Optimization of parameters in preparation of PCM microcapsules based on melamine formaldehyde through dispersion polymerization

Microencapsulated phase change materials have attracted special attention due to their wide applications in saving and releasing energy. Here, microencapsulation of hexadecane (HD) in melamine formaldehyde shell was carried out through in situ dispersion polymerization in the aqueous media. Some important parameters such as stabilizer type and amount, surfactant amount, homogenization conditions as the critical affective factors on final particle size, morphology, and thermal resistance of the microcapsules were investigated extensively. The obtained microcapsules were concurrently analyzed by SEM, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) techniques. SEM images showed that the best stabilization was achieved by polyvinyl alcohol. Also, particle size, as an indication of surface area for heat transfer properties, showed a decrement by increasing stabilizer amount, surfactant amount, and homogenization speed. The amount of entrapped HD and efficiencies of microencapsulation were determined by DSC, and the reason for observing such changes were discussed in detail. Thermal stability of the microcapsules as an important property for their performance was investigated, too. The results illustrated that an improved thermal stability would be obtained by an efficient stabilization in the emulsification step. Also the highest thermal stability up to 388 °C was reached at homogenization speed of 6,000 rpm. Finally, the optimized conditions for desirable encapsulation were proposed in such systems.     

Ultrasound-assisted dehydrogenation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones

In this study, various 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones were synthesized and the dehydrogenation of these compounds by potassium peroxydisulfate in aqueous acetonitrile under thermal and sono-thermal conditions were investigated. Whereas the effect of the nature of 4-substituent influences the rate of reaction, the application of sonic waves decreases drastically the time of thermal reaction.     

Preparation of N-Arylsulfonyl Imines from Sulfonamides and Aryl Aldehydes Using Magnesium Oxide as a Heterogeneous and Reusable Catalyst Under Solvent-Free Conditions

An efficient solvent-free procedure for the preparation of N-arylsulfonyl imines from sulfonamides and aryl aldehydes in the presence of a catalytic amount of magnesium oxide and tetrabutylammonium bromide (TBAB) under microwave irradiation is described. The advantages of this method are good to high yields, short reaction times, low cost, and matching with green chemistry protocols.     

Remote nano-optical beam focusing lens by illusion optics

In this paper, as a new application of illusion optics, a nano-optical plasmonic focusing lens structure is proposed to manipulate the light remotely by employing illusion optics theory. Plasmonic nano-optic lenses that enable super-focusing beyond the diffraction limit have been proposed as an alternative to the conventional dielectric-based refractive lenses. In the presence of an illusion device, the electromagnetic plane-waves can penetrate into a metal layer and a clear focus appears. When the illusion device is removed, waves are blocked to transmit through the metal wall. In comparison with conventional methods, our proposed method avoids any physical changes or damages in the original structure. The proposed structure can be realized by isotropic layered materials, using effective medium theory. The special feature of the proposed structure and the device concepts introduced in this work gives it an opportunity to be used as a flexible element in ultrahigh nano-scale integrated circuits for miniaturization and tuning purposes.     

Determination of the pesticide naptalam and its degradation products by positive and negative ion mass spectrometry

N-1-Naphthylphtalamic acid (naptalam) and its degradation products, 1-naphthylamine and N-(1-naphthyl) phthalimide were simultaneously determined in river water by two independent mass spectrometric (MS) methods. These were negative ion MS (NIMS) and programmable temperature vaporizer gas chromatography mass spectrometry (PTV-GC MS) with electron impact ionization (positive ions). Prior to the NIMS analysis, the samples were preconcentrated by solid phase extraction (SPE) of C₁₈ membrane discs. The PTV-GC MS studies were performed without any preconcentration procedure. Selected ion monitoring (SIM) and internal standardization with naphthalene were applied in both methods. The limits of determination (LOD) of NIMS studies were 230, 270 and 260 ng L^–1 for naptalam, 1-naphthylamine and N-(1-naphthyl) phthalimide, respectively, with relative standard deviation (RSD) < 1% (n = 5) and of PTV-GC MS 17, 11 and 15?ng L^–1 (RSD < 0.7%, n = 5). The LOD, linearity, RSD and time required for these methods are far better than for HPLC analyses.     

A novel multicomponent Zr-catalyzed synthesis of functionalized pyrano[3,2-b]pyrrole derivatives

A novel, efficient, and rapid procedure, one-pot condensation of 3-hydroxypyrrole, malononitrile, and aromatic aldehydes, with 10 mol % bis[N-(3,5-dicumylsalicylidene)anthracylaminato]zirconium(IV) dichloride as catalyst, in the presence of ultrasonic irradiation, has been developed for synthesis of 5-amino-7-aryl-6-cyano-4H-pyrano[3,2-b]pyrrole derivatives.     

Polyoxometalates and Metal–Organic Frameworks Based Dual-Functional Catalysts for Detoxification of Bis(2-Chloroethyl) Sulfide and Organophosphorus Agents

Catalysis Surveys from Asia - The bis(2-chloroethyl) sulfide, commonly named sulfur mustard, as a vesicant agent and the tabun, sarin, soman, and venomous X as organophosphorus nerve agents are the...