Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate.
Pharmaceuticals, especially antibiotics, constitute an important group of aquatic contaminants given their environmental impact. Specifically, tetracycline antibiotics (TCs) are produced in great amounts for the treatment of bacterial infections in both human and veterinary medicine. Several studies have shown that, among all antibiotics, oxytetracycline hydrochloride (OTC HCl) is one of the most frequently detected TCs in soil and surface water. The results of the photocatalytic degradation of OTC HCL in aqueous suspensions (30 mg·L−1) of 0.5 wt.% cobalt-doped TiO2 catalysts are reported in this study. The heterogeneous Co-TiO2 photocatalysts were synthesized by two different solvothermal methods. Evonik Degussa Aevoxide P25 and self-prepared TiO2 modified by the same methods were used for comparison. The synthesized photocatalysts were characterized by X-ray powder diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV/vis diffuse reflectance spectroscopy (DRS), and N2 adsorption (BET) for specific surface area determination. The XRD and Raman results suggest that Ti4+ was substituted by Co2+ in the TiO2 crystal structure. Uv/visible spectroscopy of Co-TiO2-R showed a substantial redshift in comparison with bare TiO2-R. The photocatalytic performance of the prepared photocatalysts in OTC HCL degradation was investigated employing Uv/vis spectroscopy and high-performance liquid chromatography (HPLC). The observed initial reaction rate over Co-TiO2-R was higher compared with that of Co-TiO2-HT, self-prepared TiO2, and the commercial P25. The enhanced photocatalytic activity was attributed to the high surface area (153 m2·g−1) along with the impurity levels within the band gap (2.93 eV), promoting the charge separation and improving the charge transfer ability. From these experimental results, it can be concluded that Co-doping under reflux demonstrates better photocatalytic performances than with the hydrothermal treatment.
Aims: cobalt doped TiO2 composites were synthesized with the aim to decrease the TiO2 band gap which results in enhanced visible absorption and then loaded with 1 wt.% of platinum for promoting the formation of molecular hydrogen. Background: Controversial results of the cobalt-based compounds create doubts about the photocatalytic activity of the cobalt doped TiO2 materials. Thus, cobalt doped TiO2 composites were synthesized, and the photocatalytic activity was checked for the hydrogen generation. Objective: The objective of this study is the synthesis of photocatalysts that are highly active for the photocatalytic hydrogen evolution. Methods: The TiO2 and Co-TiO2 photocatalysts were synthesized using two different methods that are reflux and hydrothermal synthesis. Additionally, The Pt deposition on the prepared TiO2 and Co-TiO2 catalysts (1 wt.% Pt) was performed by the photoplatinization method. Result: The results showed that the reduction of protons over bare TiO2 and Co-TiO2 materials is possible from the thermodynamic point of view. The evolution of molecular hydrogen from aqueous methanol employing 1 wt.% platinum loaded on 0.5 wt.% Co-TiO2 photocatalysts under simulated solar light irradiation was investigated. The platinized CoTiO2 composites along with the platinized TiO2 samples have shown high photocatalytic hydrogen evolution. Higher hydrogen evolution rates were determined in the presence of all platinized materials, and a maximum of 317 μmol h-1 is observed on a Pt/Co-TiO2 photocatalyst prepared by a hydrothermal method. Conclusion: EPR results confirmed that the defects observed in the sample prepared within the hydrothermal processing were in the surface and have better crystallinity, while the defects detected on the samples prepared by reflux synthesis were less crystalline. The nature of semiconductor materials was explored through the determination of the flatband potential using the Mott–Schottky equation. The Mott−Schottky analysis of electrochemical impedance measurements showed that all semiconductors were n-type semiconductors and that cobalt doping induces impurity level within the band gap of TiO2. The experimental results of photocatalytic hydrogen generation from methanol-reforming showed that the Co- doping does not affect the photocatalytic activity of both Pt/Co-TiO2 catalysts. Despite that, the Pt/Co-TiO2-HT was the best photocatalyst under simulated solar light and show a maximum hydrogen evolution rate of 317 ± 44 μmol h-1. Other: Based on the experimental results, a possible mechanism for the continuous photocatalytic activity of Pt/Co-TiO2 photocatalysts under simulated solar light is proposed.
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