Effect of silver incorporation on structural and optical properties of TiO 2 thin films prepared via non-aqueous sol-gel route

Effects of vanadium doping on microstructures and optical properties of TiO2

Sol-gel fabrication of Ag-Coated ZnO quantum dots nanocomposites with excellent photocatalytic activity

TiO2 nanofibers doped with rare earth elements and their photocatalytic activity

ZnO is an effective photocatalyst applied to the degradation of organic dyes in aqueous media. In this study, the UV-light and sunlight-driven photocatalytic activities of ZnO nanoparticles are evaluated. A handheld Lovibond photometer was purposefully calibrated in order to monitor the dye removal in outdoor conditions. The effect of ZnO defect states, i.e., the presence of zinc and oxygen defects on the photocatalytic activity was probed for two types of dyes: fuchsin and methylene blue. Three morphologies of ZnO nanoparticles were deliberately selected, i.e., spherical, facetted and a mix of spherical and facetted, ascertained via transmission electron microscopy. Aqueous and non-aqueous sol-gel routes were applied to their synthesis in order to tailor their size, morphology and defect states. Raman spectroscopy demonstrated that the spherical nanoparticles contained a high amount of oxygen vacancies and zinc interstitials. Photoluminescence spectroscopy revealed that the facetted nanoparticles harbored zinc vacancies in addition to oxygen vacancies. A mechanism for dye degradation based on the possible surface defects in facetted nanoparticles is proposed in this work. The reusability of these nanoparticles for five cycles of dye degradation was also analyzed. More specifically, facetted ZnO nanoparticles tend to exhibit higher efficiencies and reusability than spherical nanoparticles.

The resurgence of photocatalytic activity of TiO2 is driven in past few decades owing to its potential to meet several contemporary global challenges, such as pollutant degradation, nonfossil fuel production from CO2, or H2 generation from aqueous solutions [1]. Among three TiO2 polymorphs anatase TiO2 (A-TiO2), rutile TiO2 (R-TiO2) and brookite TiO2, first two are the mostly investigated phases for photocatalytic application. However, the use of TiO2 photoelectrodes is limited owing to the recombination of photo-generated (e-h) pairs in the bulk, and also at the electrode/electrolyte interface. The overall efficiency associated with A-TiO2 is still considered to be higher with respect to R-TiO2 due to higher charge carrier mobility and slower charge recombination kinetics [2].Nevertheless, proper ratio of anatase-rutile phases (Degussa P25) is superior in photocatalytic activity than that of pure rutile or anatase phase. On the other hand, anodic TiO2 nanotubes TNTs have attracted wide interest due to their high surface-to-volume ratio with preferential electron transport towards the Ti back-contact, and a scalable synthesis by electrochemical anodization [3]. However, thermal annealing is needed to obtain anatase and rutile phases, besides achieving suitable ratio of mixed-phases for relatively high photocatalytic performance through efficient inter-granular charge transfer and minimizing the recombination processes. Temperature induced changes in surface morphology, grain size, crystal structure and composition also have significant influence on the photo-electrochemical properties of TNTs. Here, we report the synthesis of TNTs, and the correlation of optical band gap with structural transformation from anatase to rutile through intermediate mixed phases as a function of temperature and their corresponding effect on photocatalysis application. This is confirmed by means of UV-Vis spectroscopy, X-ray diffraction (XRD) and Raman Spectroscopy. X-ray Photoelectron Spectroscopy (XPS) analyses has also been carried out to understand the change in chemical behavior with annealing temperature, gives a clear evidence of sub-stoichiometric to stoichiometric TiO2 (Ti4+) phase transformation with increasing temperature via removal of the fluorine (F) species from the NT surface which eventually changes the crystallinity of the samples as observed in XRD patterns. Further, to comprehend the change in the local coordination environment of the constituent atoms in TiO2 nanotubes with annealing temperature, the samples have been characterized by X-ray Absorption Spectroscopy (XAS). Density functional theory (DFT) has also been employed to understand the underlying mechanism.

