title: Photocatalytic reduction of Cr(VI) in the presence of NO3- and Cl- electrolytes as influenced by Fe(III).
abstract: Photoreduction of Cr(VI) involving Fe is strongly affected by the presence of organic or inorganic compounds in an acidic environment. In this study, we have found a new pathway of Cr(VI) photoreduction in the presence of Fe-(III) that is influenced by two inorganic electrolytes (i.e., NO3- and Cl-) and the pH. In NO3- and Cl- systems without Fe(III), Cr(VI) photoreduction could occur and was independent of the Cr(VI) concentration. The zero-order rate constant of the photoreduction reaction increased when the solution pH was decreased from 2 to 1; the reaction rate was higher in the NO3- system than in the Cl- system. The higher reaction rate in the NO3- system was attributed to the photolysis of NO3-, which resulted in the formation of NO2- for reduction of Cr(VI). Conversely, the effect of Fe-(III) addition on the increase in Cr(VI) photoreduction rate in the Cl- system was more significant than that in the NO3- system. The addition of Fe(III) to the Cl- system caused the formation of [Fe(OH2)5Cl]2+, the photolysis of which subsequently resulted in the formation of Fe(II) for reduction of the Cr(VI). This study suggests that the photolysis of NO3- and Fe-Cl complex may contribute significantly to Cr(VI) reduction in surface water that receives electroplating wastewater containing high levels of NO3-, Cl-, and Fe-(III). Therefore, under the acidic conditions that are favorable for Fe-Cl complex formation or in the presence of NO3-, the effects of inorganic components on Cr(VI) photoreduction cannot be ignored for the precise evaluation of the transformation of Cr in the environment.
authors: Department of Soil & Environmental Sciences, National Chung Hsing University, Taichung, Taiwan 40227.
authors: Chia-Lian
authors: CL
authors: Hsu
authors: Shan-Li
authors: SL
authors: Wang
authors: Yu-Min
authors: YM
authors: Tzou
mesh_terms: D002384:Catalysis; D015392:Chemistry, Inorganic / Q000379:methods; D002712:Chlorides / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry*; D009930:Organic Chemicals; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry / Q000379:methods*; D010782:Photolysis; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D002712:Chlorides; D004573:Electrolytes; D009566:Nitrates; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D014867:Water; D002857:Chromium; D007501:Iron; D010100:Oxygen