Pretreatment of switchgrass by ammonia fiber explosion (AFEX)

The effects of ammonia fiber explosion (AFEX) pretreatment of switch grass using its major process variables are reported. The optimal pretreatment conditions for switchgrass were found to be near 100°C reactor temperature, and ammonia loading of 1:1 kg of ammonia: kg of dry matter with 80% moisture content (dry weight basis [dwb]) at 5 min residence time. Hydrolysis results of AFEX-treated and untreated samples showed 93% vs 16% glucan conversion, respectively. The ethanol yield of optimized AFEX-treated switchgrass was measured to be about 0.2 g ethanol/g dry biomass, which is 2.5 times more than that of the untreated sample.     

Preconcentration and determination of ultra trace amounts of arsenic(III) and arsenic(V) in tap water and total arsenic in biological samples by cloud point extraction and electrothermal atomic absorption spectrometry

A new approach for developing a cloud point extraction-electrothermal atomic absorption spectrometry has been described and used for determination of arsenic. The method is based on phase separation phenomenon of non-ionic surfactants in aqueous solutions. After reaction of As(V) with molybdate towards a yellow heteropoly acid complex in sulfuric acid medium and increasing the temperature to 55 °C, analytes are quantitatively extracted to the non-ionic surfactant-rich phase (Triton X-114) after centrifugation.To decrease the viscosity of the extract and to allow its pipetting by the autosampler, 100 μl methanol was added to the surfactant-rich phase. An amount of 20 μl of this solution plus 10 μl of 0.1% m/v Pd(NO₃)₂ were injected into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry.Total inorganic arsenic(III, V) was extracted similarly after oxidation of As(III) to As(V) with KMnO₄. As(III) was calculated by difference. After optimization of the extraction condition and the instrumental parameters, a detection limit (3σ_B) of 0.01 μg l⁻¹ with enrichment factor of 52.5 was achieved for only 10 ml of sample. The analytical curve was linear in the concentration range of 0.02-0.35 μg l⁻¹. Relative standard deviations were lower than 5%. The method was successfully applied to the determination of As(III) and As(V) in tap water and total arsenic in biological samples (hair and nail).     

Selective extraction and preconcentration of cerium(IV) in water samples by cloud point extraction and determination by inductively coupled plasma optical emission spectrometry

Cloud point extraction (CPE) was used for the selective extraction and separation of cerium(IV) from aqueous solutions. The method is based on the formation of cerium(IV)-n-p-tolylbenzohydroxamic acid (n-TBHA) complex that is extracted into the micellar phase (Triton X-114) at a temperature above the cloud point temperature (CPT). After phase separation, the surfactant rich phase was diluted up to 1.0 mL and determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). Under the optimum extraction conditions and instrument parameters, by preconcentration of only 10.0 mL of sample in the presence of 0.09% Triton X-114, an enhancement factor of 13.8 was obtained. The analytical curve was linear in the range of 1.5–1200 μg L⁻¹ and the detection limit was 0.4 μg L⁻¹. The method was applied to the determination of Ce(IV) in water samples with satisfactory results.     

Determination of ultra trace amounts of bismuth in biological and water samples by electrothermal atomic absorption spectrometry (ET-AAS) after cloud point extraction

A new approach for a cloud point extraction electrothermal atomic absorption spectrometric method was used for determining bismuth. The aqueous analyte was acidified with sulfuric acid (pH 3.0-3.5). Triton X-114 was added as a surfactant and dithizone was used as a complexing agent.After phase separation at 50 °C based on the cloud point separation of the mixture, the surfactant-rich phase was diluted using tetrahydrofuran (THF). Twenty microliters of the enriched solution and 10 μl of 0.1% (w/v) Pd(NO₃)₂ as chemical modifier were dispersed into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry. After optimizing extraction conditions and instrumental parameters, a preconcentration factor of 196 was obtained for a sample of only 10 ml. The detection limit was 0.02 ng ml⁻¹ and the analytical curve was linear for the concentration range of 0.04-0.60 ng ml⁻¹. Relative standard deviations were <5%.The method was successfully applied for the extraction and determination of bismuth in tap water and biological samples (urine and hair).     

