Density functional theory and GGA-PW91 exchange correlation function were performed to simulate the bonding behavior of hydroxyl and epoxy groups on the graphene surface.We compared the different binding energies for two epoxy groups,as well as one hydroxyl group and one epoxy group on all possible positions within a 6-fold ring,respectively.The calculated results suggest that two oxygen-containing groups always tend to bind with the neighboring carbon atoms at the opposite sides.Moreover,two hydroxyl groups on the meta position are unstable,and one of the hydroxyl groups easily migrates to the para position.In contrast to the disperse arrangement,the aggregation of multiply hydroxyl groups largely enhances the binding energy of every hydroxyl group.It is worth noting that the binding sites and hydrogen bonds play an important role in stability.Our work further points out the number of oxygen-containing groups and the location of oxide region largely influence the electronic properties of graphene oxide.
Based on density functional theory and generalized gradient approximation calculations, the adsorption of Co2B2 and Ni2B2 clusters on the rutile TiO2 (110) surface has been investigated utilizing periodic supercell models. Unambiguously, the results demonstrate that the hollow site turns out to be preferable for Co2B2 cluster while Ti2 site is for Ni2B2 cluster to adsorb. Orbital population analysis indicates a strong interaction between Co2B2 and O atom of TiO2 surface, which can be attributed to the overlap of Co 3d and surface O 2p orbital. Similarly, for Ni2B2 , the bonding interaction occurs mostly through the interaction of Ni 3d/4s and O 2p orbitals. Note that, there is also an interaction within the Co2B2 clusters (Ni2B2) through B 2s/2p and Co 3d orbitals (Ni 3d/4s). Moreover, orbital analysis results shows that the strong bonding between Ni2B2 and Ti2 site is due to the overlap of HOMO of Ni2B2 and d-orbital of five-coordinated titanium atoms.
Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal.Thus in this paper,we embark on a systematic study for Pd n (n=1-5) clusters adsorbed on TiO2 (110) surface based on DFT-GGA calculations utilizing periodic supercell models.A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction,while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface.According to the transition states (TSs) search,the adsorbed Pd trimer tends to triangular growth mode,rather than linear mode,while the Pd4 and Pd5 clusters prefer three-dimensional (3D) models.However,the oxygen vacancy has almost no influence on the promotion of Pd n cluster nucleation.Additionally,of particular significance is that the Pd-TiO2 interaction is the main driving force at the beginning of Pd nucleation,whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger.It is hoped that our theoretical study would shed light on further designing high-performance TiO2 supported Pd-based catalysts.
