Ricardo Gómez

The present study presents the results obtained from evaluating the photocatalytic behavior of a series of sulfated CeO₂ materials in the photocatalytic degradation of the herbicide 2,4-dichlorophenoxyacetic acid. The CeO₂ photocatalytic support was prepared using the precipitation synthesis method. Subsequently, the support was wetly impregnated with different contents of sulfate ions (0.5, 1.0, and 2.0 wt.%). The materials were characterized using X-ray diffraction, nitrogen physisorption, infrared spectroscopy, diffuse reflectance UV–Vis spectrophotometry, and thermal analysis. The characterization results showed that the sulfation of the material promoted an increase in the surface area and a decrease in the average size of the crystallites. Likewise, it was possible to demonstrate the surface sulfation of the support through bidentate coordination of the sulfate groups to the semiconductor metal. Concerning photoactivity, the convenience of the surface modification of CeO₂ was confirmed because the sulfate groups acted as capturers of the electrons generated during the photocatalytic process, reducing the frequency of recombination of the charge carriers and allowing the availability of the gaps to favor the degradation reaction of the contaminant. Finally, it was evident that a percentage of 1.0 wt.% of the sulfate anion is the optimal content to improve the photocatalytic properties of CeO₂.

In this work, a layered double hydroxide support modified with cadmium was synthesized by a one-pot coprecipitation method. Then, it was sulfured in different percentages by a solvothermal method. Next, the samples were analyzed using various characterization techniques like XRD, DRS, FTIR, N₂ physisorption, PL spectroscopy, TEM, and SEM. Finally, the synthesized and uncalcined materials were assessed in hydrogen production from water and a methanol-water solution under UV-light irradiation. The results showed that the sulphuration improves the photocatalytic activity, reaching a maximum rate constant of hydrogen production of 7403 µmol/g∙h in a methanol-water solution and 1326 µmol/g∙h in water.

The synthesis and characterisation of Ti–Zr mixed oxides containing 1 to 10 wt.% of Zr is herein reported. In addition, the samples were tested as photocatalysts in the generation of hydrogen from aqueous methanol solutions. The solids were prepared by sol-gel and then characterised by X-ray diffraction, high resolution electron microscopy, X-ray photoelectron spectroscopy, physisorption of nitrogen, scanning electron microscopy, UV-vis and Raman spectroscopies. The results show the presence of anatase as a predominant structure and the oxides present larger specific surface areas than that of pure titania. A maximum value of 168 m²/g was determined for the sample with 5 wt.% of zirconium. The calculated band gap energies varied from 3.05 to 3.15 eV. It was observed that the greater the zirconium content in the solid, the higher the generation rate of hydrogen when testing the Ti–Zr solids as photocatalysts. Under our experimental conditions, the best catalyst, Ti–Zr oxide with 10 wt.% Zr, showed a production rate of 2100 μmol of H₂/h which was about tenfold higher than that observed for pure titania.

BACKGROUND: The composite materials ZrO₂/Zn₅(OH)₆(CO₃)₂ were prepared in only one step by chemical co‐precipitation and thermal hydrolysis of urea. ZrO₂ was added at 5, 8 and 10 mol%. The samples were dried at 80 °C and characterized by adsorption–desorption of N₂ isotherms, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, and diffuse reflectance (DRS), UV–visible, Fourier‐transform infrared (FTIR) and X‐ray photoelectron (XPS) spectroscopies. The materials were assessed in the photodegradation of phenol and polychlorinated phenolic molecules under UV‐light irradiation. The possible mechanism was discussed from studies that corroborated or discarded the formation of the species •OH, •O₂⁻ and h⁺.RESULTS: The addition of ZrO₂ to Zn₅(OH)₆(CO₃)₂ resulted in a composite material with high photoactivity. The material containing 8 mol% of ZrO₂ (ZnZr‐8.0%) was the sample with the best percentages of photodegradation and mineralization. The photodegradation enhancement was achieved partly by an increment in the specific surface area and principally due to localized states originating in the composite interphase which improved charge transfer. XPS study revealed that the ZrO₂ addition increases the oxygen vacancies which enhanced the organic molecule photodegradation via direct hole attack.CONCLUSION: The ZnZr composite system constitutes an excellent alternative for the photodegradation of persistent organic pollutants due to the low cost, high stability and null toxicity of the support Zn₅(OH)₆(CO₃)₂. © 2019 Society of Chemical Industry

Reaction rate for 4-nitrophenol photoreduction over ZrO₂–TiO₂ increases 19 times due to the synergistic interaction between methanol and sulfite ions.