With fossil-fuel consumption at an all-time high, air pollution is becoming one of the most prominent problems of the 21st century. In addition to their devastating effects on the environment, sulfur-based pollutants are problematic for infrastructure by undermining the structural stability of various oxide-based surfaces found in clays and clay minerals. Calcite (CaCO3) and alumina (α-Al2O3) are two such mineral oxides with surfaces that are potentially susceptible to damage by sulfur-based adsorbates. Their surface interactions with a wide range of sulfur-based pollutants, however, have yet to be studied adequately at the atomistic level. This problem can be addressed by utilizing density functional theory (DFT) to provide molecular-level insights into the adsorption effects of H2S, SO2, SO3, H2SO3, and H2SO4 molecules on calcite and alumina surfaces. DFT can be used to compare different types of adsorption events and their corresponding changes in the geometry and coordination of the adsorbates, as well as delineate any possible mineral-surface reconstructions. The hypothesis driving this comparative study was that the mineral-oxide surface structure will dictate the surface adsorption reactivity, i.e. the flat carbonate unit in calcite will behave differently from the Al–O octahedra in alumina under both vacuum and hydrated surface conditions. The set of sulfur-based adsorbates tested here exhibited a wide range of interactions with alumina and fewer with calcite surfaces. Events such as hydrogen bonding, sulfate formation, atom abstraction, and the formation of surface water groups were more prevalent in alumina than calcite and were found to be dependent on the surface termination. The results of this work will prove instrumental in the design of clay and mineral-based materials resilient to sulfur-based pollutants for use in construction and infrastructure such as smart building coatings and antifouling desalination membranes, as DFT methods can garner the atomistic insights into mineral-surface reactivity necessary to unlock these transformative technologies.

In this work, molecular dynamics simulations to explore the crack propagation and fracture behavior of Cu/Nb metallic nanolayered composites (MNCs) were performed. The results of this study are consistent with the previous experimental results, which illustrated that cracks in Cu and Nb layers may exhibit different propagation paths and distances under the isostrain loading condition. The analysis reveals that the interface can increase the fracture resistance of the Nb layer in Cu/Nb MNCs by providing the dislocation sources to generate the plastic strain at the front of the crack. Increasing the layer thickness can enhance the fracture resistance of both Cu and Nb layers, as the critical stress for activating the dislocation motion decreases with the increment of the layer thickness. In addition, grain boundaries (GBs) in polycrystalline Cu/Nb samples would decrease the fracture resistance of Nb layer by promoting the crack propagate along the GBs, i.e., intergranular fracture, while the effect of interface and layer thickness on the fracture resistance of MNCs will not be altered by introducing the GBs in MNCs.