Kinetic and mechanistic study of photocatalytic degradation of flame retardant Tris (1-chloro-2-propyl) phosphate (TCPP)

Abstract

In the present work, a comprehensive study on the application of TiO2 photocatalysis for the removal of the flame retardant tris (1-chloro-2-propyl) phosphate (TCPP) from both ultrapure water (UW) and real wastewater (WW) is presented. All the photocatalytic experiments were conducted using environmental relevant concentrations of TCPP, inherent pH and simulated solar irradiation with the view to simulate real environmental conditions. Degradation followed apparent first-order kinetics with rate constants varying from kapp=14.2×10−2min−1 to kapp=1.41×10−2min−1 for initial TCPP concentrations in the range of 25–500μgL−1 while mineralization was accomplished in prolonged irradiation times as monitored by the release of chlorine and phosphate ions. Scavenging studies were carried out in UW, indicating that photogenerated HO in the catalyst surface are the main species participating in the photocatalytic mechanism. Experiments using secondary treated wastewater showed a significant retardation of TCPP photocatalytic degradation mainly due scavenging effects and competitive adsorption of aromatic and phenolic compounds and inorganic ions, such as HCO3−, contained in the wastewater matrix. The transformation products were elucidated by UPLC-TOF-MS instrumentation and hydroxylation, oxidation, dechlorination and dealkylation have been identified as the principal photocatalytic transformation routes before complete mineralization. Toxicity assays in UW and WW were also conducted using Vibrio fischeri as tested organism showing a progressive toxicity decrease along the treatment till low values. Measurements showed a higher initial toxicity and a slower decrease in WW that is attributed to the more complex matrix regarding chemical pollutants and their transformation products formed during the treatment as well as scavenging effects.