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

Abstract

The present research reports the synthesis of ZrO2-doped TiO2 photocatalysts at different ZrO2 contents (1, 3 and 5% wt.) synthesized by the sol–gel method. The samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction, attenuated total reflectance-Fourier transform infrared, ultraviolet–visible, X-ray photoelectron spectroscopy and N2 adsorption–desorption analysis. The photocatalytic activity of the ZrO2-doped TiO2 was investigated against the dyes methyl orange and rhodamine B through mineralization studies. The ZrO2-doped TiO2 samples presented a semiglobular-ovoid agglomerate shape around 500–800 nm. The samples presented high crystallinity of the TiO2 anatase phase, XPS suggested the formation of Zr–O–Ti bonds and the samples were classified as mesoporous materials with slight changes in the optical features in comparison with pure TiO2. Our study shows that the ZrO2-doped TiO2 composites exhibited a higher photocatalytic activity than just utilizing the synthetized TiO2 and a commercial P25. The different degradation behaviors are attributed to differences in the textural properties, and to the different optical absorptions of the samples due to structural defects created by the level of doping of Zr4+ ions into the TiO2 lattice. Reaction kinetics parameters were calculated by the Langmuir–Hinshelwood model, and a third run cycle of the ZrO2-doped TiO2 at 1% wt. achieved a photocatalytic degradation of 78.1 and 75.5% for RhB and MO, respectively.

One-Pot Synthesis of TiO2/Hectorite Composite and Its Photocatalytic Degradation of Methylene Blue

“…Two strong peaks of Ti 2p at 458.8 eV and 464.6 eV are attributed to the Ti 2p3/2 and Ti 2p1/2 (Ti-O bond), respectively, indicating the existence of the Ti 4+ chemical state in the TH-2 photocatalyst [32]. Two peaks at 457.9 eV and 463.6 eV correspond to the Ti 3+ 2p3/2 and Ti 3+ 2p1/2, respectively, which confirms the formation of Ti 3+ [38,39].…”

“…Ultraviolet-Visible Diffuse Reflectance Spectra (UV-Vis DRS) Figure 6 gives the UV-Vis DRS, and the optical absorption capacity of hectorite is weak in the wavelength range of 200-800 nm, which is probably attributed to its composition and particle size [10]. All the composite photocatalysts present an intense optical absorption under 425 nm compared with the single hectorite, indicating the electron Ti-O transformation of TiO 2 after the intercalation of titanium cations [32]. The insertion of TiO 2 inside the layers of hectorite may modify the electronic structure and thus the band gap energy, promoting a shift in the absorption spectra [15,32].…”

“…All the composite photocatalysts present an intense optical absorption under 425 nm compared with the single hectorite, indicating the electron Ti-O transformation of TiO 2 after the intercalation of titanium cations [32]. The insertion of TiO 2 inside the layers of hectorite may modify the electronic structure and thus the band gap energy, promoting a shift in the absorption spectra [15,32]. The band gap values were obtained with Equation ( 2):…”

“…to the Si-O bond from silicon lattice [32,37]. The surface adsorption of F (≡Ti-F) and surface -OH can proceed as follows (Equation ( 3)) [34], while it is difficult to see the peak of -OH as F occupies more space on the surface of the TiO2/hectorite.…”

“…According to the spectrum of O 1s for TH-2 (Figure 7c), the peak at 530.1 eV demonstrates the existence of crystal lattice oxygen O 2 − and the peak at 532.1 eV is mainly related to the Si-O bond from silicon lattice [32,37]. The surface adsorption of F (≡Ti-F) and surface -OH can proceed as follows (Equation ( 3)) [34], while it is difficult to see the peak of -OH as F occupies more space on the surface of the TiO 2 /hectorite.…”