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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. [ABSTRACT FROM AUTHOR]

This study evaluated the synthesis, characterization, and activity of fluorinated titanium dioxide materials (TiO2 - F1% and TiO2 -- F5%) in-situ modified by the sol-gel method in the esterification reaction of levulinic acid conducted by catalytic and photocatalytic processes. The physicochemical properties of the materials were determined by X-ray diffraction, UV--Vis diffuse reflectance spectroscopy, thermal analysis, and pyridine adsorption. It was found that the inclusion of fluoride anion causes a decrease in the levulinic acid conversion by photocatalytic reaction; however, in the catalytic activation, a slight increase in the conversion using the fluoride materials was observed. Finally, the reaction in the presence of halogenated solvents (CCl4) by photolysis reaction favors a conversion of 100% in 1h. [ABSTRACT FROM AUTHOR]

BACKGROUND Photocatalytic degradation is considered as an effective and eco‐friendly alternative for removal of persistent pollutants. The enhancement of the photocatalytic properties of conventional photocatalysts such as CeO2 can be realized by surface modification with metals or nonmetals, which allows a reduction in the recombination frequency of charge carriers. In this study, superficially phosphated CeO2 materials with various anion contents obtained using an impregnation method were evaluated in the photodegradation of phenol under UV irradiation. RESULTS: The addition of phosphate anions promoted an increase in the surface area and a slight decrease in the crystallite size. The anchorage of the phosphate anions was via bidentate mode. An enhancement in the degradation of the pollutant was evidenced using the phosphated materials with respect to the results observed using unmodified CeO2. Also, an effect of the content of anions was evidenced, the optimal amount being equal to 1.0 wt%. CONCLUSIONS: The surface modification of CeO2 with phosphate anions favors a control of the physical and chemical properties of the semiconductor and the effective separation of electron–hole pairs, which leads to an increase in the photocatalytic activity. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Photocatalytic water splitting is an attractive alternative for hydrogen generation because it is considered a clean and environment‐friendly process. TiO2 semiconductor has been widely used in photocatalysis, however, its efficiency is limited due to the high recombination of the charge carriers. Many methods have been proposed to enhance TiO2 photoactivity, including modification with nonmetal ions and coupling with other semiconductor oxides. In this present work a series of CuO/TF photocatalysts with different CuO content were synthesized by impregnation of fluorinated TiO2 (TF) powder. These materials were characterized by several techniques and were studied in the hydrogen production reaction from a methanol/water solution under UV irradiation. RESULTS: The impregnation of the TF powder with Cu(NO3)2•H2O leads to the generation of crystalline and mesoporous materials and the existence of copper in the form of CuO. HRTEM results indicated the formation of heterojunctions between TiO2 and CuO phases. CuO(1.0)/TF photocatalyst was four times more active than TiO2 and fluorinated TiO2 support. CONCLUSIONS: The coexistence of fluoride and CuO species on TiO2 improves the photocatalytic properties of the semiconductor and the reduction of the H+ ions to H2 is considerably better than that achieved with TiO2, TF and CuO/TiO2 materials. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Phosphated TiO2 photocatalysts with different phosphate content were synthesized by in situ phosphatation of sol-gel TiO2. H3PO4 was used as a hydrolysis catalyst and as an anionic precursor. The solids were analyzed by several techniques to determine the structural, textural and optical characteristics. The photoactivity of the materials was tested in the degradation of 4-chlorophenol and 2,4-dichlorophenol, under UV irradiation. RESULTS XRD patterns showed that the presence of phosphate anions decreases the crystallite size without modification of the anatase phase. Specific surface areas higher than the pristine TiO2 were obtained on the phosphated samples. The presence of bidentate phosphates attached to the surface was identified by FTIR. The photoactivity of the materials tested in the degradation of 4-chloropehol and 2,4-dichlorophenol showed notable improvement on phosphated TiO2. The degradation rate of the chlorophenolic compounds increases with the degree of substitution in the aromatic ring. Thus, the degradation rate of 2,4-dichlorophenol is higher than that of 4-chlorophenol. High efficiency in the degradation of the molecules after the recycling of the photocatalysts was observed. CONCLUSION The modification in situ of TiO2 with low phosphate content promotes higher photocatalytic activity than that of unmodified TiO2 and Degussa P-25 in the photodegradation of the chlorophenolic compounds. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

