Formation Of Intermediate Compounds Research Articles

Enhanced photocatalytic degradation of acephate pesticide over MCM-41/Co3O4 nanocomposite synthesized from rice husk silica gel and Peach leaves

Novel green nanocomposite from mesoporous MCM-41 and Co3O4 was synthesized from rice husk based silica gel and using the green extract of Peach leaves as reducing reagent. The composite was labeled as RH-MCM-41/Co3O4 and characterized by different techniques as green photocatalyst in the degradation of Acephate pesticide under visible light illumination. The composite showed well developed spherical MCM-41 particles decorated by nano Co3O4 nanoparticles with stunning surface area and low bandgap energy (1.51 eV). The composite displayed superior photocatalytic activities in the oxidation of Acephate which reflected in a complete degradation of different concentrations of it after 40 min (50 mg/L), 60 min (100 mg/L), 100 min (150 mg/L) and 140 min (200 mg/L) using 0.25 g of the composite. The complete removal of the present TOC for treatment of 100 mg/L acephate was achieved using 0.25 g after 70 min reflecting the formation of intermediate compounds during the oxidation steps. The reported intermediate compounds are CH3C(O)NH2, CH3O(CH3S)P(O)NH2, (CH3O)2P(O)SCH3, CH3OP(O)(OH)2, CH3SS(O)2CH3, and (COOH)2. All the formed intermediate compounds were degraded under the visible light photocatalytic activity of RH-MCM-41/Co3O4 into NO3−, SO42-, PO43-, and CO2 as final products.

Reactions’ Mechanisms and Applications of Hydrogen Peroxide

Hydrogen peroxide is a key substance in the appearance of life and maintenance of the life-supporting conditions on the Earth. Electron transfer processes between H2O2 and various reducers are of major interest for the environment, natural life, technology, etc. An overview of structure, proprieties and main reactions of hydrogen peroxide in model and real systems is presented. The authors try to find the answers to the following questions: why this substance has the unique and specific dual reduction-oxidation properties, what is the connection between its structure and reactions, what role it plays in the catalytic reduction processes occurring in the natural environment and technological systems, accompanied by the formation of intermediate compounds, active radicals, complete and partial charge transfer complexes, etc. The thermodynamic possibility of the synchronous two-electron transfer during the inner sphere reaction with the involvement of metal ion complexes capable of changing the valence by two units is discussed. The role of the partial charge transfer structures which combine the properties of the initial reagents and the expected reaction products is demonstrated. Such complexes can be decomposed both reversibly and irreversibly. In case when the single-electron transfer is thermodynamically preferable, the main oxidizing particle is OH-radical, capable to interact non-selectively with almost all the water-soluble organic substances. Special attention is paid to the photo initiation of peroxidase transformation processes. The results of our multi-annual research of these issues are reported.

ORGANIC-INORGANIC PEROVSKITE CH3NH3PbI3: MORPHOLOGICAL, STRUCTURAL AND PHOTOELECTROPHYSICAL PROPERTIES

The organic-inorganic perovskite films CH3N-H3PbI3 were synthesized from solutions with different ratios of initial reagents (PbI2 to CH3NH3I were taken in the ratio 1:1, 1:2 and 1:3). To deposit films of organic-inorganic perovskite, solutions with different ratio of initial reagents were applied to the substrates by the spin-coating method. The organic-inorganic perovskites synthesized were of one chemical composition in spite of the fact that different chemical reactions proceeded during the synthesis. It was found that the formation of perovskite occurs according to different schemes depending on the ra-tio of PbI2 and CH3NH3I: without the formation of intermediate compounds (at ratio 1:1) and with the formation of one (CH3NH3)2PbI4 (1:2) and two intermediate compounds (CH3NH3)3PbI5, (CH3NH3)2PbI4 (1:3).It was established that regardless of the ratio of the initial reagents, organic-inorganic perovskites with different morphology are formed. At the ratio of the initial reagents 1:1, needle particles formed, and at the ratio of 1:2 and 1:3, particles have the form of a maple leaf and round shape, respectively.To improve the film stability, polyvinyl butyral polymer was used. It is an amorphous colorless pol-ymer which is characterized by high optical properties, environmental (in particular, H2O, O2 and O3) and light resistance. The stability of films of organic-inorganic perovskite without and with a polymer were investigated by XRD, fluorescence spectroscopy and non-contact optical methods. The stability of the films was evaluated by the content of the additional phase of PbI2, which is formed due to the degradation of the organic-inorganic perovskite film CH3NH3PbI3. It was established that the presence of a polymer layer results in improved stability of samples and decrease the rate of surface recombination velocity compared to samples without a polymer layer.The diffusion length of minority charge carriers of the organic-inorganic perovskite films with the polymeric layer was estimated by the method of spectral dependences of the surface photovoltage. The spectra of surface photovoltage and the diffusion length of minority charge carriers of organic-inorganic perovskites with a polymer layer were compared with the literature data for samples without a polymer layer. This comparison shown that the characteristics of the samples with polymer layer are somewhat worse. It is determined that the organic-inorganic perovskite with the polymer layer is characterized by a smaller diffusion length (by 10%) of the minority charge carriers. The prepared perovskite films CH3NH3PbI3 are promising for the development of effective solar cells.