A Theoretical Study of 1‐D and 2‐D Helium Lattices

One‐ and two‐dimensional (1‐D and 2‐D) helium lattices have been studied using ab initio RHF/6–31G** computations. Structural, physical and thermochemical properties have been calculated and analyzed for the 1‐D and 2‐D He_N lattices respectively up to N = 50 and N = 36. Asymptotic properties of the 1‐D He_N lattices are obtained by extrapolating N‐dependence properties to large values of N. Analysis of the results show that the bulk per‐atom interaction (binding) energies increase while the optimized interatomic distances (bond lengths) slightly decrease with the increase in size of the 1‐D He_N lattices and both reach their asymptotic values of 0.352 cm^?1 and 3.18775 Å, respectively. Between the square and hexagonal (packed) structures of the 2‐D He_N lattices, the latter is more favored. Extrapolated values of the calculated properties, including lattice parameter, binding and zero point energies, heat capacity, and entropy have also been calculated for both 1‐D and 2‐D He_N lattices. The surface densities for monolayer films of helium atoms with square and hexagonal configurations have been calculated to be respectively 9.84 × 10¹⁸ and 1.04 × 10¹⁹ helium atoms/cm² which are comparable to the experimental value of 2.4 × 10¹⁹ helium atom/m² well within the typical large and directional error bars of the experiments. Surface effects have been investigated by comparing the packed He_N2‐D lattices with the same value of N but with different geometries (arrangements). This comparison showed that the He_N lattices prefer arrangements with the smallest surface area.     

A new Cu Schiff base complex with histidine and glutaraldehyde immobilized on modified iron oxide nanoparticles as a recyclable catalyst for the oxidative homocoupling of terminal alkynes

The novel functionalized Fe₃O₄@SiO₂@APTMS@Glu-His@Cu complex was prepared from modification of iron oxide nanomagnet particles with (3-aminopropyl) trimethoxysilane (APTMS) and glutaraldehyde–histidine Schiff base followed by complexation with Cu(I) salt. Characterization of this complex was carried out by means of FTIR, XRD, SEM, TEM and VSM techniques. The complex was found to successfully catalyze the oxidative homocoupling of phenylacetylene, 4-tert-butylphenylacetylene, 1-ethynyl-4-fluorobenzene and pent-1-yn-3-ol with 67–100 % conversions and 95–100 % selectivities. Magnetic recovery and recycling of the catalyst without significant decrease in activity is described in this presentation.     

X-Ray and NMR Structural Data of Ethynylbenziodoxolones (EBXs) Reagents and Their Analogues

First synthesized in 1991, EthynylBenziodoXolones (EBXs) – cyclic hypervalent iodine reagents derived from 2-iodobenzoic acid – are now among the most versatile electrophilic alkynylation reagents. Due to their cyclic structure, these reagents exhibit enhanced stability compared to previously used alkynyl iodonium salts. Over the last decade, both the iodoheterocycle and the arene ring have been extensively modified to fine-tune the reactivity of the reagents, resulting in new analogues such as Ethynylbenziodoxoles (EBxs) or N-heterocyclic reagents. In this article, we have for the first time compiled the structural data available for EBXs and their analogues, focusing especially on X-Ray and NMR data. For selected compounds, molecular electrostatic potentials (MEP) have also been calculated. When considering the tight relationship between structure and reactivity in hypervalent iodine reagents, the collected data is expected to be highly useful for further developments in the field.     

A Bifunctional Electrocatalyst for OER and ORR based on a Cobalt(II) Triazole Pyridine Bis-[Cobalt(III) Corrole] Complex

As alternative energy sources are essential to reach a climate-neutral economy, hydrogen peroxide (H₂O₂) as futuristic energy carrier gains enormous awareness. However, seeking for stable and electrochemically selective H₂O₂ ORR electrocatalyst is yet a challenge, making the design of—ideally—bifunctional catalysts extremely important and outmost of interest. In this study, we explore the application of a trimetallic cobalt(II) triazole pyridine bis-[cobalt(III) corrole] complex Co^IITP[Co^IIIC]₂ 3 in OER and ORR catalysis due to its remarkable physicochemical properties, fast charge transfer kinetics, electrochemical reversibility, and durability. With nearly 100 % selective catalytic activity towards the two-electron transfer generated H₂O₂, an ORR onset potential of 0.8 V vs RHE and a cycling stability of 50 000 cycles are detected. Similarly, promising results are obtained when applied in OER catalysis. A relatively low overpotential at 10 mA cm⁻² of 412 mV, Faraday efficiency 98 % for oxygen, an outstanding Tafel slope of 64 mV dec⁻¹ combined with superior stability.     

Production and properties of a biosurfactant obtained from a member of the Bacillus subtilis group (PTCC 1696)

The production and properties of a biosurfactant, synthesized by a member of the Bacillus subtilis group (PTCC 1696) which was isolated from an Iranian oil field, have been investigated. The biosurfactant, which was produced as a primary metabolite associated with the growth of PTCC 1696, was able to reduce the surface and interfacial tension of media to 26.7 and 0.1 mN/m, respectively. Crude biosurfactant and acid precipitated biosurfactant have critical micelle concentrations of 10 and 100 mug/ml, respectively. The stability of the biosurfactant at different salinities, pH and temperature and also its emulsifying activity have been investigated. It is an effective surfactant at very low concentrations over a wide range of temperatures, pHs and salt concentrations and also has the ability to emulsify oil, which is essential for enhanced oil recovery.