Blue–green luminescence by SWCNT/ZnO hybrid nanostructure synthesized by a simple chemical route

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Abstract

A hybrid nanostructure of single wall carbon nanotubes (SWCNTs) and zinc oxide (ZnO) nanoparticles (NPs) is synthesized by a chemical precipitation method at room temperature. Characterization by SEM/EDAX, HRTEM, and Raman and FTIR spectroscopy establishes the nanohybrid structure of the synthesized sample. The average size of ZnO nanocrystallites is 15 nm and they randomly adhere to the surfaces of the SWCNT bundles. The structure is further confirmed by XRD study. Characteristic UV–visible absorption is observed with a strong absorbance peak at 263 nm. Photoluminescence (PL) study shows a broad emission spectrum in the blue–green region, under UV excitation from 220 to 250 nm wavelength. Such composites may find wide applications as tailored luminescent materials for optoelectronic and sensor devices.

Introduction

Carbon nanotubes (CNTs) since their discovery in the year 1991 [1] have been continuously drawing attention of researchers due to their fascinating physical and chemical properties [2]. The modification of CNTs by surface functionalization and hybridization with other nanostructures can drastically change their physical properties to transform them into functional nanomaterials with desired properties, which may find several novel applications in useful devices. For the last few years, optical properties of modified carbon nanotubes have become one of the major concerns for the researchers [3], [4], [5], [6]. CNTs modified with nanocrystalline metal oxides are emerging as optical materials with tuned luminescence characteristics. Binary oxides such as ZnO, CdO, In2O3, TiO2 and SnO2 have unique features, which make them widely used as gas sensors [7] and as bases for creating and tuning many novel material properties [8]. ZnO is one of the hardest materials in the II–VI semiconductor family and hence does not suffer from any dislocation degradation [9]. Scope of its applications in optoelectronics such as blue colour light emitting phosphors [10], [11], as fluorescence labels in medicine and biology, in controlling units as UV photodetectors, as high flame detectors [12] and as nanosensors of various gases has been extensively investigated. CNT/ZnO heterostructure can extend the scope of potential applications of CNTs [13], [14], [15] as a tailored luminescent material. Synthesis of CNT/ZnO nanohybrid by physical adsorption method has been reported earlier [13], [16], [17], [18].

The authors report a simple chemical technique to prepare SWCNT/ZnO hybrid structure using a chemical precipitation route. Significant photoluminescence property of the composite, distinguished from individual luminescence characteristics of SWCNT and ZnO nanoparticles, is reported.

Section snippets

Experimental details

We procured SWCNTs (1–2 nm outer diameter, length 1–3 μm and purity >95%) from Chengdu Organic Chemicals Co., Ltd., Chinese Academy of Sciences and further purified them by high temperature oxidation at 350 °C followed by acid treatment, which includes sonication of SWCNTs in 6 M HCl. The acid treated SWCNTs are then washed thoroughly with deionized water to make pH neutral. Filtration of SWCNT using Millipore filtration apparatus has been done followed by drying at room temperature. By a simple

Results and discussions

The presence of ZnO is confirmed by EDAX analysis of the hybrid structure as shown in Fig. 1. Au is present due to gold coating of the sample film. The inset of Fig. 1 shows the SEM micrograph of SWCNT/ZnO hybrid nanostructure. It is clearly observed from the micrograph that ZnO nanocrystallites have coated the surfaces of SWCNT bundles. The XRD patterns of pristine SWCNT (i.e. the purified SWCNT) and SWCNT/ZnO hybrid structure are shown in Fig. 2. The peaks centered at 26°, 42° and 44°

Conclusions

Synthesis of SWCNT/ZnO hybrids consisting of ZnO nanocrystals of average size 15 nm has been achieved following a very lucid wet chemical process. The composite nanostructure of SWCNT bundles decorated with ZnO nanocrystals has been confirmed by SEM, HRTEM and XRD studies. FTIR analysis and EDAX spectrum revealed that ZnO nanoparticles are deposited on the surfaces of SWCNTs. At UV excitations from 220 to 250 nm, significant visible photoluminescence in the blue–green region of the spectrum has

Acknowledgement

The authors acknowledge with thanks the support from Dr. D. Sukul and Dr. A.K. Patra, Department of Chemistry, NIT Durgapur, for PL and FTIR study. They are grateful to NIT Durgapur and Government of India for financial support. They also extend their sincere thanks to Dr. R. Mitra and Dr. A. Roy of IIT Kharagpur, for making available the HRTEM and Raman spectroscope facilities.

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