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 elect...

Preparation of hollow core/shell CeO2@TiO2 with enhanced photocatalytic performance

“…Finally, the hollow core/shell structure was achieved with the complete removal of templates. Possibly, separation of inner core and outer shell can be due to the rate of the shell being not well matched with the rate of C microspheres disintegration [39]. Ti(OH) 4 nucleates formed a hollow shell and C-Ce(OH) 3 collapsed inward to form a movable core, which led to separation of core and shell.…”

Hierarchical MoS2 Shells Supported on Carbon Spheres for Highly Reversible Lithium Storage

“…[32][33] The obtained carbon spheres (ca. 0.25 g) were re-dispersed into H 2 O (50 mL) by ultrasonication.…”

“…[32][33] The panoramic field-emission scanning electron microscopy (FESEM) image showed that these carbon spheres are highly uniform with an average size of about 800 nm (Figure 1 a). A magnified FESEM image revealed that the surface of carbon spheres is composed of fine nanoparticles (Figure 1 b) of the presence of large amount of hydrophilic functional groups on the surface, these carbon spheres are very attractive as hard templates for the growth of nanostructured shells.…”

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

“…[7] Lai et al designed ag eneral route for the synthesis of several oxide multi-shelled hollow microspheres using carbonaceous microspheres as templates,w hich manifest improved gassensing properties. [9] Zeng and Xiong reported the synthesis of multishelled Cu 2 Shollow spheres by aserial ion-exchange method. [10] Nevertheless,t here have been no reports to date on the formation of non-spherical hollow structures with complex geometry solely by in situ selective inhibition of growth in certain planes.…”