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.

Paracetamol in the environment and its degradation by microorganisms

“…To our knowledge, this is the first description of the biodegradation pathway for paracetamol. The initial steps are partially different from the reactions previously described for photocatalytic and electro-Fenton degradation of paracetamol (Brillas et al 2009;Yang et al 2009) (Fig. 5c), in which hydroquinone has been identified as the main transformation products.…”

“…Nowadays, paracetamol wastewater is mainly treated by chemical oxidation processes such as electrochemical (Brillas et al 2005), ozonation (Andreozzi et al 2003), H 2 O 2 /UV oxidation (Andreozzi et al 2003;Skoumal et al 2006), TiO 2 photocatalysis (Yang et al 2008(Yang et al , 2009, and solar photoelectro-Fenton oxidation (Li et al 2007). Although these chemical methods may be available for treating these pollutants, the harsh reaction conditions, the generation of secondary pollutants, and the high operational cost associated with these methods have often made them not a desirable choice (Li et al 2007;Chen et al 2010).…”

Degradation of paracetamol by pure bacterial cultures and their microbial consortium

“…To our knowledge, this is the first description of the biodegradation pathway for paracetamol. The initial steps are partially different from the reactions previously described for photocatalytic and electro-Fenton degradation of paracetamol (Brillas et al 2009;Yang et al 2009), in which hydroquinone has been identified as the main transformation products. Gusseme et al (2011) also reported that hydroquinone was a temporary transformation product of paracetamol degradation by two bacterial strains, D. tsuruhatensis and P. aeruginosa.…”

“…Peak B had the same (n03) retention time and mass spectrum as an authentic sample of derivatized 4-aminophenol. 4-Aminophenol was also indentified as a main intermediate during photocatalytic degradation of paracetamol (Yang et al 2009). …”

“…It may enter the environment mainly from manufacturing wastes (Philips et al 2010;Skoumal et al 2006). Currently, paracetamol wastewater is mainly treated by chemical oxidation processes such as electrochemical (Brillas et al 2005), ozonation (Andreozzi et al 2003), H 2 O 2 /UV oxidation (Andreozzi et al 2003;Skoumal et al 2006), TiO 2 photocatalysis (Yang et al 2008(Yang et al , 2009, and solar photoelectro-Fenton oxidation (Li et al 2007). Although these chemical methods may be available for treating these pollutants, the harsh reaction conditions, the generation of secondary pollutants, and the high operational cost associated with these methods have often made them not a desirable choice (Chen et al 2010;Li et al 2007).…”