, and taken up by plants. The aim of this study was to evaluate the degree of species interconversion that may occur during the extraction of exchangeable Cr(VI) from silty-clay soil with phosphate buffer in order to establish an extraction method that would be effective, accurate and with minimal or no species interconversions. The Cr(VI) concentration in soil extracts was determined by speciated isotope dilution inductively coupled plasma mass spectrometry (SID-ICP-MS). The study was performed on soil samples from a field treated with tannery waste for 17 years. Samples were spiked by enriched stable isotopic solutions of ⁵⁰Cr(VI) and ⁵³Cr(III) that were added to phosphate buffers (0.1 M KH₂PO₄-K₂HPO₄ (pH 7.2) and/or 0.1 M K₂HPO₄ (pH 8)). To optimize extraction, mechanical shaking and/or ultrasound-assisted extraction were compared. The separation and detection of Cr species was performed by high-performance liquid chromatography (HPLC) ICP-MS. When mechanical shaking was applied, 90 % reduction of Cr(VI) was induced by extraction with 0.1 M KH₂PO₄-K₂HPO₄, while with 0.1 M K₂HPO₄ reduction was around 40 %. To shorten the extraction time and the possibility of species interconversions, ultrasound-assisted extraction was further applied only with 0.1 M K₂HPO₄. For total extraction of exchangeable Cr(VI) with a maximum 10 % reduction of Cr(VI), five consecutive ultrasound-assisted extractions were needed.

p-Fluorphenyl group as an indicator of charge on the carbon atom in aromatic compounds

A linear equation is presented for determining, from the chemical shift of¹⁹F in a p-fluorophenyl group, the effective charge of that CH fragment of the original aromatic molecule the carbon atom of which is bonded to the fluorophenyl indicator group. It has been shown that for a cyclic aromatic 6-electron system determination of the effective charges of the CH fragments by quantum-chemical calculations and the evaluation of this charge from the¹⁹F chemical shift of the corresponding p-fluorophenyl substituents lead to coincident results.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2219–2222, October, 1989.The authors are grateful to N. P. Gambaryan for fruitful discussions.     

The degradation mechanism of sulfonated poly(arylene ether sulfone)s in an oxidative environment

The degradation of sulfonated aromatic hydrocarbons based polymer electrolyte membranes is an important issue for fuel cell stability. However, its mechanism is relatively unclear. We have conducted accelerated radical tests and degradation product analysis for various sulfonated poly(arylene ether sulfone) (SPES) compounds. We evaluated the chemical durability of SPES, and observed its degradation mechanism under oxidative attack by hydrogen peroxide. Various SPES compounds were synthesized from 4,4′-biphenol, 4,4′-dihydroxy diphenyl sulfone, and 4,4′-dihydroxy benzophenone comonomers, and their physical properties were evaluated. SPES copolymerized with 4,4′-dihydroxy diphenyl sulfone had a higher durability towards oxidative attack compared with the other compounds studied, and SPES copolymerized with 4,4′-dihydroxy benzophenone exhibited the lowest durability.     

Stable carbon ((12/13)C) and nitrogen ((14/15)N) isotopes as a tool for identifying the sources of cyanide in wastes and contaminated soils--a method development

The occurrence of iron-cyanide complexes in the environment is of concern, since they are potentially hazardous. In order to determine the source of iron-cyanide complexes in contaminated soils and wastes, we developed a method based on the stable isotope ratios ¹³C/¹²C and ¹⁵N/¹⁴N of the complexed cyanide-ion (CN⁻). The method was tested on three pure chemicals and two industrials wastes: blast-furnace sludge (BFS) and gas-purifier waste (GPW). The iron-cyanide complexes were converted into the solid cupric ferrocyanide, Cu₂[Fe(CN)₆]·7H₂O, followed by combustion and determination of the isotope-ratios by continuous flow isotope ratio mass spectrometry. Cupric ferrocyanide was obtained from the materials by (i) an alkaline extraction with 1 M NaOH and (ii) a distillate digestion. The [Fe(CN)₆]⁴⁻ of the alkaline extraction was precipitated after adding Cu²⁺. The CN⁻ of the distillate digestion was at first complexed with Fe²⁺ under inert conditions and then precipitated after adding Cu²⁺. The δ¹³C-values obtained by the two methods differed slightly up to 1-3‰ for standards and BFS. The difference was larger for alkaline-extracted GPW (4-7‰), since non-cyanide C was co-extracted and co-precipitated. Therefore the distillate digestion technique is recommended when determining the C isotope ratios in samples rich in organic carbon. Since the δ¹³C-values of BFS are in the range of −30 to −24‰ and of −17 to −5‰ for GPW, carbon seems to be a suitable tracer for identifying the source of cyanide in both wastes. However, the δ¹⁵N-values overlapped for BFS and GPW, making nitrogen unsuitable as a tracer.     

