ABSTRACT
CONTEXT: Bisphenol A is an endocrine disruptor that may cause harmful effects on human health. Some residues of this compound have been found in water bodies, alerting for its possible risk as an environmental pollutant. Thus, this work proposes the use of pristine and oxidized phosphorene as removers of bisphenol A, through an adsorption mechanism. Our results indicate that the main interactions exhibited by the complexes are hydrogen bonds, van der Waals, and n-π stacking. All complexes show adsorption energies less than -1.08 eV for the gas phase, and -0.65 eV for the aqueous environment, suggesting that the models may be good capturers of this pollutant. According to the electronic properties, the systems are good donators/acceptors of charge; likewise, they are suitable to sense bisphenol A, because of their changes in |LUMO-HOMO| gap energy. The values obtained suggest that the number of oxygen atoms in the models is important for their adsorption capabilities; hence, the modulation in the oxidation is significant to enhance such properties. METHODOLOGY: Density functional theory calculations were implemented at the PBE-D3/TZVP level of theory in the ORCA 5.0 program, to evaluate the adsorption of bisphenol A on pristine and oxidized phosphorene models and propose the last as removers of this molecule. The visualization of the structures was done in the VMD code.
ABSTRACT
The origin of non-additivity in hydrogen bonds (H-bonds), usually termed as H-bond cooperativity, is investigated in H-bonded linear chains. It is shown that H-bond cooperativity originates solely from classical electrostatics. The latter is corroborated by comparing the H-bond cooperativity in infinitely-long H-bonded hydrogen cyanide, 4-pyridone and formamide chains, assessed using density functional theory (DFT), against the strengthening of the dipole-dipole interaction upon the formation of an infinite chain of effective point-dipoles. It is found that the magnitude of these effective point-dipoles is a consequence of mutual polarization and additional effects beyond a polarizable point-dipole model. Nevertheless, the effective point-dipoles are fully determined once a single H-bond is formed, indicating that quantum effects involved in H-bonding are circumscribed to nearest-neighbor interactions only; i.e. in a linear chain of H-bonds, quantum effects do not contribute to the H-bond non-additivity. This finding is verified by estimating cooperativity along the dissociation path of H-bonds in the infinite chains, using two empirical parameters that account for polarizability, together with DFT association energies and molecular dipoles of solely monomers and dimers.
ABSTRACT
The influence of the anion nature and layer composition on the anion-layer interaction in Mg-Al layered double hydroxides (LDHs) is investigated using density functional theory. Changes in the strength of the anion-layer interaction are assessed calculating the potential energy surface (PES) associated to the interlayer anion (OH(-)/Cl(-)) in Mg-Al-OH and Mg-Al-Cl LDHs. The layer composition is varied changing the divalent to trivalent cation proportion (R). Mg-Al-OH is thus investigated with R = 2, 3, 3.5 and Mg-Al-Cl with R = 3. It is found that the PES for OH(-) in Mg-Al-OH/R = 3 presents wider energy basins and lower energy barriers than any other of the investigated compositions. It is shown that the latter is connected to the number of hydrogen bonds formed by the anions. These results have interesting implications for understanding the enhancement of the physicochemical properties of LDHs upon changing composition.
