title: Photocatalytic reduction of nitrite to dinitrogen in aqueous suspensions of metal-loaded titanium(IV) oxide in the presence of a hole scavenger: an ensemble effect of silver and palladium co-catalysts.
abstract: Nitrite (NO(2)(-)) was photocatalytically reduced to dinitrogen (N(2)) in an aqueous suspension of two kinds of titanium(iv) oxide particles loaded with palladium and silver (Pd-TiO(2) and Ag-TiO(2)) at pH 8 under irradiation of UV light in the presence of sodium oxalate as a hole scavenger. The two metal-loaded TiO(2) photocatalysts had different roles in conversion of NO(2)(-) to N(2) and worked in an effective ensemble without conflict: (1) Pd-TiO(2) induced photocatalytic disproportionation of NO(2)(-) to N(2) and nitrate (NO(3)(-)) and (2) Ag-TiO(2) selectively reduced the thus-formed NO(3)(-) back to NO(2)(-) (partially to N(2)) with oxalate acting as a hole scavenger. When Pd-TiO(2) was used alone for NO(3)(-) reduction in the presence of sodium oxalate, Pd-TiO(2) induced fruitless photocatalytic decomposition of oxalate to carbon dioxide and dihydrogen. The presence of Ag-TiO(2) suppressed the fruitless decomposition of oxalate by Pd-TiO(2) because Ag-TiO(2) continuously provided NO(2)(-) in the reaction system using oxalate as a hole scavenger and Pd-TiO(2) therefore only worked as a photocatalyst for disproportionation of NO(2)(-) to N(2) and NO(3)(-) as it did when used alone.
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, Kowakae, Higashiosaka, Osaka 577-8502, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Gekko
authors.forename: Keiji
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kominami
mesh_terms: D002384:Catalysis; D016166:Free Radical Scavengers / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009573:Nitrites / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010070:Oxalates / Q000737:chemistry; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D055668:Photochemical Processes; D012834:Silver / Q000737:chemistry*; D013535:Suspensions; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D016166:Free Radical Scavengers; D009573:Nitrites; D010070:Oxalates; D013535:Suspensions; D014867:Water; C009495:titanium dioxide; D012834:Silver; D010165:Palladium; D014025:Titanium; D009584:Nitrogen