Role of micro-structure and interfacial properties in the higher photocatalytic activity of TiO2-supported nanogold for methanol-assisted visible-light-induced splitting of water

Abstract

This paper deals with the textural, microstructural and interfacial properties of Au/TiO(2) nanocomposites, in relation to their photocatalytic activity for splitting of water. TiO(2) samples of two different morphologies were employed for dispersing different cocatalysts, such as: Au, Pt, Ag or Cu, for the sake of comparison. The samples were characterized using powder XRD, XPS, UV-visible, thermoluminescence, SEM, HRTEM and SAED techniques. Compared to other metal/TiO(2) photocatalysts, Au/TiO(2) with an optimum gold loading of 1 wt% was found to exhibit considerably higher activity for visible light induced production of H(2) from splitting water in the presence of methanol. Further, the sol-gel prepared TiO(2) (s.TiO(2)), having spherical grains of 10-15 nm size, displayed better photoactivity than a Degussa P25 catalyst. The electron microscopy investigations on s.TiO(2) revealed significant heterogeneity in grain morphology of individual TiO(2) particles, exposure of the lattice planes, metal dispersion, and the interfacial metal/TiO(2) contacts. The gold particles were found to be in a better dispersed state. O(2) TPD experiments revealed that the gold nanoparticles and Au/TiO(2) interfaces may serve as distinct binding sites for adsorbate molecules. At the same time, our thermoluminescence measurements provide an insight into Au-induced new defect states that may facilitate the semiconductor-to-metal charge transfer transition. In conclusion, the superior photocatalytic activity of Au/TiO(2) may relate to the grain morphology of TiO(2), dispersion of gold particles, and the peculiar architecture of metal/oxide heterojunctions; giving rise in turn to augmented adsorption of reactant molecules and their interaction with the photo-generated e(-)/h(+) pair. The role played by methanol as a sacrificial reagent in photocatalytic splitting of water is discussed.

Methyl Formate Production on TiO2(110), Initiated by Methanol Photocatalysis at 400 nm

“…A small fraction of the CH 2 O product desorbs during irradiation, as evidenced by a TOF signal of CH 2 O (Figure 9), which corresponds to desorption of ∼0.01 ML during the first 30 min of irradiation. Most of the disappearance of CH 2 O appears to be from conversion to formate, as revealed in the TPD spectra shown in Figure 10, which were collected at m/z = 28(C 2 40 and the cracking pattern of HCOOH collected with our mass spectrometer, we concluded that the 486 K peak 3 OH was dosed first. The m/z ratios correspond to fragments of various possible isotopic variants of methanol, formaldehyde, and methyl formate.…”

“…A study of CH 2 ) for 0.5 ML of CH 3 OH adsorbed initially on TiO 2 (110). The decomposition of CH 3 OH to CH 2 O and HCOOCH 3 results in surplus H atoms, which transfer to BBO sites.…”

“…Our earlier TPD study of CD 3 OH photo-oxidation on TiO 2 (110) described the stepwise dissociation to CD 3 O and CD 2 O in the absence of coadsorbed oxygen. 24 We have extended these experiments and have observed methyl formate production with a significant isotope effect.…”

“…Then CH 3 O underwent photo-oxidation to HCOOCH 3 in a two-step process where the CH 3 O dissociated to CH 2 O and a crosscoupling reaction involving an HCO intermediate led to the formation of HCOOCH 3 . In this study, the preoxidation of the surface was considered to be essential to the initial formation of adsorbed CH 3 O, and the HCO intermediate was an indication of the hole-mediated dissociation of CH 2 O by a bridge-bonded oxygen (BBO) atom.…”

Promote water photosplitting via tuning quantum well states in supported metal clusters

“…7 Gold nanoparticles supported on titania exhibit photocatalytic activity for water splitting under uv, visible, and near-infrared light. [8][9][10] When they have landed on a surface, different atomic configurations of gold cluster have been found depending on the nature of the supporting substrate, for instance, atomic chains on NiAl(110), 11 two-dimensional (2D) plates on alumina/NiAl(110), 12 and three-dimensional (3D) clusters on iron oxide and titania. 13,14 In general small Au nanoparticles maintain high stability even in water solutions, making them suitable for catalytic applications.…”