General synthesis of mesoporous spheres of metal oxides and phosphates

Monodisperse and high-surface-area mesoporous inorganic spheres of various compositions including metal oxides, mixed oxides, and metal phosphates are prepared by templating mesoporous carbon spheres which are replicated from spherical mesoporous silica. Due to the rigid and thermally stable framework of carbon template, the crystalline phases of the obtained metal oxide spheres can be readily tailored by controlling crystalline temperatures. Moreover, the sphere morphologies can be changed from solid structure to hollow structure in some cases by changing the polarity of the precursor, due to the hydrophobic nature of carbon template.     

Hydrothermal Synthesis of Unique Hollow Hexagonal Prismatic Pencils of Co3V2O8⋅n H2O: A New Anode Material for Lithium‐Ion Batteries

Hollow structures of transition‐metal oxides, particularly mixed‐metal oxides, could be promising for various applications such as lithium‐ion batteries (LIBs). Compared to the synthesis of metal oxide hollow spheres by the template method, non‐spherical metal oxide hollow hexagonal polyhedra have not been developed to date. Herein, we report the controlled hydrothermal synthesis of a new phase of Co₃V₂O₈?n H₂O hollow hexagonal prismatic pencils (HHPPs), which is composed of uniform structural units. By varying the amount of NaOH in the presence of NH₄⁺ and without any template or organic surfactant, the hexagonal prismatic pencils gradually transform from solid into hollow structures, with sizes varying from 5 to 20 μm. The structure of pencils can be preserved only in a limited range of the molar ratio of OH^?/NH₄⁺. As a new anode material for LIBs, such hollow pencils exhibit impressive lithium storage properties with high capacity, good cycling stability, and superior rate capability.     

Use of carbonaceous polysaccharide microspheres as templates for fabricating metal oxide hollow spheres

A general method for the synthesis of metal oxide hollow spheres has been developed by using carbonaceous polysaccharide microspheres prepared from saccharide solution as templates. Hollow spheres of a series of metal oxides (SnO2, Al2O3, Ga2O3, CoO, NiO, Mn3O4, Cr2O3, La2O3, Y2O3, Lu2O3, CeO2, TiO2, and ZrO2) have been prepared in this way. The method involves the initial absorption of metal ions from solution into the functional surface layer of carbonaceous saccharide microspheres; these are then densified and cross-linked in a subsequent calcination and oxidation procedure to form metal oxide hollow spheres. Metal salts are used as starting materials, which widens the accessible field of metal oxide hollow spheres. The carbonaceous colloids used as templates have integral and uniform surface functional layers, which makes surface modification unnecessary and ensures homogeneity of the shell. Macroporous films or cheese-like nanostructures of oxides can also be prepared by slightly modified procedures. XRD, TEM, HRTEM, and SAED have been used to characterize the structures. In a preliminary study on the gas sensitivity of SnO2 hollow spheres, considerably reduced "recovery times" were noted, exemplifying the distinct properties imparted by the hollow structure. These hollow or porous nanostructures have the potential for diverse applications, such as in gas sensitivity or catalysis, or as advanced ceramic materials.     

General Synthesis of Multi‐Shelled Mixed Metal Oxide Hollow Spheres with Superior Lithium Storage Properties

Complex hollow structures of transition metal oxides, especially mixed metal oxides, could be promising for different applications such as lithium ion batteries. However, it remains a great challenge to fabricate well‐defined hollow spheres with multiple shells for mixed transition metal oxides. Herein, we have developed a new “penetration–solidification–annealing” strategy which can realize the synthesis of various mixed metal oxide multi‐shelled hollow spheres. Importantly, it is found that multi‐shelled hollow spheres possess impressive lithium storage properties with both high specific capacity and excellent cycling stability. Specifically, the carbon‐coated CoMn₂O₄ triple‐shelled hollow spheres exhibit a specific capacity of 726.7 mA h g^?1 and a nearly 100 % capacity retention after 200 cycles. The present general strategy could represent a milestone in design and synthesis of mixed metal oxide complex hollow spheres and their promising uses in different areas.     

Self‐Templated Formation of Uniform NiCo2O4 Hollow Spheres with Complex Interior Structures for Lithium‐Ion Batteries and Supercapacitors

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template‐based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed‐metal‐oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo₂O₄ hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo₂O₄ hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium‐ion batteries and supercapacitors. This approach can be an efficient self‐templated strategy for the preparation of mixed‐metal‐oxide hollow spheres with complex interior structures and functionalities.     