Investigation of the kinetics and the morphology of cementation products formed during purification of a synthetic zinc sulfate electrolyte

In zinc production, the purity of incoming zinc solution is of great importance. The presence of cobalt in the electrolyte used for zinc production lowers the current efficiency of zinc deposition and affects the purity of the zinc product. For this reason, cobalt must be removed from the electrolyte prior to zinc electrowinning. Cobalt removal is commonly achieved by the addition of metallic zinc dust through a process called cementation. The mechanism by which cementation occurs is not well understood. Parameters, such as cementation time, temperature, solution pH, concentration of activators, concentration of zinc ions in the electrolyte were investigated in this study. It was concluded that cobalt cementation could be described by a first order rate equation with an activation energy of 45 kJ/mol. Temperature played a significant role on the kinetics while the presence of hydrogen, intermediate compound formation, and zinc ions inhibited the cobalt cementation. Cu/Sb activators were cemented within the first 90 s and gave synergistic effect on cobalt cementation. Surface compounds on the cementation product were identified as mainly Zn(OH)2 and ZnSO4. Redissolution of cobalt did not occur from cemented cobalt but from dissolution of intermediate Co(OH)2 and CoSO4 salts.

Pyridyl Azo‐Based Naphthyl Acetate for Sensing of Hydrazine and Perborate in Sol‐Gel Medium

AbstractPyridyl azo‐based naphthyl acetate 1 has been designed and synthesized. Compound 1 acts as progelator in CH3CN‐H2O (1:1, v/v) and exhibits reactivity towards nucleophilic substrate for ester hydrolysis. In the presence of hydrazine and perborate, the solution of 1 in CH3CN‐H2O (1:1, v/v) undergoes gelation due to formation of intermediate compound 2 through removal of acetyl group. Gelation study reveals that while compound 2 in CH3CN‐H2O (1:1, v/v) forms gel, compound 1 remains in solution. Hydrazine brings gelation rapidly than perborate and validates their visual sensing. The deacetylation reaction has been supported by various spectroscopic data. Compound 1 in solution is also responsive to hydrazine with reasonably low detection limit. Other substrates, including perborate, did not generate a measurable response. As a proof‐of‐principle application, a test strip of compound 1 was shown to allow the detection of hydrazine in solution and vapor states. To the best of our knowledge, this is the first example of stimuli responsive low molecular weight gelator (LMWG) which dosimetrically senses hydrazine and perborate under different conditions.

Insight into How Telomeric G-Quadruplexes Enhance the Peroxidase Activity of Cellular Hemin.