This work aimed to study NiO/F–TiO 2 composites in the photocatalytic degradation of 4-chlorophenol. F–TiO 2 support was prepared by in-situ fluorination of TiO 2 using the sol-gel method. The heterostructured materials were prepared by wet impregnation method, varying NiO content (0.5, 1.0, and 2.0% wt). The solids were characterized by X-ray fluorescence, X-ray diffraction, nitrogen physisorption, diffuse reflectance UV–Vis spectrophotometry, infrared spectroscopy, and X-ray photoelectron spectroscopy. The characterization studies showed that the coupling of TiO 2 with fluoride ions promoted the generation of ≡Ti–F surface species that could be responsible for the decrease in the recombination frequency of charge carriers and the increased photoactivity. In addition, it was found that the coupling of NiO/F–TiO 2 semiconductors improved the photocatalytic properties of the fluorinated support, obtaining higher percentages of degradation and mineralization of the phenolic contaminant. These results are possibly a consequence of factors such as the formation of larger crystallites, lower band gap energies, and the generation of p-n type interfacial heterojunctions that potentiate the proper separation of electron-hole pairs. An effect of NiO content on photoactivity was observed, being a percentage of 1.0% wt the optimum in this photocatalytic treatment. [Display omitted] • The NiO/F–TiO2 heterojunction system improves the photocatalytic degradation of 4-chlorophenol. • The NiO percentage affects photocatalytic activity, being 1.0% wt. The optimal content. • A better dispersion of NiO on F–TiO2 improves the photocatalytic activity due to slightly lower energy gaps (Eg). • NiO favors the generation of p-n heterojunctions promoting charge transfer and separation of the electron/hole pair. [ABSTRACT FROM AUTHOR]

The interest in the removal of emerging contaminants has increased in the last decade. Photocatalytic degradation using p-n heterojunctions could effectively provide the degradation of these type of substances that are persistent in the environment. In this work, the synthesis, characterization, and photocatalytic evaluation of TiO 2 –F as well as CuO/TiO 2 –F and NiO/TiO 2 –F composite materials were studied in the photo-assisted degradation of caffeine using UV radiation. The fluorination of titanium dioxide induced changes in some physicochemical properties of the materials, which contributed to a decrease in surface area and bandgap energy as well as an increase in crystallite size as compared to pristine TiO 2. ≡Ti–F species were evidenced to be formed, which could favor charge separation processes. A highest segregation of CuO species in comparison with NiO on the surface of TiO 2 –F could be formed, which could increase defect sites and decrease the band gap. The formation of a heterojunction between the semiconductors was evidenced, responsible for the observed improvements in photocatalytic properties of the composite materials. The photocatalytic tests evidenced an important degradation of caffeine; however, mineralization was incomplete. The stability of the composite materials and their potential use in the photocatalytic treatment of caffeine was evaluated by reuse tests. [Display omitted] • Caffeine, a persistent and toxic emergent compound, could be easily degraded using CuO or NiO on TiO 2 –F. • A caffeine photodegradation of 90 and 88% was reached using CuO/TiO 2 –F and NiO/TiO 2 –F, respectively. • TiO 2 –F coupled with CuO and NiO increase the effective separation of the charge carriers. • CuO/TiO 2 –F and NiO/TiO 2 –F shown a rate of hydroxyl radical generation 2.2 and 1.5 higher than that achieved using the TiO 2 –F. [ABSTRACT FROM AUTHOR]