Effects of oxygen flow ratios and annealing temperatures on Raman and photoluminescence of titanium oxide thin films deposited by reactive magnetron sputtering

Characterization of mesoporous nanocrystalline TiO 2 photocatalysts synthesized via a sol-solvothermal process at a low temperature

Effect of fuels on combustion synthesis of TiO2 – Towards efficient photocatalysts for methylene blue oxidation and Cr (VI) reduction under natural sunlight

Synergistic enhancement of photocatalytic and antimicrobial efficacy of nitrogen and erbium co-doped ZnO nanoparticles

Up to date, titanium dioxide (TiO2) thin film has attracted considerable interest as the most promising material for a variety of applications and products in the environmental and energy fields, including self-cleaning surfaces, air and water purification systems, and photoelectrochemical conversion because of its outstanding chemical stability and electrical properties, etc [1]. Among the three phases of TiO2, anatase TiO2 has higher photocatalytic activity than rutile and brookite TiO2. Anatase TiO2 films can be synthesized by various methods. However, there were still issues on synthesizing the stable pure anatase phase TiO2 using different methods. Compared with other reported methods, the mist chemical vapor deposition (mist CVD) [2] is an alternative method to synthesize TiO2 thin films, by which the growth of oxide thin film can be precisely controlled according to our previously research [3]. In this research, anatase TiO2 thin films were fabricated on glass by mist CVD method. The precursor solution (150 ml) was prepared by dissolving acetylacetone (0.9 ml) and titanium tetraisopropoxide (TTIP, 0.9 ml) in water and methanol. In order to investigate the temperature on structural, optical and photocatalytic properties of TiO2 films, the deposition temperature were set at room temperature, 200˚C and 400˚C for comparison. During the mist CVD process, mist droplets were generated from the precursor solution by ultrasonic atomization at 2.4 MHz and transferred to the reaction chamber by N2 carrier gas. The structural properties of TiO2 thin films were investigated by X-ray diffraction , Raman spectroscopy and scanning electron microscope, atomic force microscope . The optical properties of TiO2 thin films were investigated by transmittance spectroscopy.According to the morphological analysis, TiO2 films of 300nm with uniform surface were observed from the deposition temperature of 400˚C. There was no thin film at room temperature and some isolated particles observed at 200˚C. Examining the GIXRD patterns of TiO2 films deposited at 400˚C, the following diffraction peaks (101), (004), (200), (211), (201), (204) and (215) were observed, which corresponds to the diffraction peaks of anatase phase TiO2. The transmittance of TiO2 films was higher than 75 % in the visible region. The photocatalytic efficiency of TiO2 film showed the photocatalytic efficiency due to a maximum number of {001} facets and a large surface area.In summary, the pure anatase phase TiO2 thin films could be synthesized at 400˚C by mist CVD method. The obtained anatase TiO2 films showed high photocatocatalytic efficiency. The growth mechanism of pure anatase TiO2 films will be revealed in the paper.References V. Baryshnikova, L. A. Filatov, A.S. Petrov, and S. E. Alexandrov, Chemical Vapor Deposition, 21, 327-333 (2015).Kawaharamura, K. Mori, H. Orita, T. Shirahata, S. Fujita, and T. Hirao, Japanese Journal of Applied Physics, 52, 035501 (2013). Li, C. Li, T. Kawaharamura, D. Wang, N. Nitta, M. Furuta, H. Furuta, and A. Hatta, Transactions of the Materials Research Society of Japan, 39[2], 161-164 (2014).