Ordered mesoporous carbon as an efficient heterogeneous catalyst to activate peroxydisulfate for degradation of sulfadiazine

Catalytic potential of carbon nanomaterials in peroxydisulfate（PDS） advanced oxidation systems for degradation of antibiotics remains poorly understood. This study revealed ordered mesoporous carbon（type CMK） acted as a superior catalyst for heterogeneous degradation of sulfadiazine（SDZ） in PDS system, with a first-order reaction kinetic constant（k） and total organic carbon（TOC） mineralization efficiency of 0.06 min^–1 and 59.67% ± 3.4% within 60 min, respectively. CMK catalyzed PDS sy...     

Ordered mesoporous carbon as an efficient heterogeneous catalyst to activate peroxydisulfate for degradation of sulfadiazine

Catalytic potential of carbon nanomaterials in peroxydisulfate（PDS） advanced oxidation systems for degradation of antibiotics remains poorly understood. This study revealed ordered mesoporous carbon（type CMK） acted as a superior catalyst for heterogeneous degradation of sulfadiazine（SDZ） in PDS system, with a first-order reaction kinetic constant（k） and total organic carbon（TOC） mineralization efficiency of 0.06 min^–1 and 59.67% ± 3.4% within 60 min, respectively. CMK catalyzed PDS sy...     

Surface degradation of ethylene-propylene-diene monomer (EPDM) containing 5-ethylidene-2-norbornene (ENB) as diene in artificial weathering environment

Ethylene-propylene-diene monomer (EPDM) containing 5-ethylidene-2-norbornene (ENB) as diene was exposed to an artificial weathering environment produced by a xenon lamp light exposure and weathering equipment for different time periods. The surface chemical changes were detected by Specular Reflection Fourier Transform Infrared (SR-FTIR) spectroscopy, Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The change in surface color, contact angle and morphology was monitored by spectrophotometer, optical contact angle measuring device and Scanning Electron Microscope (SEM). Furthermore, surface energy was calculated through contact angles of water and formamide. The results showed that hydroxyl, carbonyl and ester groups were formed during exposure to this artificial weathering environment. EPDM surface became redder, yellower and lighter in the first stage of aging and then remained almost unchanged. The contact angles of water and formamide decreased to a minimum and then increased slowly. The surface degradation is a zero order reaction. In addition, the plausible degradation mechanism was proposed.     

Stable bis(diisopropylamino)cyclopropenylidene (BAC) as ligand for transition metal complexes

Several nickel(0), palladium(II), and rhodium(I) complexes have been prepared using for the first time the stable bis(diisopropylamino)cyclopropenylidene (BAC). Based on single crystal X-ray diffraction studies and spectroscopic data, the structural and electronic properties of these complexes are discussed. Moreover, their similarities and differences with the analogous NHC complexes are emphasized.     

Stable monovalent aluminum(i) in a reduced phosphomolybdate cluster as an active acid catalyst

Low-valent aluminum Al(i) chemistry has attracted extensive research interest due to its unique chemical and catalytic properties but is limited by its low stability. Herein, a hourglass phosphomolybdate cluster with a metal-center sandwiched by two benzene-like planar subunits and large steric-hindrance is used as a scaffold to stabilize low-valent Al(i) species. Two hybrid structures, (H₃O)₂(H₂bpe)₁₁[Al^III(H₂O)₂]₃{[Al^I(P₄Mo^V₆O₃₁H₆)₂]₃·7H₂O (abbr. Al₆{P₄Mo₆}₆) and (H₃O)₃(H₂bpe)₃[Al^I(P₄Mo^V₆O₃₁H₇)₂]·3.5H₂O (abbr. Al{P₄Mo₆}₂) (bpe = trans-1,2-di-(4-pyridyl)-ethylene) were successfully synthesized with Al(i)-sandwiched polyoxoanionic clusters as the first inorganic-ferrocene analogues of a monovalent group 13 element with dual Lewis and Brønsted acid sites. As dual-acid catalysts, these hourglass structures efficiently catalyze a solvent-free four-component domino reaction to synthesize 1,5-benzodiazepines. This work provides a new strategy to stabilize low-valent Al(i) species using a polyoxometalate scaffold.

