title: Photocatalytic oxidation of paracetamol: dominant reactants, intermediates, and reaction mechanisms.
abstract: The role of primary active species (ecb(-), hvb(+), *OH, HO2*, O2*(-), and H2O2) during photocatalytic degradation of paracetamol (acetaminophen) using TiO2 catalyst was systematically investigated. Hydroxyl radicals (*OH) are responsible for the major degradation of paracetamol with a second-order rate constant (1.7 x 10(9) M(-1) s(-1)) for an *OH-paracetamol reaction. A total of 13 intermediates was identified and classified into four categories: (i) aromatic compounds, (ii) carboxylic acids, (iii) nitrogen-containing straight chain compounds, and (iv) inorganic species (ammonium and nitrate ions). Concentration profiles of identified intermediates indicate that paracetamol initially undergoes hydroxylation through *OH addition onto the aromatic ring at ortho (predominantly), meta, and para positions with respect to the -OH position of paracetamol. This initial *OH hydroxylation is followed by further oxidation generating carboxylic acids. Subsequent mineralization of smaller intermediates eventually increases ammonium and nitrate concentration in the system.
authors.affiliation: Division of Environmental Science and Engineering, National University of Singapore, Singapore. eseyl@nus.edu.sg
authors.forename: Liming
authors.initials: L
authors.lastname: Yang
authors.forename: Liya E
authors.initials: LE
authors.lastname: Yu
authors.forename: Madhumita B
authors.initials: MB
authors.lastname: Ray
mesh_terms: D000082:Acetaminophen / Q000032:analysis / Q000737:chemistry*; D002384:Catalysis; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D014025:Titanium / Q000737:chemistry
chemical_list: C009495:titanium dioxide; D000082:Acetaminophen; D014025:Titanium