title: Enhanced photocatalytic activity of chromium(VI) reduction and EDTA oxidization by photoelectrocatalysis combining cationic exchange membrane processes.
abstract: A novel technology of photoelectrocatalysis (PEC) combining with cationic exchange membrane (CEM) was proposed for simultaneous reduction of chromium(VI) and oxidization of EDTA. The application of CEM was used to enhance the efficiency for prevention of the re-oxidation of reduced chromium with the electron-hole pairs. In this study, effects of current density, pH, TiO2 dosage, hydraulic retention time (HRT), light intensity and EDTA/Cr(VI) molar ratio were all investigated. The results showed that the optimum conversion efficiency occurred at 4mA/cm(2) with the presence of CEM. Higher conversion efficiencies were observed at lower pH due to the electrostatic attractions between positive charged TiOH2(+), and negatively charged Cr(VI) and EDTA. The optimum TiO2 loading of 1g/L was depended mainly on the acidic pH range, especially at higher HRT and irradiation intensity. In addition, higher EDTA/Cr(VI) molar ratio enhanced the reduction efficiency of Cr(VI), indicating EDTA plays the role of hole scavenger in this system. Moreover, incomplete EDTA decomposition contributes to the occurrence of intermediates, including nitrilotriacetic acid, iminodiacetic acid, glycine, oxamic acid, lyoxylic acid, oxalic acid, acetic acid and formic acid, as identified by GC/MS. Consequently, transformation pathway was determined from these analyzed byproducts and molecular orbital package analysis.
authors: Institute of Environmental Engineering and Management, National Taipei University of Technology, No. 1, Sec. 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan. der11065@hotmail.com
authors: Hung-Te
authors: HT
authors: Hsu
authors: Shiao-Shing
authors: SS
authors: Chen
authors: Yi-Fang
authors: YF
authors: Tang
authors: Hsing-Cheng
authors: HC
authors: Hsi
mesh_terms: D002384:Catalysis; D002614:Chelating Agents / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D008027:Light; D008567:Membranes, Artificial; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D014025:Titanium / Q000737:chemistry / Q000528:radiation effects; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D008567:Membranes, Artificial; D014874:Water Pollutants, Chemical; D002857:Chromium; C009495:titanium dioxide; C074702:chromium hexavalent ion; D004492:Edetic Acid; D014025:Titanium