Yurong Ma

Self-supported Li4Ti5O12 nanosheet arrays for lithium ion batteries with excellent rate capability and ultralong cycle life

Facile fabrication of well-aligned Li4Ti5O12 (LTO) nanosheet arrays grown directly on conductive Ti foil was achieved by hydrothermal growth in LiOH solution. The reaction between Ti foil and LiOH led to the growth of vertically aligned, rectangular lithium titanate oxide hydrate (H-LTO) nanosheet arrays, which could be converted into LTO nanosheet arrays through topotactic transformation via thermal decomposition. An appropriate LiOH concentration was essential for the formation of densely aligned H-LTO nanosheet arrays on the substrate. It was proposed that the formation of the H-LTO nanosheet arrays was through kinetics-controlled growth during the hydrothermal metal corrosion process. When used as a binder-free anode for LIBs, the self-supported LTO nanosheet arrays standing on Ti foil exhibited an excellent rate capability (a reversible capacity of 163 mA h g−1 and 78 mA h g−1 at 20 C and 200 C, respectively) and an outstanding cycling performance (a capacity retention of 124 mA h g−1 after 3000 cycles at 50 C). Furthermore, a flexible lithium ion battery, which could be fully recharged within 30 s and was able to light an LED, was assembled by using the LTO nanosheet arrays as the anode.

Kinetics-controlled growth of aligned mesocrystalline SnO 2 nanorod arrays for lithium-ion batteries with superior rate performance

A general method for facile kinetics-controlled growth of aligned arrays of mesocrystalline SnO2 nanorods on arbitrary substrates has been developed by adjusting supersaturation in a unique ternary solvent system comprising acetic acid, ethanol, and water. The hydrolysis processes of Sn(IV) as well as the nucleation and growth of SnO2 crystals were carefully controlled in the mixed solvents, leading to an exclusively heterogeneous nucleation on a substrate and the subsequent growth into mesocrystalline nanorod arrays. In particular, aligned arrays of hierarchically structured, [001]-oriented mesocrystalline SnO2 nanorods with four {110} lateral facets can be readily grown on Ti foil, as well as many other inert substrates such as fluoride-doped tin oxide (FTO), Si, graphite, and polytetrafluoroethylene (Teflon). Due to the unique combination of the mesocrystalline structure and the one-dimensional nanoarray structure, the obtained mesocrystalline SnO2 nanorod arrays grown on metallic Ti substrate exhibited an excellent rate performance with a high initial Coulombic efficiency of 65.6% and a reversible capacity of 720 mA·h/g at a charge/discharge rate of 10 C (namely, 7,820 mA/g) when used as an anode material for lithium-ion batteries.Graphical abstract

Solution-phase synthesis of inorganic hollow structures by templating strategies

The solution-phase synthesis of hollow micro- and nanostructures by using suitable templates such as hard templates, soft templates and reactive templates has attracted considerable attention in recent years. This paper is focused on the template synthesis of inorganic hollow structures with tailored size, morphology, and architecture, with emphasis on the templating strategies recently developed in our lab for the facile solution-phase synthesis of novel inorganic hollow structures. The formation mechanisms of the hollow structures via different kinds of templates are discussed in depth to show the general concepts for the preparation processes. The properties and applications of hollow structures are briefly described, demonstrating the promising and broad application fields of hollow materials.

Amperometric hydrogen peroxide biosensor based on the immobilization of heme proteins on gold nanoparticles–bacteria cellulose nanofibers nanocomposite

A novel matrix, gold nanoparticles-bacterial cellulose nanofibers (Au-BC) nanocomposite was developed for enzyme immobilization and biosensor fabrication due to its unique properties such as satisfying biocompatibility, good conductivity and extensive surface area, which were inherited from both gold nanoparticles (AuNPs) and bacterial cellulose nanofibers (BC). Heme proteins such as horseradish peroxidase (HRP), hemoglobin (Hb) and myoglobin (Mb) were successfully immobilized on the surface of Au-BC nanocomposite modified glassy carbon electrode (GCE). The immobilized heme proteins showed electrocatalytic activities to the reduction of H(2)O(2) in the presence of the mediator hydroquinone (HQ), which might be due to the fact that heme proteins retained the near-native secondary structures in the Au-BC nanocomposite which was proved by UV-vis and IR spectra. The response of the developed biosensor to H(2)O(2) was related to the amount of AuNPs in Au-BC nanocomposite, indicating that the AuNPs in BC network played an important role in the biosensor performance. Under the optimum conditions, the biosensor based on HRP exhibited a fast amperometric response (within 1s) to H(2)O(2), a good linear response over a wide range of concentration from 0.3 μM to 1.00 mM, and a low detection limit of 0.1 μM based on S/N=3. The high performance of the biosensor made Au-BC nanocomposite superior to other materials as immobilization matrix.