Synthesis of morphology-controllable mesoporous Co3O4 and CeO2

Recently, extensive works have been devoted to the morphology control of mesoporous materials with respect to their use in various applications. In this paper, we used two kinds of mesoporous silica, SBA-15 rods and spheres as hard templates to synthesize morphology-controllable mesoporous metal oxides. By carefully controlling the loading of metal precursors in the mesopores of the hard template, mesoporous Co₃O₄ and CeO₂ with different morphologies, such as micrometer-sized rod, hollow sphere, saucer-like sphere, and solid sphere were conveniently obtained. The structural properties of these materials were characterized by XRD, BET, SEM and TEM. In addition, it is found that the differences observed in the textural properties of the two mesoporous metal oxides nanocasted from the same template can be attributed to the properties of metal precursors and the interaction between metal oxide and SiO₂. Thus-obtained mesoporous metal oxides with such special morphologies may have a potential application in the field of environmental catalytic oxidation.     

General and Facile Syntheses of Metal Silicate Porous Hollow Nanostructures

Porous hollow nanostructures have attracted intensive interest owing to their unique structure and promising applications in various fields. A facile hydrothermal synthesis has been developed to prepare porous hollow nanostructures of silicate materials through a sacrificial‐templating process. The key factors, such as the concentration of the free metal cation and the alkalinity of the solution, are discussed. Porous hollow nanostructures of magnesium silicate, nickel silicate, and iron silicate have been successfully prepared by using SiO₂ spheres as the template, as well as a silicon source. Several yolk–shell structures have also been fabricated by a similar process that uses silica‐coated composite particles as a template. As‐prepared mesoporous magnesium silicate hollow spheres showed an excellent ability to remove Pb²⁺ ions in water treatment owing to their large specific surface and unique structures.     

Fabrication and photocatalytic properties of SnO2 double-shelled and triple-shelled hollow spheres

SnO₂ double-shelled and triple-shelled hollow spheres were tailored by adjusting concentration of tin (IV) chloride solution during the process of the tin (IV) ions infused carbonaceous spheres. The structures of these SnO₂ multi-shelled hollow spheres were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and their possible formation mechanism were also discussed. In virtue of triple-shelled hollow porous structure and higher specific surface area, SnO₂ triple-shelled hollow spheres exhibited enhanced photocatalytic properties compared to SnO₂ double-shelled hollow spheres.     

Template free fabrication of hollow hematite spheres via a one-pot polyoxometalate-assisted hydrolysis process

Uniform hollow hematite (α-Fe₂O₃) spheres with diameter of about 600-700 nm and shell thickness lower than 100 nm are obtained by direct hydrothermal treatment of dilute FeCl₃ and tungstophosphoric acid H₃PW₁₂O₄₀ solution at 180 °C. The hollow spheres are composed of robust shells with small nanoparticles standing out of the surface and present a high-surface area and a weak ferromagnetic behavior at room temperature. The effect of concentration of H₃PW₁₂O₄₀, reaction time and temperature for the formation of the hollow spheres are investigated in series of experiments. The formation of the hollow spheres may be ascribed to a polyoxometalte-assisted forced hydrolysis and dissolution process.     

Cu3V2O8 hollow spheres in photocatalysis and primary lithium batteries

In this paper, Cu₃V₂O₈ hollow spheres have been successfully synthesized via a liquid precipitation method with colloidal carbon spheres as template followed by a subsequent heat treatment process. On the basis of XRD analysis, SEM observation, and TG-DSC analysis of the precursor and products, the formation mechanism of Cu₃V₂O₈ hollow spheres was proposed. UV–vis diffuse reflectance spectra showed that the Cu₃V₂O₈ hollow spheres exhibit strong absorption in a wide wavelength range from UV to visible light. The photocatalytic activity experiment indicated that the as-prepared Cu₃V₂O₈ hollow spheres exhibited good photocatalytic activity in degradation of methyl orange (MO) under 150-W xenon arc lamp light irradiation. Furthermore, electrochemical measurements showed that the Cu₃V₂O₈ hollow spheres exhibited high discharge capacity and excellent high-rate capability, indicating potential cathode candidates for primary lithium batteries used in long-term implantable cardiac defibrillators (ICDs).     

