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    Adsorption mechanisms investigation of methylene blue on the (001) zeolite 4A surface in aqueous medium by computational approach and molecular dynamics
    (Elsevier, 2022) Khnifira, M.; El Hamidi, S.; Sadiq, M.; Simsek, S.; Kaya, S.; Barka, N.; Abdennouri, M.
    The cationic methylene blue (CMB) and its pmtonated forms have been studied by computational tools to predict their adsorption behavior on zeolite 4A. The interaction nature has been exhaustively studied in terms of energy gap (Delta E-g), global reactivity descriptors, Fukui functions, adsorption energy, density of states and natural bond orbital analysis. It was found that the protonated CMB (N36N35) molecule is less stable, more electmphilic and very reactive. The highest contribution to the lowering of the stabilization energy (E-2) for all systems was mainly due to the intramolecular charge transfer from the lone pair of the nitrogen atoms as a donor orbital to pi* as an acceptor orbital. DFT calculations revealed that N36 and N35 site of CMB was faced with a lower energy gap (Delta E-g) and chemical hardness (eta) as well as a higher electron accepting power compared to other sites. Monte Carlo molecular modeling simulation (MCMM) confirmed the predominant of electrostatic interactions and p-p electron coupling. The studied compounds prefer to have configurations that facilitate p-p interaction, which is evident from the parallel orientation of CMB with zeolite surface. The dynamic parameters show that the adsorption of methylene blue is exothermic and spontaneous chemisorption.
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    Adsorption of methylene blue cationic dye onto brookite and rutile phases of titanium dioxide: Quantum chemical and molecular dynamic simulation studies
    (Elsevier, 2021) Khnifira, M.; El Hamidi, S.; Mahsoune, A.; Sadiq, M.; Serdaroglu, G.; Kaya, S.; Qourzal, S.
    This study reports the statistical physics modeling of the methylene blue cationic dye (MBCD) adsorption in aqueous solution on TiO2 surface. In order to comprehend the adsorption performance, theoretical investigations were done to collect extensive information about the chemical and physical properties of the molecules using quantum chemical parameters (QCP). Also, molecular dynamic and quantum descriptors were applied to better understand the dye adsorption on different phases of TiO2 (i.e., bmokite and rutile). The molecular structures of MBCD acts as good electron donators to an empty d orbital of TiO2 due to the availability of electrons in both the lone pair on the N atoms and 't electrons of the aromatic rings. The reactivity of optimized molecular structures was confirmed by the quantum chemical descriptors. Modeling results showed that the adsorption was performed with a horizontal position of MBCD molecules on both surfaces. Overall, the TiO2 showed the highest adsorption energies for protonated MBCD (N36N35) (-886.533 kcal/mol (MBCD/rutile-TiO2)) > -626.428 kcal/mol (MBCD/brookite-TiO2)), which implies that these sites prompt the adsorption on both surfaces. The analysis of the adsorption energy values showed an exothermic chemisorption process, which could be governed by steric parameters according to the results obtained with the molecular dynamics modeling.