Monovalent aluminum(i) species was successfully stabilized using a reduced phosphomolybdate scaffold as a dual-acid catalyst for a four-component domino reaction.

Low- or sub-valence aluminum compounds are increasingly growing into a significant frontier subject in coordination and modern organic synthetic chemistry owing to their unique singlet carbene character, Lewis acid/base properties and catalytic reactivity.¹ However, low-valence aluminum(i) compounds have inherent electron deficiency and exhibit thermodynamic instability, making them prone to self-polymerization with metal–metal bonds² or disproportionation³ to metallic Al and Al(iii) species. Inspired by the special stabilizing effect of metallocene compounds, a ligand stabilization strategy has recently been undertaken to stabilize the low-valence aluminum center.^4,5 In this regard, the utilized ligand should satisfy two key criteria: (i) sufficient steric hindrance is required to inhibit monomer polymerization; and (ii) a suitable electronic effect is needed to stabilize the aluminum(i) center. A few organometallic Al(i) compounds protected by bulky organic groups have been prepared such as [(Cp*Al)₄] (Cp* = C₅Me₅),⁶ and [(CMe₃)₃SiAl₄].⁷ However, despite having the ligand effect, most of these Al(i) compounds still decompose in aqueous solutions or heating conditions. In contrast to organometallic Al(i) compounds, inorganic Al(i) structures, i.e. monomeric monohalides, only exist in gaseous form at high temperature⁸ and to the best of our knowledge, no stable inorganic Al(i) compound is known at room temperature due to thermodynamic instability. Therefore, exploring efficient strategies to synthesize stable inorganic Al(i) compounds remains highly desired but a great challenge.Polyoxometalates (POMs), a diverse family of inorganic molecular clusters based on early-transition metals (W, Mo, V, Nb, and Ta), have extensively attracted attention in research in various fields of materials science, coordination chemistry, medicinal chemistry and catalysis science.^9–11 Owing to their adjustable constituent elements and well-defined structures, POMs have been considered as promising inorganic ligands to stabilize high- and low-valent metal ions. For instance, Rompel et al.¹² reported one Keggin-type [α-CrW₁₂O₄₀]⁵⁻ anion in which a labile {Cr^IIIO₄} tetrahedral unit was assembled at the center of the cluster. Li and co-workers employed a monolacunary Keggin-type inorganic ligand to stabilize a high-valent Cu³⁺ ion.¹³ As a unique member of the POM family, the hourglass-type phosphomolybdate cluster {M[P₄Mo^V₆O₃₁]₂}ⁿ⁻ (abbr. M{P₄Mo₆}₂), consisting of two [P₄Mo^V₆O₃₁]¹²⁻ (abbr. {P₄Mo₆}₂) subunits bridged by one metal (M) center, represents a fully reduced metal-oxo cluster. With all Mo atoms in the oxidation state of (+5), a more negative charge is endowed to the cluster surface.^14,15 Such high electron density of {M[P₄Mo^V₆O₃₁]₂}ⁿ⁻ polyoxoanions provides an electron-rich local environment for the possible stabilization of unusual-valence metals. It is worth noting that the [P₄Mo^V₆O₃₁]¹²⁻ subunit presents near-planar triangular structures with the side sizes ranging from 7.50–7.92 Å (Fig. S1^†). The structural feature can supply sufficient steric hindrance to restrain the polymerization of low-valence metal species. Moreover, the six Mo atoms in each [P₄Mo^V₆O₃₁]¹²⁻ subunit arrange in a planar hexagonal-ring structure like a benzene ring, implying that such {M[P₄Mo^V₆O₃₁]₂}ⁿ⁻ clusters may have a similar delocalized electron structure to conjugated benzene or cyclopentadiene. These features make [P₄Mo^V₆O₃₁]¹²⁻ a promising candidate with respect to organic protecting groups to construct an inorganic ‘ferrocene’ analogue of Al(i) (Scheme 1). Therefore, we