Reactivity of sub 1 nm supported clusters: (TiO2)n clusters supported on rutile TiO2 (110)

Abstract

Access to the full text of the published version may require a subscription. surface. We find that all three clusters adsorb strongly with adsorption energies ranging from -3 eV to -4.5 eV. The more stable adsorption structures show a larger number of new Ti-O bonds formed between the cluster and the surface. These new bonds increase the coordination of cluster Ti and O as well as surface oxygen, so that each has more neighbours. The electronic structure shows that the top of the valence band is made up of cluster derived states, while the conduction band is made 15 up of Ti 3d states from the surface, resulting in a reduction of the effective band gap and spatial separation of electrons and holes after photon absorption, which shows their potential utility in photocatalysis. To examine reactivity, we study the formation of oxygen vacancies in the clustersupport system. The most stable oxygen vacancy sites on the cluster and show formation energies that are significantly lower than in bulk TiO 2 , demonstrating the usefulness of this composite 20 system for redox catalysis. Rights © The Royal Society of Chemistry 2011. This is the Accepted

TiO2 nanocluster modified-rutile TiO2 photocatalyst: a first principles investigation

“…This process would involve adsorption of water at the nanocluster, adsorbing most likely at undercoordinated Ti sites and likely dissociating into H and OH, with adsorption of H at the titanyl oxygen atoms 65 , which 30 may be important for realistic photocatalytic activity. While this is an important issue to examine, it requires a detailed modelling and experimental treatment, and therefore lies beyond the scope of this paper, which is to examine the basic properties of potential photocatalysts, but this is work that is 35 being undertaken. To study the effect of modifying the rutile (110) surface with the TiO 2 clusters on the electronic structure, figure 4 terminal oxygen atoms on the clusters dominate the top of the cluster-derived VB states (supporting information, figure S3, in which the PEDOS for terminal cluster oxygen and nonterminal cluster oxygen are shown).…”

“…Extrapolating the linear part of the plot of absorption coefficient against photon energy gives the optical gap. While DFT calculations are excellent at providing details on 35 the electronic properties of the type of heterostructures studied in this paper, screening many different adsorption structures becomes unfeasible for structures of the size considered herein. Therefore, a realistic atomistic potential based model can be used to determine favourable adsorption 40 structures for further refinement with DFT.…”

“…45 In understanding the findings of these experimental studies and in particular, the effect of surface modification on the light absorption properties and on the reactivity, density functional theory (DFT) simulations of TiO 2 modified with small metal oxide clusters have confirmed the origin of the 50 band gap reduction in FeO x modified rutile TiO 2 34 as well as the origin of the enhanced UV or visible light activity of SnO 2 -modified anatase 32 or rutile 33 TiO 2 . In addition, we previously showed that sub-nm diameter (TiO 2 ) n clusters, with n=2-4, adsorbed on the rutile TiO 2 (110) surface can lead to a 55 reduced band gap compared to pure rutile TiO 2 , which should enhance the photocatalytic activity in these heterostructures 35 , although a focus in that paper was on the reactivity of these structures. DFT simulations have also shown that modifying the rutile (110) surface with small transition metal oxide 60 nanoclusters, e.g.…”

“…Moreover 30 photoluminescence (PL) spectroscopy indicated a decrease in electron-hole recombination 30 . In subsequent work, Tada and co-workers have studied NiO 31 and SnO 2 32,33 modified TiO 2 for their ability to enhance visible or UV photocatalytic activity of TiO 2 ; with NiO- 35 modified TiO 2 showing similar visible light absorption and enhanced photocatalytic activity to FeO x modified TiO 2 . Interestingly, while SnO 2 -modified anatase TiO 2 showed only UV activity 32 , SnO 2 modified rutile displayed some visible light activity and improved UV activity 33 .…”

“…A leading material is titanium (IV) dioxide, TiO 2 , which is cheap, readily available and non-toxic. Since the band gap of the rutile and anatase forms of TiO 2 lies in the UV region (typically in the range of 3 eV to 3.2 eV) a major activity in 35 delivering widespread photocatalytic technologies is to shift the band gap in order to have a material that will be active in the visible region of the solar spectrum, thus using a larger fraction of the available solar energy than that available in the UV 8,9 . 40 Until recently, most efforts in modifying TiO 2 to enhance visible light absorption have focused on substitutional cation or anion doping at Ti or O sites [10][11][12][13][14][15][16][17][18] to achieve a band gap reduction.…”