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As the main source of atmospheric sulfate aerosol, the aqueous-phase oxidation of SO 2 has been of great concern. Traditionally, the aqueous-phase oxidation of SO 2 is considered a consumption process of atmospheric oxidation capacity; however, we report here that •OH radicals and other reactive oxygen species (ROS) can be generated in the photochemical reactions of bulk HSO 3 − solution. This •OH production pathway results in the fast sulfate formation in the photooxidation of dissolved SO 2. The photochemical process is determined to be pH-dependent in which sulfate formation is promoted by decreasing pH. Hence, a light - driven acidic positive feedback mechanism is proposed that the oxidation of dissolved SO 2 and the formation of •OH radicals have a synergistic promoting effect. These results indicate that the photochemistry of dissolved SO 2 could be a missing source of aqueous •OH radicals as well as sulfate at regional to global scales. [Display omitted] • Aqueous-phase photooxidation of SO 2 is an important sulfate formation pathway. • Acidity promotes rather than inhibits the aqueous-phase photooxidation of SO 2. • SO 2 is not only a consumer but also an initiator of reactive oxygen species. [ABSTRACT FROM AUTHOR]

Abstract: Ta3N5 was synthesized by nitridation of Ta2O5 under NH3 flow at 700°C. The catalyst was pure Ta3N5 according to X-ray diffraction (XRD), and was about 5nm in size with a BET specific surface area 52.8m2/g. When Ta3N5 was added to Fe3+/H2O2 solution (known as Fenton-like system), most Fe3+ were adsorbed on the Ta3N5 surface and could not react with H2O2 in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe3+ ions were reduced to Fe2+ rapidly and Fe2+ were reoxidized by H2O2 on the Ta3N5 surface, thus a fast Fe3+/Fe2+ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta3N5/Fe3+/H2O2 system could efficiently decompose H2O2 to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N,N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results. [Copyright &y& Elsevier]

Abstract: Titanium dioxides (TiO2) nanoparticles with one-dimensional (1D) geometry, nanorods and nanostripes, were used as photocatalysts to photodegrade Rhodamine B (RhB) under ultraviolet (UV) and visible irradiation. The nanorods catalyst exhibited very interesting photocatalytic properties: under the UV irradiation its catalytic activity was slightly below that of the well-known TiO2 catalyst P25, while under visible light it exhibited a better activity than P25. This fact indicates that the nanorods have a superior ability to utilize less energetic but more abundant visible light. Moreover, the 1D TiO2 nanoparticles can be readily separated from aqueous suspensions by sedimentation after the reaction. With these advantages the 1D TiO2 catalysts have a great potential for environmental applications. Various analytical techniques were employed to characterize TiO2 catalysts and monitor the photocatalytic reaction. It was found that the catalytic performance of the catalysts is greatly dependent on their structures: The superior activity of P25 (consists of anatase and rutile nanocrystals) under UV light results probably from the interfacial interaction between anatase and rutile nanocrystals in this solid, which do not exist in the nanorods (only anatase). The titanate nanostripes (titanate) can absorb UV photons with shorter wavelength only. [Copyright &y& Elsevier]