Yolk-shell TiO2 Research Articles

Unique kinetics feature and excellent photocatalytic performance of tetracycline photodegradation using yolk-shell TiO2@void@TiO2:Eu3+

The multifunctional yolk-shell TiO2 @void@TiO2:Eu3+ calcined at different temperatures were successfully fabricated by sacrificial template method for the photodegradation of tetracycline. The impacts of yolk-shell and calcination temperature on the photoluminescence and photocatalytic properties have been investigated in detail. The photoluminescence results show that sample calcined at 800 °C exhibits the strongest red emission. The photocatalytic efficiency for tetracycline reached 90.34 % in 50 min at 20 mg/L TC solution by sample calcined at 900 °C. The kinetics fitting curves is with different slopes, which is reported for the first time so far. Meanwhile, the photocatalytic mechanism and possible photodegradation pathway of tetracycline were proposed. Compared with the double-shell samples, the yolk-shell samples show a high photodegradation rate within 5 min and unique kinetics feature. The analysis of photocatalytic kinetics provides a new idea for studying the photocatalysis mechanism. The rapid tetracycline photodegradation by the yolk shell material also provides new strategies for practical water purification.

Optimizing inner voids in yolk-shell TiO2 nanostructure for high-performance and ultralong-life lithium-sulfur batteries

The TiO 2 nanosheets constructed yolk-shell sulfur-TiO 2 (S@void@TiO 2 ) architecture with optimized inner voids demonstrates high-performance and ultralong-life for Li-S battery. • Designing TiO 2 nanosheets constructed yolk-shell TiO 2 (S@void@TiO 2 ) nanostructure for Li-S battery. • Verifying intense chemical interaction via the hybridization of Li 1 s, S 2p and O 2p orbitals in S@void@TiO 2. • Optimizing the inner voids for volume expansion to guarantee the cathode integrity. • Improving the electrolyte wettability and Li + kinetics in S@void@TiO 2. • Realizing high capacity and long cycle with a small capacity decay for Li-S battery. A TiO 2 nanosheets constructed yolk-shell architecture with tunable inner voids is designed and prepared as sulfur host for high-performance and ultralong-life Li-S battery. With the integration of TiO 2 nanosheets to form yolk-shell sulfur-TiO 2 (S@void@TiO 2 ) architecture with controllable inner voids, the S@void@TiO 2 composite with optimized inner voids provides sufficient contacting sites to improve the utilization of insulating sulfur and allows sulfur to freely expand without destroying the electrode. In particular, the density functional theory (DFT) calculations from molecular level reveal that the hybridization of Li 1s, S 2p and O 2p orbitals ensures the effective chemisorption between polysulfides and TiO 2 with long-term cycling stability. Consequently, the optimized S@void@TiO 2 electrode maintains a capacity of 766 mAhg −1 after 1000 cycles at 0.2C. Even at 2C for 400 cycles, the capacity still retains at 511 mAhg −1 , representing the best results of TiO 2 -based nanostructures for Li-S batteries. This work illustrates that carefully design novel yolk-shell structure is important to address the shortages of sulfur-based cathodes for advanced Li-S battery.

Synthesis of 3D CQDs/urchin-like and yolk-shell TiO2 hierarchical structure with enhanced photocatalytic properties

A novel CQDs/TiO2 hierarchical structure with enhanced photocatalytic properties was achieved by uniformly decorating urchin-like and yolk-shell TiO2 microspheres (UYTMs) with carbon quantum dots (CQDs) through an environmentally friendly hydrothermal process. The CQDs were firstly synthesized by the electrochemical method, and the TEM, Raman and PL characterizations strongly indicated that the as-prepared CQDs exhibited good dispersion, high crystallinity and unique up-conversion properties. The UYTMs synthesized by a NaOH-assisted hydrothermal process showed stable 3D hierarchical structure and large surface area, which was beneficial for light absorption and contacting with contamination. The good combination of CQDs and UYTMs was further successfully achieved during the hydrothermal process, and demonstrated by a series of tests. The photocatalytic experiments suggested that the CQDs/UYTMs exhibited better photocatalytic activities than the pure UYTMs and P25 under both visible and UV light irradiation. The CQDs/UYTMs combining with 6 wt% of CQDs showed the best photocatalytic efficiency, while excessive CQDs tended to inhibit the photocatalytic activity. According to the results and discussions, a possible mechanism in improving the photocatalytic efficiency of the CQDs/UYTMs is significantly proposed. The up-conversion property of CQDs can broaden the absorption spectrum of CQDs/UYTMs to the visible light. Moreover, the CQDs, as the electron reservoirs, are efficient to separate the electrons and holes, leading to an improved photocatalytic activity of CQDs/UYTMs.

