Zhao Deng

Tailoring CuO nanostructures for enhanced photocatalytic property

We report on one-pot synthesis of various morphologies of CuO nanostructures. PEG200 as a structure directing reagent under the synergism of alkalinity by hydrothermal method has been employed to tailor the morphology of CuO nanostructures. The CuO products have been characterized by XRD, SEM, and TEM. The morphologies of the CuO nanostructures can be tuned from 1D (nanoseeds, nanoribbons) to 2D (nanoleaves) and to 3D (shuttle-like, shrimp-like, and nanoflowers) by changing the volume of PEG200 and the alkalinity in the reaction system. At neutral and relatively low alkalinity (OH(-)/Cu(2+)≤3), the addition of PEG200 can strongly influence the morphologies of the CuO nanostructures. At high alkalinity (OH(-)/Cu(2+)≥4), PEG200 has no influence on the morphology of the CuO nanostructure. The different morphologies of the CuO nanostructures have been used for the photodecomposition of the pollutant rhodamine B (RhB) in water. The photocatalytic activity has been correlated with the different nanostructures of CuO. The 1D CuO nanoribbons exhibit the best performance on the RhB photodecomposition because of the exposed high surface energy {-121} crystal plane. The photocatalytic results show that the high energy surface planes of the CuO nanostructures mostly affect the photocatalytic activity rather than the morphology of the CuO nanostructures. Our synthesis method also shows it is possible to control the morphologies of nanostructures in a simple way.

Well-Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro-Meso-Macropore Systems Showing Enhanced Catalytic Performance

Preparation and characterization of well-organized zeolitic nanocrystal aggregates with an interconnected hierarchically micro-meso-macro porous system are described. Amorphous nanoparticles in bimodal aluminosilicates were directly transformed into highly crystalline nanosized zeolites, as well as acting as scaffold template. All pores on three length scales incorporated in one solid body are interconnected with each other. These zeolitic nanocrystal aggregates with hierarchically micro-meso-macroporous structure were thoroughly characterized. TEM images and (29)Si NMR spectra showed that the amorphous phase of the initial material had been completely replaced by nanocrystals to give a micro-meso-macroporous crystalline zeolitic structure. Catalytic testing demonstrated their superiority due to the highly active sites and the presence of interconnected micro-meso-macroporosity in the cracking of bulky 1,3,5-triisopropylbenzene (TIPB) compared to traditional zeolite catalysts. This synthesis strategy was extended to prepare various zeolitic nanocrystal aggregates (ZSM-5, Beta, TS-1, etc.) with well-organized hierarchical micro-meso-macroporous structures.

Walnut-like Porous Core/Shell TiO2 with Hybridized Phases Enabling Fast and Stable Lithium Storage

TiO2 is a promising and safe anode material for lithium ion batteries (LIBs). However, its practical application has been plagued by its poor rate capability and cycling properties. Herein, we successfully demonstrate a novel structured TiO2 anode with excellent rate capability and ultralong cycle life. The TiO2 material reported here shows a walnut-like porous core/shell structure with hybridized anatase/amorphous phases. The effective synergy of the unique walnut-like porous core/shell structure, the phase hybridization with nanoscale coherent heterointerfaces, and the presence of minor carbon species endows the TiO2 material with superior lithium storage properties in terms of high capacity (∼177 mA h g-1 at 1 C, 1 C = 170 mA g-1), good rate capability (62 mA h g-1 at 100 C), and excellent cycling stability (∼83 mA h g-1 was retained over 10 000 cycles at 10 C with a capacity decay of 0.002% per cycle).

Three‐Dimensionally Ordered Macroporous Titania with Structural and Photonic Effects for Enhanced Photocatalytic Efficiency

The three dimensional photonic crystals concept has been employed for photocatalysis. Slow photons observed in photonic crystal structures will enhance the absorption of materials when the photon energy matches the absorbance of the materials, which would improve the photocatalytic efficiency. In this work, three dimensionally ordered macroporous (3DOM) titania was prepared by applying the colloidal templating method with a range of pore diameters. Calcination at different temperatures to remove the templates resulted in different crystalline phases. The structural and photonic properties were characterized and their effects on photocatalytic activity are presented as well. A strong effect of the pore diameter on the photocatalytic activity was observed and correlated with the photon energy involved in the photodegradation process of organics. A very interesting phenomenon was also observed: the sample prepared by using PS spheres of 250 nm had a high photocatalytic efficiency, which mismatched the effect of pore diameter, probably owing to the slow photon effect.

Self-templated synthesis of microporous CoO nanoparticles with highly enhanced performance for both photocatalysis and lithium-ion batteries

Discrete and uniform microporous CoO nanoparticles with open nanochannels around 1 nm were one-pot synthesized by the self gas-leaching method via the thermal decomposition of a Co–oleylamine complex. CoO particle-sizes can be tuned from 50 to 13 nm by controlling the concentration of the cobalt precursor, accompanying a change of the long and winding nanochannels to short and straight nanochannels. It was shown that exposing the particle interiors to external active reactants via the shorter and straighter microporous nanochannels in smaller CoO nanoparticles can greatly enhance their photocatalytic efficiency. Most importantly, all the as-synthesized microporous CoO nanoparticles showed a very highly reversible capacity and cycling stability for lithium storage. The discharge and charge capacities of the microporous CoO sample with short straight nanochannels and the smallest particle size (1432.8 and 1200 mA h g−1, respectively) are up to two times higher than those of the commercial CoO powder (673.7 and 539 mA h g−1, respectively) and that of the theoretical value of CoO (715 mA h g−1) owing to the enlarged surface area, very small particle size for increased electrode and electrolyte contact and the heightened diffusion efficiency in short nanochannels for electrolyte and Li ions. The presence of microporous voids could effectively buffer the stress induced during lithium insertion–deinsertion alleviating the pulverization of electrode material, thereby giving extraordinary cycling stability.

