Degradation of pyrene by UV radiation

The photodegradation of pyrene (Py) in the presence of acetic acid (AA) occ urs through a radical mechanism and is faster than in organic solvents (met hanol). PyH. (absorption maximum in the UV/VIS spectra lambda(max)=395 nm i n AA, lifetime tau=similar to 2 mu S in oxygen saturated solution) was iden tified as an intermediate in the photodegradation in AA. Absorption of a ph oton by ground state of Py also leads to the formation of excited states (P y-1* and Py-3), which deexcite to the ground state without chemical changes . Singlet oxygen O-1(2) formed by energy transfer from Py-3 to dissolved ox ygen does not react with Py. PyH-. and PyH+. were not found following excit ation under the given conditions. The rate of photodegradation can be consi derably increased by addition of water and hydrogen peroxide. The accelerat ing effect of hydrogen peroxide consists in photolytic formation of reactiv e hydroxyl radicals, which attack the pyrene nucleus. (C) 2000 Elsevier Sci ence S.A. All rights reserved.