Photocatalytic Oxidation Of Paracetamol: Dominant Reactants, Intermediates, And Reaction Mechanisms

摘要

The role of primary active species (e_(cb)~- , h_(vb)~+, ~·OH, HO_2~·, O_2~(·-) , and H_2O_2) during photocatalytic degradation of paracetamol (acetaminophen) using TiO_2 catalyst was systematically investigated. Hydroxyl radicals (~·OH) are responsible for the major degradation of paracetamol with a second-order rate constant (1.7 × 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.