Visible light-sensitive TiO₂-based nanomaterials are widely investigated for photocatalytic applications under high power (≥300 W) UV and visible light. The formation of charge transfer complexes (CTCs) between bidentate ligands and nanocrystalline TiO₂ promotes visible light absorption and constitutes a promising alternative for environmental remediation under reduced visible light power. However, the efficiency of photodegradation, the volatilization profile of bidentates, and the role of reactive oxidizing species (ROS) are not fully understood. In this study, thermogravimetric analyses coupled with mass spectroscopy (TGA-MS) were performed on TiO₂-Acetylacetone (ACAC) CTC. TiO₂-ACAC CTC calcined at 300 °C (TiO₂-A300) was applied for the photocatalytic degradation of chlorophenol (4-CP) and tetracycline (TC) under low power visible light (26 W). Furthermore, the ROS scavengers isopropanol and benzoquinone were added for studying the photocatalytic role of •OH and ^•O₂⁻ radicals. The TGA-MS showed the release of ACAC fragments, such as ethyl ions and acetone, in the range between 150 °C and 265 °C, while between 300 °C and 450 °C only CO₂ and H₂O were released during oxidation of ACAC. The photocatalytic abatement of tetracycline (68.6%), performed by TiO₂-A300, was ~two times higher than that observed for chlorophenol (31.3%) after 6 h, indicating a distinct participation of ROS in the degradation of these pollutants. The addition of the ROS scavenger revealed ^•O₂⁻ radicals as primarily responsible for the high efficiency of TiO₂-ACAC CTC under reduced visible light. On the other hand, the •OH radicals are not efficiently generated in the CTC. Therefore, the development of heterostructures based on TiO₂-ACAC CTC can increase the generation of ROS through coupling with semiconductors capable of generating •OH under visible light.

The improvement of photocatalytic activity of TiO₂-based nanomaterials is widely investigated due to the tentative of their industrialization as environmental photocatalysts and their inherently low solar spectrum sensitivity and rapid recombination of charge carriers. Coupling of oxygen-based bidentate diketone to nanocrystalline TiO₂ represents a potential alternative for improving the holdbacks. Formation of TiO₂-acetylacetone charge transfer complex (CTC) by sol-gel route results in a hybrid semiconductor material with photodegradation activity against toxic NO_x gas. In this research, the influence of the chelating agent acetylacetone (ACAC) content on the CTC photocatalytic efficiency under visible light was evaluated. A high content of ACAC in the CTC is not a decisive factor for efficiency of photocatalytic reactions. In fact, the highest efficiency for NO_x degradation (close to 100%, during 1 h of visible light exposure) was reported for the material calcined in air at 300 °C with the content of strongly bonded acetylacetone not higher than 3 wt.%. Higher calcination temperature (400 °C) left TiO₂ almost completely depleted in ACAC, while at the highest applied temperature (550 °C) a portion of anatase was transformed into rutile and the sample is free of ACAC. The analyses pointed out that superoxide anion radical (O₂⁻) plays an active role in photo-oxidation of NO_x. Our findings indicate that this CTC has both high visible light spectral sensitivity and photocatalytic efficiency.

Novel hybrid core-shell structures, in which up-converting (UC) NaYF₄:Yb,Tm core converts near-infrared (NIR) to visible (Vis) light via multiphoton up-conversion processes, while anatase TiO₂-acetylacetonate (TiO₂-Acac) shell ensures absorption of the Vis light through direct injection of excited electrons from the highest-occupied-molecular-orbital (HOMO) of Acac into the TiO₂ conduction band (CB), were successfully synthesized by a two-step wet chemical route. Synthesized NaYF₄:Yb,Tm@TiO₂-Acac powders were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, diffuse-reflectance spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence emission measurement. Tetracycline, as a model drug, was used to investigate the photocatalytic efficiencies of the core-shell structures under irradiation of reduced power Vis and NIR spectra. It was shown that the removal of tetracycline is accompanied by the formation of intermediates, which formed immediately after bringing the drug into contact with the novel hybrid core-shell structures. As a result, ~80% of tetracycline is removed from the solution after 6 h.

The increasing insertion of intermittent energy sources into the energy grid is leading to new challenges in terms of stability and control of such systems. In this scenario, mechanisms capable to store energy can be employed to improve its quality. The use of a Flywheel Energy Storage System (FESS) is suitable for applications requiring high power density for short periods of time. This article presents the modeling, simulation and analyzes for the control of a Variable Reluctance Machine applied to a FESS, as well as its connection to the power grid through a back-to-back converter. The control of the DC-link is made by the grid side converter, while the machine side converter controls the current injected into the grid/consumed by the machine. Matlab/Simulink ^® was used in the modeling, and the results show bidirectional operation, with good performance of the designed controllers.