Novel decahedral TiO 2 photocatalysts modified with Ru or Rh NPs: Insight into the mechanism

Photodegradation of 2,4-D (dichlorophenoxyacetic acid) with Rh/TiO2; comparative study with other noble metals (Ru, Pt, and Au)

In this work the effect of noble metal on the photodegradation of 2,4-dichlorophenoxyacetic acid herbicide using TiO₂ as support was studied. The metals and concentration were: Rh, Ru, Pt and Au and 1, 0.98, 1.89, and 1.91 wt% respectively. Rhodium was taken as reference for this experiment. The samples were characterized by X-Ray Diffraction (XRD), UV-vis absorption spectra, N₂ physisorption (BET Specific Surface Area), High Annular Angle Analysis Darkfield (HAADF) and Transmission Electron Microscopy Scanning (STEM), H₂ chemisorption, optical emission spectroscopy with inductive coupling plasma analysis (ICP-OES), solid fluorescence, X-ray Photoelectron Spectroscopy (XPS) and OH quantification. The presence of the anatase crystalline phase was mostly confirmed in all samples. The band gap decreased with the presence of metal (from 3.24 to 2.92 eV). The specific area was a function of the metal particle size. The metal particle diameter showed the following sequence Pt > Ru > Au > Rh. By XPS, TiO₂ does not manifest changes in oxidation states, but when impregnated with metals, only Pt shows the highest abundance of any oxidized state (Pt²⁺). The presence of metal reveals less electron–hole recombination compared with titanium oxide. The results of photocatalytic activity showed that Pt and Rh are the two metals with the highest mineralization (99.0 and 98.3%, respectively).

The optimum catalyst for the photocatalytic degradation of 2,4-D was Rh (1%)/TiO₂ by UV radiation. The Rh presents a strong metal-support interaction and improves the photocatalytic properties of TiO₂, modifying its band gap energy.

Enhanced Photodegradation of p-Nitrobenzoic Acid by Binary Mixtures with Ba2+/TiO2 and MCM-41

A novel Ba(II)/TiO₂-MCM-41 composite was synthesized using binary mixtures with Ba²⁺/TiO₂ and MCM-41, and Ba²⁺ as a doping ion of TiO₂. The specific surface area and pore structure characterizations confirm that a mesoporous structure with a surface area of 341.2 m²/g and a narrow pore size distribution ranging from 2 to 4 nm was achieved using Ba(II)/TiO₂-MCM-41. Ba(II)/TiO₂ particles were synthesized into 10-15 nm particles and were well dispersed onto MCM-41. The diffraction peaks in the XRD patterns of TiO₂-MCM-41 and Ba(II)/TiO₂-MCM-41 were all attributed to anatase TiO₂. By taking advantage of MCM-41 and Ba²⁺, the photocatalytic performance of Ba(II)/TiO₂-MCM-41 was remarkably enhanced by suppressing its rutile phase, by lowering the band gap energy, and by facilitating the dispersion of TiO₂. Therefore, the photodegradation efficiencies of p-nitrobenzoic acid (4 × 10^-4 mol/L) by various photocatalysts (60 min) under UV light irradiation are arranged in the following order: Ba(II)/TiO₂-MCM-41 (91.7%) > P25 (86.3%) > TiO₂-MCM-41 (80.6%) > Ba(II)/TiO₂ (55.7%) > TiO₂ (53.9%). The Ba(II)/TiO₂-MCM-41 composite was reused for five cycles and maintained a high catalytic activity (73%).

Highly selective visible-light-triggered CO2 fixation to cyclic carbonates under mild conditions using TiO2/multiwall carbon nanotubes (MWCNT) grafted with Pt or Pd nanoparticles

Visible light-induced CO2 fixation to cyclic carbonates catalyzed by Pd//TiO2/MWCNT photocatalyst.

High-throughput HSE study on the doping effect in anatase TiO2

Systematic study on the doping effects of anatase TiO₂ doped with 40 kinds of elements by high-throughput HSE06 calculations.

