Dan Mao

Multishelled TiO2 hollow microspheres as anodes with superior reversible capacity for lithium ion batteries

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles.

Direct hydrothermal synthesis of single-crystalline hematite nanorods assisted by 1,2-propanediamine

Uniform alpha-Fe2O3 nanorods with high aspect ratios were synthesized in large scale by a simple and direct 1,2-propanediamine-assisted hydrothermal method. The resultant products were characterized by x-ray diffraction scanning electron microscopy, and transmission electron microscopy. The as-synthesized alpha- Fe2O3 nanorods were single crystalline and uniform, with an average aspect ratio greater than 10. The effects of various experimental parameters on the morphology of products, such as 1,2-propanediamine content, pH value, concentration of FeCl3 and reaction temperature, were studied. In the formation process of alpha- Fe2O3 nanorods, the 1,2-propanediamine not only provides OH(-) but also plays a role for retaining the rod-like morphology of hematite. The magnetic properties including Morin transition and coercivity of the samples with different synthesis conditions and aspect ratios were also investigated in detail.

Hierarchically Mesoporous Hematite Microspheres and Their Enhanced Formaldehyde‐Sensing Properties

There is intense interest in the synthesis of hierarchically porous materials (such as micro–mesoporous, bimodalmesoporous, and meso–macroporous materials), possessing multilevel porous structures and high specifi c surface areas, that can provide many novel properties and have important prospects in practical industrial processes, such as catalysis, adsorption, separation, chemical sensing, electrode materials, and biomaterials engineering. [ 1–3 ] Based on the organictemplate route, many hierarchically porous metal oxides have been synthesized, such as TiO 2 , ZrO 2 , WO 3 , Nb 2 O 5 , Ta 2 O 5 , Al 2 O 3 , and CeO 2 , [ 4–9 ] whose walls are almost amorphous or semicrystalline. However, a crystallized wall structure can be expected to provide better thermal and mechanical stability, as well as superior electric and optical properties. [ 10–12 ] However, it still remains a challenge to obtain hierarchically porous materials with crystalline walls as most of these metal oxides often suffer from structural collapse during their crystallization. Recently, the surfactant-directed assembly of preformed crystalline nanoparticles into mesostructures was successfully utilized to synthesize some crystalline mesostructured materials. For example, Corma et al. reported mesoporous CeO 2 assembled from CeO 2 nanocrystals, [ 13,14 ] Niederberger and co-workers prepared mesoporous SnO 2 using SnO 2 nanocrystals, [ 15 ] and Li and co-workers also realized the synthesis of porous 3D spheres using various nanocrystals, such as Ag, Ag 2 S, and Ag 2 Se. [ 16,17 ] However, this approach requires multistep procedures, including the synthesis and collection of nanoparticles with well defi ned shapes and sizes, their redispersion without agglomeration in assembly solution, and the fi nal assembly. Moreover, the assembly in the above-mentioned cases usually occurred on a single-scale level and thus resulted in materials with single-level porous structures. In this Communication, we demonstrate that the dual assembly of nanoparticles can be realized directly at its synthetic solution, without collection and redispersion procedures, and that this fi nally allows us to obtain a hierarchical porous material.

pH-Regulated Synthesis of Multi-Shelled Manganese Oxide Hollow Microspheres as Supercapacitor Electrodes Using Carbonaceous Microspheres as Templates

Multi‐shelled Mn2O3 hollow microspheres have been achieved through a pH‐regulated method and used as supercapacitor electrodes. The designed unique architecture allows efficient use of pseudo‐capacitive Mn2O3 nanomaterials for charge storage with facilitated transport for both ions and electrons, rendering them high specific capacitance, good rate capability, and remarkable cycling performance.

