title: Photocatalytic treatment of 4-chlorophenol in aqueous ZnO suspensions: intermediates, influence of dosage and inorganic anions.
abstract: The photocatalytically driven removal of eco-persistent 4-chlorophenol from water using ZnO is reported here. Kinetic dependence of transformation rate on operating variables such as initial 4-chlorophenol concentration and photocatalyst doses was investigated. A complete degradation of 4-chlorophenol at 50 mg L(-1) levels was realised in 3h. Analytical profiles on 4-chlorophenol transformation were consistent with the best-line fit of the pseudo zero-order kinetics. The addition of small amounts of inorganic anions as SO(4)(2-), HPO(4)(-), S(2)O(8)(2-) and Cl(-) revealed two anion types: active site blockers and rate enhancers. Fortunately, Cl(-) and SO(4)(2-) commonly encountered in contaminated waters enhanced the rate of 4-chlorophenol degradation. The reaction intermediates and route to 4-chlorophenol mineralisation were elucidated by combined RP-HPLC and GC-MS methods. In addition to previously reported pathway products of 4-chlorophenol photo-oxidation catechol was detected. A radical mechanism involving o-hydroxylation is proposed to account for the formation of catechol.
authors.affiliation: Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, UPM Serdang, Selangor DE, Malaysia.
authors.forename: Umar Ibrahim
authors.initials: UI
authors.lastname: Gaya
authors.forename: Abdul Halim
authors.initials: AH
authors.lastname: Abdullah
authors.forename: Zulkarnain
authors.initials: Z
authors.lastname: Zainal
authors.forename: Mohd Zobir
authors.initials: MZ
authors.lastname: Hussein
mesh_terms: D000838:Anions; D002396:Catechols; D002733:Chlorophenols / Q000737:chemistry / Q000528:radiation effects*; D007700:Kinetics; D010782:Photolysis; D013535:Suspensions; D014873:Water Pollutants / Q000528:radiation effects*; D018508:Water Purification / Q000379:methods; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D000838:Anions; D002396:Catechols; D002733:Chlorophenols; D013535:Suspensions; D014873:Water Pollutants; C029107:4-chlorophenol; C034221:catechol; D015034:Zinc Oxide