441 research outputs found
Removal of malathion from various waters by advanced oxidation processes
Summary: The degradation of malathion was investigated under various conditions, including ultrasound (US) irradiation, ultraviolet (UV) irradiation, and the combination of US/UV, UV/ZnO, UV/H2O2, and US/UV/ZnO/H2O2. In addition, the effect of the operational parameters, such as the initial concentration of the catalyst, the initial malathion concentration, the initial salt concentration (NaHCO3 and Na2SO4), and pH, were studied. Analyses were performed by a gas chromatography-mass spectroscopy instrument. The k values were in the following order: US/UV/H2O2/ZnO > US/UV > UV/ZnO > UV/H2O2 > UV > US. ZnO concentration of 100 mg/l, malathion initial concentration of 200 μg/l, H2O2 concentration of 30 mg/l, pH of 9, and irradiation time of 105 min were the optimum conditions for degrading malathion by the US/UV/H2O2/ZnO system. Additionally, the optimized parameters were also tested for the treatment of an actual water sample containing the pesticide. As a result, the efficiency of the US/UV/H2O2/ZnO system was higher in the distilled water sample than in the actual water sample. © 2015, Chemical Society of Pakistan. All rights reserved
PHOTOCATALYTIC DEGRADATION OF CHLORPYRIFOS IN WATER USING TITANIUM DIOXIDE AND ZINC OXIDE
In the present work, degradation of chlorpyrifos in water was investigated using semiconductor oxide catalysts, i.e. zinc oxide (ZnO) and titanium dioxide (TiO2). The influence of various parameters, such as type of the catalyst, irradiation time, catalyst concentrations, pH, and sodium bicarbonate salt was also studied. Results indicated that the optimal concentration of the catalyst was 0.15 g/L. It was also found that TiO2 is a better catalyst than ZnO under the same photocatalytic reaction conditions. The highest removal efficiency was achieved at pH 9. Results from the present study suggested that the photodegradation efficiency of pesticides increases with the increase of the illumination time. The photodegradation efficiency of chlorpyrifos was found to be 80% and 90% for UV/ZnO and UV/TiO2, respectively. Photodegradation in the presence of sodium bicarbonate was slower in comparison to that without the salt. In addition, the efficiency of photocatalytic degradation in distilled water was higher than in natural water
Low-frequency electronic noise in superlattice and random-packed thin films of colloidal quantum dots
We report measurements of low-frequency electronic noise in ordered
superlattice, weakly-ordered and random-packed thin films of 6.5 nm PbSe
quantum dots prepared using several different ligand chemistries. For all
samples, the normalized noise spectral density of the dark current revealed a
Lorentzian component, reminiscent of the generation-recombination noise,
superimposed on the 1/f background (f is the frequency). An activation energy
of 0.3 eV was extracted from the temperature dependence of the noise spectra.
The noise level in the ordered films was lower than that in the weakly-ordered
and random-packed films. A large variation in the magnitude of the noise
spectral density was also observed in samples with different ligand treatments.
The obtained results are important for application of colloidal quantum dot
films in photodetectors.Comment: 24 pages, 6 figures and supplemental inf
Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in Tantalum Disulfide Thin-Film Devices
We report on switching among three charge-density-wave phases - commensurate,
nearly commensurate, incommensurate - and the high-temperature normal metallic
phase in thin-film 1T-TaS2 devices induced by application of an in-plane
electric field. The electric switching among all phases has been achieved over
a wide temperature range, from 77 K to 400 K. The low-frequency electronic
noise spectroscopy has been used as an effective tool for monitoring the
transitions, particularly the switching from the incommensurate
charge-density-wave phase to the normal metal phase. The noise spectral density
exhibits sharp increases at the phase transition points, which correspond to
the step-like changes in resistivity. Assignment of the phases is consistent
with low-field resistivity measurements over the temperature range from 77 K to
600 K. Analysis of the experimental data and calculations of heat dissipation
suggest that Joule heating plays a dominant role in the electric-field induced
transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The
possibility of electrical switching among four different phases of 1T-TaS2 is a
promising step toward nanoscale device applications. The results also
demonstrate the potential of noise spectroscopy for investigating and
identifying phase transitions in materials.Comment: 32 pages, 7 figure
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