Synthesis of Cyclic Carbonates from Olefins and CO2 over Zeolite-Based Catalysts

Metal phthalocyanine complexes (MPc; M = Cu²⁺, Co²⁺, Ni²⁺ and Al³⁺) encapsulated in zeolite-Y exhibit high catalytic activity for the cycloaddition of CO₂ to epichlorohydrin and propylene oxide yielding the corresponding cyclic carbonates. The catalysts could be separated easily from the reaction mixture and reused with little loss in activity. These environmentally benign catalysts are also more efficient than either the neat complexes or those obtained by supporting them on solids like silica.     

Reversible,repeatable and low phase transition behaviour of spin coated nanostructured vanadium oxide thin films with superior mechanical properties

Smooth, uniform and crystalline vanadium oxide thin films were deposited on quartz by spin coating technique with four different rpm i.e., 1000, 2000, 3000 and 4000 and subsequently post annealed at 350, 450 and 550?°C in vacuum. Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) techniques were utilized for microstructural characterizations and phase analysis, respectively, for vanadium oxide powder and deposited film. Nanorods were observed to be grown after vacuum annealing. X-ray photoelectron spectroscopy (XPS) technique was utilized to study the elemental oxidation state of deposited vanadium oxide films. Thermo-optical and electrical properties such as solar transmittance (τ_s), reflectance (ρ_s), absorptance (α_s), infrared (IR) emittance (ε_ir) and sheet resistance (R_s) of different thin films were evaluated. Based on the optical characteristics the optimized condition of the film processing was identified to be spin coated at 3000?rpm. Subsequently, the nanoindentation technique was utilized to measure hardness and Young's modulus of the optimized film. The measured nanomechanical properties were found to be superior to those reported for sputtered vanadium oxide films. Finally, temperature dependent phase transition characteristics of optimized vanadium oxide films were studied by differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition was found to occur in the range of 44–48?°C which was significantly lower than the phase transition temperature (i.e., 68?°C) of bulk VO₂.     

Facile One‐Step Assembly of Bona Fide SUMO Conjugates by Chemoenzymatic Ligation

The post‐translational conjugation of the small ubiquitin‐like modifiers (SUMOs) to target proteins occurs through a complex machinery that involves sequential action of at least three enzymes. SUMOylation performs crucial regulatory functions in several cellular processes. The availability of well‐defined SUMO conjugates is necessary for untangling the mechanism of SUMOylation. However, assembly of homogeneous SUMO conjugates represents a challenge because of the multi‐step synthesis involved and the unwieldiness of the reconstituted biosynthetic systems. Here we describe a simple one‐step chemoenzymatic strategy for conjugating engineered SUMO (eSUMO) proteins to a prefabricated isopeptide‐linked SUMO target peptide. Notably, the eSUMOs were efficiently recognized by the enzymes of the SUMOylation machinery and the SUMO conjugates served as bona fide substrates for DeSUMOylating enzymes.     

Planar,Polysilazane‐Derived Porous Ceramic Supports for Membrane and Catalysis Applications

Porous, silicon carbonitride‐based ceramic support structures for potential membrane and catalysis applications were generated from a preceramic polysilazane precursor in combination with spherical, ultrahigh‐molecular weight polyethylene microparticles through a sacrificial filler approach. A screening evaluation was used for the determination of the impact of both porogen content and porogen size on pore structure, strength, and permeability characteristics of planar specimens. By optimizing both the composition as well as cross‐linking parameters, maximum characteristic biaxial flexural strengths of 65 MPa and porosities of 42% were achieved. The evolution of an interconnected, open‐pore network during thermal porogen removal and conversion of the preceramic polymer led to air permeabilities in the order of 10^?14 m². The materials were further exposed to long‐term heat treatments to demonstrate the stability of properties after 100 h at 800°C in oxidizing, inert, and reducing environments. The determined performance, in combination with the versatile preparation method, illustrates the feasibility of this processing approach for the generation of porous ceramic support structures for applications at elevated temperatures in a variety of fields, including membrane and catalysis science.     

