Fine tuning of SAP properties via epoxy‐silane surface modification

Using 3‐[(2,3‐epoxypropoxy)‐propyl]‐trimethoxysilane as a surface modifier, superabsorbent polymers with improved gel strength in their swollen state and saline absorbency under load are synthesized. The products are characterized using attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR), rheometry, scanning electron microscopy–energy dispersive X‐ray analysis, contact angle, thermogravimetric analysis, water absorbency and gel content. The temperature and the duration effect of the surface‐treatment process on residual monomer content are also investigated by high performance liquid chromatography. The gel strength (as shown by storage modulus) and absorbency under load are improved up to 3500–4000 Pa, and 30–40 g/g, respectively. It is suggested that the surface of the superabsorbent polymer particles has been modified by two mechanisms: i.e. interpenetrating polymer network and cross‐linking. Moreover, the surface modification has enhanced thermo‐stability and prohibited undesirable gel blockage. Depending on the post‐treatment method used, the wetting behavior of particles is also altered. Copyright © 2017 John Wiley & Sons, Ltd.     

Alumina Perchloric Acid (Al 2 O 3 -HClO 4 ) as an Efficient Heterogeneous Catalyst for Modified Preparation of Trimethylsilyl Ethers

A highly efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, benzylic, secondary, hindered secondary, tertiary, phenols, and oximes with hexamethyldisilazane (HMDS) using alumina perchloric acid (Al ₂ O ₃ -HClO ₄ ) as recyclable heterogeneous catalyst in excellent yields with short reaction times (3?65 min) under ambient conditions is described.     

Synthesis and Crystal Structure of Bis(μ3-4-Oxapentan-2-onato)-Tetrakis(μ2-4-Oxapentan-2-onato)-Tetra-Magnesium Dichloride Dichloromethane

Abstract  

A new magnesium alkoxide which posses centrosymmetric tetranuclear structure derived from 1-methoxy-2-propanol, a functionalized alcohol containing asymmetric carbon. X-ray analysis of single crystal shows an open dicubane-like structure with triple-bridging alkoxo groups between alternating five- and six-coordinated magnesium atoms. There are six alkoxo bridging groups in which two of them bridge three metal centers and the other four bridge two. All of the etheric-oxygens are coordinated to magnesium and provide a rigid structure. Two chlorine atoms are bonded to five-coordinated magnesium. This compound crystallizes in the monoclinic system with a = 10.040(6) Ǻ, b = 14.004(9) Ǻ, c = 15.344(5) Ǻ, β = 95.55(9)˚, Z = 2 and V = 2147 Ǻ³ in the space group of P2₁/n.     

Mechanical buckling and free vibration of thick functionally graded plates resting on elastic foundation using the higher order B-spline finite strip method

In this study, the mechanical buckling and free vibration of thick rectangular plates made of functionally graded materials (FGMs) resting on elastic foundation subjected to in-plane loading is considered. The third order shear deformation theory (TSDT) is employed to derive the governing equations. It is assumed that the material properties of FGM plates vary smoothly by distribution of power law across the plate thickness. The elastic foundation is modeled by the Winkler and two-parameter Pasternak type of elastic foundation. Based on the spline finite strip method, the fundamental equations for functionally graded plates are obtained by discretizing the plate into some finite strips. The results are achieved by the minimization of the total potential energy and solving the corresponding eigenvalue problem. The governing equations are solved for FGM plates buckling analysis and free vibration, separately. In addition, numerical results for FGM plates with different boundary conditions have been verified by comparing to the analytical solutions in the literature. Furthermore, the effects of different values of the foundation stiffness parameters on the response of the FGM plates are determined and discussed.     

Different Dimensionalities,Morphological Advancements and Engineering of g-C3N4-Based Nanomaterials for Energy Conversion and Storage

Graphitic carbon nitride (g-C₃N₄) has gained tremendous interest in the sector of power transformation and retention, because of its distinctive stacked composition, adjustable electronic structure, metal-free feature, superior thermodynamic durability, and simple availability. Furthermore, the restricted illumination and extensive recombination of photoexcitation electrons have inhibited the photocatalytic performance of pure g-C₃N₄. The dimensions of g-C₃N₄ may impact the field of electronics confinement; as a consequence, g-C₃N₄ with varying dimensions shows unique features, making it appropriate for a number of fascinating uses. Even if there are several evaluations emphasizing on the fabrication methods and deployments of g-C₃N₄, there is certainly an insufficiency of a full overview, that exhaustively depicts the synthesis and composition of diverse aspects of g-C₃N₄. Consequently, from the standpoint of numerical simulations and experimentation, several legitimate methodologies were employed to deliberately develop the photocatalyst and improve the optimal result, including elements loading, defects designing, morphological adjustment, and semiconductors interfacing. Herein, this evaluation initially discusses different dimensions, the physicochemical features, modifications and interfaces design development of g-C₃N₄. Emphasis is given to the practical design and development of g-C₃N₄ for the various power transformation and inventory applications, such as photocatalytic H₂ evolution, photoreduction of CO₂ source, electrocatalytic H₂ evolution, O₂ evolution, O₂ reduction, alkali-metal battery cells, lithium-ion batteries, lithium–sulfur batteries, and metal-air batteries. Ultimately, the current challenges and potential of g-C₃N₄ for fuel transformation and retention activities are explored.     