Multi-shelled metal oxides prepared via an anion-adsorption mechanism for lithium-ion batteries

One of the major problems in the development of lithium-ion batteries is the relatively low capacity of cathode materials compared to anode materials. Owing to its high theoretical capacity, vanadium oxide is widely considered as an attractive cathode candidate. However, the main hindrances for its application in batteries are its poor capacity retention and low rate capability. Here, we report the development of multi-shelled vanadium oxide hollow microspheres and their related electrochemical properties. In contrast to the conventional cation-adsorption process, in which the metal cations adsorb on negatively charged carbonaceous templates, our approach enables the adsorption of metal anions. We demonstrate controlled syntheses of several multi-shelled metal oxide hollow microspheres. In particular, the multi-shelled vanadium oxide hollow microspheres deliver a specific capacity of 447.9 and 402.4mAhg(-1) for the first and 100th cycle at 1,000mAg(-1), respectively. The significant performance improvement offers the potential to reduce the wide capacity gap often seen between the cathode and anode materials.

Dually Ordered Porous TiO2-rGO Composites with Controllable Light Absorption Properties for Efficient Solar Energy Conversion

Quadruple-layered TiO2 films with controllable macropore size are prepared via a confinement self-assembly method. The inverse opal structure with ordered mesoporous (IOM) presents unique light reflection and scattering ability with different wavelengths. Cyan light (400-600 nm) is reflected and scattered by IOM-195, which is in accord with N719 absorption spectra. By manipulating the macropore size, different light responses are obtained.

Formation of Septuple-Shelled (Co2/3Mn1/3)(Co5/6Mn1/6)2O4 Hollow Spheres as Electrode Material for Alkaline Rechargeable Battery

The multishelled (Co2/3 Mn1/3 )(Co5/6 Mn1/6 )2O4 hollow microspheres with controllable shell numbers up to septuple shells are synthesized using developed sequential templating method. Exhilaratingly, the septuple-shelled complex metal oxide hollow microsphere is synthesized for the first time by doping Mn into Co3 O4 , leading to the change of crystalline rate of precursor. Used as electrode materials for alkaline rechargeable battery, it shows a remarkable reversible capacity (236.39 mAh g-1 at a current density of 1 A g-1 by three-electrode system and 106.85 mAh g-1 at 0.5 A g-1 in alkaline battery) and excellent cycling performance due to its unique structure.

Multi-shelled TiO2/Fe2TiO5 heterostructured hollow microspheres for enhanced solar water oxidation

There remains a pressing challenge in the fabrication of superior photocatalysts for light-driven water oxidation. Here, we designed and fabricated heterostructured TiO2/Fe2TiO5 hollow microspheres with single-, double-, closed-double-, triple-, and core–shell structures and different Fe/Ti molar ratios using a facile sequential templating approach. The closed-double-shelled TiO2/Fe2TiO5 hollow microspheres with 35% Fe exhibited the highest oxygen evolution reaction rate up to 375 μmol·g−1·h−1 and good stability for 5 h. The high performance can be attributed to the closed-double shell, which had more reactive sites and greater light-harvesting ability, self-supported thin shells with short charge-transfer paths, and a favorable staggered band alignment between the TiO2 and Fe2TiO5.

Sequential Templating Approach: A Groundbreaking Strategy to Create Hollow Multishelled Structures

Thanks to their distinguished properties such as optimized specific surface area, low density, high loading capacity, and sequential matter transfer and storage, hollow multishelled structures (HoMSs) have attracted great interest from scientists in broad fields, including catalysis, drug delivery, solar cells, supercapacitors, lithium-ion batteries, electromagnetic wave absorption, and sensors. However, traditional synthesis methods such as soft-templating and hierarchical self-assembly methods can hardly realize the controllable synthesis of HoMSs, thus limiting their development and application. Here, the development process of HoMSs is first succinctly reviewed and the shortcomings of the traditional synthesis method are concluded. Subsequently, the sequential templating approach, which shows great generality for the synthesis of HoMSs with controllable composition and geometry configuration and exhibits remarkable effect on the scientific research field, is introduced. The basic material science and chemical reaction mechanism involved in the synthesis and manipulation of HoMSs using the sequential templating approach are then explained in detail. In addition, the effect of the geometric characteristics of HoMSs on their application properties is highlighted. Finally, the current challenges and future research directions of HoMSs are also suggested.