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Air pollutants are usually formed by easily spreading small molecules, representing a severe problem for human health, especially in urban centers. Despite the efforts to stem their diffusion, many diseases are still associated with exposure to these molecules. The present study focuses on modeling and designing two-dimensional systems called Layered Double Hydroxides (LDHs), which can potentially trap these molecules. For this purpose, a Density Functional Theory (DFT) approach has been used to study the role of the elemental composition of LDHs, the type of counterion, and the ability of these systems to intercalate NO2 and SO2 between the LDH layers. The results demonstrated how the counterion determines the different possible spacing between the layers, modulating the internalization capacity of pollutants and determining the stability degree of the system for a long-lasting effect. The variations in structural properties, the density of states (DOS), and the description of the charge transfer have been reported, thus allowing the investigation of aspects that are difficult to observe from an experimental point of view and, at the same time, providing essential details for the effective development of systems that can counteract the spread of air pollutants.

Zinc oxide and polylactic-co-glycolic acid (ZnO-PLGA) nanocomposites are known to exhibit different biomedical applications and antibacterial activity, which could be beneficial for adding to wound dressings after different surgeries. However, possible cytotoxic effects along with various unexpected activities could reduce the use of these prominent systems. This is correlated to the property of ZnO, which exhibits different polymeric forms, in particular, wurtzite, zinc-blende, and rocksalt. In this study, we propose a computational approach based on the density functional theory to investigate the properties of ZnO-PLGA systems in detail. First, three different stable polymorphs of ZnO were considered. Subsequently, the abilities of each system to absorb the PLGA copolymer were thoroughly investigated, taking into account the modulation of electrical, optical, and mechanical properties. Significant differences between ZnO and PLGA systems have been found; in this study, we remark on the potential use of these models and the necessity to describe crucial surface aspects that might be challenging to observe with experimental approaches but which can modulate the performance of nanocomposites.

MoO3 and MoO2 systems have attracted particular attention for many widespread applications thanks to their electronic and optical peculiarities; from the crystallographic point of view, MoO3 adopts a thermodynamically stable orthorhombic phase (α-MoO3) belonging to the space group Pbmn, while MoO2 assumes a monoclinic arrangement characterized by space group P21/c. In the present paper, we investigated the electronic and optical properties of both MoO3 and MoO2 by using Density Functional Theory calculations, in particular, the Meta Generalized Gradient Approximation (MGGA) SCAN functional together with the PseudoDojo pseudopotential, which were used for the first time to obtain a deeper insight into the nature of different Mo–O bonds in these materials. The calculated density of states, the band gap, and the band structure were confirmed and validated by comparison with already available experimental results, while the optical properties were validated by recording optical spectra. Furthermore, the calculated band-gap energy value for the orthorhombic MoO3 showed the best match to the experimental value reported in the literature. All these findings suggest that the newly proposed theoretical techniques reproduce the experimental evidence of both MoO2 and MoO3 systems with high accuracy.

HfO2 can assume different crystalline structures, such as monoclinic, orthorhombic, and cubic polymorphs, each one characterized by unical properties. The peculiarities of this material are also strongly related to the presence of doping elements in the unit cell. Thus, the present paper has the main purpose of studying and comparing twelve different systems characterized by diverse polymorphs and doping percentages. In particular, three different crystalline structures were considered: the monoclinic P21/c, the orthorhombic Pca21, and the cubic Fm3¯m phases of HfO2. Each one has been studied by using Y as a doping agent with three different contents: 0% Y:HfO2, 8% Y:HfO2, 12% Y:HfO2, and 16% Y:HfO2. For all the systems, density functional theory (DFT) methods based on PBE/GGA, and on the HSE hybrid functionals were used to optimize the geometry as well as to study their optical properties. Depending on the polymorphs, Y affects the formation energy in different ways and causes changes in the optical properties. When the percentage of Y did not exceed 12%, a stabilization of the cubic phase fraction and an increase of the dielectric constant was observed. Additionally, the calculated optical bandgap energies and the refractive index are examined to provide an overview of the systems and are compared with experimental data. The bandgaps obtained are in perfect agreement with the experimental values and show a slight increase as the doping percentage grows, while only minor differences are found between the three polymorphs in terms of both refractive index and optical band gap. The adopted first principles study generates a reasonable prediction of the physical-chemical properties of all the systems, thus identifying the effects of doping phenomena.