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Due to the increasing importance of low-concentrated pollution of water resources, the photocatalytic decomposition of ibuprofen down to low ppm concentrations over zinc oxide catalyst has been studied. The aim of this work was to evaluate the degradation of the non-steroidal anti-inflammatory drug (NSAID) ibuprofen (IBP) using heterogeneous ZnO photocatalyst under UV-C irradiation. The photo catalyst was characterized by field emission scanning electron microscope (FE-SEM) and x-ray diffraction (XRD). The photocatalytic activity of ZnO nanoparticle was evaluated in a cylindrical glass reactor under VU-C irradiation light. Central composite design (CCD) and response surface methodology (RSM) were employed for modeling and optimizing the IBP degradation under different variables such as initial pH, ZnO loading, humic acid concentration, initial IBP concentration, and reaction time. The results of our experiments showed that the reaction time had its highest positive effect on IBP degradation. The correlation coefficient (R²) value of 0.856 indicated a good agreement between the experimental results and the model predictions. Optimization results showed that the maximum IBP degradation was attained at optimum conditions of pH 6.7, catalyst loading 583 mg/L, initial IBP concentration 1.5 mg/L, humic acid concentration 54 mg/L, and reaction time of 95 min. Under these conditions we achieved maximum IBP removal efficiency of 82.97%. In conclusion, ZnO was found to be an effective photo catalyst and a promising alternative for producing free OH radicals for degradation of ibuprofen as an emerging pollutant in water resources.
This study investigates the potential toxicity of TiO2 and ZnO nano-particles (nano-TiO2 and nano-ZnO) against Daphnia magna (D. magna) neonates before and after absorbing phenol. Although limited scientific investigation is conducted on possible hazards of nano-particles (NPs), no research has been carried out either on the toxicity of nano-ZnO and TiO2 in combination with other materials or on their ability to release the hazardous substances adsorbed on their surface in cells. Daphnia magna neonates exposed to different concentrations of phenol-free and phenol-loaded NPs and resulting mortality rates were recorded after 12 to 96 h. The results of mortality rates were applied to SPSS ver. 16.0 in order to calculate median lethal concentrations (LC50) of NPs. The results of experiments showed that phenol-free TiO2 was “practically nontoxic” according to EPA overview (48 h LC50: 2705 mg·L-1). But after exposure to phenol, its 48 h LC50 reached 414 mg·L-1, which means a 6-time increment in toxicity. 48 h LC50 of phenol-loaded and phenol-free nano-ZnO was 2.14 and 2.18 mg·L-1, respectively. This study showed, in contrast to nano-TiO2, that no significant difference is found between the toxicity of nano-ZnO before and after exposure to phenol. Researchers considered the amount of toxin absorbability of NPs to be one of the most important factors influencing the change in NP toxicity.
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