Electrical,mechanical, structural,and thermal behaviors of polymeric gel electrolyte membranes of poly(vinylidene fluoride‐co‐hexafluoropropylene) with the ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus lithium tetrafluoroborate

Polymeric gel electrolyte membranes based on the polymer poly(vinylidene fluoride‐co‐hexafluoropropylene) [P(VdF–HFP)] with different weight percentages of the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus 0.3M lithium tetrafluoroborate (LiBF₄) salt were prepared and characterized by scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, complex impedance spectroscopy, pulse echo techniques, and Vickers hardness (H) testing. After the incorporation of the IL plus the salt solution in the P(VdF–HFP) polymer, the melting temperature, glass‐transition temperature (T_g), degree of crystallinity, thermal stability, elastic modulus (E), and hardness (H) gradually decreased with increasing content of the IL–salt solution as a result of complexation between the P(VdF–HFP) and IL. This was confirmed by FTIR spectroscopy. A part of the IL and LiBF₄ were found to remain uncomplexed as well. The ionic conductivity (σ) of the polymeric gel membranes was found to increase with increasing concentration of the IL–salt solution. The temperature‐dependent σs of these polymeric gel membranes followed an Arrhenius‐type thermally activated behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41456.     

Fumed SiO2 nanoparticle reinforced biopolymer blend nanocomposites with high dielectric constant and low dielectric loss for flexible organic electronics

In the present study, fumed silica (SiO₂) nanoparticle reinforced poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) blend nanocomposite films were prepared via a simple solution‐blending technique. Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to elucidate the successful incorporation of SiO₂ nanoparticles in the PVA/PVP blend matrix. A thermogravimetric analyzer was used to evaluate the thermal stability of the nanocomposites. The dielectric properties such as dielectric constant (?) and dielectric loss (tan δ) of the PVA/PVP/SiO₂ nanocomposite films were evaluated in the broadband frequency range of 10^?2 Hz to 20 MHz and for temperatures in the range 40–150 °C. The FTIR and UV–vis spectroscopy results implied the presence of hydrogen bonding interaction between SiO₂ and the PVA/PVP blend matrix. The XRD and SEM results revealed that SiO₂ nanoparticles were uniformly dispersed in the PVA/PVP blend matrix. The dielectric property analysis revealed that the dielectric constant values of the nanocomposites are higher than those of PVA/PVP blends. The maximum dielectric constant and the dielectric loss were 125 (10^?2 Hz, 150 °C) and 1.1 (10^?2 Hz, 70 °C), respectively, for PVA/PVP/SiO₂ nanocomposites with 25 wt % SiO₂ content. These results enable the preparation of dielectric nanocomposites using a facile solution‐casting method that exhibit the desirable dielectric performance for flexible organic electronics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44427.     

Solution-processed white graphene-reinforced ferroelectric polymer nanocomposites with improved thermal conductivity and dielectric properties for electronic encapsulation

The recent surge in graphene research has stimulated interest in the investigation of various two-dimensional (2D) nanomaterials, including 2D boron nitride (BN) nanostructures. Among these, hexagonal boron nitride nanosheets (h-BNNs; also known as white graphene, as their structure is similar to that of graphene) have emerged as potential nanofillers for preparing thermally conductive composites. In this work, hexagonal boron nitride nanoparticles (h-BNNPs) approximately 70 nm in size were incorporated into a polyvinylidene fluoride (PVDF) matrix with different loadings (0–25 wt.%). The PVDF/h-BNNP nanocomposites were prepared by a solution blending technique and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), polarized optical microscopy (POM) and scanning electron microscopy (SEM). In addition, the thermal conductivity and dielectric properties of the nanocomposites were investigated. The incorporation of h-BNNPs in the PVDF matrix resulted in enhanced thermal conductivity. The highest value, obtained at 25 wt.% h-BNNP loading, was 2.33 W/mK, which was five times that of the neat PVDF (0.41 W/mK). The thermal enhancement factor (TEF) at 5 wt.% h-BNNP loading was 78%, increasing to 468% at 25 wt.% h-BNNP loading. The maximum dielectric constant of approximately 36.37 (50Hz, 150 °C) was obtained at 25 wt.% h-BNNP loading, which was three times that of neat PVDF (11.94) at the same frequency and temperature. The aforementioned results suggest that these multifunctional and high-performance nanocomposites hold great promise for application in electronic encapsulation.     

