Aquatic photolysis of hydroxylated polybromodiphenyl ethers under direct UV irradiation: a case study of 2'-HO-BDE-68

Synthesis and Photocatalytic Activity of Pt-Deposited TiO2 Nanotubes (TNT) for Rhodamine B Degradation

Dye wastewater has attracted more and more attention because of its high environmental risk. In this study, a novel TiO2 nanotube (TNT) catalyst was prepared and its morphology and structure were characterized. The synthetic catalyst was used to degrade Rhodamine B (RhB) under UV light and evaluated for the application performance. According to the characterization results and degradation properties, the optimum synthetic conditions were selected as 400°C calcination temperature and 10 wt% Pt deposition. As a result, the degradation efficacies were sequenced as TNT-400-Pt > TNT-500-Pt > TNT-400 > TNT-300-Pt. In addition, the effect of pH and initial concentration of RhB were explored, and their values were both increased with the decreased degradation efficacy. While the moderate volume of 11 mm of H2O2 addition owned better performance than that of 0, 6, and 15 mm. Scavengers such as tertbutanol (t-BuOH), disodium ethylenediaminetetraacetate (EDTA-Na2), and nitroblue tetrazolium (NBT) were added during the catalytic process and it proved that superoxide radical anions (O2–•), photogenerated hole (h+) and hydroxyl radical (OH•) were the main active species contributing for RhB removal. For the application, TNT-Pt could deal with almost 100% RhB, Orange G (OG), Methylene blue (MB), and Congo red (CR) within 70 min and still kept more than 50% RhB removal in the fifth recycling use. Therefore, TNT-Pt synthesized in this study is potential to be applied to the dye wastewater treatment.

Degradation of clofibric acid by UV, O3 and UV/O3 processes: Performance comparison and degradation pathways

In this study, ultraviolet (UV) irradiation, ozonation (O₃) and their combination (UV/O₃) were used to decompose clofibric acid (CA). The results show that UV system exhibited a very high CA removal rate (0.20 min^-1) but the lowest mineralization (14.8%) accompanied by the formation of more toxic products. Ozonation achieved a much lower removal rate (0.05 min^-1) but a higher mineralization efficiency (22.7%) in comparison with UV photolysis. The introduction of UV irradiation into O₃ system significantly enhanced the removal rate (0.21 min^-1) and the mineralization efficiency (68.2%) of CA. The acute toxicity of the reaction solution to Daphnia magna in the UV/O₃ process increased during the first 20 min and then decreased, which illustrates that UV/O₃ is an effective and safe method for the removal of CA. The intermediate products were identified by LC-MS analysis and the degradation pathways for all the three processes were proposed. The direct photolysis and hydrous electron reduction contributed to the CA elimination in UV alone process. In O₃ alone system, the removal of CA occurred via direct ozone oxidation and indirect free radical oxidation. The free radical, ozone, hydrous electron and direct photolysis were involved in the degradation of CA in the UV/O₃ process.

Multiple catalytic roles of chloroperoxidase in the transformation of phenol: Products and pathways

Chloroperoxidase (CPO) is a hybrid of two different families of enzymes, peroxidases and P450s. However, it is poorly understood on CPO's multiple catalytic functions. Herein, phenol was selected as a model substrate to investigate the multiple catalytic roles of CPO. Results showed that phenol was readily transformed into a variety of brominated organic compounds (BOCs) via the CPO-mediated oxidative process. A total of 16 BOCs were identified using gas and liquid chromatography coupled with mass spectrometry. Possible reaction pathways could be attributable to four CPO-mediated processes, including bromination, radical coupling, intramolecular cyclization and debromination. Higher bromide concentrations and lower pH conditions both facilitated the formation of brominated products. While a higher bromination capacity was observed in pH 3.0 solutions, CPO-mediated radical couplings were more favorable at pH 5.0 and 6.0. Although CPO might catalyze chlorination when chloride and bromide coexisted in the solution, BOCs were the dominant products of CPO-mediated phenol oxidation. Results of this study suggest that various catalytic roles of CPO may contribute to the biotic formation of BOCs in the natural environment.

Graphitic carbon nitride based nanocomposites for the photocatalysis of organic contaminants under visible irradiation: Progress, limitations and future directions

Graphitic carbon nitride (g-C₃N₄) has drawn great attention recently because of its visible light response, suitable energy band gap, good redox ability, and metal-free nature. g-C₃N₄ can absorb visible light directly, therefore has better photocatalytic ability under solar irradiation and is more energy-efficient than TiO₂. However, pure g-C₃N₄ still has the drawbacks of insufficient light absorption, small surface area and fast recombination of photogenerated electron and hole pairs. This review summarizes the recent progress in the development of g-C₃N₄ nanocomposites to photodegrade organic contaminants in water. Element doping especially by potassium has been reported to be an efficient method to promote the degradation efficacy. In addition, compound doping improves photodegradation performance of g-C₃N₄, especially Ag₃PO₄-g-C₃N₄ which can completely degrade 10mgL^-1 of methyl orange under visible light irradiation in 5min, with the rate constant (k) as high as 0.236min^-1. Moreover, co-doping enhances the photodegradation rate of multiple contaminants while immobilization significantly improves catalyst stability. Most of g-C₃N₄ composites possess high reusability enabling their practical applications in wastewater treatment. Furthermore, environmental conditions such as solution pH, reaction temperature, dissolved oxygen, and dissolved organic matter all have important effects on the photocatalytic ability of g-C₃N₄ photocatalyst. Future work should focus on the synthesis of innovative g-C₃N₄ nanocomposites for the efficient removal of organic contaminants in water and wastewater.

Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs in human serum from Shanghai, China: a study on their presence and correlations

Polybrominated diphenyl ethers (PBDEs) are becoming a public health concern because of their potential toxicity, from endocrine disruption system to neurodevelopmental impairments. Nonetheless, information on their levels in human blood is scarce. In this study, human serum samples collected in Shanghai, China, were analyzed for the concentrations of PBDEs and their hydroxylated metabolites (OH-PBDEs). Eight PBDE congeners and six OH-PBDE congeners were quantified in serum samples by gas chromatography with mass spectrometry (GC-MS) and high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). As a result, total PBDE concentration ranged from 0.280 to 12.330 ng g^-1 on a lipid weight basis lw (median: 1.100 ng g^-1 lw) and the total OH-PBDE level ranged from 0.045 to 0.363 ng g^-1 (lw) (median: 0.187 ng g^-1 lw). Among them, BDE-47 and 6-OH-BDE-47 were the predominant PBDEs and OH-PBDEs, respectively. In addition, based on the results of the Bartelett X ² test, BDE-47 significantly (p < 0.05) correlated with BDE-28, BDE-100, BDE-85, and BDE-154, whereas 3'-OH-BDE-7 significantly (p < 0.01) correlated with 3-OH-BDE-47, 2-OH-BDE-68, and 6'-OH-BDE-99. Among all donors, no significant association between age and PBDEs (or OH-PBDEs) was found. Further research on the exposure routes in the environment and metabolic processing of PBDEs in human blood is necessary.