Photocatalytic degradation of 2-chlorobiphenyl in titanium dioxide aqueous suspensions.

摘要

Degradation of polychlorinated biphenyls (PCBs) in irradiated aqueous TiO{dollar}sb2{dollar} suspensions was first systematically investigated using 2-chlorobiphenyl (2-CB) as the model congener. Biphenyl-2-ol and seven hydroxyl 2-CB isomers resulting from initial {dollar}cdot{dollar}OH radical attack were all identified using GC/FTIR/MS. Significant accumulation of these potentially toxic hydroxyl intermediates was observed, but they quickly disappeared with 2-chlorobenzaldehyde, methyl-(2-chlorophenyl) ketone, benzoic acid and 2-chlorobenzoic acid as the subsequent by-products. Hydrochloric, acetic and formic acids were also identified as the products using ion chromatography. The trace amount of carbon dioxide (CO{dollar}sb2{dollar}) evolved was quantified using GC/FTIR. 2-CB degradation pathways were proposed. After 300 min irradiation more than 90% of the starting 2-CB were mineralized to CO{dollar}sb2{dollar}.; Oxygen (O{dollar}sb2{dollar}) was critical for both initial removal and total mineralization of 2-CB. O{dollar}sb2{dollar} was first found to be needed for the degradation of biphenyl-2-ol and the hydroxyl 2-CBs, during which molecular O{dollar}sb2{dollar} and {dollar}cdot{dollar}OH radical are the key reagents in ring cleavage. The adsorption constant for O{dollar}sb2{dollar} on TiO{dollar}sb2{dollar}, in aqueous 2-CB solution/TiO{dollar}sb2{dollar} suspension was determined to be 0.88 (kPa){dollar}sp{lcub}-1{rcub}{dollar}.; The presence of {dollar}rm 10sp{lcub}-2{rcub} M of Hsb2Osb2, KIOsb4 or Ksb2Ssb2Osb8{dollar} greatly increased the degradation rate. The addition of {dollar}10sp{lcub}-2{rcub}{dollar} M {dollar}rm Hsb2Osb2{dollar} not only remarkably increased the initial removal of 2-CB and the degradation of all the aromatic intermediates but also resulted in 100% mineralization within 300 min irradiation.; 2-CB degradation demonstrated a pseudo-first-order kinetics with the reaction rate constant {dollar}(k)rm of 5.2times 10sp{lcub}-7{rcub} mol Lsp{lcub}-1{rcub} minsp{lcub}-1{rcub}{dollar}. The close match of the dark adsorption constant {dollar}(K){dollar} for 2-CB on TiO{dollar}sb2{dollar} determined from reaction kinetics study ({dollar}4.62 times 10sp5{dollar} L/mol) and that from dark adsorption experiments ({dollar}3.28 times 10sp5{dollar} L/mol) implicates that the degradation reaction takes place on TiO{dollar}sb2{dollar} surfaces.; From pH 3 to 11, a lower pH is more favorable for the degradation. Humic acids ({dollar}>{dollar}0.5 ppm) significantly inhibit the degradation. {dollar}rm HCOsb3sp-/COsb3sp{lcub}2-{rcub}{dollar} (mM/mM) of 0.3/0.64 and 0.75/1.6 showed no significant rate effect in alkaline solutions. Under neutral or acidic conditions Cl{dollar}sp-{dollar}(150 mM) inhibited the degradation. The optimum TiO{dollar}sb2{dollar} concentration for photocatalytic degradation of 2-CB was 500 mg/L.