Thermoelectric Properties of Reduced Polycrystalline Sr0.5Ba0.5Nb2O6 Fabricated Via Solution Combustion Synthesis

The thermoelectric properties of bulk polycrystalline Sr_0.5Ba_0.5Nb₂O₆ (SBN50) fabricated via solution combustion synthesis (SCS) and reduced at temperatures of 900°C–1150°C were explored. The Seebeck coefficient (S) of all samples increased over the entire range of testing temperatures; a peak S value of ?281 μV/K was obtained at 930 K for the sample reduced at 900°C. A metal‐insulator transition was observed in the electrical conductivity (σ) of samples reduced at 1000°C–1150°C, whereas only semiconducting electrical behavior was observed for the sample reduced at 900°C. An optimal balance between S and σ was achieved for the pellet reduced at 1000°C, which exhibited a maximum power factor of 1.78 μW/cm·K² at 930 K. Over a temperature range of 300–930 K, the thermal conductivity (κ) of as‐processed and reduced (1000°C) SBN50 was found to be 1.03–1.4 and 1.46–1.84 W/m·K, respectively. A maximum figure of merit (ZT) of 0.09 was obtained at 930 K for the 1000°C‐reduced sample. X‐ray photoelectron spectroscopy revealed that the Nb²⁺ peak intensity increased at higher reduction temperatures, which could possibly lead to a distortion of NbO₆ octahedra and a decrease in the Seebeck coefficient.     

Development of pellets of nifedipine using HPMC K15 M and κ-carrageenan as mucoadhesive sustained delivery system and in vitro evaluation

Polymeric mucoadhesive pellets of nifedipine were designed using computer software and they were prepared by extrusion-spheronization using HPMC K15M and κ-carrageenan with microcrystalline cellulose. A randomized rotatable two factor central composite design was applied for assessment of influence of two independent variables such as concentration of κ-carrageenan and HPMC K15M on dependent variables. Pellets were characterized by FTIR, DSC, SEM, flow properties, particle size, abrasion resistance, sphericity, drug content, percent production yield, in vitro drug release, ex vivo mucoadhesion, stability studies and similarity factor. The optimized formulation was selected based on criteria of sphericity nearest to 1.0 with maximum cumulative drug release percentage. Formulation NF6 exhibited sufficient porous spheres, free flowing and smooth surface mucoadhesion of 91.34 % and drug content 98.22 ± 0.37 %. Kinetic modeling revealed that the formulation followed the Higuchi model and showed the Quassi-Fickian drug release mechanism. The similarity factor, F2 value, was found to be 74 ± 6 and there was no significant change in drug content and ex vivo mucoadhesion after 90 days at 40 ± 2 °C, and 75 ± 5 % RH clearly indicated the optimized batch NF6 was stable. Thus, it can be concluded that use of κ-carrageenan, microcrystalline cellulose and HPMC K15M at the 20:35:10 w/w ratio could provide an effective carrier for enhancement of sphericity and sustained release of matrix pellets.     

Laser pyrolyzed organosilazane-based Al/ZrO2 composite coating on stainless steel: Resulting microstructure and mechanical properties

Protective ceramic-based coatings are frequently the most suitable solutions for problems like corrosion and wear. It has been shown that the precursor technology is suitable for the preparation of ceramic coatings by pyrolysis in a furnace. However, the required high temperature for the preparation of the ceramic coatings limits this approach to high temperature-resistant substrates. A very innovative approach to overcome this restriction is the use of laser radiation as a thermal source for the pyrolysis of the preceramic polymer. In this paper, we report on a coating system, for steel substrates, consisting of a polysilazane (Durazane 2250) bond coat and a hard and dense top-coat composed of an organosilazane (Durazane 1800) with tetragonal ZrO₂ particles and aluminum flakes as fillers pyrolyzed using Nd:YVO₄ laser. The aluminum fillers led to a significant increase in absorption of the laser energy leading to the formation of a dense coating with a thickness up to 20 μm and a mainly cellular/columnar-dendritic microstructure. The microstructure, mechanical, and tribological behaviors of these composite coatings are reported and compared to those of laser pyrolyzed glass/ZrO₂-filled polysilazane-based coatings reported in the literature.