Ultrafast Synthesis of Urchin-Like Rutile TiO₂ by Single-Step Microwave-Assisted Method

Progress in Preparation of Sea Urchin-like Micro-/Nanoparticles

Urchin-like microparticles/nanoparticles assembled from radial nanorods have a good appearance and high specific surface area, providing more exposed active sites and shortening the diffusion path of photoexcited carriers from the interior to the surface. The interfacial interaction and physical and chemical properties of the materials can be improved by the interfacial porous network induced by interlacing nano-branches. In addition, multiple reflections of the layered microstructure can absorb more incident light and improve the photocatalytic performance. Therefore, the synthesis and functionalization of three-dimensional urchin-like nanostructures with controllable size, shape, and hierarchy have attracted extensive attention. This review aims to provide an overview to summarize the structures, mechanism, and application of urchin-like microparticles/nanoparticles derived from diverse synthesis methods and decoration types. Firstly, the synthesis methods of solid urchin-like micro-/nanoparticles are listed, with emphasis on the hydrothermal/solvothermal method and the reaction mechanism of several typical examples. Subsequently, the preparation method of composite urchin-like micro-/nanoparticles is described from the perspective of coating and doping. Then, the research progress of urchin-like hollow microspheres is reviewed from the perspective of the step-by-step method and synchronous method, and the formation mechanism of forming urchin-like hollow microspheres is discussed. Finally, the application progress of sea urchin-like particles in the fields of photocatalysis, electrochemistry, electromagnetic wave absorption, electrorheological, and gas sensors is summarized.

Ag/GO/TiO2nanocomposites: the role of the interfacial charge transfer for application in photocatalysis

TiO₂semiconductor nanoparticles (NPs) in the anatase phase have presented limitations of application in photocatalysis, mainly due to the fast recombination of photoexcited electrons. The combination with other nanoparticles/nanostructures has been shown to be a promising solution for increasing photocatalytic efficiency. In this work, titanium dioxide (TiO₂) nanoparticles in different crystalline phases were prepared through a rapid microwave-assisted synthesis and modified by silver nanoparticles (Ag) and graphene oxide (GO). The samples were characterized by x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, infrared spectroscopy and gas adsorption. Crystalline anatase NPs were obtained in basic conditions (pH = 8) while in acidic conditions (pH = 1), single-crystalline rutile NPs were formed. Different previous drying methods: oven and freeze-drying used led to a differentiation in crystallographic phases obtained. Anatase TiO₂and anatase-rutile mixture NPs calcined at 400 °C showed properties as high specific surface area, crystallinity and reduced electron-hole recombination which contributed to an enhanced photocatalytic activity, when compared to the Degussa P25 photoactivity. The effect of silver nanoparticles and GO addition to TiO₂nanopowder was evaluated for photocatalysis activity. An improvement in the methylene blue and rhodamine B dyes photodegradation was observed for both anatase and rutile TiO₂nanocomposites. We noted that anatase TiO₂nanoparticles degraded 53% of rhodamine B, and when functionalized with GO, the photodegradation increased to 69%. Comparatively, the addition of silver nanoparticles to anatase TiO₂increased the dye degradation to 97% in 180 min. Hence, we revel that in the TiO₂nanocomposites, silver nanoparticles showed better interfacial charge transfer than GO, contributing more effectively to the dye photodegradation process.