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Background and purpose:As the usage of chromium in chemical industries, electroplating, leather tanning and paint processes will increase, so the chromium pollution in water has become a considerable problem. Hexavalent chromium (Cr (VI)) has been reported toxic to aquatic organisms, animals and humans. It has been known to be carcinogenic. Thus, it should be removed from wastewater before discharge to the environment directly. Photocatalyst process is one of advanced technologies in removal of organic and inorganic pollutants from water and wastewater.The aim of this study was the use of photocatalytic removal of (Cr (VI) using ZnO nanoparticles as catalyst in a batch reactor Material and Methods:In this experimental study, at first commerical ZnO nanoparticle was prepared. A point of zero charge, pHpzc, of nanoparticle was obtained using batch equilibration method. In this study, different experimental conditions such as initial Cr (VI) ion concentration (10 to 50 mg•L-1), pH (3 to 9) and nanoparticle loading (0.1 to 1gr) at various contact time (0 to 120min) and one UV irradiation intencityhave been evaluated. In addition, kinetic models involve in the photocatalic removal of Cr (VI) were investigated. Chromium (VI) concentration was determined colorimetrically at 540nm using the 1,5-diphenylcarbazide (DPC) method with detection limit of 5mgL-1 using the UV–vis spectrophotometer (Shimadzu, Japan). Results: The pHZPC for ZnO was 7.51. The obtained results showed that the removal efficiency of Cr (VI) increased with an increasing ZnO nanoparticles loading. The Cr (VI) removal percentage decreased as the initial Cr (VI) concentration increased. The maximum removal of Cr (VI) was obtained at acidic pH (86.65% for pH=3 vs. 42.55% for pH=9). Kinetic analysis of the photoreduction showed the removal of Cr (VI) is according to the Langmuir–Hinshelwood (L–H) model (R2=0.995) and the adsorption of Cr (VI) on the ZnO nanoparticle surfaces may be the controlling step in the entire reduction process. Conclusion: This study results showed UV/ZnO was an effective method in the removal of hexavalent chromium from aqueous solutionsand maybe UV/ZnO process applied in Cr (VI) removal in low concentration and acidic pH, effectively.

Keywords: Photocatalic Reduction, UV irradiation, ZnO nanoparticle, Hexavalent Chromium, Aqueous Solution

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