Ting Xia

Hydrogenated TiO2 Nanocrystals: A Novel Microwave Absorbing Material

Here, we report, for the first time, hydrogenated TiO2 nanocrystals as a novel and exciting microwave absorbing material, based on an innovative collective-movement-of-interfacial-dipole mechanism which causes collective-interfacial-polarization-amplified microwave absorption at the crystalline/disordered and anatase/rutile interfaces. This mechanism is intriguing and upon further exploration may trigger other new concepts and applications.

Built-in Electric Field-Assisted Surface-Amorphized Nanocrystals for High-Rate Lithium-Ion Battery

High-power batteries require fast charge/discharge rates and high capacity besides safe operation. TiO2 has been investigated as a safer alternative candidate to the current graphite or incoming silicon anodes due to higher redox potentials in effectively preventing lithium deposition. However, its charge/discharge rates are reluctant to improve due to poor ion diffusion coefficients, and its capacity fades quickly with rate as only thinner surface layers can be effectively used in faster charge/discharge processes. Here, we demonstrate that surface-amorphized TiO2 nanocrystals greatly improve lithium-ion rechargeable battery performance: 20 times rate and 340% capacity improvement over crystalline TiO2 nanocrystals. This improvement is benefited from the built-in electric field within the nanocrystals that induces much lower lithium-ion diffusion resistance and facilitates its transport in both insertion and extraction processes. This concept thus offers an innovative and general approach toward designing battery materials with better performance.

Directional Heat Dissipation across the Interface in Anatase–Rutile Nanocomposites

Understanding the structures and properties of interfaces in (nano-)composites helps to reveal their important influence on reactivity and overall performance. TiO2 is a technologically important material, and anatase/rutile TiO2 composites have been shown to display enhanced photocatalytic performance over pure anatase or rutile TiO2. This has been attributed to a synergistic effect between the two phases, but the origin of this effect as well as the structure of the interface has not been established. Using Raman spectroscopy, here we provide evidence of distinct differences in the thermal properties of the anatase and rutile moieties in the composite, with anatase becoming effectively much warmer than the rutile phase under laser irradiation. With the help of first-principles calculations, we analyze the atomic structure and unique electronic properties of the composite and infer possible reasons for the directional heat dissipation across the interface.

Hydrogenated black ZnO nanoparticles with enhanced photocatalytic performance

Following our previous findings on hydrogenated black TiO2 nanoparticles, here, we would like to present our exciting findings on hydrogenated black ZnO nanoparticles, which have displayed long-wavelength absorption and excellent photocatalytic performance. This further demonstrates that hydrogenation is a powerful tool to enhance the optical and photocatalytic performance of nanomaterials.

Strong Microwave Absorption of Hydrogenated Wide Bandgap Semiconductor Nanoparticles

Electromagnetic interactions in the microelectronvolt (μeV) or microwave region have numerous important applications in both civil and military fields, such as electronic communications, signal protection, and antireflective coatings on airplanes against microwave detection. Traditionally, nonmagnetic wide-bandgap metal oxide semiconductors lack these μeV electronic transitions and applications. Here, we demonstrate that these metal oxides can be fabricated as good microwave absorbers using a 2D electron gas plasma resonance at the disorder/order interface generated by a hydrogenation process. Using ZnO and TiO2 nanoparticles as examples, we show that large absorption with reflection loss values as large as -49.0 dB (99.99999%) is obtained in the microwave region. The frequency of absorption can be tuned with the particle size and hydrogenation condition. These results may pave the way for new applications for wide bandgap semiconductors, especially in the μeV regime.

Structural evolution from TiO2 nanoparticles to nanosheets and their photocatalytic performance in hydrogen generation and environmental pollution removal

The rapid depletion of the fossil fuel reserves, and the increase of green-house gas emissions and other environmental pollutants, bring up an urgent need for the development of clean energy and sustainable environmental solutions. The ability to use sunlight to produce fuels such as H2 from abundant, non-toxic resources, and to decompose environmental pollutants with benign photocatalysts, would revolutionize our civilization. TiO2 has attracted substantial interest due to its activity for generating hydrogen from water under ultraviolet (UV) light irradiation. The discovery of (001) facet control with the fluoride additive in the reactants has triggered intensive studies for model photocatalysis. Here, we found that small TiO2 nanoparticles were formed at the very beginning stage of the reaction, then were transformed into large TiOF2 crystals, and finally turned into (001)-faceted TiO2 nanosheets. TiOF2 acted as a metastable intermediate medium in the transformation from TiO2 nanoparticles into (001)-faceted TiO2 nanosheets. The (001) face showed higher activity for the photocatalytic generation of hydrogen and the photodecomposition of methylene blue and rhodamine B. The synergic effect between TiOF2 and TiO2 nanosheets or nanoparticles further improved the photocatalytic activities. This study provides us with a promising solution for solving the energy and environment problems.