Photodegradation of tetrahalobisphenol-A (X = Cl, Br) flame retardants and delineation of factors affecting the process

The photoassisted degradation (HPLC-UV absorption), dehalogenation (HPLC-IC) and mineralization (TOC decay) of the flame retardants tetrabromobisphenol-A (TBBPA) and tetrachlorobisphenol-A (TCBPA) were examined in UV-irradiated alkaline aqueous TiO2 dispersions (pH 12), and for comparison the parent bisphenol-A (BPA, an endocrine disruptor) in pH 4-12 aqueous media to assess which factor impact most on the photodegradative process. Complete degradation (2.7-2.8 x 10(-2) min(-1)) and dehalogenation (1.8 x 10(-2) min(-1)) of TBBPA and TCBPA occurred within 2 h of UV irradiation, whereas only 45-60% mineralization (2.3-2.7 x 10(-3) min(-1)) was complete within 5 h for the flame retardants at pH 12 and ca. 80% for the parent BPA. Factors examined in the pH range 4-12 that impact the degradation of BPA were the point of zero charge of TiO2 particles (pH(pzc): electrophoretic method), particle or aggregate sizes of TiO2 (light scattering), and the relative number of(center dot)H radicals(as DMPO-(OH)-O-center dot adducts: ESR spectroscopy) produced in the UV-irradiated dispersion. Dynamics of BPA degradation (2.0-2.4 x 10(-2) min(-1)) were pH-independent and independent of particle/aggregate size, but did correlate with the number of(center dot)OH radicals, at least at pHs 4 to 8-9, after which the rates decreased somewhat at pH > 9 with decreasing adsorption owing to Coulombic repulsive forces between the very negative TiO2 surface and the anionic forms of BPA (pK(a)s ca. 9.6-11.3), even though the number of(center dot)OH radicals continued to increase at the higher pHs. (C) 2008 Elsevier B.V. All rights reserved.