Smart Synthesis of Trimethyl Ethoxysilane (TMS) Functionalized Core-Shell Magnetic Nanosorbents Fe3O4@SiO2: Process Optimization and Application for Extraction of Pesticides.

In the current study, a smart approach for synthesizing trimethyl ethoxysilane-decorated magnetic-core silica-nanoparticles (TMS-mcSNPs) and its effectiveness as nanosorbents have been exploited. While the magnetite core was synthesized using the modified Mössbauer method, Stöber method was employed to coat the magnetic particles. The objective of this work is to maximize the magnetic properties and to minimize both particle size (PS) and particle size distribution (PSD). Using a full factorial design (2k-FFD), the influences of four factors on the coating process was assessed by optimizing the three responses (magnetic properties, PS, and PSD). These four factors were: (1) concentration of tetraethyl-orthosilicate (TEOS); (2) concentration of ammonia; (3) dose of magnetite (Fe3O4); and (4) addition mode. Magnetic properties were calculated as the attraction weight. Scanning electron microscopy (SEM) was used to determine PS, and standard deviation (±SD) was calculated to determine the PSD. Composite desirability function (D) was used to consolidate the multiple responses into a single performance characteristic. Pareto chart of standardized effects together with analysis of variance (ANOVA) at 95.0 confidence interval (CI) were used to determine statistically significant variable(s). Trimethyl ethoxysilane-functionalized mcSNPs were further applied as nanosorbents for magnetic solid phase extraction (TMS-MSPE) of organophosphorus and carbamate pesticides.

Computational Studies on the Thermodynamic and Kinetic Parameters of Oxidation of 2-Methoxyethanol Biofuel via H-Atom Abstraction by Methyl Radical.

In this work, a theoretical investigation of thermochemistry and kinetics of the oxidation of bifunctional 2-Methoxyethanol (2ME) biofuel using methyl radical was introduced. Potential-energy surface for various channels for the oxidation of 2ME was studied at density function theory (M06-2X) and ab initio CBS-QB3 levels of theory. H-atom abstraction reactions, which are essential processes occurring in the initial stages of the combustion or oxidation of organic compounds, from different sites of 2ME were examined. A similar study was conducted for the isoelectronic n-butanol to highlight the consequences of replacing the ϒ CH2 group by an oxygen atom on the thermodynamic and kinetic parameters of the oxidation processes. Rate coefficients were calculated from the transition state theory. Our calculations show that energy barriers for n-butanol oxidation increase in the order of α < O < ϒ < ß < ξ, which are consistent with previous data. However, for 2ME the energy barriers increase in the order α < ß < ξ < O. At elevated temperatures, a slightly high total abstraction rate is observed for the bifunctional 2ME (4 abstraction positions) over n-butanol (5 abstraction positions).

Thermochemistry and Kinetics of the Thermal Degradation of 2-Methoxyethanol as Possible Biofuel Additives.

Oxygenated organic compounds derived from biomass (biofuel) are a promising alternative renewable energy resource. Alcohols are widely used as biofuels, but studies on bifunctional alcohols are still limited. This work investigates the unimolecular thermal degradation of 2-methoxyethanol (2ME) using DFT/BMK and ab initio (CBS-QB3 and G3) methods. Enthalpies of the formation of 2ME and its decomposition species have been calculated. Conventional transition state theory has been used to estimate the rate constant of the pyrolysis of 2ME over a temperature range of 298-2000 K. Production of methoxyethene via 1,3-H atom transfer represents the most kinetically favored path in the course of 2ME pyrolysis at room temperature and requires less energy than the weakest Cα - Cß simple bond fission. Thermodynamically, the most preferred channel is methane and glycoladhyde formation. A ninefold frequency factor gives a superiority of the Cα - Cß bond breaking over the Cγ - Oß bond fission despite comparable activation energies of these two processes.

Ab initio study on the formation of triiodide CT complex from the reaction of iodine with 2,3-diaminopyridine.

The charge transfer (CT) interaction between iodine and 2,3-diaminopyridine (DAPY) has been thoroughly investigated via theoretical calculations. A Hartree-Fock, 3-21G level of theory was used to optimize and calculate the Mullican charge distribution scheme as well as the vibrational frequencies of DAPY alone and both its CT complexes with one and two iodine molecules. A very good agreement was found between experiment and theory. New illustrations were concluded with a deep analysis and description for the vibrational frequencies of the formed CT complexes. The two-step CT complex formation mechanism published earlier was supported.

Electronic, infrared, and Raman spectral studies of the reaction of iodine with 4-aminopyridine.

The reaction of iodine as an electron acceptor with the base 4-aminopyridine (4APY) has been investigated spectrophotometrically in chloroform at room temperature. The electronic absorptions, infrared and Raman spectra, photometric titration as well as elemental analysis of the obtained iodine complex indicate the formation of the pentaiodide charge-transfer complex with the general formula [(4APY)(2)](+)I(5)(-). The characteristic strong absorptions of I(5)(-) are observed around 380 and 295 nm. Far infrared and Raman spectra of the solid complex show the vibrations of the linear I(5)(-) ion with D(infinityh) symmetry at 154, 104 and 89 cm(-1) assigned to nu(s)(I--I), outer bonds, nu(s)(I--I), inner bonds and nu(as)(I--I) inner bonds, respectively.

Spectroscopic studies of the reaction of iodine with 2,3-diaminopyridine.

The charge-transfer interaction of 2,3-diaminopyridine (DAPY) and iodine has been investigated spectrophotometrically in the solvents chloroform and dichloromethane at room temperature. The results indicate the formation of 1:2 charge-transfer complex in each solvent with the observation of the two characteristic absorptions for triiodide ion around 355 and 295 nm. The iodine complex is formulated as [(DAPY)I]+.I3-. The formation of the triiodide ion, I3-, is further confirmed by the observation of the characteristic bands for non-linear I3- ion with C2v symmetry at 151 and 132 cm(-1) assigned to nu(as)(I-I) and nu(s)(I-I) of the I-I bonds and at 61 cm(-1) due to bending delta(I3-). The mid infrared spectra of (DAPY) and triiodide complex are also obtained and assigned.