Comparative study of the photodegradation of Triclosan, an emerging contaminant, by Photo-Fenton in homogeneous and micro-heterogeneous medium

AGUSTINA REYNOSO; WALTER MASSAD; JOSÉ NATERA; MATÍAS SANCHO; NORMAN A. GARCÍA

Carlos Paz

Conferencia; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (ELAFOT); 2017

UNSE / UNC /UNLP

Emerging contaminants (EC) are define as unknown or unrecognized contaminants whose presence in the environment is not necessarily new but the possible consequences that they can have in the ecosystem are being widely studied and detected. They´ve been found to have the potential to produce an ecological impact as well as adverse health effects [1]. In the present work, 5-chloro-2- (2,4-dichlorophenoxy) phenol, commonly known as Triclosan (TCS), was chosen as EC. TCS is a broad-spectrum fungicide and antimicrobial. It reaches the environment usually through wastewater and has a negative impact on aquatic ecosystems due to its persistence in natural waters causing potential long-term risks to human health [2].The Fenton and Photo-Fenton (PF) processes are characterized by generating the hydroxyl radical species HO●, which is a highly reactive ROS and often causes the mineralization of organic compounds. Traditionally, these systems are studied in aqueous media due to the high reactivity of HO● with organic solvents, therefore its study and application has been centered on water-soluble compounds.Given the low solubility of TCS in aqueous media, it was decided to work with a cyclic oligosaccharide, β-Cyclodextrin (β-CD). β-CD can receive another molecule (host) as long as it has the correct size and shape [3]. The low toxicity and cost, in addition to the intrinsic properties of CDs, leads to their use for increasing solubility, stability and bioavailability of different substances [4]. In the particular case of TCS, the association constant of the TDS-β-CD complex was determined by UV-Vis spectrophotometry using the Scott equation [5], obtaining a value of 6754 M-1. This system was computationally simulated using Gaussian 09 software.In order to evaluate the photodegradation of the EC, a study of the Photo-Fenton reaction was carried out in homogeneous (without β-CD) and micro-heterogeneous media (with β-CD). To perform the photolysis experiments a Rayonet reactor equipped with eight 8 W lamps (365 nm) was used and the degradation of the TCS was monitored by HPLC-UV. It was found that the degradation ratio of TCS in homogeneous medium (TCS solution in H2O with 10% of ACN), after 4hr of irradiation reach a 93% conversion whereas for the same conditions of irradiation in micro-heterogeneous medium (TCS solution in H2O and β-CD) is only 48%. This can be attributed to the formation of the TCS-β-CD complex, which decreases the availability of TCS for its photodegradation [6], preventing its reaction with HO● radical.These results do not provide a definitive conclusion regarding the choice of the best system. Either a certain percentage of organic solvent is used to obtain a virtually complete degradation of TCS or a more environmentally friendly system is used at the expense of a lower efficiency in the photodegradation process.[1] D. Barceló, et. al., Jorn. Present. Result 2008.[2] M. Ricarta, et. al., Aquatic Toxicology 2010, 100, 346-353.[3] S. Khaoulani, et. al., Comptes Rendus Chimie 2015, 18, 23-31.[4] N. Morin-Crini, Crini, G., Progress in Polymer Science 2013, 38, 344-368.[5] M. I. Sancho, et. al., Carbohydrate Research 2011, 346, 1978?1984.[6] T. Loftsonn, et. al., Journal of Pharmaceutical Sciences 1999, 88, 1254-1258.