The literature on photocatalytic oxidation of water pollutants often reports reaction kinetic constants, which cannot be unraveled from photoreactor type and experimental conditions. This study addresses this challenging aspect by presenting a general and simple methodology for the evaluation of fundamental "intrinsic" reaction kinetic constants of photocatalytic degradation of water contaminants, which are independent of photoreactor type, catalyst concentration, irradiance levels, and hydrodynamics. The degradation of the model contaminant, oxalic acid (OA) on titanium dioxide (TiO2) aqueous suspensions, was monitored in two annular photoreactors (PR1 and PR2). The photoreactors with significantly different geometries were operated under different hydrodynamic regimes (turbulent batch mode and laminar flow-through recirculation mode), optical thicknesses, catalyst and OA concentrations, and photon irradiances. The local volumetric rate of photon absorption (LVRPA) was evaluated by the six-flux radiation absorption-scattering model (SFM). The SFM was further combined with a comprehensive kinetic model for the adsorption and photodecomposition of OA on TiO2 to determine local reaction rates and, after integration over the reactor volume, the intrinsic reaction kinetic constants. The model could determine the oxidation of OA in both PR1 and PR2 under a wide range of experimental conditions. This study demonstrates a more meaningful way for determining reaction kinetic constants of photocatalytic degradation of water contaminants.

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Novel form of black TiO 2 nanotubes-based photocatalysts for water purification were prepared. Two features were combined: decoration of TiO 2 nanotube arrays with Ag nanoparticles (sample TiO 2-NT's@Ag) and further hydrogenation of this material (TiO 2-NT's@Ag-HA). Obtained photocatalysts show high efficiency for degradation of salicylic acid, a typical water-borne pollutant. The photocatalysts considerably exceed the photocatalytic properties of TiO 2 nanotubes and commercial TiO 2 P25 taken as a reference for modelling of the photocatalytic process. The comparison of photocatalytic activities

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International audienceWe have used a single SBA-15 silica batch (mesopore diameter of 7.1 nm) and the two-solvent impregnation technique with either pentane or cyclohexane to prepare model samples in which an initial aqueous solution of salt precursor (iron nitrate or iron chloride) is deposited mainly inside silica pores. Detailed characterization by SAXS, WAXS, Ar sorption, TEM (SAED), and UV-visible-NIR spectroscopy is described. Molecular iron species and iron oxide particles are identified. Special emphasis is given to the spatial location of the oxide particles (trapped inside silica pores or dispersed outside silica grains). The formation of hematite external particles is favored when iron chloride is used as a precursor and pentane as a solvent. Spectral signatures that can be attributed either with iron oxide particles or with iron dispersed molecular species (isolated Fe(II)/(III) ions, pairs and/or clusters, films of iron silicate) are detected by UV-visible-NIR spectroscopy. Additional neutron diffraction measurements performed on a sample particularly enriched in external hematite particles indicate a very low magnetic moment of 3.9 (1) μB per iron atom and show that external hematite particles are not significantly polluted by Si atoms. Model catalysts, all containing molecular species but particularly enriched in either external or internal iron oxide particles, were selected and tested for the catalytic Fenton decomposition (with H2O2 and diluted O2 and under artificial white light) of sodium formate and of an organic copper-containing dye (Reactive Violet 2) in water. Samples enriched in external hematite particles are significantly less active and react less rapidly than samples containing mainly iron species remaining trapped inside silica grains. Preliminary UV-visible-NIR spectra suggest that strong interactions between molecular species and internal replicated oxide particles are at the origin of an enhanced reactivity

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