An annular UV photocatalytic reactor with recirculation in batch was designed and built. The design considered low construction, simple operation and maintenance costs, availability and durability of the materials used, easy cleaning, and high standards of hygiene and safety. The TiO2 photocatalysts were synthesized by plasma electrolytic oxidation (PEO) on commercial Ti rings were compared with coatings obtained on Ti plates as a reference, and no influence of the substrate geometry on the morphology, crystallinity, or bandgap of the coatings was observed. The efficiency of the photocatalytic reactor using 10 TiO2-coated rings was tested by Cr(VI) transformation in the presence of EDTA. The Cr(VI) transformation after 5 h irradiation attained 95%; a rather high photocatalytic activity (62%) was maintained after the third use of the rings without reactivation of the photocatalyst. These coatings synthesized by PEO have not been applied in modular photocatalytic reactors until now.
The increasing demand for high-performance Wide-Bandgap (WBG) semiconductors, including GaN, SiC, and emerging Ultrawide-Bandgap (UWBG) materials such as Ga2O3 and diamond, has driven significant advancements in epitaxial growth techniques. However, achieving scalability, defect-free growth, and sustainability remains a major challenge. This review systematically evaluates Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), and other novel growth and hybrid growth techniques, emphasizing energy efficiency, defect control, and environmental impact. Industry 4.0-driven AI-based process optimization and closed-loop recycling have emerged as transformative strategies, reducing waste and improving manufacturing efficiency. Key findings reveal that HVPE enables rapid defect-free GaN fabrication, Hot-Filament CVD enhances SiC growth with superior thermal properties, and Atomic Layer Epitaxy (ALE) achieves sub-nanometer precision crucial for next-generation quantum and RF applications. Despite these advancements, p-type doping in UWBG materials, substrate compatibility, and thermal management remain unresolved challenges. Future research must focus on scalable eco-friendly epitaxy, novel doping mechanisms, and policy-driven sustainability efforts. This review provides a comprehensive roadmap for sustainable WBG semiconductor manufacturing, bridging materials innovation, energy efficiency, and industrial adoption to support the next generation of power electronics and optoelectronics.
Using examples from indigenous art in Brazil, this paper demonstrates that these works contain “hidden mathematics” (such as symmetry, striped ornaments, rows, etc.), which challenges the traditional notion of “primitive art”.
Although photocatalytic degradation of VOCs has attracted widespread attention, the efficient visible-light-driven photocatalytic degradation performance remains a challenge. This work presents the visible-light-driven photocatalytic degradation of gaseous toluene over B, Gd co-doped TiO2 nanotube arrays prepared via a controllable electrochemistry method. It was found that B and Gd co-doping strategy not only enhances the visible light responsiveness of TiO2 nanotube arrays but also introduces moderate oxygen vacancies on the surface of TiO2, which is beneficial to the formation of free hydroxyl radicals and their attack on toluene molecules. The doping order also affects the photocatalytic performance. The optimized sample achieves an enhanced degradation efficiency for toluene under visible light irradiation and exhibits considerable stability. This work may provide an efficient TiO2-based photocatalyst for the removal of volatile organic compounds for air purification and give an understanding of the mechanism of photocatalytic degradation of toluene over co-doping TiO2.
