Structural and photocatalytic properties of co-doped hybrid ZrO2–TiO2 photocatalysts

Abstract

In this study, pure TiO 2 , ZrO 2 , and hybrid ZrO 2 -TiO 2 photocatalysts were synthesized through solgel process and calcined at three different temperatures. The synthesized photocatalysts were characterized using powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FESEM), Brunauer-Emmet-Teller (BET), ultraviolet-visible (UV-Vis) spectrometer, and photoluminescence (PL) spectrometer. The PXRD patterns show that the rutile phase of TiO 2 was suppressed through co-doping with ZrO 2 and produced small crystallite size. The hybrid photocatalysts with small crystallite size recorded the highest surface area of 114.7 m 2 /g compared to pure TiO 2 and ZrO 2 photocatalysts as confirmed by BET analysis. Irregular size and shape was observed in the hybrid photocatalysts compared to spherical shape and size in TiO 2 and flaky shape in ZrO 2 as shown by the FESEM images. The optical properties of the photocatalysts investigated using UV-Vis spectroscopy showed a decrease in band gap energy of pure TiO 2 through linear extrapolation from the Tauc's plot despite the slightly higher band gap energy of the hybrid photocatalysts. However, PL analysis showed that doping of ZrO 2 into TiO 2 increased the separation efficiency of the electron-hole pairs and enhanced the photocatalytic activity. The phenol degradation of the hybrid ZrO 2 -TiO 2 photocatalysts was higher compared to those of the pure TiO 2 and ZrO 2 . Keywords Solgel • Hybrid TiO 2 -ZrO 2 photocatalysts • Phenol degradation

Photocatalytic Degradation of Rhodamine B and Methylene Orange Using TiO2-ZrO2 as Nanocomposite

“…The band gap values were acquired from the (F(R)•hv)n vs. hv plot, also known as Tauc's plot. The values of n = 1/2 apply for an indirect allowed transition [10]. Figure 5a shows the UV-Vis spectra for the TiO 2 , TZ and P25 samples.…”

“…The photoactivity of TiO 2 is strongly delimited by factors such as the interaction between the active surface and the chemical nature of the pollutants, efficiency to prevent the charge transfer recombination and the type of reactive oxygen species created by the e -/h + pairs in the aqueous medium [8,9]. TiO 2 features can be improved by adding another metal oxide such as ZrO 2 , SiO 2 , La 2 O 3 and Al 2 O 3 to produce new crystalline phases with different features than the original oxides [10]. A diversity of surface modification approaches have been applied to improve the photocatalytic activity of TiO 2 .…”

“…These features are comparable to those of TiO 2 , and both oxides could have a better performance in photodegradation applications when formed as a composite [12][13][14]. Even though ZrO 2 is considered as an inefficient photocatalyst due to its wide bad gap value (~5 eV), doping a small amount of ZrO 2 into TiO 2 has been reported to enhance the photoactivity of the mixed oxides TiO 2 -ZrO 2 [10]. Furthermore, the incorporation of ZrO 2 in the TiO 2 network can avoid the anatase-to-rutile phase transformation, prolong the lifetime of photoinduced e -/h + pairs, modify the surface acidity through OH groups, reduce the dielectric constant and the crystal size of TiO 2 , improve the thermal stability and increase the surface area, promoting photocatalytic activity [7,15,16].…”

“…They mentioned that the materials calcined at 400 and 500 • C presented a better degradation due to the optimum number of energetic states that act as electron traps and decrease the e -/h + pair recombination, whereas for materials annealed at 300 and 600 • C, these energetic states act as an energy barrier that reduces the effective charge transfer. In other study, Yaacob et al [10] prepared hybrid ZrO 2 -TiO 2 photocatalysts synthesized through the sol-gel process and calcined at 500, 600 and 700 • C for their evaluation of phenol degradation. The authors found that the photodegradation activity for phenol was in the following order: ZrO 2 -TiO 2 photocatalysts > pure TiO 2 photocatalysts > pure ZrO 2 photocatalysts.…”

Tailoring structural and optical properties of ZrO2 with nickel doping

“…Structural and optical properties of ZrO 2 can be tailored by suitable doping of cobalt, zinc, iron, nickel and copper. Nickel (Ni) dopant is gaining great interest because of its inhibition inside the ZrO 2 matrix, capacity of grain development, eco-friendly nature, good optical and electrochemical properties and being economical [39][40][41][42]. By introducing extrinsic dopant Ni, having smaller ionic radius (0.69 Å) as compared to Zr 4+ (0.84 Å) [43] may affect the defect environment, which will play an important role in tuning the structural and optical properties of ZrO 2 .…”