Dominating role of crystal structure over defect chemistry in black and white zirconia on visible light photocatalytic activity

TLDR

The study investigates how crystal structure and oxygen vacancies affect the photocatalytic performance of black versus white zirconia. Nanometric white zirconia was produced by pyrolyzing zirconium butoxide at 900–1400 °C in air, yielding predominantly monoclinic particles, while black zirconia was obtained by reducing the atmosphere at 900 °C to introduce oxygen vacancies. White zirconia achieved high methylene‑blue degradation due to its porous structure and low electron‑hole recombination, whereas black zirconia, despite oxygen vacancies, exhibited limited activity because the tetragonal phase and insufficient band‑edge states hindered photocatalysis.

Abstract

Abstract Nanometric powder particles of white zirconia were synthesized through precursor route by the pyrolysis of zirconium (IV) butoxide at varied temperatures in air ranging from 900–1400 °C and were predominantly monoclinic in nature. To control the defect chemistry, the precursor was also pyrolyzed in a reduced atmosphere at 900 °C, eventually resulting in black zirconia. The stabilization of tetragonal phase and observed color change from white to black in samples pyrolyzed under reduced atmosphere was attributed to the creation of oxygen vacancies and disorder. The black and white zirconia produced delineated the influence of crystal structure and oxygen vacancies on the photocatalytic performance. Furthermore, zirconia synthesized at lower temperatures (600 and 800 °C) in air confirmed the detrimental role of tetragonal phase on the degradation behavior of methylene blue dye. High photocatalytic degradation rate for white zirconia was attributed to the presence of increased density of nano-sized pores and low recombination rate of electron-hole pairs as confirmed by PL measurements. Interestingly, black zirconia exemplified relatively limited activity albeit presence of oxygen vacancies. This negative effect was attributed to the presence of tetragonal phase and possibly, the insufficient creation of new energy states near valence and conduction band towards Fermi energy level.