Heterostructured TiO2 Nanorod@Nanobowl Arrays for Efficient Photoelectrochemical Water Splitting

Heterostructured TiO2 nanorod@nanobowl (NR@NB) arrays consisting of rutile TiO2 nanorods grown on the inner surface of arrayed anatase TiO2 nanobowls are designed and fabricated as a new type of photoanodes for photoelectrochemical (PEC) water splitting. The unique heterostructures with a hierarchical architecture are readily fabricated by interfacial nanosphere lithography followed by hydrothermal growth. Owing to the two-dimensionally arrayed structure of anatase nanobowls and the nearly radial alignment of rutile nanorods, the TiO2 NR@NB arrays provide multiple scattering centers and hence exhibit an enhanced light harvesting ability. Meanwhile, the large surface area of the NR@NB arrays enhances the contact with the electrolyte while the nanorods offer direct pathways for fast electron transfer. Moreover, the rutile/anatase phase junction in the NR@NB heterostructure improves charge separation because of the facilitated electron transfer. Accordingly, the PEC measurements of the TiO2 NR@NB arrays on the fluoride-doped tin oxide (FTO) substrate show significantly enhanced photocatalytic properties for water splitting. Under AM1.5G solar light irradiation, the unmodified TiO2 NR@NB array photoelectrode yields a photocurrent density of 1.24 mA cm(-2) at 1.23 V with respect to the reversible hydrogen electrode, which is almost two times higher than that of the TiO2 nanorods grown directly on the FTO substrate.

Branched CNT@SnO2 nanorods@carbon hierarchical heterostructures for lithium ion batteries with high reversibility and rate capability

A novel hierarchical heterostructure consisting of carbon-coated SnO2 mesocrystalline nanorods radially aligned on carbon nanotubes (CNTs) was designed and fabricated by a two-step growth process. SnO2 nanorods were first grown directly on CNTs through a facile solvothermal reaction, which were subsequently coated with a thin layer of carbon to form a branched CNT@SnO2@carbon sandwich-type heterostructure. When used as an anode material in lithium ion batteries, the branched CNT@SnO2@C heterostructures exhibited highly reversible lithium storage behavior and excellent rate capability. The reversible capacity of the CNT@SnO2@C heterostructure reached 984 mA h g−1 at a current density of 720 mA g−1, and retained 590 mA h g−1 at 3.6 A g−1 and 420 mA h g−1 at 7.2 A g−1. This superior performance might be ascribed to the improved mechanical capability and high loading content of SnO2 of the branched architecture, the good electrical conductivity of the CNT backbones and the carbon layer, and the high electrochemical reactivity of the 1D mesocrystalline SnO2 nanorods.

Photoconductivity of single-crystalline selenium nanotubes

The photoconductivity of single-crystalline selenium nanotubes (SCSNTs) under a range of illumination intensities of a 633 nm laser is examined using a novel two-terminal device arrangement at room temperature. It is found that SCSNTs forms Schottky barriers with W and Au contacts, and the barrier height is a function of the light intensity. In the low-illumination regime below 1.46 × 10−4 µW µm−2, the Au–Se–W hybrid structure exhibits sharp on/off switching behaviour, and the turn-on voltages decrease with increasing illuminating intensities. In the high-illumination regime above 7 × 10−4 µW µm−2, the device exhibits ohmic conductance with a photoconductivity as high as 0.59 Ω cm−1, which is significantly higher than the reported values for carbon and GaN nanotubes. This finding suggests that a SCSNT is potentially a good photo-sensor material as well as a very effective solar cell material.

Robust α-Fe2O3 nanorod arrays with optimized interstices as high-performance 3D anodes for high-rate lithium ion batteries

Self-supported α-Fe2O3 nanorod arrays consisting of mesocrystalline nanorod bundles with tunable interstices were prepared by solution-phase growth coupled with chemical etching. The existence of acetic acid and sulfate ions in the hydrothermal system promoted the direct growth of α-Fe2O3 nanorod bundles with a mesocrystalline structure on a Ti substrate. The robust α-Fe2O3 nanorod arrays with optimized interstices are able to offer reduced lengths for electron transport and ion diffusion, and enough spaces to accommodate lithiation-induced volume expansion, leading to novel three-dimensional (3D) anodes with significantly improved rate capability and cyclability. When used as binder-free anodes for lithium ion batteries (LIBs), the α-Fe2O3 nanorod arrays retained a reversible capacity of 801 mA h g−1 after 500 cycles at 5 C (namely, 5 A g−1), and achieved practically valuable capacities of 499 mA h g−1 and 350 mA h g−1 at high rates of 20 C and 30 C, respectively. Furthermore, a flexible full battery with high capacity and fast charging capability was assembled using the α-Fe2O3 nanorod arrays as the anode, demonstrating their potential applications in flexible electronic devices.

Biogenic and synthetic high magnesium calcite – A review

Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties.

Facile synthesis of ZnS nanobowl arrays and their applications as 2D photonic crystal sensors

Large-area ZnS nanobowl arrays with a monolayer inverse opal structure were synthesized facilely by nanosphere lithography at solution surface (NSLSS) through direct solution deposition. It was shown that the well-defined ZnS nanobowl arrays resulted from preferential deposition of ZnS at the polystyrene sphere–solution interface. Owing to the 2D periodic structure of the hexagonally ordered nanobowl arrays and the high refractive index of ZnS, the as-prepared ZnS nanobowl arrays showed intensive structural colors and tunable photonic band-gap properties. These ZnS nanobowl arrays are able to act as effective, fast-responsive 2D photonic crystal sensors based on the refractive index changes because of their easy accessibility for both solvents and analyte molecules. The as-prepared ZnS nanobowl arrays can be used as sensitive 2D photonic crystal sensors for fast detection of organic solvents and for visual oil sensing through color changes. After surface functionalization, the ZnS nanobowl arrays can be used as effective 2D photonic crystal biosensors for sensitive detection of avidin molecules with low detection limits (less than 100 pM) and broad working range.