The toxic oxidative damage of G-quadruplexes (G4), linked to neurodegenerative diseases, may arise from their ability to bind and oxidatively activate cellular hemin. However, there have been no precise studies on how telomeric G4 enhances the low intrinsic peroxidase activity of hemin. Herein, a label-free and nanopore-based strategy was developed to explore the enhancement mechanism of peroxidase activity of hemin induced by telomeric G4 (d(TTAGGG)n ). The nanopore-based strategy demonstrated that there were simultaneously two different binding modes of telomere G4 to hemin. At the single-molecule level, it was found that the hybrid structural telomeric G4 directly binds to hemin (the affinity constant (Ka )≈106 m-1 ) to form a tight complex, and some of them underwent a topological change to a parallel structure with an enhancement of Ka to approximately 107 m-1 . Through detailed analysis of the topology and peroxidase activity and molecular modeling investigations, the parallel telomere G4/hemin DNAzyme structure was proven to be preferable for high peroxidase activity. Upon strong π-π stacking, the parallel structural telomere G4 supplied a key axial ligand to the hemin iron, which accelerated the intermediate compound formation with H2 O2 in the catalytic cycle. Our studies developed a label-free and single-molecule strategy to fundamentally understand the catalytic activity and mechanism of telomeric DNAzyme, which provides some support for utilizing the toxic, oxidative-damage property in cellular oxidative disease and anticancer therapeutics.

Fast preparation of Cu(In,Ga)Se2 and CuIn(S,Se)2 bulk materials by combustion synthesis

AbstractCuIn1‐xGaxSe2 and CuIn(SySe1‐y)2 bulk materials with relative densities of 93.4%‐96.2% have been prepared by combustion synthesis, from elementary reactants and in a reaction time of a few seconds. The samples have a chalcopyrite lattice structure, and the lattice parameters decrease with increasing x and y. The substitution of In with Ga and Se with S in CuInSe2 causes an increase in the bandgap. In combustion synthesis, the high temperature accelerates the reaction and results in fast densification, the high heating rate simplifies the reaction path and avoids the formation of intermediate compounds, and the gas pressure depresses the evaporation of reactants. As a fast, furnace‐free, and scalable technique, combustion synthesis may offer a low‐cost way to produce CuInSe2‐based materials and bring new possibilities to their commercial applications.

Використання ароматичних сполук бактеріями. І. Аеробна й анаеробна деструкція

This review summarizes current information on the extent of environmental pollution by xenobiotics of aromatic nature, and their toxic effects on living organisms. Phenols, monocyclic (benzene, toluene, xylene etc) and polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, biphenуls, pyrene, benzpyrene, pyridine etc.) are the most dangerous pollutant aromatic compounds. A variety of microorganisms capable to destroy the aromatic compounds is described. The biodegradation of aromatic pollutants is carried out by denitrifying, sulfate-reducing, photosynthetic, fermentation, iron-reducing, acetogenic bacteria and methanogens. The paper analyzes and generalizes the ways of decomposition of compounds of aromatic nature under bacterial aerobic and anaerobic conditions, describes the peripheral ways of oxidation of aromatic compounds and their regulation, examines the ability of microorganisms to use substituents in the benzene ring as a source of carbon and nitrogen. The processes of aerobic and anaerobic biodegradation of aromatic compounds have common particularities, that are the key intermediates formation. These intermediates are involved into the central metabolism of the cell due to the activity of metabolic pathways of various groups of microorganisms. Under the aerobic conditions, the rupture of benzene ring can occur between two successively connected carbon atoms carrying hydroxyl groups ( ortho -cleavage), or on other C-C bonds of the nucleus in meta -position ( meta -clea­vage). The central metabolic pathways provide a formation of intermediate compounds of the Krebs cycle. Benzoyl-CoA is a central intermediate of decomposition of aromatic xenobiotics under anaerobic conditions. In this review, different variants of benzoyl-CoA pathway for the degradation of aromatic compounds by bacteria are considered. Due to the destruction of aromatic compounds by various microorganisms, a large number of intermediate metabolites are formed. They are further degraded by bacteria of various ecological trophic groups. At the result, complete decomposition of the aromatic compounds occurs. The ability of microorganisms to decompose xenobiotics enables sol­ving a number of environmental problems associated with both the use of chemical pesticides and the discharge of untreated industrial wastewater.

