Fabrication of gas ionization sensor based on titanium oxide nanotube arrays

Gas sensors have been fabricated based on field ionization from titanium oxide nanotubes grown on titanium foil. Ordered nanaotube arrays of titanium oxides were grown by the anodization method. We measured breakdown voltages and discharge currents of the device for various gases. Our gas ionization sensors (GIS) presented good sensitivity, selectivity, and short response time. The GISs based on TiO₂ nanotube arrays showed lower breakdown voltage, higher discharge current, and good selectivity. An excellent response observed for Ar compared to other gases. Besides, by introducing 2 % CO and 4 % H₂ to N₂ flow gas, the amount of breakdown voltage shifts about 20 and 70 volts to the lower values, respectively. The GIS works at room temperature and has the ability of detect inert gases with high stability and good linearity. Besides, short response time of about 1 second for the GISs based on TiO₂ nanotube arrays makes them excellent for gas sensing applications. Sharp edges of the nanotubes, through enhancing the applied electric field, reduce operating voltage to the reasonable values and power consumption.     

Non-equilibrium STLS approach to transport properties of single impurity Anderson model

In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron–electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current–voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron–electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U²$U^2$ IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior.     

Factorizations in numerical semigroup algebras

We study a numerical semigroup ring as an algebra over another numerical semigroup ring. The complete intersection property of numerical semigroup algebras is investigated using factorizations of monomials into minimal ones. The goal is to study whether a flat rectangular algebra is a complete intersection. Along this direction, special types of algebras generated by few monomials are worked out in detail.     

Synthesis of Fulvene Vinyl Ethers by Gold Catalysis

Gold-catalyzed cyclization of 1,5-diynes with ketones as reagents and solvent provides diversely substituted vinyl ethers under mild conditions. The regioselectivity of such gold-catalyzed cyclizations is usually controlled by the scaffold of the diyne. Herein, we report the first solvent-controlled switching of regioselectivity from a 6-endo-dig- to 5-endo-dig-cyclization in these transformations, providing fulvene derivatives. With respect to the functional-group tolerance, aryl fluorides, chlorides, bromides, and ethers are tolerated. Furthermore, the mechanism and selectivity are put to scrutiny by experimental studies and a thermodynamic analysis of the product. Additionally, 6-(vinyloxy)fulvenes are a hitherto unknown class of compounds. Their reactivity is briefly evaluated, to give insights into their potential applications.     

A highly flexible green synthesis of 1H-pyrazolo[1,2-b]phthalazine- 5,10-dione derivatives with CuI nanoparticles as catalyst under solvent-free conditions

CuI nanoparticles as an efficient catalyst have been used for the preparation of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones by the four-component condensation reaction of phthalic anhydride, hydrazine monohydrate, aromatic aldehydes and malononitrile or ethyl cyanoacetate under solventfree conditions in good to excellent yields, short reaction times and environmentally benign, milder reaction conditions.     

Synthesis of 8-aryl-1H-pyrazolo[4,3-e][1,2,4]triazolo[4,3-a] pyrimidine-4(5H)-imine by using the Preyssler''s anion [NaP5W30O110] as a green and eco-friendly catalyst

Reaction of 6-hydrazino-1,5-diphenyl-1H-pyrazolo[3,4-d]pyrimidine-4-imine with aromatic aldehyde in presence of Preyssler catalyst yielded 8-aryl-1H-pyrazolo[4,3-e][1,2,4]triazolo[4,3-a] pyrimidine-4(5H)-imine. The performance of different form of Preyssler's anions including H₁₄[NaP₅W₃₀O₁₁₀], H₁₄-P₅, mixed-addenda H₁₄[NaP₅W₂₉ MoO₁₁₀], H₁₄-P₅Mo, silica supported H₁₄[NaP₅W₃₀O₁₁₀]/SiO₂ and H₁₄-P₅/SiO₂ have been investigated. The reaction results were compared with that of a conventional acid catalyst (H₂SO₄).     

Application of dispersive liquid–liquid microextraction with alcoholic solvents followed by HPLC–UV as a sensitive and efficient method for the extraction and determination of citalopram in biological samples using an experimental design

A sensitive and rapid method based on alcoholic-assisted dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for determination of citalopram in human plasma and urine samples was developed. The effects of six parameters (extraction time, stirring speed, pH, volume of extraction and disperser solvents, and ionic strength) on the extraction recovery were investigated and optimized utilizing Plackett–Burman design and Box–Behnken design, respectively. According to Plackett–Burman design results, the volume of disperser solvent, stirring speed, and extraction time had no effect on the recovery of citalopram. The optimized condition was a mixture of 172 µL of 1-octanol as extraction solvent and 400 µL of methanol as disperser solvent, pH of 10.3 and 1% w/v of salt in the sample solution. Replicating the experiment in optimized condition for five times, gave the average extraction recoveries equal to 89.42%. The detection limit of citalopram in human plasma was obtained 4 ng/mL, and the linearity was in the range of 10–1200 ng/mL. The corresponding values for human urine were 5.4 ng/mL with the linearity in the range of 10–2000 ng/mL. Relative standard deviations for inter- and intraday extraction of citalopram were less than 7% for five measurements. The proposed method was successfully implemented for the determination of citalopram in human plasma and urine samples.     

A convenient route toward one‐pot multicomponent synthesis of spirochromenes and pyranopyrazoles accelerated via quinolinic acid

In the present work, the catalytic activity of quinolinic acid (QUIN) was studied for the synthesis of spirochromene and pyranopyrazole derivatives from readily available materials. The salient features of these one‐pot multicomponent protocols are the clean reaction profile, easy isolation of products, no chromatographic separation techniques, high efficiency, short reaction time, and high yield of products plus using QUIN as a new, inexpensive, commercially available, and efficient organocatalyst.