Ultra-Sensitive Benzene Detection and Gas Sensing Mechanism of (C4H9NH3)2PbI2Br2 Organic-Inorganic Perovskite
Authors: Zhang Le-Xi , Zhu Meng-Ya , Bie Li-Jian 
Published: May 2020

Introduction

Benzene vapour is one of the general hazardous air pollutants, as well as a typical lung cancer marker, hence the permissible environment limit value has been regulated to be ~1.6 ppb (part per billion) in Europe. It is interesting to develop a portable device for detection ultra-low concentration benzene. Chemiresistive gas sensors to detect benzene have been widely investigated, however, most detection limits are in ppm level,while only a few reports are in ppb level (100 ppb)[1]. Organic-inorganic hybrid perovskites combine the excellent performance of organic materials and inorganic semiconductors, so one compound was utilized as a gas sensing material in this work. Synthesis and benzene detecting application of (C4H9NH3)2PbI2Br2 are reported, and the gas sensing mechanism is also discussed using in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRFT-IR).

Synthesis of (C4H9NH3)2PbI2Br2

Perovskite (C4H9NH3)2PbI2Br2 was synthesized through a facile mixed solution method [2]. N-butylamine (30 ml) was dissolved in 47 wt% hydroiodic acid (35 ml) and absolute ethanol (15 ml) solution under ice-water bath. The pomegranate red solution was maintained at 70 °C for 2 h in a water bath kettle, resulting in light yellow solution. Then, white powders were obtained via vacuum distillation at 90 °C for 20 min. The powders were then collected with the suction filter, washed several times with ether, and dried at 70 °C in a vacuum oven for 12 h. PbBr2 (0.8808 g) and as-obtained C4H9NH3I (0.9651 g) were mixed in 47 wt% hydroiodic acid (10 ml), 48 wt% hydrobromic acid (10 ml) and absolute ethanol (10 ml) solution. The solution was kept at 90 °C for 2 h in a water bath kettle, resulting in light yellow solution. Then, light yellow powders were obtained via vacuum distillation at 70 °C for 20 min. The powders were collected with the suction filter, washed several times with ether, and dried at 70 °C in a vacuum oven for 24 h.

S
ensor
F
abrication and Measurement

The perovskite was fabricated into a traditional resistive sensor device [3]. The sensing performance was conducted on a NS-4000 Smart Sensor Analyser (Beijing Zhong Ke Micro-Nano Networking Technology Ltd., China). The response was defined as the ratio of sensor resistance in air (Ra) to that in a target gas (Rg): Sr = Ra/Rg.

Results and Conclusions

The perovskite (C4H9NH3)2PbI2Br2 exhibits the highest response at the optimum operating temperature of 160 °C, indicating excellent selectivity, as shown in Fig. 1 (a). This gas sensor shows such ultra-high response for ppt-level benzene that has never been reported before. As can be seen in the response-recovery curves in Fig. 1 (b), the response increases fast to an equilibrium value and then decreases rapidly to the baseline in each cycle at 160 °C. The in-situ DRFT-IR spectra of (C4H9NH3)2PbI2Br2 in air and benzene at room temperature (RT) and 160 °C, respectively, confirming the gas sensing mechanism is originated from the physical adsorption-desorption of benzene molecules on the (C4H9NH3)2PbI2Br2 surface, charge transfer model of which is quite different from that of conventional metal oxides.

Fig. 1 (a) Response of the (C4H9NH3)2PbI2Br2 sensor to 500 ppt benzene, toluene, ethanol, ortho-xylene, and para-xylene gases at various operating temperatures. (b) Response-recovery curves of the gas sensor to 1–500 ppt benzene at 160 °C. (c) In-situ DRFT-IR spectra of (C4H9NH3)2PbI2Br2 in air and benzene at RT and 160 °C, respectively.

References

[1] J.H.Kim, H.W.Kim, S.S.Kim, Ultra–sensitive benzene detection by a novel approach: Core–shell nanowires combined with the Pd-functionalization, Sens. Actuators, B 239 (2017) 578–585. doi: 10.1016/j.snb.2016.08.071.
[2] M.-Y.Zhu, L.-X.Zhang, J.Yin, J.-J.Chen, L.-J. Bie, Ppt-level benzene detection and gas sensing mechanism using (C4H9NH3)2PbI2Br2 organic–inorganic layered perovskite, Inorg. Chem. Front. 5 (2018) 3046–3052. doi: 10.1039/c8qi00803e.
[3] M.-Y.Zhu, L.-X.Zhang, J.Yin, J.-J.Chen, L.-J. Bie, B.D.Fahlmand, Physisorption induced p-xylene gas-sensing performance of (C4H9NH3)2PbI4 layered perovskite, Sens. Actuators B 282 (2019) 659–664. doi: 10.1016/j.snb.2018.11.124.

Figure 1