Shao-Zhuan Huang

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.

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.

Phases Hybriding and Hierarchical Structuring of Mesoporous TiO2 Nanowire Bundles for High-Rate and High-Capacity Lithium Batteries

A hierarchical mesoporous TiO2 nanowire bundles (HM‐TiO2‐NB) superstructure with amorphous surface and straight nanochannels has been designed and synthesized through a templating method at a low temperature under acidic and wet conditions. The obtained HM‐TiO2‐NB superstructure demonstrates high reversible capacity, excellent cycling performance, and superior rate capability. Most importantly, a self‐improving phenomenon of Li+ insertion capability based on two simultaneous effects, the crystallization of amorphous TiO2 and the formation of Li2Ti2O4 crystalline dots on the surface of TiO2 nanowires, has been clearly revealed through ex situ transmission electron microcopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), Raman, and X‐ray photoelectron spectroscopy (XPS) techniques during the Li+ insertion process. When discharged for 100 cycles at 1 C, the HM‐TiO2‐NB exhibits a reversible capacity of 174 mA h g−1. Even when the current density is increased to 50 C, a very stable and extraordinarily high reversible capacity of 96 mA h g−1 can be delivered after 50 cycles. Compared to the previously reported results, both the lithium storage capacity and rate capability of our pure TiO2 material without any additives are among the highest values reported. The advanced electrochemical performance of these HM‐TiO2‐NB superstructures is the result of the synergistic effect of hybriding of amorphous and crystalline (anatase/rutile) phases and hierarchically structuring of TiO2 nanowire bundles. Our material could be a very promising anodic material for lithium‐ion batteries.

Facile synthesis of well-shaped spinel LiNi0.5Mn1.5O4 nanoparticles as cathode materials for lithium ion batteries

Spinel LiNi0.5Mn1.5O4 (LNMO) nanoparticles with well-defined polyhedral shapes and mean sizes of ca. 200 nm have been synthesized via a solid-state route using α-MnO2 nanowires as reaction precursors. A structural reorganization is believed to be responsible for the morphology evolution from tetragonal α-MnO2 nanowires to spinel LNMO nanoparticles. Galvanostatic charge–discharge measurements indicate the LNMO nanoparticles exhibit a high initial discharge capacity of 129 mA h g−1 with an 88% capacity retention over 100 cycles at 1C (147 mA h g−1), superior to those of LNMO nanorod counterparts (116 mA h g−1). The superior electrochemical performance of LNMO nanoparticles can be ascribed to their narrow particle size distribution, less particle aggregation, intimate interparticle contact, increased electrical conductivity and lithium ion insertion–extraction kinetics due to the existence of oxygen deficiency and exposed {111} crystal facets.

Gas leaching as a path to build hierarchical core–corona porous alumina nanostructures with extraordinary pollutant treatment capacity

Hierarchical core–corona porous γ-Al2O3 nanostructures have been synthesized through the reaction of toluene diluted TMA with water by controlling the methane leaching. The obtained γ-Al2O3 core–corona nanostructures exhibit high thermal stability and excellent performance for polluted water treatment.

Probing the electrochemical behavior of {111} and {110} faceted hollow Cu2O microspheres for lithium storage

Transition metal oxides with exposed highly active facets have become of increasing interest as anode materials for lithium ion batteries, because more dangling atoms exposed at the active surface facilitate the reaction between the transition metal oxides and lithium. In this work, we probed the electrochemical behavior of hollow Cu2O microspheres with {111} and {110} active facets on the polyhedron surface as anodes for lithium storage. Compared to commercial Cu2O nanoparticles, hollow Cu2O microspheres with {111} and {110} active facets show a rising specific capacity at 30 cycles which then decreases after 110 cycles during the cycling process. Via advanced electron microscopy characterization, we reveal that this phenomenon can be attributed to the highly active {111} and {110} facets with dangling “Cu” atoms facilitating the conversion reaction of Cu2O and Li, where part of the Cu2O is oxidized to CuO during the charging process. However, as the reaction proceeds, more and more formed Cu nanoparticles cannot be converted to Cu2O or CuO. This leads to a decrease of the specific capacity. We believe that our study here sheds some light on the progress of the electrochemical behavior of transition metal oxides with respect to their increased specific capacity and the subsequent decrease via a conversion reaction mechanism. These results will be helpful to optimize the design of transition metal oxide micro/nanostructures for high performance lithium storage.