Titanium dioxide (TiO2) thin films were deposited on Si wafer and glass substrates by direct current (dc) magnetron sputtering, by which the photocatalytic phase, anatase, was obtained under the optimum deposition conditions of O2/(O2+Ar) flow ratios and substrate biases. TiO2 thin films doped with Sn or Nb were prepared on glass substrates by dc/rf (radio frequency) magnetron co-sputtering, in which dc and rf were utilized for Ti and Sn or Nb targets, respectively, and the samples were post-annealed at temperatures ranging from 473 to 773 K for 1 h in ambient air. Microstructure, surface morphology, chemistry, and optical properties of the un-doped, Sn-doped, and Nb-doped TiO2 films were characterized in details by glancing incidence X-ray diffraction (GIXD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS), differential thermal analysis/thermogravimetry (DTA/TG), atomic force microscopy (AFM), UV/visable spectrophotometry, ellipsometry, and X-ray photoelectron spectroscopy (XPS). In addition, the photocatalytic activity was evaluated by measurement of the degeneration of methylene blue under UV/visible irradiation. The analytical results of GIXD show that the anatase phase is the dominant phase at an O2/(O2+Ar) flow ratio of over 40 %, whereas the films exhibit the rutile phase dispersed in amorphous matrix at an O2/(O2+Ar) flow ratio of 20 %. Microstructure and optical properties of the TiO2 films are dependent closely upon the rf power applied to the substrates as a bias. The anatase phase with columnar structure was obtained for the films prepared at rf powers of 0 and 5 W; whereas the films exhibit a rutile phase with equi-axial crystals at rf powers of 15 and 25 W. The rf-bias-assisted TiO2 films have a smoother surface than that without rf bias, and the absorbance edges shift to long wavelengths. The TiO2 films with a rutile phase have a higher refractive index, whereas better photocatalytical properties were observed for the films having anatase phase. TiO2 films with various Sn or Nb doping contents were investigated on the microstructure, optical properties, and photocatalytic activities. All the as-deposited TiO2 films on glass substrate were amorphous. The concentration of Sn in rf powers of 100 and 200 W and Nb in rf powers of 200, 300, and 400 W were 6.65 and 16.4 at.% for Sn and 1.98, 3.56, and 4.9 at.% for Nb, respectively, by X-ray photoelectron spectroscopy. GIXD revealed a polycrystalline phase for the Nb-doped films post-annealed at temperature 523 K, in contrast to the un-doped one that has to be annealed at temperature 723 K, indicating that Nb dopant can enhance the crystallization of amorphous TiO2. Furthermore, the Nb-doped film post-annealed at 673 K was found to have an anatase-dominanted phase with a fine grain microstructure, while the Sn-doped film post-annealed at 673 K was found to have a coexistence of anatase/rutile duplex and amorphous structure, as observed by using TEM. Heat treatment also induces a change in the surface morphology of the TiO2 films examined by FE-SEM. The optical properties of the TiO2 films were characterized by UV/visible spectrophotometry. The average transmittance of the Sn-doped and Nb-doped films is higher than 85%. Absorption zone in visible regime and optical band gap of the Sn-doped or Nb-doped TiO2 films increase with the doping contents. Under visible light irradiation, all the Nb-doped TiO2 films exhibit better photocatalytic activity than that of un-doped and Sn-doped ones. Among them, the Nb-doped TiO2 film with rf power of 400 W post-annealed at temperature 673 K shows the best photocatalytic performance.

Photocatalytic property of TiO 2 thin films sputtered-deposited on unheated substrates

Photocatalytic degradation of various dyes by combustion synthesized nano anatase TiO2

Titanium dioxide is a standard semiconductor material plays a vital role in environmental and energy research. Anatase to rutile phase transformation in pure TiO2 nanoparticles usually occurs in the temperature range 600 °C–700 °C with it only absorbs UV light, owing to its large bandgap of 3.2 eV. Till date, researchers and industrialists have been trying to synthesize TiO2 nanoparticles with increased anatase phase stability with reducing the bandgap of pure anatase phase to the visible region, used dopant or H2O2 precursor modification, but the long time has taken photocatalytic activity under sunlight. Here, using a novel Photon Induce Method (PIM) has reported extending the anatase to a rutile transformation temperature, which in turn reflects on the stability of the material. PIM prepared oxygen-rich TiO2 nanoparticles exhibit enhanced temperature stable anatase phase, i.e. the sample remained as pure anatase phase even after calcinating at 1000 °C with a reduced bandgap of less than 2.91 eV, stretching towards the red region of the sunlight, whereas the standard Degussa P25-TiO2 and Others are reported to exist as 100% rutile at this temperature. By tuning the oxygen vacancy preparation conditions, we can reversibly improve oxygen-rich Titania via PIM. The absence of dopant or H2O2 of pure Titania anatase nanoparticles is high chemical reactivity has important implications for antibacterial, cancer cells kill, photocatalysis and solar energy conversion.

There is a great concern about black TiO2 prepared by H2 treatment because of its ability to enhance light harvesting of TiO2. Black TiO2 shows different photocatalytic activities compared with white TiO2. However, the mechanism of photocatalytic reaction has not been clearly understood. Here, femtosecond time-resolved diffuse reflectance (fs-TRDR) spectroscopy and single-particle photoluminescence measurements were applied to gain better understanding about the relation between oxygen vacancy, charge transfer, lifetime of photogenerated charge, and photocatalytic activity. We prepared reduced TiO2 mesocrystals (R-TMC) through simple solid-state chemical reduction at moderate temperature 350 °C. R-TMC has nearly two times higher photocatalytic activity for H2 production under solar light irradiation. The presence of oxygen vacancies and Ti3+ was studied by electro paramagnetic resonance and X-ray photoelectron spectroscopy. This work confirms the findings of previous studies that enhancement of light abso...