Photocatalytic mineralization of codeine by UV-A/TiO₂--Kinetics, intermediates, and pathways.
This study investigated the photocatalytic degradation of codeine by UV-irradiated TiO2. The degradation kinetics was determined under varied conditions including the TiO2 loading, codeine concentration, and pH. Codeine and several reaction intermediates including morphine were identified and tracked during degradation using HPLC/MS-MS technique, along with TOC and IC measurements. Specifically, removal of 100 μg/L of spike codeine was complete in 3 min by contact with a 0.1 g/L suspension of TiO2 under UV irradiation at pH 7. The degradation kinetics of codeine was first-order with respect to both the catalyst TiO2 and the reactant codeine, with enhanced reaction rates with increasing pH up to pH 9. Mineralization of codeine was possible upon prolonged contact; near complete mineralization of 10 mg/L of codeine was achieved in 90 min with 0.1 g/L TiO2 under irradiation at pH 5, during which the organic nitrogen was converted to NH3-N (74%) and NO3-N (22%). Based on the identified intermediates, two degradation pathways were proposed of which one involved ipso-substitution followed by cleavage of the aromatic ring and another involved repeated hydroxylation of the codeine molecule followed by its fragmentation.
Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 106, Taiwan, ROC.
Chin-Sheng
CS
Kuo
Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 106, Taiwan, ROC. Electronic address: cflin@ntu.edu.tw.
Cheng-Fang
CF
Lin
Department of Civil and Environmental Engineering, University of Utah, Salt Lake City, UT 84112, USA.
Pui-Kwan Andy
PK
Hong
D002384:Catalysis; D003061:Codeine / Q000737:chemistry*; D007700:Kinetics; D009022:Morphine Derivatives / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry; D014025:Titanium / Q000737:chemistry* / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
D009022:Morphine Derivatives; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; D014025:Titanium; D009584:Nitrogen; D003061:Codeine
Degradation mechanism; Illicit drugs; Intermediates; Kinetics; Photocatalysis