hypothesize that hourglass-type polyoxoanion clusters are promising to stabilize the labile Al(i) center and isolate inorganic Al(i) species.Open in a separate windowScheme 1Similar ferrocene-like sandwich structure features of an inorganic hourglass-type [Al^I(P₄Mo^V₆O₃₁)₂]²³⁻ polyanion to an organometallic [(η⁵-Cp*)₂Al^I]⁺ cation.Herein, we show a [P₄Mo^V₆O₃₁]¹²⁻ cluster as an inorganic scaffold to stabilize the Al(i) center in two hybrid compounds, (H₃O)₂(H₂bpe)₁₁[Al^III(H₂O)₂]₃{[Al^I(P₄Mo^V₆O₃₁H₆)₂]₃·7H₂O (abbr. Al₆{P₄Mo₆}₆) and (H₃O)₃(H₂bpe)₃[Al^I(P₄Mo^V₆O₃₁H₇)₂]·3.5H₂O (abbr. Al{P₄Mo₆}₂) (bpe = trans-1,2-di-(4-pyridyl)-ethylene), in which the labile Al(i) center is sandwiched by two [P₄Mo^V₆O₃₁]¹²⁻ sides, forming an inorganic moiety of a ‘ferrocene’ analogue. Both Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ are experimentally determined at room temperature for the first time, and prepared by hydrothermal reactions of Na₂MoO₄·2H₂O, H₃PO₄, AlCl₃·6H₂O, ethanol and N-containing bpe at 160 °C with slightly different pH values. Notably, the combination of ethanol, N-containing bpe and high hydrothermal temperature is a prerequisite to the isolation of Al(i) species. First, both ethanol and N-containing bpe were used to provide a reducing environment under hydrothermal conditions. By combining high temperature and pressure, sufficient energy is supplied to reduce Mo⁶⁺ and Al³⁺ ions to Mo⁵⁺ and Al⁺ species, respectively. Then, Mo⁵⁺ species and phosphoric acid molecules are assembled to form [P₄Mo₆O₃₁]¹²⁻ subunits, which are subsequently combined with Al⁺ ions to form hourglass-type [Al(P₄Mo₆O₃₁)₂]²³⁻, hence effectively stabilizing Al(i) species (Fig. 1). From the perspective of stereochemistry, two highly negative [P₄Mo₆O₃₁]¹²⁻ fragments, resembling the methyl cyclopentadiene organic group, sandwich one low-valent metal Al(i) center. Hence, the construction of a strong reducing hourglass-like skeleton makes it possible to stabilize the existing Al⁺ species.Open in a separate windowFig. 1Ball-and-stick diagram showing the assembly of the hourglass-type cluster {Al(P₄Mo₆)₂}.Single crystal X-ray diffraction revealed the hourglass-type {Al(P₄Mo₆)₂} cluster in Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ (Table S1^†), in which the [P₄Mo₆O₃₁]¹²⁻ subunits have a C₃ symmetry and display a near-planar structure formed by six edge-sharing {MoO₆} octahedra with alternating short Mo–Mo single bonds and long non-bonding Mo⋯Mo contacts. The side sizes of the {P₄Mo₆} subunit range from 7.50–7.92 Å, which supplies sufficient steric hindrance to restrain the polymerization or disproportionation of low-valence Al(i) species. All Mo atoms are in a reduced oxidation state of +5 and the central Al atoms are in the +1 oxidation state, as confirmed by bond valence calculations (Table S2^†). Thus, the synthesized Al{P₄Mo₆}₂ represents a fully reduced metal–oxygen cluster. Moreover, the six Mo atoms in each {P₄Mo₆} subunit present a benzene-like planar hexagonal-ring structure with a similar π-type delocalization electron interaction with Al(i) instead of organic bulky groups. Such π-type delocalization electron interaction constructs an inorganic ‘ferrocene’ analogue of Al(i) and produces sufficient delocalization energy to stabilize Al(i) species. Considering the formation mechanism of traditional metallocenes, {P₄Mo₆} subunits with a similar strong electron-donating ability and suitable steric-hindrance effect on Cp rings, augment the stability of Al(i) species. Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ compounds also present the first isolation of aluminum-sandwiched hourglass-type clusters in POM chemistry. Importantly, regarding the inherent and strong hydrolysis of aluminum species in water, these low-valent Al(i)-containing clusters represent the first example of stable solid-state inorganic sub-valent Al(i) compounds at room temperature.The asymmetric structure of Al₆{P₄Mo₆}₆ consists of two crystallographically independent {Al(P₄Mo₆)₂} clusters sandwiched by central Al(1) and Al(4) atoms, two bridging [Al(H₂O)₂]³⁺ (Al(2) and Al(3)) cations and six protonated bpe cations (Fig. S2^†). Aluminum centers involve two kinds of oxidation states: the central Al(1) and Al(4) are in the +1 state, while the bridging Al(2) and Al(3) are in the +3 state. Both Al(1) and Al(4) display the six-coordinated octahedral configuration and bridge two {P₄Mo₆} subunits to form two {Al^I(P₄Mo₆)₂} clusters. The average lengths of Al–O bonds are 2.318–2.324 Å for Al(1) and Al(4) (Table S3^†), which are slightly longer than those of classic Al–O bonds (1.90 Å) for Al(2) and Al(3), but close to that of the Al–O bond in silica-supported alkylaluminum(i) composites.^16–20 The long Al–O lengths for Al(1) and Al(4) centers may be ascribed to the lower electron cloud density located at the surface of the Al(i) cation, resulting in slightly longer bonds with the surrounding oxygen donors.^5,21 Moreover, the small distorted extents (sum((d_ij − d_ave)/d_ave)²/coordination number) of {Al(1)O₆} (3.86 × 10⁻⁴) and {Al(4)O₆} (1.89 × 10⁻³) indicate that they are in regular octahedral geometry. Moreover, another structural feature of Al₆{P₄Mo₆}₆ is that {Al^I(P₄Mo₆)₂} clusters are connected by bridging [Al(H₂O)₂]³⁺ cationic fragments (Al(2) and Al(3)), forming an unusual chain-like arrangement (Fig. 2a). It is worth noting that the 1-D chain contains a large repeating monomer with the maximum spacing of 81.69 Å, consisting of twelve Al-containing fragments ({–Al2–Al1–Al3–Al4–Al3–Al1–Al2–Al1–Al3–Al4–Al3–Al1–}). Such a long repeating monomer is rare. Each repeating monomer has two types of symmetric systems: Al(2) in the middle of the monomer plays a center of mirror symmetry and divides the whole repeating monomer into two equidistant half-units of {–Al1–Al3–Al4–Al3–Al1–}; Al(4) in each half-unit further acts as the reverse symmetric center of two {–Al3–Al1–Al2–} subunits. The two types of symmetrical systems form the infinitely extending chain-like structure in Al₆{P₄Mo₆}₆. Since bpe is a rigid and conjugated molecular structure, an effective π⋯π stacking interaction emerges and results in a honeycomb-like supramolecular organic moiety, which accommodates these 1-D inorganic chains and stabilizes the whole Al₆{P₄Mo₆}₆ framework (Fig. S3 and S4^†).Open in a separate windowFig. 2(a) One-dimensional (1D) inorganic structure in Al₆{P₄Mo₆}₆ with a length of repeating units of 81.69 Å, consisting of twelve Al-containing fragments ({–Al2–Al1–Al3–Al4–Al3–Al1–Al2–Al1–Al3–Al4–Al3–Al1–}). (b) Four kinds of coordination environments of {AlO₆} octahedra, respectively (i = 1 − x, y, 0.5 − z; ii = 0.5 − x, 1.5 − y, 1 − z).Al{P₄Mo₆}₂ has a similar structure to Al₆{P₄Mo₆}₆ (Table S4^†), wherein the most obvious difference is that {Al^I[P₄Mo₆]₂} clusters exist in isolated form and interact with the surrounding protonated bpe cations via hydrogen bonding to form into a 3-D supramolecular framework (Fig. S5 and S6^†). The different peripheral environment around the {Al^I[P₄Mo₆]₂} cluster can affect its acidity and catalytic activity.The solid-state ²⁷Al NMR spectrum of Al₆{P₄Mo₆}₆ depicts two distinct resonances at δ = −22.34 and 27.33 ppm due to the octahedrally coordinated Al^III and Al^I sites, respectively (Fig. 3a), indicating two types of Al local environments in Al₆{P₄Mo₆}₆. In contrast, Al{P₄Mo₆}₂ displays only one sharp signal at δ = 7.20 ppm due to the octahedrally coordinated Al^I sites (Fig. 3b). The observed narrow peak-width corresponds to the highly symmetric charge distribution at the aluminum nucleus, similar to the ferrocene analogue [(η⁵-Cp*)₂Al^I]⁺.