Template free solvothermal synthesis of single crystal magnetic Fe3O4 hollow spheres,their interaction with bovine serum albumin and antibacterial activities

Uniform sized single crystal magnetic Fe₃O₄ hollow spheres (MFHS) have been synthesized through simple solvothermal method using ferric chloride hexahydrate and 1,3-propanediamine. The reaction time and the amount of 1,3-propanediamine play major roles in the formation of magnetic Fe₃O₄ hollow spheres. The synthesized products are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry techniques. The crystalline Fe₃O₄ materials are composed of well-aligned hollow sphere magnetite nanoparticles and exhibit high saturation magnetization of 57.9?emu/g and a remnant magnetization of 17.6?emu/g at room temperature. MFHS interact strongly with bovine serum albumin (BSA) and brings out considerable conformational changes in BSA as evident from the UV–vis absorption, fluorescence and circular dichroism (CD) spectroscopic studies pertaining to the interaction of synthesized MFHS and BSA. The prepared MFHS effectively inhibit the growth of Pseudomonas aeruginosa and Staphylococcus aureus.     

Multishelled Metal Oxide Hollow Spheres: Easy Synthesis and Formation Mechanism

Uniform multishelled NiO, Co₃O₄, ZnO, and Au@NiO hollow spheres were synthesized (NiO and Co₃O₄ hollow spheres for the first time) by a simple shell‐by‐shell self‐assembly allowing for tuning of the the size, thickness and shell numbers by controlling the heat treatment, glucose/metal salt molar ratio, and hydrothermal reaction time. These findings further the development of synthetic methodologies for multishelled hollow structures and could open up new opportunities for deeper understanding of the mechanisms of shell‐by‐shell self‐assembly. Moreover, the double‐shelled NiO hollow sphere exhibits a higher photocatalytic activity for degradation of methyl orange than its morphological counterparts.     

Self‐Templating Synthesis of Hollow Co3O4 Microtube Arrays for Highly Efficient Water Electrolysis

In spite of recent advances in the synthesis of hollow micro/nanostructures, the fabrication of three‐dimensional electrodes on the basis of these structures remains a major challenge. Herein, we develop an electrochemical sacrificial‐template strategy to fabricate hollow Co₃O₄ microtube arrays with hierarchical porosity. The resultant unique structures and integrated electrode configurations impart enhanced mass transfer and electron mobility, ensuring high activity and stability in catalyzing oxygen and hydrogen evolution reactions. Impressively, the apparent performance can rival that of state‐of‐the‐art noble‐metal and transition‐metal electrocatalysts. Furthermore, this bifunctional electrode can be used for highly efficient overall water splitting, even competing with the integrated performance of Pt/C and IrO₂/C.     

Novel synthesis of Fe2O3–Pt ellipsoids coated by double‐shelled La2O3 as a catalyst for the reduction of 4‐nitrophenol

A facile strategy is reported for the fabrication of Pt‐loaded core–shell nanocomposite ellipsoids (Fe₂O₃‐Pt@DSL) consisting of ellipsoidal Fe₂O₃ cores, double‐layered La₂O₃ shells and deposited Pt nanoparticles (NPs). The formation of the doubled‐shelled structure uses Fe₂O₃‐Pt@mSiO₂ as template sacrificial agent and it involves the re‐deposition of silica and self‐assembly of metal oxide units. The preparation methods of double‐shelled metal oxides avoid repeated coating and etching and could be utilized to fabricate other shaped double‐shelled composites. Characterization results indicated that the Fe₂O₃‐Pt@DSL nanocomposites possessed mesoporous structure and tunable shell thickness. Moreover, due to the formation of Fe₂O₃ and La₂O₃ composites, Pt NPs can also be stabilized via deposition on chemically active oxides with a synergistic effect. Therefore, as a catalyst for the reduction of 4‐nitrophenol, Fe₂O₃‐Pt@DSL showed superior catalytic activity and reusability due to structural superiority and enhanced composite synergy. Finally, well‐dispersed Pt NPs were encapsulated into the void between the shell layers to construct the Fe₂O₃‐Pt@DSL‐Pt catalyst.     

Synthesis of Single‐Component Metal Oxides with Controllable Multi‐Shelled Structure and their Morphology‐Related Applications

Multi‐shelled hollow spheres metal oxides, namely materials with more than three shells, have attracted increasing attention due to their unique structure. The preparation methods of typical metal oxides including NiO, Co₃O₄ and ZnO etc. have been summarized in this review. Simultaneously, the parameters that influence the ultimate morphologies, shell number as well as the compositions have also been discussed. The potential application fields in energy conversion and storage, electromagnetic wave absorption, photocatalysis that related to the unique structure are also highlighted. Finally, the future researches of multi‐shelled hollow spheres metal oxides are further discussed.     

