In Situ Time-Resolved Energy-Dispersive XAFS Study on Photodeposition of Rh Particles on a TiO₂ Photocatalyst

Abstract

It is the first report to observe the real-time behavior of photodeposition and the continuous structural change of Rh metal particles anchored on a TiO2 photocatalyst from an aqueous solution of Rh trivalent ions in the liquidsolid suspension by an in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis. The DXAFS analysis uncovered that the Rh trivalent ions are adsorbed on the surface of the TiO2 photocatalyst, followed by reducing to the Rh metal particles by acceptance of electrons because the coordination number of a RhRh bond evaluated by the Fourier transforms of EXAFS spectra and the amount of the Rh trivalent ions determined by the ICP analysis linearly increased and decreased with elongation of photoirradiation time, respectively. The generation rates of the Rh metal particles and the diminution rates of the Rh trivalent ions depended on the type of sacrificial reagents and tends to become slower in the order corresponding to methanol > ethanol ≫ 1-propanol >2-propanol. The coordination number of a RhRh bond stopped increasing after 90 min of photoirradiation in the case of methanol. The coordination number was evaluated to 10, although that of Rh foil is 12, suggesting the generation of Ultrafine Rh particles on TiO2.

The effect of Fe–Rh alloying on CO hydrogenation to C2+ oxygenates

“…7a. Based on previous studies, the first shell peak at 2.76 Å in the Rh-only data can be assigned to the Rh-Rh bond [14,[38][39][40]. With the addition of Fe, this peak begins to broaden and eventually splits into two distinct peaks at 2.53 Å and 2.79 Å at the highest Fe loading.…”

A surface science perspective on TiO2 photocatalysis

“…In the absence of an electrochemical setting, this oxidation process must take place on the same photocatalyst in which reductive deposition of the metal is occurring. Research from several groups [233,555,1113,1118,1124,1132,1135,1136,1138,[1149][1150][1151]1156,1158] has shown that choice of the sacrificial electron donor (usually an organic) is key to efficient metal photoreduction. This is not simply an issue of balancing redox potentials (although that is important), but also selecting an electron donor that does not compete for surface sites or otherwise interfere with the metal reduction process.…”

In Situ Observation of Nucleation and Growth Process of Gold Nanoparticles by Quick XAFS Spectroscopy

“…Of these, quick X-ray absorption fine-structure (XAFS) spectroscopy is one of the most useful methods to observe AuNP formation process in situ because the chemical state and the structure of AuNP can be analyzed from the spectra. [15,16,17] Recently, Polte et al observed the formation process of AuNPs with citric acid by coupled in situ XANES and small-angle X-ray scattering (SAXS) spectroscopy. [18] This helped to describe the mechanism of nanoparticle formation, which was found to comprise different steps of particle growth via both the coalescence of nuclei and further monomer attachment.…”