Cr TiO Research Articles

Solar-light-active mesoporous Cr-TiO2 for photodegradation of spent wash: an in-depth study using QTOF LC-MS.

A dark-coloured effluent called “spent wash” is generated as an unwanted product in sugarcane-based alcohol distilleries. Most distilleries discharge this effluent into soil or water without any treatment, causing water and soil pollution. Herein, we report chromium-doped TiO2 (Cr–TiO2) as a photocatalyst for the degradation of spent wash colour under natural sunlight. Cr-doped TiO2 nanoparticles were prepared using an aqueous titanium peroxide-based sol–gel method with titanium isopropoxide as the Ti precursor and chromium nitrate as the Cr precursor. To observe the effect of dopant on sol–gel behaviour and physicochemical properties, the Cr concentration was varied in the range 0.5–5 wt%. The crystallization temperature and time were optimized to obtain the required phase of Cr–TiO2. The physicochemical characteristics of the Cr-doped TiO2 catalyst were determined using X-ray diffraction, FE-SEM, FETEM, TG, XPS, the Brunauer–Emmett–Teller (BET) method, FT-IR, Raman, PL, ICP-MS, and UV visible spectroscopy. A shift in the absorption edge of TiO2 by doping with chromium suggested an increase in visible light absorption due to a decrease in the effective band gap. The application potential of the Cr–TiO2 catalyst was studied in the degradation of sugar-based alcohol distillery waste under natural sunlight, and the results were compared with those of undoped TiO2 and Degussa P25 TiO2. Degradation of the spent wash solution was monitored using UV-visible, gel permeation chromatography (GPC), and QTOF LC-MS. GPC and LC-MS showed significant changes in the molecular weight of spent wash colour-forming compounds due to the degradation reaction. QTOF LC-MS analysis suggested that acids, alcohols, glucosides, ketones, lipids, peptides, and metabolites were oxidized to low-molecular-weight counterparts. From the results, 5% Cr–TiO2 showed the highest degradation rate among all Cr–TiO2 samples, undoped TiO2, and Degussa P25 TiO2 under identical reaction conditions, with nearly 68–70% degradation achieved in 5 h.

Efficient visible-light-induced photocatalytic degradation of MO on the Cr–nanocrystalline titania–S

In order to improve visible light photocatalytic activities of the nanometer TiO 2, a novel and efficient Cr,S-codoped TiO 2 (Cr–TiO 2–S) photocatalyst was prepared by precipitation-doping method. The crystalline structure, morphology, particle size, and chemical structure of Cr–TiO 2–S were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) techniques, respectively. Results indicate that the doping of Cr and S, cause absorption edge shifts to the visible light region ( λ > 420 nm) compare to the pure TiO 2, reduces average size of the TiO 2 crystallites, enhances desired lattice distortion of Ti, promotes separation of photo-induced electron and hole pair, and thus improves pollutant decomposition under visible light irradiation. The photocatalytic activities of Cr–TiO 2–S nanoparticles were evaluated using the photodegradation of methyl orange (MO) as probe reaction under the irradiation of UV and visible light and it was observed that the Cr–TiO 2–S photocatalyst shows higher visible photocatalytic activity than the pure TiO 2. The optimal Cr–TiO 2–S concentration to obtain the highest photocatalytic activity was 5 mol% for both of Cr and S.

Recyclable UV and visible light photocatalytically active amorphous TiO 2 doped with M (III) ions (M = Cr and Fe)

Samples of amorphous TiO 2 doped with Cr(III) and Fe(III), designated as Cr–TiO 2 and Fe–TiO 2, were prepared via modified impregnation method. The resulting products were characterized by X-ray diffraction, scanning electron microscopy, specific surface area by the Brunauer, Emmett and Teller method, UV–vis absorption and diffuse reflectance spectroscopy, and electron spin resonance spectroscopy. Experimental results revealed that the concentrations of dopants under studied, from 0.05 to 0.2 mol%, had no effect on the phase of products. The band gap energies shifted from 3.28 eV in the undoped amorphous TiO 2 to 2.50 eV and 2.86 eV for Fe–TiO 2 and Cr–TiO 2, respectively. The doped amorphous TiO 2 showed photocatalytic activities under both UV and visible light with optimal results at 0.1 mol% dopants. Under UV irradiation, the 0.1 mol% doped samples decolorized methylene blue solutions to the same extent as the commercial TiO 2 samples (P25 and anatase) in 5 h. Under visible light, the doped samples decolorized dye solutions in 12 h while the commercial ones were much less active. The used catalysts can be recycled many times without any special treatment.

Preparation of PW 12O 403−/Cr–TiO 2 nanotubes photocatalysts with the high visible light activity

The development of photocatalysts with high visible light photocatalytic activity is of significance. In this study, PW 12O 40 3− and Cr 3+ modified TiO 2 nanotubes, a new type photocatalysts, were prepared with anodization and impregnation methods to increase the visible light catalytic activity of TiO 2. The Cr 3+ doping narrowed the band gap of TiO 2 to enhance the visible light response. Moreover, the Cr 3+ doping increased the standard reduction potential of the conduction band electrons of TiO 2 enhancing the electron transfer between conduction band electrons from TiO 2 (electron donor) and PW 12O 40 3− (electron acceptor), so electrons and holes were efficiently separated. The reaction rate constant of PW 12O 40 3−/Cr–TiO 2 was significantly higher than that of Cr–TiO 2 or PW 12O 40 3−/TiO 2, which was attributed to the synergetic effect between Cr 3+ and PW 12O 40 3− modification. The synergetic fact of PW 12O 40 3− and Cr 3+ in PW 12O 40 3−/Cr–TiO 2(2.36 at%) reached 1.42.