Dynamics of phase formation during the synthesis of magnesium diboride from elements in thermal explosion mode

The influence of the heating rate of the Mg + 2B mixture on the dynamics of the phase formation during the thermal explosion in the helium medium is investigated by the time-resolved X-ray diffraction method. It is shown that the MgB2 phase appears without the formation of intermediate compounds. The presence of impurity oxygen is a substantial factor affecting the formation kinetics of MgB2. The oxide film on the surface of magnesium particles has no time to form with the heating rate of the charge mixture of 150–200°C/min. A result of this circumstance is the reaction diffusion mechanism of the Mg + 2B = MgB2 reaction immediately after the melting of magnesium. Synthesis products mainly consist of MgB2 and MgO traces at a level of 5%. The thermal explosion temperature is 1100°C. A comparatively thick oxide film which retards melt spreading and shifts the onset of the formation reaction of MgB2 by 8–9 s grows on the magnesium surface at a heating rate of 30–50°C/min. Synthesis products contain MgB2 and up to 15% MgO. The thermal explosion temperature is 1020°C in this case.

Preparation of the Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte with high ionic conductivity

A new effective method is proposed for synthesis of the Li1.5Al0.5Ge1.5(PO4)3 powdered solid electrolyte of NASICON structure with high lithium ionic conductivity. The advantage of the method consists in use of a liquid-phase precursor based on the water-soluble Ge(IV) oxalate complex. Chemical interaction in a multicomponent solution containing a liquid-phase precursor results in a target product without the formation of intermediate compounds. This makes it possible to diminish considerably the synthesis temperature (to 650°C) and duration of preparation of Li1.5Al0.5Ge1.5(PO4)3 powders owing to a better homogenization of the reaction mixture and also to simplify the technological operations. The synthesized Li1.5Al0.5Ge1.5(PO4)3 powders are studied by the XRD, DSC/TG, and IR spectroscopy methods, as well as by chemical analysis, SEM, and impedance spectroscopy. The conditions are determined for production of polycrystalline Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte with the maximum bulk ionic conductivity of 1 × 10–3 S/cm at room temperature.

EPOXIDATION OF ALLYL ALCOHOL TO GLYCIDOL WITH HYDROGEN PEROXIDE AT TITANIUM SILICALITE

It was studied the epoxidation mechanism of allyl alcohol using titanosilicate zeolite (TS-1) at 40°C by means of procedures for the nomination and discrimination of mechanism hypotheses. The hypotheses was carried out using the literature data and the preliminary experiment results. Discrimination hypothetical mechanisms implemented on the basis of the univariate results of the kinetic experiment, varying concentrations of allyl alcohol, hydrogen peroxide and glycidol. The most probable mechanism involves the hydrogen peroxide and allyl alcohol adsorption at the catalyst active centers and the glycidol formation at a reversible stage in the interaction of the adsorbed molecules of the reactants. Considered hypotheses include a different sequence of interaction of the reactants with active catalyst centre. In addition, hypotheses take into account the formation of intermediate compounds as well as inactive products of the interaction of substances present in the reaction system, with the active centers on the silicalite surface. For each hypothesis, it was formulated the corresponding system of differential equations and carried out the estimation of the rate constants. The quality of the experimental data description was judged by the residual sums of squared deviations and correlation coefficients. The best results are obtained for the hypothesis involving the hydrogen peroxide and allyl alcohol adsorption at the two active catalyst centers with subsequent interaction of the resultant intermediates between them, with the formation of glycidol adsorbed on one center, free catalyst centre and molecule of water. Formation of free glycidol occurs at a reversible stage. A significant part of the active centers of the catalyst increasing the concentration of glycidol is associated with it. This is the main reason for the decrease of the reaction rate, apart from reducing the concentration of the reactants.

