Oxalic acid removal from wastewater using multi-walled carbon nanotubes: Kinetic and equilibrium analysis

Oxalic acid adsorption from aqueous solution is studied in this work. Multi-walled carbon nanotubes (MWCNT) were used as an adsorbent. The investigated adsorption variables are equilibrium time, initial acid concentration, and temperature. The experimental results were presented using equilibrium isotherm and kinetic models. The used equilibrium models are Langmuir, Freundlich, and Temkin adsorption isotherms. And the kinetic models are Elovich, Lagergren pseudo-first-order and pseudo-second-order kinetic models. The thermodynamics studies were carried out at three different temperatures: 278, 298, and 318 K. Langmuir isotherm was the best fitted equilibrium model for the experimental data. The all applied kinetic models fitted the data suitably.     

Multicomponent Reactions of Furan‐2,3‐diones: Synthesis and Characterizations of Furo[3,2‐c]pyran‐4‐ones

Furo[3,2‐c]pyran‐4‐ones, which possess a natural‐product skeleton, are synthesized via a simple, one‐pot, three‐component reaction of furan‐2,3‐diones with dialkyl acetylenedicarboxylates and Ph₃P.     

Radical scavenging and antioxidant activity of tannic acid

Tannic acid, a naturally occurring plant polyphenol, is composed of a central glucose molecule derivatized at its hydroxyl groups with one or more galloyl residues. In the present paper, we examines the in vitro radical scavenging and antioxidant capacity of tannic acid by using different in vitro analytical methodologies such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination using by Fe³⁺–Fe²⁺ transformation method, superoxide anion radical scavenging by riboflavin–methionine-illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe²⁺) chelating activities. Also, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol and trolox, a water-soluble analogue of tocopherol, were used as the reference antioxidant radical scavenger compounds.Tannic acid inhibited 97.7% lipid peroxidation of linoleic acid emulsion at 15 μg/mL concentration. On the other hand, the above mentioned standard antioxidants indicated an inhibition of 92.2%, 99.6%, 84.6% and 95.6% on peroxidation of linoleic acid emulsion at 45 μg/mL concentration, respectively. In addition, tannic acid had an effective DPPH scavenging, ABTS⁺ radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, Fe³⁺ reducing power and metal chelating on ferrous ions activities. Also, those various antioxidant activities were compared to BHA, BHT, α-tocopherol and trolox as references antioxidant compounds. The present study shows that tannic acid is the effective natural antioxidant component that can be used as food preservative agents or nutraceuticals.     

Enantioselective synthesis of cyclic, quaternary oxonitriles

Quaternary oxonitriles are stereoselectively generated from the union of five-, six-, and seven-membered 2-chloroalkenecarbonitriles with chiral alcohols via a Claisen rearrangement. The strategy rests on a new conjugate addition-elimination of allylic alkoxides to 2-chlorocycloalkenecarbonitriles to afford substituted 2-alkoxyalkenenitriles. Subsequent thermolysis unmasks a cyclic oxonitrile while selectively forming a new quaternary center with enantiomeric ratios typically greater than 9:1. The overall alkylation strategy addresses the challenge of enantioselectively generating hindered, quaternary centers while simultaneously installing ketone, nitrile, and olefin functionalities.     

Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory

The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or anti-ferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second-and first-order phase transitions besides triple point (T P ), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points, as well as to determine the type of behaviour, and N-type behaviour in N′eel classification nomenclature existing in the system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions.     

Numerical simulation of partially coherent broadband optical imaging using the finite-difference time-domain method

Rigorous numerical modeling of optical systems has attracted interest in diverse research areas ranging from biophotonics to photolithography. We report the full-vector electromagnetic numerical simulation of a broadband optical imaging system with partially coherent and unpolarized illumination. The scattering of light from the sample is calculated using the finite-difference time-domain (FDTD) numerical method. Geometrical optics principles are applied to the scattered light to obtain the intensity distribution at the image plane. Multilayered object spaces are also supported by our algorithm. For the first time, numerical FDTD calculations are directly compared to and shown to agree well with broadband experimental microscopy results.     

Schwarzian derivative as a proof of the chaotic behaviour

In recent years, a sufficient condition for determining chaotic behaviours of the non-linear systems has been characterized by the negative Schwarzian derivative (Hac?bekiro?lu et al, Nonlinear Anal.: Real World Appl. 10, 1270 (2009)). In this work, the Schwarzian derivative has been calculated for investigating the quantum chaotic transition points in the high-temperature superconducting frame of reference, which is known as a nonlinear dynamical system that displays some macroscopic quantum effects. In our previous works, two quantum chaotic transition points of the critical transition temperature, T _c, and paramagnetic Meissner transition temperature, T _PME, have been phenomenologically predicted for the mercury-based high-temperature superconductors (Onba?l? et al, Chaos, Solitons and Fractals 42, 1980 (2009); Aslan et al, J. Phys.: Conf. Ser. 153, 012002 (2009); Çataltepe, Superconductor (Sciyo Company, India, 2010)). The T _c, at which the one-dimensional global gauge symmetry is spontaneously broken, refers to the second-order phase transition, whereas the T _PME, at which time reversal symmetry is broken, indicates the change in the direction of orbital current in the system (Onba?l? et al, Chaos, Solitons and Fractals 42, 1980 (2009)). In this context, the chaotic behaviour of the mercury-based high-temperature superconductors has been investigated by means of the Schwarzian derivative of the magnetic moment versus temperature. In all calculations, the Schwarzian derivatives have been found to be negative at both T _c and T _PME which are in agreement with the chaotic behaviour of the system.     

Effects of the bond dilution on the phase diagrams of a spin-1 transverse Ising model with crystal field interaction on a honeycomb lattice

A bond diluted spin-1 Ising model with crystal and transverse field interactions is examined for honeycomb lattice by introducing an effective field approximation that takes into account the correlations between different spins that emerge when expanding the identities. The effects of the crystal field as well as the transverse field and dilution on the phase diagrams and order parameter m_z are discussed in detail. A number of interesting and unusual phenomena such as reentrant phenomena and three successive phase transitions originating from the crystal field as well as the transverse field and bond dilution have been found.