Combined DFT and NBO approach to analyze reactivity and stability of (CuS) n (n = 1–12) clusters

Electronic Properties and CO2-Selective Adsorption of (NiB)n (n = 1~10) Clusters: A Density Functional Theory Study

In this study, we investigated the electronic properties and selective adsorption for CO₂ of nickel boride clusters (NiB)_n, (n = 1~10) using the first principles method. We optimized the structures of the clusters and analyzed their stability based on binding energy per atom. It was observed that (NiB)_n clusters adopt 3D geometries from n = 4, which were more stable compared to the plane clusters. The vertical electron affinity, vertical ionization energy, chemical potential, and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap were calculated. Our results revealed that (NiB)₆ and (NiB)₁₀, with high chemical potential, exhibit a higher affinity for CO₂ adsorption due to a charge delivery channel that forms along the Ni→B→CO₂ path. Notably, (NiB)₁₀ demonstrated a more practical CO₂ desorption temperature, as well as a broader window for the selective adsorption of CO₂ over N₂. The density of states analysis showed that the enhanced CO₂ adsorption on (NiB)₁₀ can be attributed to the synergistic effect between Ni and B, which provides more active sites for CO₂ adsorption and promotes the electron transfer from the surface to the CO₂ molecule. Our theoretical results imply that (NiB)₁₀ should be a promising candidate for CO₂ capture.

Interaction of H2O with (CuS)n, (Cu2S)n, and (ZnS)n small clusters (n = 1-4, 6): relation to the aggregation characteristics of metal sulfides at aqueous solutions

The interaction of H₂O onto small CuS, Cu₂S, and ZnS clusters was theoretically studied by Density Functional Theory computations to get insights into the aggregation characteristics of metal sulfides at aqueous solutions. The results show the charge-controlled interactions with polarized solvent molecules are favored on the ZnS clusters compared with CuS and Cu₂S clusters. Moreover, the chemical adsorption of H₂O molecules is energetically favored onto ZnS clusters with higher interaction energies of up to 35.4 kcal/mol compared with CuS and Cu₂S clusters (up to 31.3 kcal/mol), where the stability of H₂O adsorption decreases as the size of the clusters increases. However, thermochemical analysis shows that the adsorption of H₂O on copper sulfides is not a spontaneous process at room temperature. Additionally, the electrostatic energy of H₂O onto the Cu₂S and CuS clusters is lower than that associated with the H₂O-H₂O interactions, suggesting that copper precipitates prefer to bind between them at early stages of the precipitation process due to an unfavorable solvent-solute interaction. Dispersion forces play a relative key role in the interaction of water on copper sulfides, while for zinc sulfide clusters, the adsorption energy is slightly influenced by dispersion contributions. Accordingly, the aggregation of zinc sulfides in a water environment is expected to be lower compared with copper sulfides, and where the aggregation characteristics are not determined by the binding energy of the sulfides, but of the ability to interact with the solvent molecules. These statements were confirmed by experimental optical microscopy analysis and settling tests during precipitation processes in water. Therefore, this work allows proposing a simple strategy to study the aggregation characteristics of metal sulfides, which turns useful for use in hydrometallurgical applications.