Theoretical investigation on RuO2 nanoclusters adsorbed on TiO2 rutile (110) and anatase (101) surfaces

A combined experimental and theoretical study of RuO2/TiO2 heterostructures as a photoelectrocatalyst for hydrogen evolution

We report a joint experimental and theoretical study of RuO₂/TiO₂ heterostructures. In the experimental section, mesoporous RuO₂/TiO₂ heterostructures were prepared by impregnation of mesoporous TiO₂ nanoparticles which were synthesized from a new precursor, Na₂[Ti(C₂O₄)₃], in an aqueous solution of ruthenium(III) chloride followed by calcination at 300 °C. Using various techniques, the prepared TiO₂ and RuO₂/TiO₂ heterostructures were extensively characterized. The photoelectocatalytic application of the as-prepared heterostructures was then investigated toward the hydrogen evolution reaction (HER). The results illustrated that RuO₂ is dispersed uniformly on the TiO₂ surface. The loading of RuO₂ on TiO₂ decreases the band gap energy and extends the absorption edge to the visible light region. This wide absorption extends the photoelectrocatalytic activity of RuO₂/TiO₂ heterostructures. To obtain a deeper understanding of the increase of the photoelectrocatalytic activity of RuO₂/TiO₂ heterostructures compared to pure TiO₂, theoretical calculations at the density functional theory (DFT) level were performed on some model clusters of pure TiO₂ and the RuO₂/TiO₂ heterostructure. The theoretical results elucidated that the recombination ratio of electron-hole pairs decreases effectively for RuO₂/TiO₂ compared to pure TiO₂.

Construction of Dual-Site Atomically Dispersed Electrocatalysts with Ru-C5 Single Atoms and Ru-O4 Nanoclusters for Accelerated Alkali Hydrogen Evolution

Rationally integrating multi-active sites into one ideal catalyst is an effective approach to accelerate multistep reactions by synergic catalysis. Herein, a universal and facile room temperature impregnation strategy is developed to construct Ru atomically dispersed catalyst (Ru ADC) with Ru-C₅ single atoms and Ru oxide nanoclusters (≈1.5 nm), which can also be extended to prepare Ir, Rh, Pt, Au, and Mo atomically dispersed catalysts (ADCs). It is found that the obtained Ru ADC largely boosts alkali hydrogen evolution by concerted catalysis between single atoms and sub-nanoclusters, which only needs an overpotential of 18 mV at 10 mA cm^-2 . Further mechanistic studies reveal that Ru-C₅ single atoms and Ru oxide nanoclusters with Ru-O₄ configuration in one catalyst can synergically boost water molecule capture, water dissociation, and hydrogen release. This study opens up a simple method to synthesize dual-site metal ADCs for synergic catalysis of typical multistep reactions.

Investigation of energy band alignments and interfacial properties of rutile NMO2/TiO2 (NM = Ru, Rh, Os, and Ir) by first-principles calculations

In the field of photocatalysis, constructing hetero-structures is an efficient strategy to improve quantum efficiency. However, a lattice mismatch often induces unfavorable interfacial states that can act as recombination centers for photo-generated electron-hole pairs. If the hetero-structure's components have the same crystal structure, this disadvantage can be easily avoided. Conversely, in the process of loading a noble metal co-catalyst onto the TiO₂ surface, a transition layer of noble metal oxides is often formed between the TiO₂ layer and the noble metal layer. In this article, interfacial properties of hetero-structures composed of a noble metal dioxide and TiO₂ with a rutile crystal structure have been systematically investigated using first-principles calculations. In particular, the Schottky barrier height, band bending, and energy band alignments are studied to provide evidence for practical applications. In all cases, no interfacial states exist in the forbidden band of TiO₂, and the interfacial formation energy is very small. A strong internal electric field generated by interfacial electron transfer leads to an efficient separation of photo-generated carriers and band bending. Because of the differences in the atomic properties of the components, RuO₂/TiO₂ and OsO₂/TiO₂ hetero-structures demonstrate band dividing, while RhO₂/TiO₂ and IrO₂/TiO₂ hetero-structures have a pseudo-gap near the Fermi energy level. Furthermore, NMO₂/TiO₂ hetero-structures show upward band bending. Conversely, RuO₂/TiO₂ and OsO₂/TiO₂ hetero-structures present a relatively strong infrared light absorption, while RhO₂/TiO₂ and IrO₂/TiO₂ hetero-structures show an obvious absorption edge in the visible light region. Overall, considering all aspects of their properties, RuO₂/TiO₂ and OsO₂/TiO₂ hetero-structures are more suitable than others for improving the photocatalytic performance of TiO₂. These findings will provide useful information for understanding the role and effects of a noble metal dioxide as a transition layer between a noble metal co-catalyst and a TiO₂ photocatalyst.

Ru/TiO2-catalysed hydrogenation of xylose: the role of the crystal structure of the support

Lattice matching holds the secret to the Ru-catalysed hydrogenation of xylose to xylitol, a key reaction in practical biomass conversion.

DRIFTS evidence for facet-dependent adsorption of gaseous toluene on TiO2 with relative photocatalytic properties

Effective adsorption is of great importance to the photocatalytic degradation of volatile organic compounds. Herein, we succeeded in the preparation of anatase TiO2 with clean dominant {001} and {101} facets. By using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) equipped with a homemade reaction system and a coupling gas-dosing system, we found that TiO2 with dominant {001} facets exhibits higher toluene adsorption capacity than TiO2 with dominant {101} facets, which may be attributed to the different number of unsaturated 5c-Ti capable of forming the main active adsorption sites (terminal Ti-OH species). TiO2 with dominant {001} facets shows a significantly high photocatalytic degradation performance, with its degradation rate being 6 times higher than that of dominant {101} facets. Combined with simulation results, it is suggested that the synergetic effects of the formation of specific active adsorption sites, the low adsorption energy for toluene, and preservation of the free molecularly adsorbed water on the surface promote the degradation of gaseous toluene on the dominant {001} facets. This study exemplifies that the facet-dependent adsorption of volatile organic compounds is one of the most important factors to effectively engineer photocatalysts for air purification.