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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]

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]

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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]

Different composites based on ZnO/Ag3PO4 and ZnO–malachite (Cu2(OH)2CO3) were synthesized in order to determine their effectiveness in the treatment of municipal and industrial wastewaters (mainly polluted by enteropathogenic bacteria, dyes, and heavy metals). The addition of Ag3PO4 and malachite did not significantly modify the physicochemical properties of ZnO; however, the optical properties of this oxide were modified as a result of its coupling with the modifiers. The modification of ZnO led to an improvement in its effectiveness in the treatment of municipal and industrial wastewater. In general, the amount of malachite or silver phosphate and the effluent to be treated were the determining factors in the effectiveness of the wastewater treatment. The highest degree of elimination of bacteria from municipal wastewater and discoloration of textile staining wastewater were achieved by using ZnO/Ag3PO4 (5%), but an increase in the phosphate content had a detrimental effect on the treatment. Likewise, the highest Fe and Cu photoreduction from coal mining wastewater was observed by using ZnO–malachite (2.5%) and ZnO/Ag3PO4 (10%), respectively. Some of the results of this work were presented at the fourth Congreso Colombiano de Procesos Avanzados de Oxidación (4CCPAOx). [ABSTRACT FROM AUTHOR]

In this study, titanium dioxide powder obtained by the sol-gel method and TiO2 nanotubes, were prepared. In order to increase the TiO2 photoactivity, the powders and nanotubes obtained were modified by dye sensitization treatment during the oxide synthesis. The sensitizers applied were Quinizarin (Q) and Zinc protoporphyrin (P). The materials synthesized were extensively characterized and it was found that the dye sensitization treatment leads to modify the optical and surface properties of Titania. It was also found that the effectiveness of the dye-sensitized catalysts in the phenol and methyl orange (MO) photodegradation strongly depends on the dye sensitizer employed. Thus, the highest degradation rate for MO was obtained over the conventional Q-TiO2 photocatalyst. In the case of the nanotubes series, the most effective photocatalyst in the MO degradation was based on TiO2-nanotubes sensitized with the dye protoporfirin (ZnP). Selected catalysts were also tested in the phenol and MO photodegradation under visible light and it was observed that these samples are also active under this radiation. [ABSTRACT FROM AUTHOR]

In this study, commercial and lab-prepared TiO2 were modified by fluorination and platinum photodeposition; and the effect of these modifications over the physicochemical and photocatalytic properties of TiO2 was evaluated. It was found that F and Pt addition leads to the modification of the optical and textural properties of TiO2. The materials prepared were tested in the photocatalytic degradation of different organic dyestuffs such as methylene blue (MB) and methyl orange (MO); the degradation of commercial anilines employed in the staining of natural fibers was also evaluated. Photocatalysis was also studied in this work as an eco-friendly treatment of wastewater coming from handicrafts factories. In general it was observed that the effectiveness of the photocatalytic treatment strongly depends on the substrate to be degraded, thus, fluorinated and platinized commercial Titania (Pt-F-P25) showed the best photocatalytic performance in the MB and MO photodegradation and in contrast, in the case of the anilines the highest degradation was obtained over commercial TiO2 fluorinated (F-P25). These results can be explained by differences observed in the structure and in the adsorption of these dyestuffs over the photocatalysts surfaces. F-P25 photocatalyst also demonstrated to be the best material for the treatment of real wastewater coming from handicrafts factories. [ABSTRACT FROM AUTHOR]

MgAl Layered Double Hydroxides (LDH) with molar ratio Mg/Al = 3 and MgAlSn containing 5, 10 and 15wt% of tin were synthesized by the co-precipitation method. The solids were characterized by X-ray diffraction (XRD), N 2 sorption, infrared spectroscopy (FTIR), Scanning Electron Microscopy coupled to a detector for energy dispersive X-ray spectroscopy microanalysis (SEM/EDS), Transmission Electron Microscopy (TEM) and UV–Vis spectroscopy (UV–Vis) in order to determine the crystalline structure, textural properties, vibrational modes of the LDH, morphology and tin content, as well as the band gap of the solids. The photocatalytic behaviors of synthesized materials were tested in phenol degradation under UV irradiation. The results showed that MgAlSn 15% present the highest activity with 80% degradation of the contaminant molecule after 3 hours of exposure to light. [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]