Determination of trace metal concentration in compost, DAP, and TSP fertilizers by neutron activation analysis (NAA) and insights from density functional theory calculations

Structure Elucidation of Menthol-Based Deep Eutectic Solvent using Experimental and Computational Techniques

The structural properties and nonbonding interactions of a menthol-based deep eutectic solvent (DES) were investigated in detail employing experimental and computational methods. A mass spectrometry analysis confirmed the formation of 1:1 l-menthol/acetic acid. A molecular dynamics simulation was used to figure out energetically most favorable cluster conformers of the 1:1 l-menthol/acetic acid system. Density functional theory at the ωB97XD/6-311G (d,p) level of theory was employed to optimize the isolated structures and to calculate their thermochemical properties. Both experimental and computed IR spectra were analyzed for the samples. Additionally, vibrational circular dichroism (VCD) spectra of the samples were measured to prove the chirality transfer. Principal component analysis (PCA) was used to make the data interpretation more vivid. All the spectral data analyses and nanostructure elucidation proved the spontaneous formation of the DES through the formation of strong hydrogen bonding. Experimental solvatochromism and computed highest occupied molecular orbital-lowest unoccupied molecular orbital gaps validated the reasoning. Moreover, comparative VCD and IR spectral analyses clearly indicated a chirality transfer from the chiral menthol to achiral acetic acid. This study suggests that various techniques, such as mass spectrometry, IR, solvatochromism, and computed IR-VCD could be useful and important tools to elucidate nanostructure and nonbonding interactions of a DES. VCD could be used as an excellent complementary technique to IR spectroscopy for a chiral molecule-based DESs.

Adsorption Mechanism of Methylene Blue by Graphene Oxide-Shielded Mg-Al-Layered Double Hydroxide From Synthetic Wastewater

Pollution of water resources by various pollutants is a global environmental issue, particularly, dye pollution has a major contribution to it. From various studies, it is confirmed that adsorption is an excellent remediation technique compared to others. Mg-Al-layered double hydroxides (LDHs) intercalated with NO₃^- ions act as an effective adsorbent-removing ionic species like heavy metal and dyes. Another popular nanomaterial is graphene oxide (GO), which is successfully used as an adsorbent for different pollutants like dye and heavy metal ions. It is prepared based on the modified Hummers method. In this study, GO was introduced on the surface of LDH to improve its adsorption capacity. The adsorption process is well described by the Freundlich model. The maximum adsorption capacity was obtained at around 0.5 and 0.85 mmol of methylene blue (MB) per gram of Mg-Al LDH and modified Mg-Al LDH with GO, respectively. The reaction kinetics of MB with both adsorbents is determined to be the pseudo-second-order. To get more insights of the mechanism, molecular dynamics (MD) simulation was conducted among the modified Mg-Al LDH with GO and MB molecules at both low- and high-concentration environments, which demonstrated that the developed composite adsorbs MB molecules predominantly onto its GO surface and then the MB molecules are adsorbed by the LDH surface. C-H···O (2.49-3.04 Å) and pi-donor···H-O (2.45-3.05 Å) are the major driving forces behind the strong adsorbability. Besides, S···H-O, S···O,N···O-H, pi···lone pair, pi···sigma, pi···cation, and alkyl···hydrophobic interactions play important roles in stabilizing the MB molecules onto the surface of the composite.