Elsevier

Ceramics International

Volume 38, Issue 8, December 2012, Pages 6659-6664
Ceramics International

Controlled synthesis and optical properties of doughnut-aggregated hollow sphere-like CuS

https://doi.org/10.1016/j.ceramint.2012.05.053Get rights and content

Abstract

Three-dimensional (3D) doughnuts-like copper sulfide (CuS) particles were successfully synthesized by a facile microwave hydrothermal method employing polyvinylpyrrolidone (PVP) as the surfactant. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy and UV–vis diffuse reflectance spectra. Results show that the products are selectively fabricated by varying the S/Cu molar ratio from 3 to 7, exhibiting a morphology change from uniform aggregated spheres to single doughnuts-like structures. Comparison of the UV–vis absorption spectra of these particles reveals that an obvious red-shift of ∼70 nm is found from the single doughnuts to the assembled doughnuts. Moreover, these spectra were calculated to show the bandgap of the as-prepared CuS particles varies from 1.46 eV to 1.64 eV with the morphology change from the single doughnuts-like to the aggregated spheres-like structures, respectively, indicating that the optical properties of the product may be strongly related to the state of their morphologies.

Introduction

In recent years, there has been increasing interest in the controlled synthesis of inorganic nano/microstructures with hollow interiors because of their widespread potential applications in the photonic crystals, catalysis, artificial cells, drug delivery and the protection of light sensitive components [1]. The general approach for preparation of hollow structures has involved the use of various removable or sacrificial templates, including hard ones such as monodisperse silica [2] or polymer latex spheres [3] as well as soft ones. However, hollow structures prepared from hard templating routes usually suffer from disadvantages related to high cost and tedious synthetic procedures. It is highly desirable to develop one-pot synthesis of hollow inorganic materials without hard templates.

As one of the most important semiconductors, copper sulfide (CuS) is a promising material with potential applications in many fields, such as photothermal conversion [4], electrodes [5], and solar cell devices [6]. The controlled synthesis and self-organization of CuS with special morphologies and sizes have attracted considerable attention in the recent decades due to their outstanding properties and potential applications in numerous fields. Considerable efforts have been devoted to the synthesis of various CuS morphologies such as nanorods [7], nanowires [8], nanoplates [9], [10], nanoflakes [11] and tubular structures assembled by nanoflake-built microspheres [12]. Besides, the preparation CuS particles with hollow sphere-like strucutures is also under investigation [3], [13], [14] to show potential technological applications in optical [3] and sensoring [14] properties. However, long reaction times [3], [14] and difficulties in controlling uniform shaped structures [15] still exist to expect further investigation on both synthesize approach improvment and precise morphology control of CuS particles.

In this work, a facile and economical microwave hydrothermal method is employed to prepare 3D CuS hollow microspheres aggregated by doughnut-like structures firstly. Besides, the aggregation of doughnuts can be controlled. The uniform aggregated doughnuts-like spheres and single doughnuts can be selectively fabricated by varying the S/Cu molar ratios from 3 to 7. And the bandgap of CuS particles changes with different aggregation of doughnuts. We propose that this finding might prove useful to control bandgap of semiconductors by varying the aggregations of building-blocks.

Section snippets

Experimental

In a typical synthesis process, Cu(NO3)2·3H2O (0.726 g, 3 mmol), thiourea (0.684 g, 9 mmol), and PVP K30 (average molecular weight: 40000 g/mol) (0.4 g, 3.6 mmol, calculated in terms of the repeating unit C6H9NO FW=111) were dissolved in deionized water (50 mL) and stirred vigorously. The mixture was sealed in a 100 mL Teflon-lined autoclave. This autoclave was then put into an MDS-8 microwave hydrothermal system (Shanghai Sineo Microwave Chemistry Technology Co. Ltd., China). The operating power was

Synthesis of doughnut-aggregated hollow spheres

Fig. 1A shows the typical FESEM images of products prepared at the S/Cu molar ratio of 3. The obtained particles showed a spherical morphology with an average diameter of ∼2 μm. An interesting feature shown in Fig. 1B is that each sphere is assembled by many doughnuts-like structures with diameter of ∼500 nm. These doughnuts have a concave surface, which appears to be formed by circles of different layers grown from inside out. Besides, several holes found on the surface of the sphere indicates

Summary

In summary, we have successfully synthesized aggregated hollow sphere-like CuS particles by a facile microwave hydrothermal method with the assistance of PVP. The results show that the S/Cu molar ratio is found to greatly affect the product morphology without changing its phase. By varying the S/Cu molar ratios from 3 to 7, the obtained CuS particles could be selectively fabricated to show aggregated spheres and single doughnuts-like structures. And doughnuts with controllable size and

Acknowledgments

This work was supported by Research and National Natural Science Foundation of China (No.50942047), Innovation Team Assistance Foundation of Shaanxi University of Science and Technology (No.TD 09-05), Natural Science Foundation of Shaanxi province (09JK361) and Postgraduate Innovation Team Assistance Foundation of Shaanxi University of Science and Technology.

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