Enhanced nitrate reduction by metal deposited g-C3N4/rGO/TiO2 Z-schematic photocatalysts: Performance and mechanism comparison of Pd-Cu and Ag.

Deposition of bimetals on Z-scheme photocatalysts has been reported to improve the nitrate nitrogen (NO 3 −) reduction properties. However, it is not clear whether bimetal deposition possesses advantage over single metal deposition and what is the different reaction mechanisms. In this work, the g-C 3 N 4 (Pd-Cu)/rGO/TiO 2 and g-C 3 N 4 (Ag)/rGO/TiO 2 composites with bimetallic Pd-Cu and single metal Ag deposited on the graphitic carbon nitride/reduced graphene oxide/titanium dioxide (g-C 3 N 4 /rGO/TiO 2) Z-scheme photocatalyst were prepared, and their photocatalytic NO 3 − reduction properties and the mechanisms under visible light irradiation were studied. The results showed that the NO 3 − and total nitrogen (TN) removal efficiencies of g-C 3 N 4 (Pd-Cu)/rGO/TiO 2 were 57.78% and 20.1%, respectively, 1.15 and 1.72 times higher than those of g-C 3 N 4 (Ag)/rGO/TiO 2. This can be ascribed to that Pd-Cu enriched more electrons and absorbed more NO 3 − molecules due to the different charge densities, and the NO 3 − reduction process were enhanced by the staged NO 3 −→NO 2 − and NO 2 −→N 2 /NH 4 + processes on Cu and Pd. The effects of reductive species were demonstrated to be photogenerated electrons > ·OH (·CO 2 −) > ·O 2 − in g-C 3 N 4 (Ag)/rGO/TiO 2 , while it was photogenerated electrons > ·O 2 − > ·OH (·CO 2 −) in g-C 3 N 4 (Pd-Cu)/rGO/TiO 2 , which may be caused by the better O 2 reduction property of the latter. Finally, the cyclic experiment proved the good stability of both materials. This work provided some reference for design of metal deposited Z-scheme photocatalysts for various reduction reactions. [Display omitted] • The g-C 3 N 4 (Cu-Pd)/rGO/TiO 2 and g-C 3 N 4 (Ag)/rGO/TiO 2 composites were prepared. • The NO 3 − reduction performances and mechanisms were studied and compared. • The reductive species in g-C 3 N 4 (Ag)/rGO/TiO 2 were e– > ·OH (·CO 2 −) > ·O 2 −. • The reductive species in g-C 3 N 4 (Cu-Pd)/rGO/TiO 2 were e– > ·O 2 − > ·OH (·CO 2 −). [ABSTRACT FROM AUTHOR]