General Synthesis and Gas‐Sensing Properties of Multiple‐Shell Metal Oxide Hollow Microspheres

Abstract

Hollow spheres with nanometer-to-micrometer dimensions, controlled internal structure, and shell composition have attracted tremendous attention because of their potential application in catalysis, drug delivery, nanoreactors, energy conversion and storage systems, photonic devices, chemical sensors, and biotechnology.[1] Single-shell and double-shell hollow spheres of various compositions have been synthesized by a number of methods, such as vesicles, emulsions, micelles, gas-bubble, and hard-templating methods.[2] More recently, efforts have focused on the fabrication of hollow spheres with multiple shells, as these materials are expected to have better properties for applications such as drug release with prolonged release time, heterogeneous catalysis, lithiumion batteries, and photocatalysis.[3] For example, multipleshell hollow microspheres of Cu 2 O have been prepared by vesicle templating and an intermediate-templating phasetransformation process. [3a,b] Multiple-shell azithromycin hollow microspheres were fabricated by hierarchical assembly.[3c] Cao and co-workers reported the synthesis of tripleshelled SnO 2 hollow microspheres by chemically induced selfassembly in the hydrothermal environment which exhibited enhanced electrochemical performance.[3d] Yao and co-workers reported excellent cycle performance and enhanced lithium storage capacity of multiple-shell Co 3 O 4 hollow microspheres synthesized by oriented self-assembly.[4] These preparative methods, however, are suited for each specific material and cannot be applied generally to a wide range of materials. Currently, there is no general synthetic approach for fabricating multiple-shell hollow nanostructures of any desired material.Herein, we present a straightforward and general strategy to prepare metal oxide hollow microspheres with a controlled number of shells. Carbonaceous microspheres were used as sacrificial templates. The microspheres were saturated with a desired metal salt solution and then heated in air; the carbonaceous template evaporates and templates the formation of metal oxide shells. The number of shells is controlled by the metal ion loading and the process is general for a wide range of metal oxide materials.Scheme 1 illustrates the general process of fabricating multiple-shell hollow metal oxide microspheres. The key to this process is the use of carbonaceous particles rich with surface functional groups available for metal ion adsorption. [5] Multiple shells are generated by supplying enough shell precursor material to the sacrificial carbonaceous spheres. Recently, our group reported the synthesis of hollow coreshell ferrite microspheres, [5b] demonstrating that carbonaceous particles can absorb a significant amount of metal ions within the interior of the particle ( Figure S1 in the Supporting Information). In this work, we extend these methods and demonstrate the general and facile synthesis of multiple-shell hollow microspheres of a wide range of different metal oxides.Figure 1 a,b shows a transmission electron micro...

Versatility of one-pot, single-step synthetic approach for spherical porous (metal) oxide nanoparticles using supercritical alcohols

“…Among them, metal oxide nanoparticles, such as silica (SiO 2 ) [11][12][13], titanium dioxide (TiO 2 ) [14][15][16][17], cerium dioxide (CeO 2 ) [18][19][20], zirconium dioxide (ZrO 2 ) [21,22], and variants of these [23], are of particular relevance to catalytic chemistry, semiconductors, and drug delivery. Porous metal oxide nano-or micro-spheres with dimension-controlled morphology possess unique properties that are especially suited to practical applications.…”

“…Several methods exist by which to obtain these structures, including hydrothermal, sol-gel, and self-assembly methods, and combinations of these. However, these methods generally involve complex multistep 4 operations and long reaction times (several hours) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]27,28]. Recently, sizeand morphology-controlled inorganic-organic hybrid metal and metal oxide nanoparticles have been synthesized in supercritical fluids.…”

Hollow MnCo2O4 Submicrospheres with Multilevel Interiors: From Mesoporous Spheres to Yolk-in-Double-Shell Structures

“…4 Various methodologies have been developed to achieve this special nanostructure. [5][6][7][8] Heterogeneous contraction, for example, is a typical and effective route for controlled synthesis of hollow structure with different interiors, which is caused by non-equilibrium heat treatment and determined by the difference between the cohesive force and the adhesive force generated by a high heating rate. 18 However, the hollow structure is obtained as it is after calcinations and cannot be tuned because of the smaller weight loss.…”

Self‐Template Synthesis of Hybrid Porous Co3O4–CeO2 Hollow Polyhedrons for High‐Performance Supercapacitors

“…Among these synthetic strategies, template-directed synthesis routes have been considered as the most effective method for the preparation of hollow structuredm aterials. [12][13][14] In recenty ears, metal-organic frameworks (MOFs), a new class of porous materials,h avea ttracted particulara ttentions as promisingc andidates for gas storage/separation, catalysis, chemical sensing, electric energy storage devices, etc. [15][16][17][18][19] More recently,M OFs have been proven to be availablet emplates for synthesizingh ollow structured materials with controlled morphology and compositions.…”