Electrospun Polyethylene Terephthalate/Graphene Nanocomposite as a New Solid-Phase Microextraction Fiber Coating for Enhanced Determination of Organochlorine Compounds

A new unbreakable solid-phase microextraction fiber coating based on polyethylene terephthalate/graphene nanocomposite was developed. The nanocomposite coatings were prepared by an electrospinning technique using a polyethylene terephthalate (PET) polymer solution containing the dispersed graphene on the outer surface of a stainless-steel rod. The applicability of polyethylene terephthalate/graphene nanocomposite coatings was examined by extraction of organochlorine compounds (OCs) including heptachlor epoxide, aldrin, γ-HCH, and β-HCH from aqueous samples in headspace mode. Influential parameters on extraction efficiency such as polymer concentration, the weight ratio of components, the electrospinning time, time and temperature of extraction, the salt concentration, and desorption condition were investigated. Eventually, the developed method was validated by gas chromatography micro electron capture detector (GC-µECD). At the optimum conditions, the intra-day relative standard deviations for the determination of chloro compounds in distilled water spiked at the levels of 400, 800, and 1500 ng L^??1 were 1.9–7.3% (n?=?3), the limit of detection is between 5 and 30 ng L^??1, and the calibration plots cover the 100 to 5000 ng L^??1 range. Inter-day precision values obtained for three replicates measured on different days were in the range of 2.6–9.5% at concentration levels of 400, 800, and 1500 ng L^??1. The method was applied to the analysis of (spiked) water samples and relative recoveries were found to range from 81 to 106%.     

Synergistic flotation of U(VI)-alizarin complex with some diamines followed by spectrophotometric determination of U(VI) using 4,4′-diaminophenylmethane

In this work, synergistic flotation of U(VI)-alizarin complex at the presence of some diamine compounds was firstly investigated by the spectrophotometric method. The flotation process was carried out on aliquots of 100 ml of U(VI) solutions containing alizarin and the diamine at pH of 5.00 using n-heptane. The floated layer was then dissolved in acetonitrile and its absorbance was measured. Since the synergistic effect of 4,4′-diaminophenylmethane (dapm) was much more than the others, it was used for the determination of U(VI) by this method. Beer's law was obeyed (λ_max = 591 nm) in the range of 5 × 10⁻⁷ to 1 × 10⁻⁵ mol l⁻¹ with the apparent molar absorptivity of 1.12 × 10⁶ l mol⁻¹ cm⁻¹, and a correlation coefficient of 0.9991. The detection limit (n = 7) was 1 × 10⁻⁷ mol l⁻¹, and the R.S.D. (n = 7) obtained for 4 × 10⁻⁶ mol l⁻¹ of U(VI) was 2.23%. Except that only a few analogous cations, which could be masked by EDTA, no interference was observed at the presence of various conventional ions, even at high concentrations. The reliability and applicability of the method were confirmed using some geological standard reference materials and spiked synthetic water samples, respectively.     

Effect of diluent and reaction parameter on selective oxidation of propane over MoVTeNb catalyst using nanoflow catalytic reactor

The selective oxidation of propane to acrylic acid over an MoVTeNb mixed oxide catalyst, dried and calcined before reaction has been studied using high-throughput instrumentation, which is called nanoflow catalytic reactor. The effects of catalyst dilution on the catalytic performance of the MoVTeNb mixed oxide catalyst in selective oxidation of propane to acrylic acid were also investigated. The effects of some reaction parameters, such as gas hourly space velocity （GHSV） and reaction temperature, for selective oxidation of propane to acrylic acid over diluted MoVTeNb catalyst have also been studied. The configuration of the nanoflow is shown to be suitable for screen catalytic performance, and its operating conditions were mimicked closely to conventional laboratory as well as to industrial conditions. The results obtained provided very good reproducibility and it showed that preparation methods as well as reaction parameters can play significant roles in catalytic performance of these catalysts.     

Diastereoselective functionalizations of enecarbamates derived from pipecolic acid towards 5-guanidinopipecolates as arginine mimetics

Various substituents could be diastereoselectively introduced into the 5-position of pipecolic acid via electrophilic or free-radical-initiated addition to the carbon-carbon double bond of endocyclic enecarbamates derived from pipecolic acid. This study allowed the diastereoselective synthesis of both cis- and trans-5-guanidino pipecolates, which were designed as constrained arginine mimetics and whose potential inhibition of nitric oxide synthase (NOS) was evaluated with three NOS isoforms.