SnO₂ nanoparticles-reduced graphene oxide nanocomposites for NO₂ sensing at low operating temperature

Abstract

SnO₂ nanoparticles-reduced graphene oxide (SnO₂-rGO) nanocomposites have been successfully prepared by a facile method via hydrothermal treatment of aqueous dispersion of GO in the presence of Sn salts. The combined characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate the successful formation of SnO₂-rGO nanocomposites. To demonstrate the product on sensing application, gas sensors are fabricated using SnO₂-rGO nanocomposites as sensing materials and investigated for detection of NO₂ at low operating temperature (50 °C). It is found that SnO₂-rGO nanocomposites exhibit high response of 3.31 at 5 ppm NO₂, which is much higher than that of rGO (1.13), and rapid response, good selectivity and reproducibility. Furthermore, the reason for enhancing sensing performance by addition of SnO₂ nanoparticles has also been discussed.

Introduction

A large amount of NO₂ has been released to the environment from combustion facilities and automobiles annually, and therefore, the detection of NO₂ has been attracted considerable interest because NO₂ is harmful to plants and respiratory system of human beings and animals [1], [2]. Up to now, numerous techniques have been successfully developed to detect trace levels of NO₂ in atmosphere, such as chemiluminescence [3], ion chromatography [4], spectrophotometry [5], etc. Although these above-mentioned methods can detect NO_x precisely, they suffer from drawbacks such as high cost, complex and time-consuming process, limiting their wide applications. Much effort has been devoted to develop highly effective methods for NO₂ detection. As a result, various solid-state NO₂ sensors based on semiconductors [6], solid electrolytes [7], optic fiber [8] and surface acoustic wave (SAW) devices [9] have been successfully proposed. Among them, metal oxide semiconductors-type NO₂ sensors have been widely studied due to their unique properties such as small size, low cost, low detection limit, fast response and recovery. For example, WO₃-based nanocrystallines [10], ZnO nanowires [11], SnO₂ nanoribbons [12], and In₂O₃ nanoparticles [13] exhibit good performances for detection of NO₂ as sensing materials. However, these sensors hold an obvious disadvantage of high operating temperature, resulting in high power consumption and difficulty in integration. Therefore, development of economical and sensitive method for detection of NO₂ at low operating temperature is highly desired.

Graphene, a two-dimensional sheet of sp²-hybridized carbon atoms has been received much attention due to its unique physical and chemical properties [14], [15], [16]. Particularly, graphene and reduced graphene oxide (rGO) have been considered as promising gas sensing materials for detection of gases at room temperature due to the enormously high electron mobility at room temperature [17], [18], [19], [20], [21], [22]. Although various NO₂ sensors have been successfully constructed by using graphene-based materials, the relatively poor performances such as low response, long response and recovery times should be further improved [23], [24], [25], [26], [27], [28]. Recently, preparation of graphene and metal oxides nanocomposites have been proved to be an effective method for constructing high performance NO₂ sensors [29], [30], [31]. However, these sensors still need high temperature to achieve the sensing properties. Accordingly, it is still a challenge for preparation of graphene-based NO₂ sensors with good sensing performances at low operating temperature.

In this paper, SnO₂ nanoparticles-reduced graphene oxide (SnO₂-rGO) nanocomposites have been successfully synthesized by a hydrothermal route. This method requires high concentrations of a GO precursor and introduction of a trace amount of SnO₂ nanoparticles into the reaction system. Most importantly, the SnO₂-rGO nanocomposites can be used as an effective sensing material for detection of NO₂ at low operating temperature (50 °C). It is found that SnO₂-rGO nanocomposites exhibit better response, faster response and recovery toward NO₂ than those of rGO. Furthermore, sensing mechanism for the detection of NO₂ is also discussed.