Constructing Rh–Rh3+ modified Ta2O5@TaON@Ta3N5 with special double n–n mutant heterojunctions for enhanced photocatalytic H2-evolution

A multiple core–shell heterostructure Rh–Rh³⁺ modified Ta₂O₅@TaON@Ta₃N₅ nanophotocatalyst was successfully constructed through nitriding Rh³⁺-doped Ta₂O₅ nanoparticles, which exhibited a much higher carrier separation efficiency about one order of magnitude higher than the Ta₂O₅@Ta₃N₅ precursor, and thus an excellent visible light photocatalytic H₂-evolution activity (83.64 μmol g⁻¹ h⁻¹), much superior to that of Rh anchored Ta₂O₅@TaON (39.41 μmol g⁻¹ h⁻¹), and improved stability due to the residual Rh–O/N in the Ta₃N₅ shell layer. Rh-modifying significantly extended light absorption to the overall visible region. Localized built-in electric fields with hierarchical potential gradients at the multiple interfaces including a Rh/Ta₃N₅ Schottky junction and double n–n Ta₃N₅/TaON/Ta₂O₅ mutant heterojunctions, drove charge carriers to directionally transfer from inside to outside, and efficiently separate. Enhanced photoactivity was ascribed to a synergetic effect of improved light absorption ability, increased carrier separation efficiency, and accelerated surface reaction. A promising strategy of developing excellent Ta₃N₅-based photocatalysts for solar energy conversion is provided by constructing double n–n mutant heterojunctions.

Localized built-in electric fields at multiple hierarchical interfaces facilitate the efficient separation and fast inside-out directional transfer of photogenerated carriers.

Solar Light Induced Photon-Assisted Synthesis of TiO₂ Supported Highly Dispersed Ru Nanoparticle Catalysts

Ru/TiO₂ are promising heterogeneous catalysts in different key-reactions taking place in the catalytic conversion of biomass towards fuel additives, biofuels, or biochemicals. TiO₂ supported highly dispersed nanometric-size metallic Ru catalysts were prepared at room temperature via a solar light induced photon-assisted one-step synthesis in liquid phase, far smaller Ru nanoparticles with sharper size distribution being synthesized when compared to the catalysts that were prepared by impregnation with thermal reduction in hydrogen. The underlying strategy is based on the redox photoactivity of the TiO₂ semi-conductor support under solar light for allowing the reduction of metal ions pre-adsorbed at the host surface by photogenerated electrons from the conduction band of the semi-conductor in order to get a fine control in terms of size distribution and dispersion, with no need of chemical reductant, final thermal treatment, or external hydrogen. Whether acetylacetonate or chloride was used as precursor, 0.6 nm sub-nanometric metallic Ru particles were synthesized on TiO₂ with a sharp size distribution at a low loading of 0.5 wt.%. Using the chloride precursor was necessary for preparing Ru/TiO₂ catalysts with a 0.8 nm sub-nanometric mean particle size at 5 wt.% loading, achieved in basic conditions for benefitting from the enhanced adsorption between the positively-charged chloro-complexes and the negatively-charged TiO₂ surface. Remarkably, within the 0.5–5 wt.% range, the Ru content had only a slight influence on the sub-nanometric particle size distribution, thanks to the implementation of suitable photo-assisted synthesis conditions. We demonstrated further that a fine control of the metal Ru nanoparticle size on the TiO₂ support was possible via a controlled nanocluster growth under irradiation, while the nanoparticles revealed a good resistance to thermal sintering.

Design of Ag/ and Pt/TiO2-SiO2 nanomaterials for the photocatalytic degradation of phenol under solar irradiation

The design of hybrid mesoporous TiO₂-SiO₂ (TS1) materials decorated with Ag and Pt nanoparticles was performed. The photocatalytic degradation of phenol under artificial solar irradiation was studied and the activity and selectivity of the intermediate products were verified. TiO₂-SiO₂ was prepared by sol-gel method while Ag- and Pt-based photocatalysts (TS1-Ag and TS1-Pt) were prepared by photodeposition of the noble metals on TS1. Two series of photocatalysts were prepared varying Ag and Pt contents (0.5 and 1.0 wt%). An increase in the photocatalytic activity up to two and five times higher than TS1 was found on TS1-Ag-1.0 and TS1-Pt-1.0, respectively. Changes in the intermediate products were detected on Ag- and Pt-based photocatalysts with an increase in the catechol formation up to 3.3 and 6.6 times higher than that observed on TS1, respectively. A two-parallel reaction mechanism for the hydroquinone and catechol formation is proposed. A linear correlation between the photocatalytic activity and the surface concentration of noble metals was found indicating that the electron affinity of noble metals is the driven force for both the increase in the photoactivity and for the remarkable changes in the selectivity of products.