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In order to make clear the roles of dissolved O2 in the photocatalytic decomposition of organic pollutants and to discriminate different degradation pathways (N-deethylation, chromophore cleavage, and mineralization) during the degradation of dye, the photodegradation of rhodamine B (RhB) has been investigated using vanadate and/or platinum species as electron acceptors in the presence or absence of O2 under visible light irradiation. It was found that with VO2+ as electron acceptor, RhB underwent efficient N-deethylation under visible light irradiation and O2 was found to slow down this process significantly. Little mineralization has been observed in the presence and absence of O2 in VO2+ systems. By contrast, Pt(IV) resulted in the cleavage of conjugated chromophore structure (bleaching) of RhB dye under the otherwise identical conditions. In this case, the presence of O2 did not affect the bleaching rate of the dye, but enhanced greatly the mineralization. Both cleavage of conjugated chromophore structure and N-deethylation occurred simultaneously upon the coaction of VO2+ and Pt(IV) under visible light irradiation. The mineralization yield of the combined system was evidently higher than the expected summation of separate ones. TOC, XPS, and ESR results indicate that in the VO2+ and Pt(IV) combined system VO2+ not only oxidized RhB leading to deethylation but also oxidized the reduced Pt(II) to regenerate Pt(IV) leading to the further cleavage of chromophore structure of RhB, which behaved quite different from the separate ones. A mechanism was also proposed to interpret the different pathways for the oxidative photodecomposition of RhB under visible irradiation.

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a b s t r a c tIn this investigation, a facile modification of g-C 3 N 4 through co-pyrolysis of melamine and sodium nitrate or potassium nitrate was reported and the as-synthesized samples were characterized by a collection of techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and elemental analysis. Based upon the analysis, we speculated that the g-C 3 N 4 framework was partially destroyed to produce cyano-containing fragments, which resulted into the variation of physical and optical properties, further affecting the adsorption and photocatalytic performance of g-C 3 N 4 on the dye methylene blue. Furthermore, we found that nitrate anions rather than sodium or potassium ions had important effect on the structure and photocatalytic performance of g-C 3 N 4 . In addition, the photocatalysis mechanism and reusability test were also investigated and discussed in the study.

a b s t r a c tA series of TiO 2 hybrids composited with exfoliated g-C 3 N 4 nanosheets (CNs) were successfully synthesized through a facile sol-gel method and fully characterized by X-ray diffraction patterns (XRD), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV-vis diffuse reflectance spectra (UV-vis DRS). The CNs-TiO 2 hybrids were exposed to visible light irradiation and showed much higher catalytic capability toward degrading dye rhodamine B (RhB) comparing with bare TiO 2 and N-TiO 2 . The sample CNs-TiO 2 -0.05 exhibited the largest apparent reaction rate constant among all CNs-TiO 2 hybrids, which was 2.4 times and 7.0 times as high as bare TiO 2 and N-TiO 2 , respectively. The enhanced catalytic efficiency could be mainly attributed to the well-matched band gap structure with heterojunction interface, suitable specific surface area, and favorable optical property. In addition, active species trapping experiments were conducted, revealing that photoinduced holes (h + ) had a severe influence on catalytic outcome, through which a possible catalytic mechanism was finally realized and proposed.

A novel strategy to tweak the oxygen evolution activity of nanofilms by exploiting the film-substrate redox interaction.

Located in Central South China, Hunan province is rich in mineral resources. To study the influence of mining on Cd pollution to local agricultural eco-system, the paddy soils and rice grain of Y county in northern Hunan province were intensively monitored. The results were as follows: (1) Total Cd (T-Cd) content in the soils of the county ranges from 0.13 to 6.02 mg kg(-1), with a mean of 0.64 mg kg(-1), of which 57.5% exceed the allowable limit specified by the China Soil Environmental Quality Standards. T-Cd in the soils varies largely, with the coefficient of variation reaching 146.4%. The spatial distribution of T-Cd in the soils quite matches with that of mining and industries. The content of HCl-extractable Cd (HCl-Cd) in the soils ranges from 0.02 to 2.17 mg kg(-1), with a mean of 0.24 mg kg(-1). A significant positive correlation exists between T-Cd and HCl-Cd in the soils (r = 0.770, ρ < 0.01). (2) Cd content in the rice produced in Y county ranges from 0.01 to 2.77 mg kg(-1), with a mean of 0.46 mg kg(-1). The rate of rice with Cd exceeding the allowable limit specified by the Chinese Grain Security Standards reaches 59.6%; that with Cd exceeding 1 mg kg(-1), called as "Cd rice," reaches 11.1%. (3) Cd content in the rice of Y county is positively significantly correlated with HCl-Cd (r = 0.177, ρ < 0.05) but not significantly with T-Cd in the soils (r = 0.091, ρ > 0.05), which suggests that the amount of Cd accumulating in the rice is more affected by its availability in the soils, rather than the total content. (4) The dietary intake of Cd via rice consumption in Y county is estimated to be 179.9 μg day(-1) person(-1) on average, which is far beyond the allowable limit specified by FAO/WHO and the target hazard quotients of Cd much higher than 1, suggesting the high risk on human health from Cd exposure.

The photolysis of tetrabromobisphenol A (TBBPA) in aqueous solution under simulated solar light irradiation was studied under different conditions to find out mechanisms and pathways that control the transformation of TBBPA during photoreaction. Particular attention was paid to the identification of intermediates and elucidation of the photolysis mechanism of TBBPA by UPLC, LC/MS, FT-ICR-MS, NMR, ESR, and stable isotope techniques ( 13 C and 18 O). The results showed that the photolysis of TBBPA could occur under simulated solar light irradiation in both aerated and deaerated conditions. A magnetic isotope effect (MIE)-hydrolysis transformation was proposed as the predominant pathway for TBBPA photolysis in both cases. 2,6-Dibromophenol and two isopropylphenol derivatives were identified as photooxidation products of TBBPA by singlet oxygen. Reductive debromination products tribromobisphenol A and dibromobisphenol A were also observed. This is the first report of a photolysis pathway involving the formation of hydroxyl-tribromobisphenol A.