Photocatalytic conversion of nitrite to dinitrogen on Pd/TiO2 coupled with the photooxidation of aquatic pollutants

Abstract

Nitrite (NO2−) is photocatalytically reduced to dinitrogen (N2) in an aqueous suspension of titanium(IV) oxide particles loaded with palladium under irradiation of UV light in the presence of arsenite (As III) as a OH radical scavenger. When Pd/TiO2 was used alone for NO2− reduction in the absence of arsenite, photocatalytic re-oxidation of NO2− occured and NO2− was almost completely converted to NO3−. Arsenite exhibits an OH radical scavenging effect and suppresses the NO3- production preventing the coupling with NO2- and OH radicals. Pd loaded TiO2 exhibited the highest N2 yield among different metals. This result suggests that Pd loaded TiO2 particles acted as storage sites for photogenerated electrons and effectively transferred the electrons to NO2−. Furthermore, photocatalytic reaction in Pd/TiO2, hydrogen is used as reducing agent produced according to the photocatalytic reduction of NO2− to N2. Effect of the amount of Pd, different water pollutants and pH of the suspension on the reaction rate were also examined.