Use of TiO 2/Cr-MCM-41 molecular sieve irradiated with visible light for the degradation of thiophene in the gas phase

Photocatalytic processes using TiO 2 and UV radiation to eliminate pollutants are not yet suitable for industrial facilities due to their high consumption of energy. Transition metals incorporated onto mesoporous MCM-41 molecular sieves impregnated with TiO 2 constitute an alternative that allows the use of solar light. In this study, Cr-substituted MCM-41 were synthesized (Si/Cr = 100, 50 and ∞) and impregnated with TiO 2 (10 and 20 wt.%). Raman results showed the formation of anatase. Electronic spectroscopy and EPR exposed the formation of trivalent chromium after impregnation with TiO 2, which is related to a Cr–TiO 2 interaction. The synthesized photocatalysts, as well as TiO 2 P25, were tested in the degradation of thiophene in gaseous phase. A test with UV lamp showed 100% of conversion for 20%TiO 2/Cr-MCM-41(100) and exceeded the activity of TiO 2 P25, probably due to the higher dispersion of TiO 2 on the surface of the molecular sieve. During tests using visible light and 20%TiO 2/Cr-MCM-41(50) higher conversions than those of 20%TiO 2/Cr-MCM-41(100) and TiO 2 P25 were observed. These results indicate that chromium concentration is a key factor influencing the photocatalytic activity under visible light.

Nanocrystalline (Mg, Fe, Cr)TiO 3 perovskite inclusions in olivine from a mantle xenolith, Udachnaya-East kimberlite pipe, Siberia

Olivine grains from an ilmenite–garnet–peridotite nodule from the kimberlite pipe Udachnaya–Wostotschnaya, Siberia have been investigated by TEM methods (electron diffraction, HREM, AEM, EELS). The nodule is a high-temperature garnet peridotite, which equilibrated at about 1200–1300 °C and 200 km depth. TEM investigation of several olivine grains revealed nanometre-sized inclusions of (Mg,Fe,Cr)TiO 3 perovskite together with ilmenite. Both types of inclusions exhibit a typical grain size of about 50 nm. The crystal structure of the perovskite inclusions is monoclinic with a 0=1.095 nm, b 0=0.5169 nm, c 0=0.743 nm and the monoclinic angle β=95°. The orientation relationship between perovskite and olivine is (101) ol//(300) per and [010] ol//[01¯0] per. This observation combined with the experimentally determined ilmenite/perovskite phase boundary [A. Metha, K. Leinenweber, A. Navrotsky, M. Akaogi, Calorimetric study of high-pressure polymorphism in FeTiO3: stability of the perovskite phase, Phys. Chem. Minerals, 21 (1994) 207–212] [8] allows the use of perovskite in olivine as a geobarometer. The presence of perovskite in olivine suggests that the peridotite originated at pressures of 8–10 GPa, significantly higher than the pressure of last silicate equilibration (4.5–6.5 GPa).

Gas sensing mechanism of TiO 2-based thin films

Two classes of thin film gas sensors have been studied: TiO 2 doped with Cr or Nb and TiO 2–SnO 2 mixed systems. Thin films have been prepared by the reactive sputtering from mosaic targets. It is demonstrated that titanium dioxide doped with Nb and Cr should be considered as a bulk sensor. Its performance is governed by the diffusion of point defects, i.e. very slow diffusion of Ti vacancies for TiO 2: 9.5 at% of Nb and fast diffusion of oxygen vacancies in the case of TiO 2: 2.5 at% Cr sensor. The corresponding response times are 55 min for TiO 2: 9.5 at% of Nb and 20 s for TiO 2: 2.5 at% Cr. In turn, sensors based on TiO 2–SnO 2, particularly those of the SnO 2-rich composition, belong to the group of surface sensors.

Effect of MoO 2 and TiO 2 on electrodeposition and properties of chromium coating

The process of chromium electroplating from a low-concentrated (120 g l −1 CrO 3) bath with additive Limeda Ch-3 and fine-dispersion suspensions of molybdenum dioxide (MoO 2) and titanium dioxide (TiO 2) particles has been studied. The effects of these fine-dispersion particles, capable of co-deposition with chromium matrix, on certain characteristics of the coating have been considered in this work. A lower rate of the formation of composite Cr–MoO 2 and Cr–TiO 2 compared with that of Cr coating is supposed to be related to the adsorptive capacity of MoO 2 and TiO 2 and desorption of their hydrides from the electrode surface. It has been shown that high-dispersed particles of MoO 2 may be used to reduce hydrogenation of the substrate. Moreover, MoO 2, as well as TiO 2 particles, have an effect on such coating properties as hardness, ductility, internal stresses and a high-temperature resistance.