MoO3/SnO2 Nanocomposite-Based Gas Sensor for Rapid Detection of Ammonia

Ammonia is harmful to human health, however, the detection limit of the sensor based on traditional semiconductor gas sensors is high and the speed is slow. Constructing heterostructure is an effective method to improve the performance of sensors. In this article, 1-D MoO
₃
nanorods and SnO
₂
nanoparticles are successfully combined to obtain MoO
₃
/SnO
₂
nanocomposite. The 1-D structure can increase the speed of electron transport, while the nanoparticles on the surface increase the specific surface area, more importantly, the structure maximizes the interface area between the two materials which can transfer electronic more efficiently. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and Barrett–Joyner–Halenda (BJH) are used to analyze the microstructure and elemental composition of MoO
₃
/SnO
₂
. The diameter of MoO
₃
/SnO
₂
nanocomposite is approximately 200 nm and the distribution is uniform. The response of MoO
₃
/SnO
₂
nanocomposite to 100-ppm NH
₃
is 12.7 at 280 °C, and the response/recovery time is 13/2 s. The detection limit for NH
₃
can reach 10 ppb (response 1.3), which enables rapid detection of NH
₃
at low concentration. Electron transport requires more energy to overcome the contact barrier between pure SnO
₂
nanoparticles, which can also lead to electron emission and noise increase. However, the sensitive electrons of MoO
₃
/SnO
₂
nanocomposite can transmit electrons along the 1-D rod-like structure of MoO
₃
, which undoubtedly accelerates the efficiency of electron transmission. Moreover, n-n heterojunction formed between MoO
₃
and SnO
₂
to bend the SnO
₂
band and show better sensitivity to NH
₃
. Therefore, MoO
₃
/SnO
₂
nanocomposite shows a low detection limit and a rapid response/recovery speed. Nevertheless, the nanoparticles on the surface of MoO
₃
/SnO
₂
nanocomposite begin to agglomerate with the increase of SnO
₂
content, which leads to the decrease of gas-sensitive response. The formation process of MoO
₃
/SnO
₂
composites is also discussed in this article. The excellent gas sensing results show that MoO
₃
/SnO
₂
composites are a promising gas sensing material.