Amorphous silicon dioxide films arise naturally by exposure of silicon surfaces to atmospheric environments. When used as electrodes in Li-ion batteries, the characterization of surface lithiation is relevant to the understanding of the performance of Si anodes. In this work, density functional theory analyses of the lithiation of an amorphous silicon dioxide film reveal the lithiation mechanisms and the role of the surface functional groups on the lithiation reactions and on the structure of the lithiated film. The surface concentration of silanol groups and structure of the optimized model of amorphous hydroxylated silicon dioxide film agree with those observed experimentally. It is found that Li is incorporated via breaking of Si−O bonds and partial reduction of the Si atoms. Evaluation of the formation energy for lithiation of the film indicates that the film would saturate at a Li/Si ratio of 3.48. Analyses of radial distribution functions and coordination numbers show the evolution of the structure upon lithiation, indicating the presence of Li 6 O complexes stabilized by the surrounding Si atoms.

Ordered mesoporous silica materials are considered promising supports for the development of novel hydroprocessing catalysts. Specifically, the mesoporous silica SBA-15 exceeds because of high specific surface area, wall thickness, and pore size distribution, features that make this material more stable at environments at which hydroprocessing reactions take place. However, the SBA-15 lacks strong Brønsted acid sites and this fact still hinders its widespread commercial use. In this work we report density functional theory analyses of the structure and acidity properties of the SBA-15 surface. Periodic boundary models are used and the temperature dependence of the silanol surface density is taken into account. Surface modification by isomorphic substitutions with aluminum and titanium is investigated. It is found that aluminum substitution favors creation of bridging hydroxyl groups. However, surface modifications with aluminum and titanium also create local structural distortions inducing H-bond interactions which improve the acidity properties of hydroxyl groups on the surface. Calculation of vibrational frequencies of O−H bonds are used to quantify the surface acidity properties.

Thermal activation processes modify the structure and acidity of Zr-based MOFs.