Direct photoconversion of nitrite to dinitrogen on Pd/TiO2 coupled with photooxidation of aquatic pollutants

Nitrate (NO3−) and nitrite (NO2−) are ubiquitous aquatic pollutants and should be controlled for water quality. Although diverse methods of nitrate/nitrite reduction have been developed, most require chemical reductants and external energy inputs. Nitrite is oxidized by photogenerated hydroxyl radicals (•OH) in an aqueous suspension of Pd-loaded TiO2 (Pd/TiO2) with producing nitrate as a major product. The main photoconversion product of nitrite is changed from nitrate to N2 on Pd/TiO2 in the presence of aquatic pollutants (arsenite (As(III)) or 4-chlorophenol (4-CP)) which can suppress the photooxidation of NO2− by scavenging holes/•OH. The photogenerated H2 on Pd/TiO2 serves as a main reductant and was immediately consumed for reducing nitrite to N2. The presence of As(III) or 4-CP also enhanced the durability of Pd/TiO2 by efficiently scavenging hole/•OH that may oxidize Pd nanoparticles. The proposed process can be a viable treatment option for nitrite-contaminated water containing various aquatic pollutants.