ArticleMaterials ScienceControlling synthesis and gas-sensing properties of ordered mesoporous In2O3-reduced graphene oxide (rGO) nanocomposite
Introduction
There is an increasing concern on semiconducting metal oxide gas sensors in past decades regarding the awareness of environmental protection and human health. Various nanostructured metal oxides with high surface area have widely investigated as sensing materials 1., 2., 3., 4., 5.. Among them, ordered mesoporous metal oxides have attracted considerable attention since their accessible pores benefit not only the diffusion of gas molecules for increasing response rate, but also the reduction in aggregation and sintering for enhancing their thermal stability under high temperature during the fabrication and work process of gas sensor 6., 7., 8., 9., 10., 11., 12., 13.. For example, Tiemann and co-workers [13] reported the improved sensitivity of mesoporous In2O3 to CH4. Mao et al. [14] also reported the enhanced sensitivity of hierarchically mesoporous hematite microsphere toward formaldehyde (HCHO). Lai et al. [15] presented a low-cost synthesis of mesoporous In2O3 with tunable pore wall thickness by directly using solvent-extracted mesoporous silica with different pore sizes as a template. The gas testing results showed that the sensitivity of mesoporous In2O3 to HCHO sharply increases with reducing the pore wall thickness. The gas-sensing properties of those mesoporous metal oxide sensors could be further improved by doping noble metals. Tu et al. [16] reported that Pt-doped mesoporous In2O3 possess a significantly higher response than those without doping Pt. Lai et al. [17] reported the enhanced gas-sensing properties of Ag-doped mesoporous In2O3 toward HCHO. Nevertheless, the rising cost resulted from noble metals may limit their practical application.
Graphene is a kind of interesting material with some extraordinary properties including ultra-large specific surface area, unusual mechanical strength and high electrical conductivity, which has attracted enormous attention 18., 19.. Recently, several groups have reported that the gas-sensing properties of metal oxide sensors could be significantly improved after coupled with graphene. For example, Deng et al. [20] have synthesized an reduced graphene oxide (rGO)-conjugated Cu2O nanowire mesocrystal via a one-pot hydrothermal treatment of copper (II) acetate in the presence of o-anisidine and graphene oxide (GO), which exhibit a higher response to NO2 than individual Cu2O nanowire or rGO. Choi et al. [21] have also reported the enhanced response of SnO2 nanofibers functionalized with rGO to acetone and hydrogen sulfide. To the best of our knowledge, however, there is no report on ordered mesoporous metal oxide–rGO nanocomposite for gas sensors.
In this work, we have successfully synthesized ordered mesoporous In2O3 nanoparticles via the nanocasting route directly using mesoporous silica as a hard template and then mixed them with rGO to form an ordered mesoporous In2O3-rGO nanocomposite under the assistant of ultrasonication (Scheme 1). The gas-sensing testing results exhibit that ordered mesoporous In2O3-rGO nanocomposite possesses significantly enhanced response and relatively high selective toward ethanol, which suggests the potential application of the ordered mesoporous In2O3-rGO nanocomposite for detecting ethanol.
Section snippets
Synthesis of ordered mesoporous In2O3 nanoparticles
Ordered mesoporous silica KIT-6 was synthesized at hydrothermal temperature of 130 °C according to the established procedures [22]; 0.6 g of KIT-6 was dispersed in 10 mL of ethanol, followed by addition of 1.2 g of hydrated indium nitrate under stirring in a Teflon beaker. After all the solvent had evaporated, the resulting powder was heated in a ceramic crucible in an oven at 250 °C for 3 h, in order to decompose indium nitrate. Finally, the silica template was removed at room temperature using 2
Results and discussion
Low-angle XRD patterns of mesoporous silica template KIT-6, mesoporous In2O3 and mesoporous In2O3-rGO nanocomposite are shown in Fig. 1a. KIT-6 displays three resolved diffraction peaks, which could be indexed as the (211), (220) and (332) reflections of the Ia3d symmetry. Mesoporous In2O3 also exhibits a diffraction peak, suggesting that the ordered mesostructure was to some degree transformed into In2O3 replica via the negative structural replication, although this peak is relatively broader
Conclusions
In summary, we have successfully synthesized ordered mesoporous In2O3 nanoparticle-rGO nanocomposite via a combining hard-template and ultrasonic mixing method. The resultant mesoporous In2O3 nanoparticle-rGO nanocomposite exhibited much high response to ethanol compared to those pure mesoporous In2O3 without rGO, which suggests the potential application of such novel nanostructured material for detecting ethanol gas. Similar strategy could be extended to other mesoporous metal oxide–rGO
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (21006116, 51362024), the Natural Science Foundation of Ningxia (NZ12111, NZ14010) and, the Prophase Research Special Project of the National Basic Research Program of China (2012CB723106). Xiaoyong Lai thanks the West Light Foundation of The Chinese Academy of Sciences.
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