Synthesis and ethanol sensing properties of Al-doped ZnO nanofibers

doi:10.1016/j.cap.2012.08.019

Current Applied Physics

Volume 13, Issue 2, March 2013, Pages 403-407

https://doi.org/10.1016/j.cap.2012.08.019 Get rights and content

Abstract

Undoped and Al-doped ZnO nanofibers were synthesized via a simple electrospinning method, and then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman scattering and photoluminescence (PL) spectroscopy. The ethanol sensing properties of the sensor based on the nanofibers were also investigated. The results show that the sensor fabricated from Al-doped ZnO nanofibers exhibits better gas sensing performance than that fabricated from the undoped ZnO nanofibers, and the gas sensing mechanism is discussed.

Highlights

► Undoped and Al-doped ZnO nanofibers were synthesized by electrospinning method. ► Al doping does not change the crystal structures and morphology of ZnO nanofibers. ► The ethanol sensing properties of ZnO nanofibers can be enhanced by Al doping.

Introduction

Recently, metal oxide semiconductors have attracted much attention for the detection of toxic and pollutant gases due to their advantageous features such as high response, low cost and portability [1], [2], [3], [4]. Among these semiconductor metal oxides, ZnO, non-toxic and inexpensive n-type semiconductor, is one of the most attractive candidates for the detection of combustible or toxic gases. So far, many efforts have been done to investigate the sensing properties of ZnO responding to various gases including NH₃, H₂, CO, H₂S, C₂H₅OH and so on [5], [6], [7], [8], [9]. Although the utilization of ZnO in the field of sensing gases has a long history, it has been, somewhat limited in the real applications, due to high working temperature, low sensitivity and poor selectivity [10].

To improve the sensing properties, a general way is to downsize semiconductor material into the nanoscale, which can considerably improve the sensing performance as a result of its the increased surface areas. One-dimensional (1D) ZnO nanostructures such as nanowires, nanorods, and nanofibers have been successfully achieved via various methods including chemical vapor deposition, hydrothermal, template-assisted and electrospinning [11], [12], [13], [14]. Among these methods, electrospinning is a facile, versatile and effective method to manufacture 1D nanofibers, which have an extremely large surface to volume ratio and length to diameter ratio. Such structure is helpful for improving gas sensing properties through offering large surface area for chemical reaction and small dimension for effective electron transport.

Doping is another important and effective way to improve the sensing properties of semiconductors. Several metal elements such as Cu, Pd have been tried as the dopant into ZnO nanomaterials for enhancing the sensing properties [15], [16]. Aluminum (Al) as a dopant can serve as a donor in the ZnO lattice and induce chemical defects, which can significantly improve the electrical, optical and sensing properties of ZnO. Navale et al. [17] studied Al-doped ZnO nanomaterials NO_x gas sensor, while methanol sensing properties of Al-doped ZnO thin films have been investigated by Sahay and Nath [18]. Li et al. [2] have studied Al-doped ZnO nanotetrapods for detection of ethanol vapor. Recently, the fabrication and electrical, optical properties of electrospun Al-doped ZnO nanofibers have been reported [19], [20], [21], [22]. However, rare investigations concern the ethanol sensing properties of electrospun Al-doped ZnO nanofibers. In this work, we will report the fabrication of Al-doped ZnO nanofibers via electrospinning technique. The effects of Al doping on the crystal structure, optical and ethanol sensing properties of the nanofibers will be investigated.

Section snippets

Experimental

In a typical procedure, 30 ml polyvinyl ethanol (PVA, M_w 80,000) solution (10 wt%), 2.19 g Zn(CH₃CO₂)₂·2H₂O and the suitable amount of AlCl₃ (0 g or 0.053 g) were mixed together and stirred for 1 h at 50 °C, meanwhile 2 ml ethanol was slowly dropped into the solution. This mixture was aged at room temperature for 2 h. Then, the mixture was loaded into a glass syringe for electrospinning. The precursor solutions were electrospun at a positive voltage of 8 kV, and the tip-to-collector distance

Results and discussion

Fig. 1(a) and (b) shows the SEM images of as-synthesized undoped and Al-doped ZnO nanofibers after calcinations at 650 °C for 3 h. Both of them are highly dominated by the nanofibers with diameters of about 100 nm and lengths of several millimeters, indicating a large length to diameter ratio. The surfaces of the undoped and Al-doped ZnO nanofibers appear rough porous structures in Fig. 1(c) and (d), and the nanofibers are composed of nanoparticles connected to each other with diameters around

Conclusion

Undoped and Al-doped ZnO nanofibers with diameters of around 100 nm were synthesized using the electrospinning method. The nanofibers with rough surface exhibit the hexagonal structure, and Al doping does not change the crystal structures of ZnO nanofibers. The sensing measurements show that Al-doped ZnO nanofibers exhibit better ethanol sensing properties than undoped ZnO nanofibers, and the response and recovery time is as fast as 5 s and 9 s, respectively. The improvement of gas sensing

Acknowledgments

The authors gratefully acknowledge the financial support of the Foundation for University Middle-aged Key Teacher by Henan Province (Grant No. 2010GGJS-001), and Technology Project on Key Problems of Henan Province (Grant Nos. 082101510007 and 112102210282).

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Synthesis and ethanol sensing properties of Al-doped ZnO nanofibers

Abstract

Highlights

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgments

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Mater. Lett.

Sens. Actuators, B: Chem.

Sens. Actuators, B: Chem.

Physica E

Mater. Sci. Eng., B

J. Colloid Interface Sci.

J. Alloys Compd.