The effect of Zr loading in Zr/TiO2 prepared by pressurized hot water on its surface, morphological and photocatalytic properties

Zr/TiO2 anatase photocatalysts with 0.5, 1, 2, 5 and 7.5 mol.% Zr were prepared using pressurized hot water crystallization and their photocatalytic activity was explored in acid orange 7 photodegradation. Parent TiO2 was also prepared and tested. From all tested photocatalysts, 2 mol.% Zr/TiO2 showed the highest photoactivity, and 7.5 mol.% Zr/TiO2 showed the lowest photoactivity. The poor photoactivity of 7.5 mol.% Zr/TiO2 can be explained by the amorphous ZrO2 present in the surface layer (~1–3 μm depth) of TiO2 anatase nanocrystallite agregates which changed the aggregate morphology and shielded the anatase nanocrystallite surface. The type and amount of defects (e.g., oxygen vacancies, lattice defects) did not effect the photoactivity of Zr/TiO2 in AO7 photodegradation. The addition of Zr to TiO2 significantly affects the photocatalyst morphology and the location where amorphous ZrO2 forms. The optimal Zr loading in TiO2 was determined to be 2 mol.%.