A huge number of parabens, esters of p-hydroxybenzoic acid, are used in cosmetic and personal care products as preservative substances. Due to their detrimental effects on ecosystem and human health, taking precautionary measures to remove these compounds is an important task regarding the environmental issues. In this study, a silica (SiO2) nanotube has been selected as a novel sensor to adsorb the most common parabens which are methyl paraben and propyl paraben molecules. To this aim, density functional theory (DFT) calculations were used to evaluate the properties for investigated compounds. The calculated adsorption energies of the most stable configurations for methyl parban@SiO2 and propyl paraben@SiO2 complexes were found to be –0.238 and –0.242 eV, respectively. The electronic properties of nanotubes experienced dramatic changes in case of interactions with parabens, which led to declining the HOMO/LUMO energy gap of the nanotube to its original value. Such adsorption could also enhance the electrical conductivity of the nanotubes meaning that the utilized SiO2 nanotube could detect the existence of methyl and propyl parabens molecules in the environment. As a concluding remark, the investigated SiO2 nanotube could work as a possible sensor for hazardous paraben with the importance of environmental issues.

Density functional theory (DFT) calculations were performed to stabilize a representative C16Mg8O8 nanocage derived from C32 and Mg16O16 counterparts for selective adsorption of carbon monoxide (CO) and nitrogen monoxide (NO) gaseous molecules. After obtaining optimized structures, molecular features were evaluated for describing the model systems. Diagrams of density of states (DOS) revealed that the energy differences between frontier molecular orbital levels of the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) of the stabilized C16Mg8O8 nanocage could provide a more proper semiconductor in comparison with each of the original C32 and Mg16O16 cages. To explore the advantage of such C16Mg8O8 nanocage for CO and NO gases adsorption, molecular descriptors such as energies, geometries, and electronic structures were characterized for all possible adsorption configurations of bimolecular formation of gas . . .  nanocage. Significant changes of HOMO and LUMO levels besides the values of corresponding energy gaps of C16Mg8O8 nanocage in singular and bimolecular systems could help to recognize adsorption of each of CO and NO gaseous molecules. Furthermore, more variations of energy gaps in the process of gas . . .  nanocage bimolecular formation could lead to more sensitivity of nanocage for detection of adsorbed gases. As a consequence, the investigated C16Mg8O8 nanocage was introduced for differential recognition of CO and NO gases regarding several environmental health issues.

Density functional theory (DFT) calculations have been performed to investigate the adsorption of hydrogen (H2), nitrogen (N2) and carbon monoxide (CO) diatomic gaseous molecules at the surface of Li + contained C16B8P8 fullerene-like nanostructure (Li + @C16B8P8). The evaluated results from the optimized structures indicated that the adsorption processes could be taken placed for the interacting gas and fullerene systems. Moreover, the electronic properties indicated that the electrical conductivities of Nano Clusters systems are changed after the adsorption processes, in which it could be a signal for detection or sensing of the existence of the gas in the environment. These changes lead to declining the HOMO/LUMO gap of the Fullerene-Like Nano Cage to its original value. As a finding of this work, it could be mentioned that the Li + @C16B8P8 fullerene-like nano cage could be considered as a suitable adsorbent for the CO, N2 and H2 gaseous. It means that the utilized Li + @C16B8P8 Fullerene-Like Nano Cage can detect the existence of gas in the environment.

The interactions between boron carbide (BC) nanocluster of B16C16 and H2O, NO2, CO, and CH4 small molecules were investigated by using density functional theory (DFT) computations to exploit the structural and electronic properties of the adsorbate/cluster complexes. The calculated adsorption energies of the most stable states are -16.6, -0.17, -1.28, -0.18 eV for NO2, CO, H2O, and CH4 molecules, respectively. Meanwhile, the interactions between CO and CH4 molecules and the cluster induce dramatic changes to the cluster electronic properties so that the molecular orbital (HOMO/LUMO) gap of cluster decreased its original value. It was shown that the phenomenon leads to an increment in the electrical conductivity of the cluster at a definite temperature. Furthermore, it is revealed that the adsorptions of NO2 and H2O molecules have no significant effects on the electronic properties of the cluster. Thus, this work suggests that the investigated B16C16 nano-cage could work as a selective gas sensor device towards CO, CH4, NO2 and H2O molecules. Original Res earch Arti cle http://www.ajchem-b.com Fig. 1. Geometrical presentations of pristine and small-molecule decorated B16C16 nano-clusters. Interacting distances are shown in Å.