Photocatalytic Activity under Simulated Sunlight of Bi-Modified TiO 2

The synthesis of Bi-modified TiO2 thin films, with different Bi contents, is reported. The obtained materials were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), X-ray diffraction (XRD), photoluminescence (PL), and diffuse reflectance spectroscopy (DRS), in order to obtain information on their chemical composition, vibrational features, and optical properties, respectively. Compositional characterization reveals that the bismuth content can be varied in an easy way from 0.5 to 25.4 at. %. Raman results show that the starting material corresponds to the anatase phase of crystalline TiO2, and Bi addition promotes the formation of bismuth titanates, Bi2Ti2O7 at Bi contents of 10.4 at. % and the Bi4Ti3O12 at Bi contents of 21.5 and 25.4 at. %. Optical measurements reveal that the band gap narrows from 3.3 eV to values as low as 2.7 eV. The photocatalytic activity was tested in the degradation reaction of the Malachite Green carbinol base dye (MG) as a model molecule under simulated sunlight, where the most relevant result is that photocatalytic formulations containing bismuth showed higher catalytic activity than pure TiO2. The higher photocatalytic activity of MG degradation of 67% reached by the photocatalytic formulation of 21.5 at. % of bismuth is attributed to the presence of the crystalline phase perovskite-type bismuth titanate, Bi4Ti3O12

Multiphase photo-capillary reactors coated with TiO2 films: preparation, characterization and photocatalytic performance

Quartz capillaries were assessed as multiphase photocatalytic reactors. The tested reaction was the salicylic acid (2-dihidroxibenzoic acid) oxidation. The catalyst (TiO2) was either in slurry or immobilized by sol-gel method onto the capillary wall. All experiments were conducted under oxygen flow and Taylor flow hydrodynamic regime. TiO2 Films were characterized by Raman spectroscopy, diffuse reflectance UV-Vis spectroscopy and scanning electronic microscopy. The effect of two synthesis variables was established. These variables were volumetric ratio of precursors solutions (i-PrO:2-propanol:nitric acid) and number of capillary coating cycles. These variables were found to importantly affect film homogeneity and oxidation rate. The highest initial reaction rate (106.32x10-6 mol dm-3s-1) was obtained when using the TiO2 as film prepared with a precursors volumetric ratio of 1:15:1 and with two coating cycles. For comparison purposes, the same oxidation process was conducted in a stirred reactor and it was found that the reaction rate value is diminished by almost four times in comparison with that obtained under Taylor flow in the capillary reactor. Selectivity was found to be dependant on the type of catalyst addition, slurry or immobilized. Catalytic films employed in this non-common reaction system were 2 reused three times losing less than 10% of their photocatalytic activity. The photonic efficiency was found to be two orders of magnitude higher in the coated capillary reactor than in the slurry stirred reactor.L. Hurtado acknowledges CONACYT-Mexico the scholarship No. 56499. Project PRODEP for advanced oxidation processes is also acknowledged for financial support

Evaluation of the efficiency of water treatment by a solar heating and distillation system

Presently, many industries discharge colored wastewater without any treatment to water bodies such as rivers and lakes affecting flora and fauna. Due to its chemical composition, its self-purification in phreatic bodies is complicated. Although there are chemical, physical and biological treatments dedicated to the degradation of this type of compounds, they present economic and energetic disadvantages. This study reports the use of solar energy for the treatment of water containing carmine red dye at 25 ppm. The system consists of the coupling of two modules; the first heats wastewater using a parabolic heater, while the second separates clean water (distilled) from pollutants. It was observed that when a galvanized ZnO plate is introduced into the distillation unit a photodegradation process takes place improving the characteristic of the concentrate. Optimal conditions allow an efficiency of 87 % in the production of the distilled water obtained. Parameters such as pH, Conductivity, COD, Turbidity and Total Solids, indicate that the distilled water complies with the maximum permissible limits for water quality established in Mexican regulations. A 93 % photodegradation of carmine red dye wastewater was detected within 120 min during the process, which was verified by UV-Vis and IR characterization

Nanoestructuras basadas en Bi soportadas en películas delgadas de TiO2 y su desempeño fotocatalítico

"Se reporta la preparación de materiales compuestos por nanoestructuras basadas en bismuto soportadas sobre películas de dióxido de titanio (TiO2) y su aplicación como fotocatalizadores para la degradación de una solución del colorante verde de malaquit