Elsevier

Powder Technology

Volume 264, September 2014, Pages 36-42
Powder Technology

Microwave hydrothermal disassembly for evolution from CuO dendrites to nanosheets and their applications in catalysis and photo-catalysis

https://doi.org/10.1016/j.powtec.2014.05.012Get rights and content

Highlights

  • Microwave hydrothermal synthesis of CuO nanosheets and dendrites was achieved.

  • Morphology evolution from dendrite to sheet was found.

  • Catalytic and photo-catalytic properties of CuO were investigated.

Abstract

CuO nanosheets and dendrites have been synthesized by a microwave hydrothermal method. The synthesized CuO nanostructures were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transition electron microscopy (TEM). The formation process was discussed, which revealed that the disassembly of sheet-built CuO dendrites contributed to the formation of discrete CuO nanosheets under microwave hydrothermal conditions. However, such a disassembly process was inhibited by an ultrasonic heat pretreatment before the microwave hydrothermal treatment. The synthesized CuO nanostructures were active toward the thermal decomposition of ammonium perchlorate (AP) and allowed the decomposition temperature of AP to decrease. Furthermore, the synthesized CuO nanostructures promoted the photodegradation of rhodamine B and methyl orange.

Introduction

Copper oxide (CuO) has proven to be a versatile material, being useful in many practical fields such as catalysis, gas sensors, lithium-ion battery, and water treatment [1], [2], [3], [4]. It is generally agreed that the performances of nanomaterials are related to their size, morphology, and aggregates. In recent years, much effort has been devoted to the synthesis of size- and morphology-controlled CuO nanomaterials due to their large surface areas and potential size and shape effects. A range of synthetic methods such as hydrothermal/solvothermal, thermal oxidation and reflux, have been developed to prepare various CuO nanomaterials such as nanorods, nanowires, nanoplates, nanobelts, and nanosheet-built flowers [1], [5], [6], [7]. However, these methods suffer from shortcomings such as time-consuming fabrication, tedious manipulation, and poor size distribution.

On the other hand, the microwave heat provides a promising method to synthesize CuO nanomaterials in a short time (in minutes) with high yields [8]. In particular, the microwave hydrothermal approach combines the advantages of microwave rapid heating and hydrothermal crystallization, and allows for the production of CuO nanostructures with well-defined morphology [9], [10], [11], [12], [13]. For example, urchin-like CuO architectures have been synthesized via a microwave hydrothermal self-assembly within a short time of 15 min [10]. Also, spherical and flower-like CuO nanostructures could be quickly fabricated via a microwave hydrothermal method in a Cu(NO3)2–urea or Cu(CH3COO)2–urea aqueous solution [13]. Recently, we have also synthesized various shaped CuO nanoparticles using an additive-mediated microwave hydrothermal approach [14], [15]. Despite these successful cases, CuO nanosheets and their aggregates, i.e. dendrites, have seldom been synthesized by the microwave hydrothermal approach. Furthermore, the investigation of the formation process and properties of such CuO nanostructures would further promote the development of this novel method, and also be favorably viewed for commercial applications.

Here, we report a microwave hydrothermal approach for the controllable synthesis of individual CuO nanosheets and nanosheet-built dendrites without or with an ultrasonic pretreatment. A microwave hydrothermal disassembly process of CuO dendrites is found to be responsible for the formation of discrete individual CuO nanosheets, while this process is hindered through the ultrasonic pretreatment. To shed light on their potential applications, the synthesized CuO nanostructures have been applied in the catalytic thermal decomposition of ammonium perchlorate (NH4ClO4, AP) and visible photo-degradation of organic dyes.

Section snippets

Preparation of CuO nanostructures

All chemical reagents were analytical grade, with the exception of PEG-400 (chemical grade) purchased without any further purification. CuO nanostructures were prepared by extending our previous synthetic method [15]. For the preparation of individual CuO nanosheets: 2.50 g of CuSO4·5H2O and 10 mL of PEG-400 were dissolved in 110 mL of distilled water, followed by quickly adding 60 mL of solution containing NaOH (5.00 g) and urea (10.00 g). After stirring for 10 min, the blue suspension was

X-ray diffraction (XRD) and morphology analyses

The crystal structure and morphology of the CuO precursors were characterized by XRD and SEM, as shown in Fig. 1. Fig. 1a displays the XRD patterns of the CuO precursors, in which all the diffraction peaks can be perfectly indexed to pure phase of Cu(OH)2 with a orthorhombic structure (JCPDS no. 13-0420). Moreover, the diffraction peaks for the precursor 2 are much narrower than those for the precursor 1, indicating an improved crystallinity when pretreated with sonication. The SEM image (Fig. 1

Conclusions

CuO nanosheets and dendrites were selectively synthesized by a facile microwave hydrothermal method. It was found that nanosheet-built CuO dendrites were disassembled into discrete individual CuO nanosheets under microwave hydrothermal conditions. Such a microwave-assisted disassembly process was hindered when the CuO precursor was pretreated by sonication. The catalytic activities of the as-synthesized CuO nanostructures were evaluated by promoting the thermal decomposition of AP and

Acknowledgments

This work was supported by NSFC (21163020) and the Excellent Doctor Innovation Program of Xinjiang University (No. XJUBSCX-2012005).

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