Electrochemical Characterization of Novel Organoborohydride Compounds

Sodium borohydride (NaBH4) is a solid white powder that finds wide application as a reducing agent in organic and inorganic synthesis [1]. This compound possesses relatively mild reducing abilities, but certain applications call for reducing powers greater than NaBH4, while others require the reducing powers to be attenuated. Organic chemists have successfully tuned the reducing power of NaBH4by attaching organic electron donating or withdrawing groups to the boron center, which can also drive regio- and stereoselectivity. These organoborohydrides have received much recent attention for their role in frustrated Lewis pair systems [2], as well as in hydrogen fuel carriers. Computational methods have established the tuning power of different organic substituents on the boron center, but experimentally quantifying reducing power remains difficult [3]. The present study seeks to quantify reducing power using electrochemical methods and elucidate the relationship between organic tuning group and reducing ability. In this work, benzylborohydride (C7H7BH3Na) was prepared by reduction of potassium benzyltrifluoroborate with a metal hydride. The compound structure was further characterized by multinuclear NMR and FTIR. Whereas, the electrochemical characterization was carried out using a standard three-electrode setup, by cyclic voltammetry (CV) in static conditions and by linear scan voltammetry (LSV) using a rotating ring-disk electrode (RRDE) system. Platinum and gold disk macroelectrodes and microelectrodes were used to study the electrooxidation of these compounds. The organoborohydrides were tested in DMSO + 0.03 M C7H7BH3Na at temperatures ranging from 25 to 65 ºC. The results were directly compared with NaBH4solutions in the same experimental conditions. The main electrochemical parameters were calculated, including number of exchanged electrons, charge transfer coefficient, reaction rate constant, and diffusion coefficient for the selected range of temperatures. Moreover, the activation energy for the benzylborohydride oxidation reaction was calculated assuming Arrhenius behavior. The formation of intermediate compounds was checked by RRDE studies, elucidating the possible steps involved in the oxidation mechanism. Several other organoborohydride compounds are planned to be studied and that will allow finding a direct relationship between organic substituents and the reducing power of the borohydride center. 1. H.O. House, Modern synthesis reactions, Benjamin, W.A., Menlo Park, CA, 1972. 2. J. Paradies, Metal-free hydrogenation of unsaturated hydrocarbons employing molecular hydrogen, Angew. Chem. Int. Ed. 53 (2014) 3552. 3. Z.M Heiden, A.P. Lathem, Establishing the hydride donor abilities of main group hydrides, Organometallics 34 (2015) 1818.

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

Rare-earth metals, particularly neodymium, dysprosium, and praseodymium are becoming increasingly important in the transition to a green economy due to their essential role in permanent magnet applications such as in electric motors and generators. With the increasingly limited rare-earth supply and complexity of processing Nd, Dy, and Pr from primary ores, recycling of rare-earth based magnets has become a necessary option to manage supply and demand. Depending on the form of the starting material (sludge or scrap), there are different routes that can be used to recover neodymium from secondary sources, ranging from hydrometallurgical (based on its primary production process), electrochemical to pyrometallurgical. Pyrometallurgical routes provide solution in cases where water is scarce and generation of waste is to be limited. This paper presents a systematic review of previous studies on the high-temperature (pyrometallurgical) recovery of rare earths from magnets. The features and conditions at which the recycling processes had been studied are mapped and evaluated technically. The review also highlights the reaction mechanisms, behaviors of the rare-earth elements, and the formation of intermediate compounds in high-temperature recycling processes. Recommendations for further scientific research to enable the development of recovery of the rare-earth and magnet recycling are also presented.

An effective method for the preparation of high temperature stable anatase TiO2 photocatalysts

An efficient, rapid and straightforward method for the preparation of nitrogen and fluorine (N, F) codoped high temperature stable anatase using a microwave pre-treatment is reported. Using a single source, ammonium fluoride (NH4F) for both nitrogen and fluorine, effective doping of the precursor titanium isopropoxide (TTIP) was possible. These samples were characterised for their structural and optical properties using X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman spectroscopy and UV–vis spectroscopy. In terms of the anatase to rutile transition enhancement using a novel microwave assisted technique, the sample prepared in a composition of 1:8 TiO2: NH4F at 1200°C was seen to be most effective, having stable anatase present at 57.1% compared to undoped TiO2 being 100% rutile from 900°C. This method involves the production of ammonium oxofluorotitanates (NH4TiOF3) at low temperatures. The inclusion of these intermediates greatly reduces the particle size growth and delays the anatase to rutile transition. The photocatalytic activity of these materials was studied by analysing the degradation of an organic dye, rhodamine 6G as a model system and the rate constant was calculated by pseudo-first-order kinetics. These results showed that the doped sample (0.0225min−1) was three times more active than the undoped sample (0.0076min−1) and over seven times faster than the commercial TiO2 photocatalyst standard Degussa P-25 calcined at 1200°C (0.0030min−1). The formation of intermediate compounds, oxofluorotitanates, was identified as the major reason for a delay in the anatase to rutile transition.

