Defective Black TiO2: Effects of Annealing Atmospheres and Urea Addition on the Properties and Photocatalytic Activities

Abstract

A series of black TiO2 with and without the addition of urea were successfully prepared using a simple one-step synthetic method by calcination under different atmospheres (vacuum, He, or N2). The physicochemical, optical, and light-induced charge transfer properties of the as-prepared samples were characterized by various techniques. It was found that a vacuum atmosphere was more beneficial for the formation of oxygen vacancies (OVs) than the inert gases (He and N2) and the addition of urea-inhibited OVs formation. The samples annealed in the vacuum condition exhibited better visible-light adsorption abilities, narrower bandgaps, higher photo-induced charge separation efficiency, and lower recombination rates. Hydroxyl radicals (·OH) were the dominant oxidative species in the samples annealed under a vacuum. Finally, the samples annealed under vacuum conditions displayed higher photocatalytic activity for methylene blue (MB) degradation than the samples annealed under He or N2. Based on the above, this study provides new insights into the effects of annealing atmospheres and urea addition on the properties of black TiO2.

Photocatalytic Reduction of Nitrates and Combined Photodegradation with Ammonium

“…The oxygen defectivity forming upon partial reduction of titania (black or grey titania) can also alter the ratio between the two main phases depending on the way reduction is achieved. A possible increase in the anatase/rutile ratio even after annealing at high temperature has been reported [23]. DR-UV-Vis analysis was performed in order to calculate the band gap (BG) of the active materials.…”

Advanced Photocatalytic Nanomaterials for Energy Conversion and Environmental Remediation

“…These eleven papers were devoted to achieving high-efficiency photocatalysts by broadening the light absorption range, inhibiting the photo-induced electrons and holes recombination, and promoting the extraction of photo-induced charges for chemical reactions. The strategies include defect engineering [1], element doping [2,3], morphology manipulation [3,4], and binary and ternary composite fabrication [5][6][7][8][9][10][11]. Herein, we will provide a brief introduction to these works.…”

“…Defect engineering and element doping can modulate the band structure of a semiconductor and have, thus, been widely used to broaden the light absorption range and improve the utilization of photo-generated charges of photocatalytic materials. A series of black TiO 2 was prepared by Zhou et al [1] by altering the calcination atmospheres of the samples. Their results show that a vacuum atmosphere favors the formation of oxygen vacancies in TiO 2 , which leads to better visible-light adsorption, a narrower bandgap, and higher photo-induced charge separation, thus achieving a higher photocatalytic degradation capacity for methylene blue (MB) in comparison with inert atmospheres (He and N 2 ).…”