Study On The Reaction Mechanism Of Benzene And Its Derivatives With Hydroxyl Radical In Aqueous Phase By Transient Absorbance Spectra Technique

It has been widely accepted that the reactive oxygen species (ROS) in the hydrosphere are ubiquitously involved in the oxidation process of organic pollutants and can therefore exert significant impact on the transfer, conversion, fate and ecological effect of these compounds. Nevertheless, we witnessed relatively few microscopic researches on the kinetics, mechanisms and detailed reaction pathways of these processes. To rectify this, the current studies introduce the laser flash photolysis (LFP) -transient absorption spectra technique into the research on the photochemical reactions inside the aqueous solutions of the benzene (chlorobenzene, nitrobenzene) and H₂O₂ (HNO₂, NO₂ ) and directly monitor these reactions on the ns ms timescale. Some complementary analytical methods as GC-MS and steady state UV-vis absorption spectroscopy are also applied to help elucidate the reaction mechanisms. The dissertation is mainly composed of two parts.Part 1 is on the 266 nm laser flash photolysis of the mixed aqueous solution of benzene or some of its derivatives chlorobenzene and nitrobenzene with H₂O₂ under oxygenated/deoxygenated conditions and under different pH environments. The observed transient absorption peaks were assigned and the related reaction rate constants were derived. It was found that the OH radical from the 266 nm photolysis of H₂O₂ is capable of forming adducts with benzene, chlorobenzene and nitrobenzene at rate constants of (6.3 8.0) × 10⁹ Lmol^-1.s^-1, (4.3 7.1) × 10⁹ L-mol^-1.s^-1 and (3.6 6.0) × 10⁹ L-mol^-1.s^-1, respectively. The above reaction rate constants were found to be dependent on the pH value of the solution and the specific structure of target organic molecules. Formation of the peroxy radicals was observed under oxygenated conditions at rate constants of 3.3 × 10⁸ Lmol^-1.s^-1, 6.8 ×10⁸ Lmol^-1.s^-1 and 6.6 × 10⁷ Lmol^-1.s^-1 for the above listed three benzene or benzene derivatives. These radicals may undergo unimolecular decomposition or further reactions with H₂O₂, possibly leading to the ring cleavage.Part 2 is on the 355 nm laser flash photolysis of the mixed aqueous solution of benzene or some of its derivatives chlorobenzene and nitrobenzene with HNO₂. Both...