Facile and fast synthesis of porous TiO2 spheres for use in lithium ion batteries

Porous anatase TiO2 spheres have been synthesized by a microwave-assisted hydrothermal reaction of spherical particle precursors followed by annealing in air. The synthesized TiO2 spheres are formed by interconnected nanocrystals with size of 8.7 nm in average and have grain diameters of 250-400 nm. After annealing at 500°C, the TiO2 samples maintain spherical shape and develop highly mesoporous characteristics with a specific surface area of 151 m(2) g(-1). The TiO2 samples annealed at 750°C consist of larger aggregated particles with diameters of 500-900 nm and still retain mesoporous anatase structure, but with a reduced specific surface area of 25.6 m(2) g(-1). Electrochemical studies reveal that the porous TiO2 spheres annealed at 500°C own very high and stable lithium ion (Li(+)) storage capacities of 207, 184, 166, and 119 mA h g(-1) at 0.5, 1, 2, and 5C (850 mA g(-1)) rates, respectively, owing to their highly porous nanostructures and fine spherical morphology. In contrast, the TiO2 spheres annealed at 700°C exhibit modest electrochemical performance due to their reduced pore structures and larger crystallite size. The prepared porous TiO2 spherical particles show great promise for use as high performance anode materials for lithium ion batteries (LIBs).

High photocatalytic activity enhancement of titania inverse opal films by slow photon effect induced strong light absorption

The photonic effect on the photocatalytic activity of the continuous titania inverse opal (TiO2-IO) films differing only by the air sphere size (185 and 165 nm) and prepared by a colloid crystal template approach and annealing at different temperatures (700 and 800 °C) has been investigated by aqueous solution degradation of dye pollutants using mesoporous TiO2 thin films as the reference. The high quality of TiO2 inverse opal films has been confirmed by a blue shift of the Photonic Band Gap (PBG) with increasing light incident angle. Excellent agreement was found between theoretical and experimental reflectance spectra, confirming the photonic crystal structure of the samples. The slow photon light absorption enhancement effect inducing highly improved photocatalytic degradation of dye pollutants has been revealed in an aqueous reaction system. When compared with the mesoporous (m-TiO2) films obtained under the same conditions, all the TiO2-IO films demonstrate a much higher photocatalytic activity. At a light incident angle of 0°, the TiO2-IO-700 film (air sphere size: 185 nm) showed a better photocatalytic activity than that of TIO2-IO-800 (air sphere size: 165 nm). Most importantly, with increasing light incident angle, the photocatalytic activity of the TiO2-IO-700 film decreases whilst that of the TiO2-IO-800 film increases sharply due to the enhancement of light absorption related to a slow photon effect, generating more electron-holes. The present work revealed that photocatalytic activity can be dramatically enhanced by utilizing slow photons located at the PBG edges with energies close to the electronic bandgap of the semiconductor. The study using the slow-photon effect on the basis of photonic crystals to improve the photocatalytic activity by enhancing the light absorption could be an important future research direction. The slow-photon effect can open a new exciting avenue to all the fields related to light absorption including solar cells, optical telecommunications and optical computing.

Facile synthesis of hierarchical and porous V2O5 microspheres as cathode materials for lithium ion batteries

Hierarchical and porous V2O5 microspheres have been fabricated by a refluxing approach followed by annealing in air. The resulting porous V2O5 microspheres typically have diameters of 3-6 μm and are constructed of intertwined laminar nanocrystals or crosslinked nanobricks. It is found that the vanadyl glycolates rinsed with water have pronounced pore structures than that rinsed with ethanol alone. In addition, the configuration of the vanadyl glycolates microspheres can be tuned during the refluxing along with stirring. The possible formation processes of the vanadyl glycolates and V2O5 products have been discussed based on the experimental data. Electrochemical tests indicate that the hierarchical and porous V2O5 microspheres exhibit relatively high and stable Li(+) storage properties. The porous V2O5 microspheres assembled by intertwined nanoparticles maintain reversible Li(+) storage capacities of 102 and 80 mAh g(-1), respectively; whilst the porous V2O5 microspheres assembled by crosslinked nanobricks maintain reversible Li(+) storage capacities of 100 and 85 mAh g(-1) over 100 cycles at current rates of 0.5 and 1 C, respectively. The superior Li(+) storage performance of the hierarchical and porous V2O5 microspheres could mainly be ascribed to the improved electrode/electrolyte interface, reduced Li(+) diffusion paths, and relieved volume variation during lithiation and delithiation processes.

Three-Dimensional (3D) Bicontinuous Hierarchically Porous Mn2O3 Single Crystals for High Performance Lithium-Ion Batteries.

Bicontinuous hierarchically porous Mn2O3 single crystals (BHP-Mn2O3-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn2O3-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn2O3-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn2O3-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g−1 at 100 mA g−1 after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g−1 at 1 Ag−1). These values are among the highest reported for Mn2O3-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn2O3-SCs are suitable for charge transfer at the electrode/electrolyte interface.

A stable, reusable, and highly active photosynthetic bioreactor by bio-interfacing an individual cyanobacterium with a mesoporous bilayer nanoshell.

An individual cyanobacterium cell is interfaced with a nanoporous biohybrid layer within a mesoporous silica layer. The bio-interface acts as an egg membrane for cell protection and growth of outer shell. The resulting bilayer shell provides efficient functions to create a single cell photosynthetic bioreactor with high stability, reusability, and activity.