Phase formation dynamics upon thermal explosion synthesis of magnesium diboride

Time-resolved X-ray diffraction was used to study the dynamics of phase formation in magnesium diboride produced by self-propagating high-temperature synthesis in the thermal explosion mode. The MgB2 phase was demonstrated to emerge without the formation of intermediate compounds. The effect of the mixture heating rate on the formation mechanism of the MgB2 phase was established. The presence of oxygen impurities has a significant impact on the kinetics and formation mechanism of MgB2. If the heating rate exceeds 150°/min, the oxide coating is not formed around the magnesium particles, which results in the solid-phase reaction of Mg+2B=MgB2 through a reaction diffusion mechanism. Moreover, the self-ignition temperature of the mixture is lower than the melting point for magnesium. Mechanical activation of the mixture leads to variations in the kinetics of MgB2 formation, significantly increases the period of simultaneous existence of Mg and MgB2, and reduces the temperature at which the reaction occurs.

Growth of Paecilomyces variotii in B0 (diesel), B100 (biodiesel) and B7 (blend), degradation and molecular detection.

The introduction of biodiesel to diesel may allow the fuel to be more susceptible to microorganism growth, especially during incorrect storage. To evaluate the effect of adding biodiesel in pure diesel on the growth of Paecilomyces variotii, microcosms containing pure diesel (B0), blend diesel/biodiesel (B7) and pure biodiesel (B100) were used. In microcosm with minimal mineral medium and B0, B7 or B100, after 60 days, the biomass (dry weight) formed at interface oil-water in B7 and B100 was significantly higher when compared to that of B0. Infrared analysis showed reduction of the carbonile fraction in B7 and B100 suggesting formation of intermediate compounds in B7. To monitor possible contamination of fuel storage tank by P. variotii samples were collected and analysed by specific-PCR assay for detection of P. variotii spores in the aqueous phase. This method was able to detect a minimum of 103 spores ml-1, corresponding to 0.0144 ng µl-1 of DNA. Specificity was tested against Aspergillus fumigatus and Pseudallescheria boydii.

Study on the hydrogen storage properties and reaction mechanism of NaAlH4–Mg(BH4)2 (2:1) with and without TiF3 additive

In this work, hydrogen storage properties and reaction mechanism of NaAlH4–Mg(BH4)2 (2:1) composites system with and without additive have been investigated. The secondary-hydride system was found to initiate a transformation of the NaAlH4/Mg(BH4)2 to Mg(AlH4)2/NaBH4 during ball milling, and there was a mutual destabilization among the hydrides. Three major dehydrogenation steps were observed in the systems, which corresponded to the decomposition of Mg(AlH4)2, MgH2, and NaBH4. Temperature-programmed desorption results showed that the TiF3-doped NaAlH4–Mg(BH4)2 (2:1) composite sample started to release hydrogen at about 75 °C, which was 60 °C lower than that of undoped NaAlH4–Mg(BH4)2 (2:1) composite sample. In addition, the reaction pathway of the NaAlH4–Mg(BH4)2 (2:1) composite system, and the mechanisms that worked in this composite during the de/rehydrogenation process were determined by X-ray diffraction. The Kissinger analysis has shown that the apparent activation energy, EA, for decomposition of NaBH4 in the NaAlH4–Mg(BH4)2–TiF3 composite reduced to 139.85 kJ/mol compared with 155.73 kJ/mol in NaAlH4–Mg(BH4)2 composite. It is believed that the enhancement of the de/rehydrogenation properties of undoped NaAlH4/Mg(BH4)2 was attributed to the formation of intermediate compounds, including Mg–Al and Mg–Al–B alloys, upon dehydrogenation, which changed the thermodynamics of the reactions by altering the de/rehydrogenation pathway. Meanwhile, as for the doped sample, the TiF3 component played a catalytic role through the formation of Ti-containing and F-containing catalytic species, which might have promoted the interaction of Mg(AlH4)2 and NaBH4, and thus, further improved the dehydrogenation of the NaAlH4–Mg(BH4)2 (2:1) system.

