Pd@Bi2Ru2O7/BiVO4 Z-Scheme Heterojunction Nanocomposite Photocatalyst for the Degradation of Trichloroethylene.

Photocatalytic degradation of chlorinated persistent organic pollutants is a very challenging process due to the high redox potential of the C-Cl bond that requires wide band gap catalysts that are activated under UV light. Designing a Z-scheme heterojunction between visible light-activated metal oxides with compatible band gaps enables these redox potentials. Herein, we report the design of a pyrochlore/Aurivillius Z-scheme heterojunction to enhance the photocatalytic activity of BiVO4 for the degradation of trichloroethylene. We prepared Bi2Ru2O7/BiVO4 heterostructured photocatalysts by a controlled hydrothermal approach. Upon optimizing the Bi2Ru2O7 ratio to 1.0 wt %, the heterostructured photocatalyst demonstrated enhanced activity in the degradation of trichloroethylene (TCE) under simulated sunlight irradiation compared to bare BiVO4 and Bi2Ru2O7, respectively. Decorating the surface of the catalyst with palladium nanodomains to create the Pd@Bi2Ru2O7/BiVO4 nanocomposite showed a substantial increase in the photocatalytic degradation of TCE. The material characterization indicated that the architecture of the material provides a synergy of enhancing the redox potential of the photocatalyst and improving the charge carrier dynamics. Furthermore, the photoelectrochemical characterization confirmed that the dual heterojunctions in the Pd@Bi2Ru2O7/BiVO4 nanocomposite resulted in improved interfacial charge carrier transfer and enhanced the electron/hole separation efficiency compared to the nonpalladized catalysts. This work provides a promising approach for band gap engineering of visible light photocatalysts for the degradation of halogenated persistent organic pollutants.

Persistence of aerially-sprayed naled in coastal sediments.

Aerial sprays of the organophosphate pesticide, naled, were intensified over beach areas during the summer of 2016 to control the locally-acquired Zika outbreak in the continental U.S. Concerns were raised in beach frequented areas about contaminated sediments. The aim of this study was to evaluate the persistence and levels of naled and its byproduct, dichlorvos, in sediments obtained from the affected areas. Laboratory experiments were designed to simulate the effect of various natural conditions on the decomposition of naled in three sediment types (beach sand, marl, and calcinated beach sand). The three sediment samples were also exposed to field aerial sprays. After 30 min of exposure, more dichlorvos was detected in the sediments than naled, with 33 to 43% of the molar concentration initially applied as either naled or dichlorvos. Under dark conditions, trace levels of naled were observed after 24 h on sediments. Higher temperature accelerated the natural decomposition of both naled and dichlorvos in sediments. The half-life of naled ranged from 3 to 5 h at 22.5 °C and ranged from 1 to 3 h at 30 °C. Expedited decomposition of naled was observed under sunlight conditions with a half-life of naled of 20 min. In the field, only dichlorvos was detected in the sediment samples at concentrations between 0.0011 and 0.0028 µmol/g 1 h after aerial sprays. This data can be used towards a risk assessment that evaluates exposures to naled and dichlorvos through beach sands impacted by aerial spray activities.