⁵ Noticeably, Al^I resonance in Al₆{P₄Mo₆}₆ appears at a lower magnetic field compared to Al{P₄Mo₆}₂, due to the different peripheral environment around the hourglass {Al(P₄Mo₆)₂} cluster. XPS spectra of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ further affirm the valence states of Al and Mo elements (Fig. S7 and Table S5^†). The Al 2p XPS profile of Al₆{P₄Mo₆}₆ reveals two peaks at 74.39 and 73.75 eV ascribed to Al^III and Al^I, respectively (Fig. 3c). The area ratio of the two peaks is close to 1 : 1, in consistence with the chemical structure of Al₆{P₄Mo₆}₆. The high-resolution Al 2p XPS spectrum of Al{P₄Mo₆}₂ displays a weaker broad peak attributed to the low amount of Al⁺ (Fig. 3d). Moreover, the structural stabilities of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ were investigated by soaking them in water for 24 hours. Fig. S9–S11^† show the comparison of XRD, IR and XPS spectra of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ before and after soaking in water. It can be found that the characteristic diffraction peaks in XRD after soaking for 24 hours still show good agreement with the simulated data (Fig. S9^†). The characterized absorption bands in IR spectra also exhibit good match with the original Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ (Fig. S10^†). The XPS spectra of Al₆{P₄Mo₆}₆ after soaking in water were also obtained. There is basically no change in the high-resolution spectra of Al 2p with the Al^I/Al^III atomic ratios of ca. 1 : 1 (Fig. S11^†). The spectroscopic and theoretical observations verify that the low valence Al(i) species can stably exist in the reduced phosphomolybdates in the solid state (Fig. S12 and Table S6^†). Moreover, the acidities of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ were measured to be 0.27 and 0.442 mmol g⁻¹, respectively, demonstrating the promising potential of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ as dual-acid catalysts.Open in a separate windowFig. 3(a and b) ²⁷Al NMR spectra of solid Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂; (c and d) XPS spectra of Al in Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂.The catalytic performance of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ was evaluated via a solvent-free four-component domino reaction for the synthesis of pharmaceutical intermediate 1,5-benzodiazepine (Table 1). With Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ as catalysts, the yields of the final product 8aaa reach 83% and 75%, respectively (Table 1, entries 1 and 2). Almost no 8aaa is observed without the acid catalysts, even when the reaction is set for a long time (Table 1, entry 3). This clarifies the excellent catalytic performance of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂. Typical Brønsted acid p-TsOH and Lewis acid AlCl₃ as control samples yield only 43% and 29% 8aaa, respectively (Table 1, entries 4 and 5), much lower than those attained by Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂ catalysts. Moreover, (H₂en)₁₂[{Na_0.8K_0.2(H₂O)}₂{Na[Mo₆O₁₂(OH)₃(HPO₄)₂(PO₄)₂]₂}₂]·7H₂O^22,23 (abbr. {Na[P₄Mo₆]₂}) in contrast achieved 72% yield of 8aaa in 30 min, slower than that of Al₆{P₄Mo₆}₆ and Al{P₄Mo₆}₂. This indicates the advantage of the unique dual-acid features of Al(i)-stabilized reduced phosphomolybdate clusters with multiple Lewis and Brønsted acid active centers, in which the synergistic effect between the Al species and reduced phosphomolybdate cluster contributes to the catalytic activity.Comparison tests of one-pot synthesis of 1,5-benzodiazepine 8aaavia a four-component domino reaction^a