Synthesis of urchin-like and yolk–shell TiO2 microspheres with enhanced photocatalytic properties

ABSTRACTThe novel urchin-like and yolk–shell titania microspheres (henceforth called UYTMs) with nanowires/microspheres hierarchical structures were successfully synthesized by a synthetic sol–gel and hydrothermal method without using any template. Uniform TiO2 microspheres were firstly prepared by the sol–gel method, and the great monodispersed properties was delicately regulated by using the surfactant of KCl, aniline and a proper amount of water. The urchin-like yolk–shell morphology was further achieved by a NaOH-assisted hydrothermal process, and the diameter and shell thickness of the UYTMs were highly controlled by the concentration of NaOH. The detailed morphology, chemical composition and crystallinity of the UYTMs were systematically characterized by several techniques, and the underlying formation mechanisms was attentively discussed as well. The photodegradation of methylthionine chloride experiments indicated the UYTMs showed much better photocatalytic activity than that of commercial P25. This is mainly because the UYTMs exhibited much more reactive sites, higher adsorption ability and tuned optical absorption behaviour owing to their large specific surface area, hierarchical structures and the special hollow yolk–shell structure.

Anchoring ultrafine metallic and oxidized Pt nanoclusters on yolk-shell TiO2 for unprecedentedly high photocatalytic hydrogen production

We demonstrate an alkali modification process to produce highly dispersed ultrafine Pt nanoclusters with metallic Pt0 and oxidized Pt2+ species as co-catalyst anchored on nanosheet-constructed yolk-shell TiO2 (NYTiO2-Pt) acting as light harvesting reactor for highly efficient photocatalytic H2 production. Benefiting from the high surface area, highly dispersed ultrafine Pt nanoclusters (~0.6nm) with Pt0 and Pt2+ species and special nanosheet-constructed yolk-shell structure, this novel light harvesting reactor exhibits excellent performance for photocatalytic H2 production. The NYTiO2-Pt-0.5 (0.188wt% Pt) demonstrates an unprecedentedly high H2 evolution rate of 20.88mmolh−1g−1 with excellent photocatalytic stability, which is 87 times than that of NYTiO2-Pt-3.0 (0.24mmolh−1g−1, 1.88wt% Pt), and also much higher than those of other TiO2 nanostructures with the same Pt content. Such H2 evolution rate is the highest reported for photocatalytic H2 production with such a low Pt content under simulated solar light. Our strategy here suggests that via alkali modifying the photocatalysts, we can not only enhance the H2 production for solar energy conversion but also significantly decrease the noble metal content for cost saving.

One-pot hydrothermal synthesis of yolk–shell structured TiO2 mesoporous microspheres with enhanced gas sensing and photocatalytic performance

A one-pot hydrothermal synthesis of yolk–shell structured TiO2 mesoporous microspheres was demonstrated. Titanium sulfate was used as titanium source, urea and ammonium fluoride were used as morphology-controlling agents. The synthesis process was economical and environmental-friendly. Various characterization techniques were employed to clarify the micro-morphological features of the yolk–shell TiO2 microspheres. By controlling the reaction time, the microspheres with tunable interior structure from solid to yolk–shell structure was obtained. The possible formation mechanism of the yolk–shell TiO2 microspheres was discussed in detail according to a series of contrast experiments. Importantly, the yolk–shell TiO2 microspheres were successfully applied as gas sensing material for the first time. Thanks to the distinctive configuration (hollow interiors and porous shells), the yolk–shell TiO2 microspheres exhibited an obvious improvement in response to acetone compared with the solid TiO2 mesoporous microspheres and mono-morphological TiO2 nanoparticles. Moreover, the yolk–shell TiO2 microspheres also showed a potential application in the field of photocatalysis. This work not only provides a new approach for the synthesis of yolk–shell TiO2 with tunable interior structure, but also offers a new material platform for gas sensing application.

Yolk-Shell TiO2@C Nanocomposite as High-Performance Anode Material for Sodium-Ion Batteries.

