Surface Phases and Photocatalytic Activity Correlation of Bi2O3/Bi2O4-x Nanocomposite

UV-visible radiations were used to induce surface modifications in Bi2O3 leading to the formation of Bi2O3/Bi2O4-x nanocomposite. Despite the complexity of the degradation mechanisms, which depend on the nature of the pollutants, our results indicate that Bi2O3/Bi2O4-x-based materials are very promising as photocatalysts

A High-Frequency (95 GHz) Electron Paramagnetic Resonance Study of B-doped TiO2 photocatalysts

A high-field and high-frequency (HF, 95 GHz) electron paramagnetic resonance (EPR) study has been carried on B-doped TiO2. Several paramagnetic species are observed both in the dark and under UV irradiation which are resolved employing the high resolution of HFEPR. The behaviour of the EPR signals may be interpreted in terms of a sensitization of the B-doped TiO2 to visible light. A paramagnetic species interacting with a B atom is found. The Hamiltonian parameters of this species carry important information on its electronic structure. The analysis of the hyperfine values reveals that the spin density is mainly centred on the B and asymmetrically distributed in two p B orbitals. Insights into the B local structure in the semiconductor are gained

Photocatalytic Production of Hydrogen Over Tailored Cu-Embedded TiO2

Copper nanoparticles embedded into TiO2 showed promising photocatalytic hydrogen production using water/methanol solution. Preformed metal nanoparticles, surrounded by a porous TiO2 matrix, were prepared by microemulsion method. XRD and HRTEM analysis indicated the presence of the anatase polymorph with minor traces of ruble and brookite. The performances of this nanostructured system were compared with those of a similar material prepared by conventional impregnation method. Using TiO2 with identical structural and textural properties, a significantly lower CO chemisorption was measured for the impregnated sample with respect to the embedded one. Even though it is not possible to discriminate between the different ratio of the Cu containing species in the two samples, this is an indication that the embedded system presents highly accessible copper species and in a slightly larger quantity with respect to the corresponding impregnated sample. Consistently XRD and preliminary HRTEM investigations indicates presence of smaller Cu/CuOx particles in the embedded catalyst. A CO adsorption capacity similar to that of the embedded system was obtained by impregnating with copper nitrate a TiO2, obtained by sol gel method. This last system present however a more significant contribution of the ruble phase. Notably, Cu embedded material showed significantly superior performances with respect to all the other samples. In this regard an optimal combination of low particle size, accessible active phase, ratio of Cu/CuOx, presence of the more active anatase phase and excellent interfacial contact between Cu and surrounding TiO2 particles was found critical. This latter aspect can lead to a better synergic electron/hole transfer which allow improved activity

Synthesis, characterization and photocatalytic performance of transition metal tungstates

Tungstates of divalent transition metals (MIIWO4, M = CoII, NiII, CuII, ZnII) were synthesized by reaction of transition metal nitrates with sodium tungstate. The precipitates were then calcined at 500 \ub0C. The materials were characterized by means of ICP-AES elemental analysis, UV\u2013Visible spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and surface area analysis. The higher activity for the decolourization of Methylene Blue (MB) and Methyl Orange (MO) of ZnWO4 compared to that of the other investigated tungstates was correlated with its strong tendency of excitons self-trapping

Photocatalytic H2 and added-value byproducts: the role of metal oxide systems in their synthesis from liquid oxygenates

The growing demand for hydrogen for industrial use and as a fuel pushes for innovative and sustainable production strategies, which can be applied both in centralized, large-scale plants and in delocalized small units. At present, hydrogen is mainly produced by steam reforming of natural gas or oil. Nevertheless, the shortage of fossil fuel reserves and the increasing concern regarding environmental pollution have stimulated the search for alternative production routes, among which photocatalysis over metal oxide semiconductors represents a strategically attractive solution. Whereas the direct splitting of water is still a challenging issue because of intrinsic process drawbacks, a valuable alternative for a sustainable photocatalytic H2 production is the use of biomass-derived compounds as raw materials. Upon photoactivation in the presence of an appropriate semiconductor, such feedstocks can undergo oxidation to CO2 with simultaneous H2 production in the so-called photoreforming process. When the oxidation is selective rather than complete, the process might be of further interest due to the added value of the obtained carbon-containing by-products. This microreview focuses on recent developments in this field, with particular attention to the use of representative biomass-derived oxygenated compounds, such as methanol, ethanol, glycerol, and sugars

Photocatalytic H2 and added-value by-products - the role of metal oxide systems in their synthesis from oxygenates

The growing demand for hydrogen for industrial use and as a fuel pushes for innovative and sustainable production strategies, which can be applied both in centralized, large-scale plants and in delocalized small units. At present, hydrogen is mainly produced by steam reforming of natural gas or oil. Nevertheless, the shortage of fossil fuel reserves and the increasing concern regarding environmental pollution have stimulated the search for alternative production routes, among which photocatalysis over metal oxide semiconductors represents a strategically attractive solution. Whereas the direct splitting of water is still a challenging issue because of intrinsic process drawbacks, a valuable alternative for a sustainable photocatalytic H2 production is the use of biomass-derived compounds as raw materials. Upon photoactivation in the presence of an appropriate semiconductor, such feedstocks can undergo oxidation to CO2 with simultaneous H2 production in the so-called photoreforming process. When the oxidation is selective rather than complete, the process might be of further interest due to the added value of the obtained carbon-containing by-products. This microreview focuses on recent developments in this field, with particular attention to the use of representative biomass-derived oxygenated compounds, such as methanol, ethanol, glycerol, and sugars

Nanostructured Cu/TiO2 photocatalysts for H2 production from ethanol and glycerol aqueous solutions

The Cu photodeposited on pure anatase or multi-phase TiO2 leads to the formation of nanostructured visible-light driven photocatalysts, which are active in the valorization of ethanol or glycerol