Lichens as biomonitors for the determination of polycyclic aromatic hydrocarbons (PAHs) in Caracas Valley,Venezuela

Biomonitoring of PAH air pollution using lichens was carried out. Sixteen PAHs were studied in 11 locations along the valley of Caracas (Venezuela). The results of this work indicate that 14 of the 16 analysed PAHs were highly accumulated into the lichen thalli of Pyxine coralligera Malme. PAH levels in the samples revealed that the several volatile PAHs (naphthalene, acenaphtylene, acenaphtene, and fluoranthene) have the highest levels in the majority of the studied locations. The fluoranthene/pyrene and phenantrene/antracene ratios suggested that the major sources of PAHs are anthropogenic, mainly associated with gasoline and diesel combustion (pyrolytic) and unburnt oil derivates (petrogenic). The total PAH concentrations obtained in the present study were in the range of 0.24 to 9.08?µg/g, similar to those reported by other works in European and Asian cities.     

Migration of plutonium isotopes in forest soil profiles in Lublin region (Eastern Poland)

The distribution of Pu isotopes in three profiles of forest soil in Lublin region was determined. The retention half-time and migration velocity of^239,240Pu originated from global and Chernobyl fallouts was calculated. The average rate of migration of the global fallout plutonium was 0.4 cm/year and that of the Chernobyl one 0.7 cm/year. Good correlation between Pu concentration and organic matter contents was found only in the case of podzolic soil profile. In two profiles a good negative correlation between Pu activity and exchangeable pH of the soil layer was determined.     

Turnover of stable carbon isotopes in the muscle, liver, and breath CO2 of alpacas (Lama pacos)

Stable carbon isotope analysis of animal liver and muscle has become a widespread tool for investigating dietary ecology. Nonetheless, stable carbon isotope turnover of these tissues has not been studied in large mammals except with isotopically labelled tracer methodologies, which do not produce carbon half-lives analogous to those derived from naturalistic diet-switch experiments. To address this gap, we studied turnover of carbon isotopes in the liver, muscle, and breath CO2 of alpacas (Lama pacos) by switching them from a C3 grass diet to an isonitrogenous C4 grass diet. Breath samples as well as liver and muscle biopsies were collected and analyzed for up to 72 days to monitor the incorporation of the C4-derived carbon. The data suggest half-lives of 2.8, 37.3, and 178.7 days for alpaca breath CO2, liver, and muscle, respectively. Alpaca liver and muscle carbon half-lives are about 6 times longer than those of gerbils, which is about what would be expected given their size. In contrast, breath CO2 turnover does not scale readily with body mass. We also note that the breath CO2 and liver data are better described using a multiple-pool exponential decay model than a single-pool model.     

Titration of vanadium(IV) with cerium(IV) sulphate, with ferroin as indicator, in aqueous alcohol as a facile reaction medium

A new procedure for the titration of vanadium(IV) with cerium(IV) sulphate, with ferroin as indicator, in aqueous alcohol medium, is reported. The visual titration gives accurate results but potentiometric titration fails in this medium; this failure is attributed to the sluggish indicator electrode behaviour. Experimental conditions for preliminary quantitative photochemical reduction of vanadium(V) with alcohol have been established.     

MoS2 incorporated carbon allotropes (activated carbon,graphene, MWCNT) as electrodes in symmetric supercapacitors

Symmetric supercapacitor devices were fabricated from MoS₂ incorporated carbon allotropes such as activated carbon (AC)/MoS₂, graphene/MoS₂ and MWCNT/MoS₂. The device performance was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The electrochemical properties of the devices fabricated from carbon allotropes (activated carbon, graphene, MWCNT) were remarkably enhanced to above 50% by the incorporation MoS₂ phases. Out of the three fabricated devices, electrochemical performance of AC/MoS₂ as found to be superior. The specific capacitance and energy density of this device is 216 ​F/g and 6.2 ​Wh/Kg respectively with excellent higher rate capability and longer cyclic durability. The devices fabricated from graphene/MoS₂ and MWCNT/MoS₂ has exhibited a specific capacitance value of 202 ​F/g and 161 ​F/g with an energy density value of 5.68 ​Wh/Kg and 3.95 ​Wh/Kg respectively.