Yolk-shell TiO2@C nanocomposites have been synthesized successfully through a simple self-catalyzing solvothermal method. The structural and morphological characterizations reveal that TiO2@C nanocomposite has a yolk-shell microsphere morphology with diameters of 1-2 μm, and both yolk and shell are composed of TiO2 nanoparticles (∼10 nm). The as-prepared yolk-shell TiO2@C composites exhibit superior sodium storage properties, with a specific capacity of 210 mAh g-1, an outstanding cycle life of 85% capacity retention of 2000 cycles and extraordinary rate performance at 40 C rate. All the results indicate that the yolk-shell TiO2@C nanocomposite can be suggested as a promising anode material for high-performance sodium-ion batteries.

Constructing graphite-like carbon nitride modified hierarchical yolk–shell TiO2 spheres for water pollution treatment and hydrogen production

Here we present a new visible light active composite based on porous graphitic carbon nitride decorated hierarchical yolk–shell TiO2 spheres for water pollution treatment and H2 evolution.

Hierarchical nanosheet-constructed yolk-shell TiO₂ porous microspheres for lithium batteries with high capacity, superior rate and long cycle capability.

A hierarchical nanosheet-constructed yolk-shell TiO2 (NYTiO2) porous microsphere is synthesized through a well-designed, one-pot, template-free solvothermal alcoholysis process using tetraethylenepentamine (TEPA) as the structure directing reagent. Such a yolk-shell structure with a highly porous shell and dense mesoporous core is quite advantageous as an anode material for lithium ion batteries (LIBs). The outer, 2D nanosheet-based porous (15 nm) shell and the nanocrystal-based inner mesoporous (3 nm) core provide a stable, porous framework, effective grain boundaries and a short diffusion pathway for Li(+) and electron transport, facilitating lithium insertion/extraction. The voids between the core and the shell can not only store the electrolyte due to capillary and facilitate charge transfer across the electrode/electrolyte interface but also buffer the volume change during the Li(+) insertion/extraction. As a result, NYTiO2 demonstrates excellent Li(+) capacity with outstanding cycle performance and superior rate capability at different rates for >700 cycles, retaining a 225 mA h g(-1) reversible capacity after 100 cycles at 1 C. In particular, the reversible capacity can still be maintained at 113 mA h g(-1) after 100 cycles at 10 C. We also observe the formation of homogeneously distributed 5-10 nm Li2Ti2O4 nanocrystallites on the surface of the nanosheets during the discharge-charge process. The synergy of the yolk-shell structure with dual mesopores in the shell and core and the Li2Ti2O4 nanocrystallites endow the hierarchical NYTiO2 with high reversible capacity, excellent rate capability and outstanding cycle performance.

Template-free synthesis of homogeneous yolk–shell TiO2 hierarchical microspheres for high performance lithium ion batteries

The homogeneous yolk–shell TiO2 hierarchical microspheres (TiO2 HYSHMs) consisting of small nanoparticles have been fabricated through a facile template-free solvothermal reaction followed by calcination. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption/desorption analysis and Fourier transform infrared spectroscopy. It was found that the microspheres have porous shell (∼100 nm in thickness) composed of small nanoparticles with an average diameter of 10 nm. The interspace between the yolk and shell is ∼150 nm. The BET specific surface area and pore volume of the sample are 151.1 m2 g−1 and 0.23 cm3 g−1, respectively. Ostwald ripening processes are proposed to explain the growth mechanism of the TiO2 HYSHMs based on a series of time-dependent experiments. As the anode materials for the lithium ion batteries, TiO2 HYSHMs exhibit a high initial discharge capacity of 267.6 mAh g−1 at 0.25 C and retain 191 mAh g−1 even after 40 cycles, indicating good electrochemical performance. These good electrochemical performances could be attributed to the short Li-ion and electron pathways, and enough elastic buffer space to accommodate large volume variation of the special yolk–shell hierarchical structure.

High-performance dye-sensitized solar cells based on hierarchical yolk–shell anatase TiO2beads

Yolk–shell TiO2 beads consisting of nanoparticles are synthesized by using a facile hydrothermal method. The influences of hydrothermal reaction temperature on the size of TiO2 particles and the photovoltaic performance of dye-sensitized solar cells (DSSCs) have been investigated in detail. A DSSC based on the yolk–shell TiO2 bead photoelectrode (∼15 μm) exhibits an energy conversion efficiency of 9.05%, which is much higher than that of P25 (7.56%). This can be mainly attributed to the fast electron transport and long electron lifetime resulting in a larger electron diffusion coefficient and higher charge collection efficiency for the former, which are confirmed by intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS). In addition, the superior light scattering ability of hierarchical yolk–shell TiO2 beads compared to P25 film measured by UV-vis diffuse spectrum also contributes to higher photocurrent and photovoltaic performance.