Investigating the role of cationic vacancy on the MgO (001) defect surface: Embedded cluster models study

Effect of the surface morphology of alkaline-earth metal oxides on the oxidative coupling of methane

Alkaline-earth metal oxides with the rocksalt structure, which are simple ionic solids, have attracted attention in attempts to gain fundamental insights into the properties of metal oxides. The surfaces of alkaline-earth metal oxides are considered promising catalysts for the oxidative coupling of methane (OCM); however, the development of such catalysts remains a central research topic. In this paper, we performed first-principles calculations to investigate the ability of four alkaline-earth metal oxides (MgO, CaO, SrO, and BaO) to catalyze the OCM. We adopted five types of surfaces of rocksalt phases as research targets: the (100), (110), stepped (100), oxygen-terminated octopolar (111), and metal-terminated octopolar (111) surfaces. We found that the formation energy of surface O vacancies is a good descriptor for the adsorption energy of a H atom and a methyl radical. The energies related to the OCM mechanism show that, compared with the most stable surface, the minor surfaces better promote the C - H bond cleavage of methane. However, as the trade-off for this advantage, the minor surfaces exhibit increased affinity for the methyl radical. On the basis of this trade-off relationship between properties, we identified several surfaces that we expect to be promising OCM catalysts. Our investigation of the temperature dependence of the Gibbs free energy indicated that, at higher temperatures, the step (100) surface exhibits properties that might benefit the OCM mechanism.

The Cycloadditions of Various Substituted Carbenes, Silylenes, and Germylenes onto the Diamond (100) Surface: A Theoretical Exploration

The cycloadditions of 21 singlet substituted carbenes, silylenes, and germylenes onto the diamond (100) surface have been theoretically studied by means of density functional theory coupled with effective cluster models. The calculated reaction energies and reaction pathways have disclosed that the substituents play an important effect on the reaction profiles for the additions of carbenes, silylenes, and germylenes onto the diamond (100) surface. Our theoretical investigations illustrate that, irrespective of carbenes, silylenes, and germylenes, the cycloadditions of those with electropositive substituents (such as H and CH(3)) onto diamond (100) are much more favorable than those with electronegative and pi-donating substituents (such as F and NH(2)) both thermodynamically and kinetically. In broad perspective, we believe that a similar reactivity trend can also be extended to that of Si (100), Ge (100), fullerene, single-walled carbon nanotube, disilenes, digermenes, silenes, and germenes because all of these materials feature an analogous bonding motif.

Predicting Facile Epoxidation of the Diamond (100) Surface by Dioxiranes and Subsequent Ring-Opening Reactions with Nucleophiles

By means of density functional theory coupled with effective cluster models, we have theoretically predicted the viability of epoxidation of the diamond (100) surface by organic dioxiranes. In addition, subsequent ring-opening reactions of the as-formed epoxide surface species with some nucleophiles, including water, ammonia, and alcohol, have also been explored. The facile epoxidation of diamond (100) by dioxiranes presents a new alternative for oxidation of the diamond (100) surface. More importantly, the as-formed epoxide-like surface species would be a useful springboard for further functionalizations of the diamond surface given the well-known abundant chemistry of organic epoxides. Therefore, this approach provides another new route to chemical functionalization of the diamond surface, which is potentially useful for leading to the improvement of diamond behavior and constructing new hybrid diamond-based materials for wide potential applications in many fields. In perspective, implications for other theoretical work are also discussed.

Organic functionalization of the Si (100) and Ge (100) surfaces by cycloadditions of carbenes and nitrenes: a theoretical prediction

By means of density functional theory (B3LYP/6-31G*) coupled with effective cluster models, we predict that the well-known cycloaddition reactions of carbenes and nitrenes to alkenes in organic chemistry can be employed as a new type of surface reaction to organically functionalize the Si (100) and Ge (100) surfaces at low temperature. The well-established abundance of carbenes and nitrenes addition chemistry in organic chemistry provides versatile flexibility of functionalizing the surfaces of Si (100) and Ge (100), which can potentially impart new organic functionalities to the semiconductors surface for novel applications in a diversity of fields. Our predictions strongly advance the concept of using organic reactions to modify the solid surface in a controlled manner and quite intriguing chemistry can lie in the material featuring the analogous bonding motif. In further perspective, implications for other theoretical work, regarding disilenes, digermenes, silenes, and germenes that all feature the bonding motif similar to alkenes, are also discussed.