Morphology Control of TiO₂ Nanoparticle in Microemulsion and Its Photocatalytic Property

TiO₂ nanoparticles with controlled morphology and high photoactivity were prepared using a microemulsion-mediated hydrothermal method in this study, and the particles were characterized by means of TEM, XRD, BET, and BJH analysis. As the hydrothermal temperature is elevated, mean pore diameter, crystalline size, and crystallinity of the particles increase gradually, while the surface area decreases significantly, and the morphology changes from a spherical into a rod-like shape. The morphology transition mechanism of the TiO₂ crystal has been put forward based on a decrease in intensity of the microemulsion interface and an increase in collision efficiency between droplets with increasing the hydrothermal temperature. The photocatalytic activity of the TiO₂ particles synthesized at 120–200 °C is relatively low due to their weak crystallinity, though they have high surface area of 146–225 m²/g and small crystalline size of 6–10 nm. However, the TiO₂ samples prepared at 250–350 °C with low surface area (28–90 m²/g) exhibit high activity on the degradation of Rhodamine B (RhB), which is comparable or higher than that of the commercial P-25. The reason is ascribed to their high crystallinity that determines material activity in this temperature region. This study reveals that the effects of the surface area, crystallinity, and crystalline size on TiO₂ activity are interdependent, and the balance between these factors is important for improving the photoactivity of the catalyst

Rapidly Constructing Multiple AuPt Nanoalloy Yolk@Shell Hollow Particles in Ordered Mesoporous Silica Microspheres for Highly Efficient Catalysis

In this work, for the first time, AuPt alloy yolk@shell hollow nanoparticles (NPs) were constructed and simultaneously embedded into hollow interiors of a mesoporous silica microsphere based on a rapid aerosol process (AuPt@SiO₂). Resin nanospheres were utilized both as a hard template to create hollow interiors inside the mesoporous silica microspheres and as carriers to transport pregrown metal nanocrystals, AuPt alloy clusters, into the microspheres. Calcination removes the resin nanospheres and causes metal nanocrystals to embed into the hollow interiors of the silica microspheres. Due to the unique yolk@shell hollow structure of the AuPt nanoalloy, ordered mesopores (67 nm) in the silica support, the synergetic effect between the AuPt alloy and the high surface area and pore volume of the microspheres, the AuPt@SiO₂ spheres showed an excellent catalytic performance for styrene epoxidation with the conversion and selectivity of 85% and 87%, respectively. Notably, the novel catalyst showed a stable catalytic performance after five cycles of usage, suggesting the possible practical applications of the AuPt nanoalloy catalyst. In addition, the catalyst also exhibited a higher activity than the commercial Pt/C catalyst for the reduction reaction of 4-nitrophenol. The approach reported in this study could potentially be used to simplify the fabrication process of yolk@shell or hollow metal nanospheres, facilitating encapsulation of monometallic and multimetallic metal nanocrystals with various nanostructures and compositions into porous supports and thus guiding the design of catalysts with a special structure and high-performance

Interpenetrated Networks between Graphitic Carbon Infilling and Ultrafine TiO₂ Nanocrystals with Patterned Macroporous Structure for High-Performance Lithium Ion Batteries

Interpenetrated networks between graphitic carbon infilling and ultrafine TiO₂ nanocrystals with patterned macropores (100–200 nm) were successfully synthesized. Polypyrrole layer was conformably coated on the primary TiO₂ nanoparticles (∼8 nm) by a photosensitive reaction and was then transformed into carbon infilling in the interparticle mesopores of the TiO₂ nanoparticles. Compared to the carbon/graphene supported TiO₂ nanoparticles or carbon coated TiO₂ nanostructures, the carbon infilling would provide a conductive medium and buffer layer for volume expansion of the encapsulated TiO₂ nanoparticles, thus enhancing conductivity and cycle stability of the C–TiO₂ anode materials for lithium ion batteries (LIBs). In addition, the macropores with diameters of 100–200 nm in the C–TiO₂ anode and the mesopores in carbon infilling could improve electrolyte transportation in the electrodes and shorten the lithium ion diffusion length. The C–TiO₂ electrode can provide a large capacity of 192.8 mA h g^–1 after 100 cycles at 200 mA g^–1, which is higher than those of the pure macroporous TiO₂ electrode (144.8 mA h g^–1), C–TiO₂ composite electrode without macroporous structure (128 mA h g^–1), and most of the TiO₂ based electrodes in the literature. Importantly, the C–TiO₂ electrode exhibits a high rate performance and still delivers a high capacity of ∼140 mA h g^–1 after 1000 cycles at 1000 mA g^–1 (∼5.88 C), suggesting good lithium storage properties of the macroporous C–TiO₂ composites with high capacity, cycle stability, and rate capability. This work would be instructive for designing hierarchical porous TiO₂ based anodes for high-performance LIBs