Study on Fe3O4/polyaniline electromagnetic composite hollow spheres prepared against sulfonated polystyrene colloid template

Fe₃O₄/polyaniline (PANI) composite hollow spheres were prepared by using sulfonated polystyrene (SPS) microspheres as templates. The sulfonic acid groups were applied to induce absorbing Fe₃O₄ nanoparticle, and subsequently, conductive PANI was grown. Finally, the polystyrene cores were selectively dissolved to yield composite hollow microspheres with electromagnetic properties. The analysis results indicated that the adsorption of Fe₃O₄ on template core by electrostatic interaction resulted in magnetic composite microspheres. The conductivity of composite hollow spheres was remarkably increased after polyvinylpyrrolidone modification which favored the growth of PANI on SPS/Fe₃O₄ and enhanced the integrity of hollow microspheres. The saturated magnetization of the composite hollow microspheres was tuned from 2.7 to 9.1 emu/g, and the conductivity was in the range from 10^?2 to 10⁰?S/cm.     

Template synthesis of tin-doped indium oxide (ITO)/polymer and the corresponding carbon composite hollow colloids

SnO₂, In₂O₃, and Sn-doped In₂O₃ (ITO)/polymer and the corresponding carbon composite hollow colloids are template synthesized. It is essential that the sulfonated gel shell of the cross-linked polystyrene hollow colloid can favorably induce adsorption of target precursors. After being calcined in air to remove the template, SnO₂, In₂O₃, and ITO hollow colloids are obtained. Because the cross-linked polymer gel can be transformed into carbon in nitrogen at higher temperature such as 800 °C, metal oxide/carbon hollow colloids are consequently derived, whose shells are mesoporous. The SnO₂-, In₂O₃-, and ITO-containing polymer or carbon composite hollow colloids will be promising in sensors, catalysts, and fuel cells as electrode materials. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

One-pot synthesis of bimetallic Fe/Co incorporated silica hollow spheres with superior peroxidase-like activity

Mesoporous silica hollow spheres with a homogenous and high content distribution of Fe and Co were synthesized by a facile one-pot hydrothermal process. The sub-nanometer bimetallic components inside the silica framework facilitate the stable fixation and the open accessibility to active sites. The co-doped Fe/Co in the spheres showed excellent peroxidase-like activity and much higher catalytic performance than their monometallic-supported spheres. The synergistic effect between Fe and Co promotes the continuous formation of functional radicals during the oxidation process and thus accelerates the reaction rate. When used for colorimetric detection of hydrogen peroxide (H₂O₂), the Fe/Co incorporated silica hollow spheres show the capability of detection of H₂O₂ in a wide range (10-250 µmol/L) and with the low detection limit of 0.012 ppm.     

Selective fabrication of porous iron oxides hollow spheres and nanofibers by electrospinning for photocatalytic water purification

Porous hematite (α-Fe₂O₃) hollow spheres and nanofibers could be obtained via electrospinning and subsequent thermal decomposition in air. The precursor could be fabricated by electrospinning using Fe(NO₃)₃ as the iron source and Polyvinylpyrrolidone (PVP) as a complexing reagent. Upon calcination, pure porous α-Fe₂O₃ hollow spheres and nanofibers could be obtained at 650 °C for 3 h. The novel hollow spheres have an abundantly porous structure as well as large surface areas. Benefitting from the special porous structure, narrow bandgap, and higher surface area, porous α-Fe₂O₃ hollow materials are used as visible-light-responsive photocatalysts. So we have investigated the visible light photodegradation behavior of porous hematite (α-Fe₂O₃) hollow spheres and nanofibers towards organic dyes, as Rhodamine B (RhB). The synergetic effects of higher surface area, pore structures promoted the photocatalytic efficiency for RhB degradation under visible light and contributed to achieving the enhanced and stable photocatalytic activity.     

混晶海胆状TiO2空心球多级结构的制备及其对亚甲基蓝的光催化降解

用简单的无模板水热法可控合成了金红石相锥刺和锐钛矿相空心球的海胆状TiO2多级结构。研究了制备介质pH值和反应时间对形貌的影响。空心球上锥刺的密度可以通过改变反应条件加以调控。对海胆状TiO2多级结构可能的形成机理进行了研究。将不同锥刺密度的TiO2空心球应用于亚甲基蓝降解的光催化研究,结果表明低锥刺密度的TiO2空心球的光催化效果优于P25-TiO2,更优于锥刺多和无锥刺的光滑TiO2空心球。