A theoretical study of regio and stereoselectivity nitration of thymol and carvacrol using DFT approach

This work is a detailed theoretical study of the nitration aromatic substitution reactions of thymol and carvacrol. In this process, a mixture of nitric and sulfuric acids is used to produce the nitronium agent NO2+. The computational calculations were performed at the Gaussian 09 using the DFT approaches. The first task of the computing study was to determine the optimized geometry of these compounds using the Becke three-parameter hybrid exchange functional and the Lee-Yang-Parr correlation functional (B3LYP) with the 6-311+G (d, p) basis set. Geometry optimization calculations have been carried out to find the global and local minima for reactants and intermediates, respectively, and to locate the saddle points for the transition states. The vibration frequencies have been calculated in order to check the character of the stationary points obtained after the geometry optimization. It is expected only positive frequencies for reactants, intermediates and products, but only one negative imaginary frequency for transition states.The analysis of the nucleophilic fk- Fukui Function and Pk- Parr functions allows characterising the C4 carbon atom as the most nucleophilic center of thymol and carvacrol, in clear agreement with the regioselectivity obtained. Calculation of activation energies, analysis of the potential energy surface and the Gibbs free energy indicates that this reaction takes place through a two-step mechanism

Box–Behnken design for the optimization of methylene blue and methyl orange removal from aqueous solution by activated carbon

In this work, experimental design approach was adopted for the optimization of the removal of anionic and cationic model dyes (methylene blue and methyl orange) by activated carbon. A Box–Behnken surface statistical design with three factors and three-level combined with response surface modelling was employed to maximize dyes removal from aqueous solution. Three factors were used; solution pH, dyes concentration and activated carbon ratio to aqueous volume. Experimental results showed that solution pH has a positive effect on the adsorption of MB and a negative effect on the adsorption of MO. MO adsorption was more influenced by dye concentration in solution compared to MB adsorption. On the other side, MB adsorption was more influenced by the mass ratio of activated carbon compared to MO adsorption. The mass ration of activated carbon influence more MB adsorption at low dye concentration. In addition, at low solution pH, MO adsorption depends strongly on its concentration in solutio

Experimental and density functional theory studies of methyl orange adsorption on Ni-Al/LDH intercalated sodium dodecyl sulfate

This study examined the application of Ni-Al layered double hydroxide (Ni-Al/LDH) intercalated with sodium dodecyl sulfate (SDS) anion as an adsorbent for the elimination of methyl orange (MO) model dye from aqueous solutions. Material has been synthesized using a co-precipitation process with a molar ratio of Ni/Al of 3. XRD, FTIR, TEM/EDX and TGA/DTA were used to determine structural, morphological and thermal properties of the material. Under varied circumstances, the adsorption capability for MO dye elimination was tested in batch mode. The experimental findings demonstrate that the greatest adsorption takes place at pH levels ranging from neutral to acidic. Kinetic data were well-suited to the pseudo-second-order model. Equilibrium isotherm adsorption data were correlated to the Langmuir model with a high adsorption capacity of 808.8 mg/g. The adsorption process was exothermic and spontaneous nature. In order to analyze the adsorbate-adsorbent interaction mechanism, the anionic dye MO structure was evaluated using the Gaussian 09 W program at the B3LYP/LANL2DZ level. The quantum descriptors examined supported the experimental results obtained in this study