Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

Abstract

In this review we describe our work on new TiO2 based photocatalysts. The key concept in our work is to form new composite structures by the modification of rutile and anatase TiO2 with nanoclusters of metal oxides and our density functional theory (DFT) level simulations are validated by experimental work synthesizing and characterizing surface-modified TiO2. We use DFT to show that nanoclusters of different metal oxides, TiO2, SnO/SnO2, PbO/PbO2, NiO and CuO can be adsorbed at rutile and anatase surfaces and can induce red shifts in the absorption edge to enable visible light absorption which is the first key requirement for a practical photocatalyst. We furthermore determine the origin of the red shift and discuss the factors influencing this shift and the fate of excited electrons and holes. For p-block metal oxides we show how the oxidation state of Sn and Pb can be used to tune both the magnitude of the red shift and also its mechanism. Finally, aiming to make our models more realistic, we present some new results on the stability of water at rutile and anatase surfaces and the effect of water on oxygen vacancy formation and on nanocluster modification. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with the suitable choice of nanocluster modifier can be applied to CO2 reduction.

Alkaline earth metal oxide nanocluster modification of rutile TiO2 (110) promotes water activation and CO2 chemisorption

“…To investigate the nature of the photoexcited state and electron and hole localisation and stability, which relate to charge separation after excitation, Figure 4 displays the excess spin density isosurfaces for the triplet electronic state of each nanocluster modified system. As described in our earlier studies 18,24,77,78,120,123 as well as other work 61,83 , this model system allows us to study the nature of the photoexcited state and the charge localisation after excitation. Imposing a triplet electronic state forces an electron into the previously empty conduction band states, leaving a hole in the valence band, thus simulating an excited electron-hole pair.…”

“…To illuminate the experimental studies and predict useful composite systems based on surface modification of TiO2 with metal oxide nanoclusters, we have presented an extensive series of density functional theory (DFT) simulations of TiO2 modified with a range of metal oxide nanoclusters; see refs. 24,71,77,78 . These have not only confirmed the origin of band gap reduction in FeOx modified rutile TiO2 43 , the origin of enhanced UV or visible light activity of SnO2modified anatase 41,42 or rutile 44 TiO2 and the effect of NiO 75 or CuO 79 modification of rutile and anatase, but have also predicted composite systems with SnO 80 and PbO 81 nanocluster modification, both of which have been experimentally confirmed 68,76 .…”

CO2 Activation on Heterostructures of Bi2O3-Nanocluster Modified TiO2: Promoting the Critical First Step in CO2 Conversion

“…Previously we have used first principles density functional theory (DFT) simulations to design heterostructured materials which are composed of TiO2 (rutile or anatase) surfaces modified with metal oxide nanoclusters. In our work, the emphasis has been on new heterostructured materials with predicted visible light absorption [44][45][46][47][48][49][50][51][52][53][54][55][56] and reduced charge recombination [45][46][47][48][49][57][58][59] . We have recently extended this work to study the interaction of molecules, such as CO2, with these metal oxide nanocluster modified TiO2 heterostructures 44,60 .…”

First-principles analysis of the stability of water on oxidised and reduced CuO(111) surfaces

“…Unlike other metal oxide surfaces such as (110) rutile and (101) anatase TiO 2 or CeO 2 (111), [17][18][19]35,36 little is known about the interaction of water with CuO surfaces. An attempt to study surface-water interactions has been presented by Zhang et al 20 They investigated the interaction of a single water molecule with perfect and defective CuO(111) surfaces using density functional theory within the GGA approximation, using the Perdew and Wang functional (PW91) for the exchange-correlation term where copper atoms were kept frozen and substituted by a DFT semi-core pseudopotential and other atoms are treated with an all-electron basis set.…”