Effect of the acid treatment conditions of kaolinite on etheramine adsorption: A comparative analysis using chemometric tools.

The present work evaluated the effect of the acid treatment conditions of natural kaolinite (NK) regarding its efficiency in removing etheramine. The treatment was conducted using sulfuric acid at the concentrations of 1 mol L-1 (KA-01), 2 mol L-1 (KA-02) and 5 mol L-1 (KA-05) at 85 °C. The obtained adsorbents were characterized by X-ray fluorescence, X-ray diffraction, N2 adsorption/desorption isotherms, zeta potential analysis and infrared spectroscopy. The Response Surface Method was used to optimize adsorption parameters (initial concentration of etheramine, adsorbent mass and pH of the solution). The results, described by means of a central composite design, were adjusted to the quadratic model. Results revealed that the adsorption was more efficient at the etheramine concentration of 400 mg L-1, pH 10 and adsorbent mass of 0.1 g for NK and 0.2 g for KA-01, KA-02 and KA-05. The sample KA-02 presented a significant increase of etheramine removal compared to the NK sample. The adsorption kinetics conducted under optimized conditions showed that the system reached the equilibrium in approximately 30 min. The kinetic data were better adjusted to the pseudo-second order model. The isotherm data revealed that the Sips model was the most adequate one. The calculation of Eads allowed to infer that the mechanism for etheramine removal in all the evaluated samples was chemisorption. The reuse tests showed that, after four uses, the efficiency of adsorbents in removing etheramine did not suffer significant modifications, which makes the use of kaolinite to treat effluents from the reverse flotation of iron ore feasible.

Intramolecular hydrogen bonds interactions in the isomers of the bilirubin molecule: DFT and QTAIM analysis.

CONTEXT: Bilirubin is an important molecule, used as a marker of some liver diseases, and it can also be toxic and cause jaundice, especially in newborns. The main treatment for neonatal jaundice is phototherapy with blue light, which is still widely studied because the photophysical processes involved are not fully understood. METHODS: Calculations based on the density functional theory (DFT) at M062X/6-31G(d,p) level were performed in order to evaluate the structural, electronic, and topological properties of bilirubin isomers. It was found that the ZZ conformation can form a greater number of hydrogen bonds, which gives the isomer greater energy stabilization compared to the other ZE, EZ, and EE isomers, and that the EE isomer is the conformer with the lowest energy of stabilization. The hydrogen bonds were characterized by the quantum theory of atoms in molecules (QTAIM) and for the ZZ isomer four hydrogen bonds (HBs) were found classified as intermediate, ∇2ρ(r) > 0, H(r) > 0. The ZE, EZ, and EE isomers show weak HBs, ∇2ρ(r) > 0, H(r) > 0.