Study of thermally activated reaction between Mn and GaAs(111) surface

We investigate the chemical reactivity of ultra-thin films of Mn on As-terminated (111) GaAs surface kept at ultra-high vacuum conditions in the temperature interval ranging from room temperature to 400°C. The experiments were performed using a customized molecular beam epitaxy system equipped with reflection high energy electron diffraction and X-ray photoelectron spectroscopy techniques. These analyses were complemented with X-ray diffraction measurements to put in evidence the formation of intermediate compounds. Only Ga1−xMnxAs and sub-arsenised MnAsx compounds are possibly formed below 200°C. The onset of the reactivity occurs around 200°C when ordered compounds such as MnAs and MnGa are observed. The formation of compounds more rich in Mn like Mn3Ga and Mn2As is found for deposition temperatures of 300 and 400°C.

Study on the hydrogen storage properties and reaction mechanism of NaAlH4–MgH2–LiBH4 ternary-hydride system

In this paper, we report the hydrogen storage properties and reaction mechanism of NaAlH4–MgH2–LiBH4 (1:1:1) ternary-hydride system prepared by ball milling. It was found that during ball milling, the NaAlH4/MgH2/LiBH4 combination converted readily to the mixture of LiAlH4/MgH2/NaBH4 and there is a mutual destabilization among the hydrides. Three major dehydrogenation steps were observed in the system, which corresponds to the decomposition of LiAlH4, MgH2, and NaBH4, respectively. The onset dehydrogenation temperature of MgH2 in this system is observed at around 275 °C, which is over 55 °C lower from that of as-milled MgH2. Meanwhile, NaBH4-relevant decomposition showed significant improvement, starts to release hydrogen at 370 °C, which is reduced by about 110 °C compared to the as-milled NaBH4. The second and third steps decomposition enthalpy of the system were determined by differential scanning calorimetry measurements and the enthalpies were changed to be 61 and 100 kJ mol−1 H2 respectively, which are smaller than that of MgH2 and NaBH4 alone. From the Kissinger plot, the apparent activation energy, EA, for the decomposition of MgH2 and NaBH4 in the composite was reduced to 96.85 and 111.74 kJ mol−1 respectively. It is believed that the enhancement of the dehydrogenation properties was attributed to the formation of intermediate compounds, including Li–Mg, Mg–Al, and Mg–Al–B alloys, upon dehydrogenation, which change the thermodynamics of the reactions through altering the de/rehydrogenation pathway.

Degradation of fluoroquinolone antibiotics and identification of metabolites/transformation products by liquid chromatography–tandem mass spectrometry

Antibiotics are a therapeutic class widely found in environmental matrices and extensively studied due to its persistence and implications for multi-resistant bacteria development. This work presents an integrated approach of analytical multi-techniques on assessing biodegradation of fluorinated antibiotics at a laboratory-scale microcosmos to follow removal and formation of intermediate compounds. Degradation of four fluoroquinolone antibiotics, namely Ofloxacin (OFL), Norfloxacin (NOR), Ciprofloxacin (CPF) and Moxifloxacin (MOX), at 10mgL−1 using a mixed bacterial culture, was assessed for 60 days. The assays were followed by a developed and validated analytical method of LC with fluorescence detection (LC–FD) using a Luna Pentafluorophenyl (2) 3μm column. The validated method demonstrated good selectivity, linearity (r2>0.999), intra-day and inter-day precisions (RSD<2.74%) and accuracy. The quantification limits were 5μgL−1 for OFL, NOR and CPF and 20μgL−1 for MOX. The optimized conditions allowed picturing metabolites/transformation products formation and accumulation during the process, stating an incomplete mineralization, also shown by fluoride release. OFL and MOX presented the highest (98.3%) and the lowest (80.5%) extent of degradation after 19 days of assay, respectively. A representative number of samples was selected and analyzed by LC–MS/MS with triple quadrupole and the molecular formulas were confirmed by a quadruple time of flight analyzer (QqTOF). Most of the intermediates were already described as biodegradation and/or photodegradation products in different conditions; however unknown metabolites were also identified. The microbial consortium, even when exposed to high levels of FQ, presented high percentages of degradation, never reported before for these compounds.