A facile two-step method was developed
to prepare core/shell ZnO/rGO
particles from ZIF-8/rGO composites. ZIF-8 particles were first grown
at the surface of rGO sheets. Next, ZIF-8 particles were transformed
into ZnO particles by thermal decomposition under air at 500 °C.
All materials were characterized by scanning electron microscopy,
transmission electron microscopy, X-ray diffraction, Raman spectroscopy,
thermogravimetric analysis, and Brunauer–Emmett–Teller
analyses. Results obtained show that ZIF-8 particles strongly associate
with rGO sheets and that the calcination of this material produces
porous core/shell ZnO/rGO particles with an average diameter of ca.
40 nm. The wt % of rGO associated with ZIF-8 particles was varied
from 5 to 20%. The ZnO/rGO (10%) particles exhibit the highest photocatalytic
activity for the degradation of the Orange II dye under simulated
solar light irradiation of weak intensity (5 mW/cm
2
). This
high photocatalytic activity was demonstrated to originate from superoxide
O
2
•–
radicals due to the efficient
trapping of photogenerated electrons in ZnO by rGO.
The Syr Darya is one of two major rivers in Central Asia supplying critical fresh water to the Aral Sea. In spite of the river's importance and agriculturally-intensive history, few studies have provided a modern evaluation of and the occurrence of pesticide residues potential effects to aquatic life. The primary goal of this investigation was to determine seasonal variations in ambient concentrations of modern and legacy pesticides in bottom sediment and water of the Syr Darya in Kazakhstan (KZ) downstream from an agriculturally-intensive watershed in Uzbekistan. Grab samples and passive samplers were used at five remote sampling stations during June 2015 to provide a baseline for ecotoxicological evaluation. Results were compared with samples collected during and after the agricultural growing season. Polar organic chemical integrative samplers (POCIS) were used in June and calibrated for time-weighted average concentrations of current use pesticides. Among legacy chlorinated pesticides measured in grab samples from the river, lindane (γ-HCH) was detected most frequently with the highest concentrations occurring during June. For all the sampling events, residues of lindane (γ-HCH) ranged from 0.014 to 0.24 μg/L detected in water samples, are among the highest concentrations reported for rivers globally. Concentrations of γ-HCH, p,p'-DDE and dieldrin were highest in October when dieldrin concentrations approached 0.4 μg/L. Sources of legacy pesticides may be either illicit upstream use or evidence of previous atmospheric contamination of glacial meltwater. Chronic exposure to these residues may lead to ecological risk to lower order organisms in both the sediment and water column.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.