Hierarchical Co2SnO4 Microspheres for Enhanced NO2 Gas Sensing Performance
Authors: Joshi Niravkumar J , DE Oliveira Osvaldo NOVAIS 
Published: July 2021

Introduction:

The living standards of the human race in the past few decades have grown at a remarkable pace. One of the most critical environmental issues is the monitoring of air quality [1]. Nitrogen dioxide (NO2) is a hazardous gas and has multiple sources like vehicular emission, combustion process, and unvented heaters present in our day-to-day life. Overexposure to this gas becomes a reason for respiratory problems in humans as well as animals. Hence, it is very crucial to detect this toxic analyte selectively at low temperatures. Various metal oxides have been explored to detect NO2 gas; however, selectivity and operation temperature are still challenging [2]. Microsensors using nanostructured oxides/binary oxides are the most suitable to minimize the current problems of gas sensors (lack of sensitivity, selectivity, and stability) since the reduction in dimensions implies a greater contribution of the surface (greater sensitivity) as well as modification of the transport mechanisms (faster processes) [3-4]. This work demonstrates the low temperature, highly sensitive NO2 detection with fast recovery speed based on hierarchical Cobalt Stannate (Co2SnO4) microspheres synthesized by a facile co-precipitation route.

Methodology:

Hierarchical Cobalt Stannate (Co2SnO4) microspheres were synthesized with the co-precipitation method with a different annealing process. The sensor film was deposited on microsensors features an interdigitated electrode which encircled platinum heater to regulate the operating temperature and ensure its uniformity. The samples' structural and surface properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (FESEM), and BET Surface area, especially to verify the nanomorphology and high surface area. Chemiresistive sensing behavior was recorded. The sensor response was calculated using the equation: Sensor Response (%) = (Ra-Rg)/Ra *100, where Ra and Rg are resistance in air and with the sensing gas, respectively.

Results and Conclusions:

Compared with the traditional metal oxide-based gas sensors, which operates at high temperature (>300 °C), specific accomplishments include (1) synthesis of Co2SnO4 microspheres with the larger surface area for higher sensing response towards NO2 gas; (2) chemiresistive gas responses of the Co2SnO4 sensor down to 1 ppm for NO2 at a low temperature of 90 °C with high sensitivity and long-term stability; (3) the morphology of microspheres for fast adsorption-desorption processes; and (4) the sensor shows the excellent reproducibility and reversibility with less power consumption (5) Co2SnO4 film exhibits a maximum sensor response of ~81 at 90°C towards NO2 with fast response (~ 24 s) and recovery time (~756 s) at one ppm. (6) the resulting sensor exhibits selectivity toward nitrogen dioxide compared to other gases such as CO2, CO, and H2.

References:

[1] Kevin W. Bowman, Toward the next generation of air quality monitoring: Ozone, Atmospheric Environment 80 (2013) 571-583. doi: 10.1016/j.atmosenv.2013.07.007

[2] Yichuan Wu, Nirav Joshi, Shilong Zhao, Hu Long, Liujiang Zhou, Ge Ma, Bei Peng, Osvaldo N Oliveira Jr., Alex Zettl, and Liwei Lin, NO2 gas sensors based on CVD tungsten diselenide monolayer, Applied Surface Science 529 (2020) 147110. doi: 10.1016/j.apsusc.2020.147110

[3] Sabu Thomas, Nirav Joshi, Vijay K. Tomer, Functional Nanomaterials: Advances in Gas Sensing Technologies. 2020: Springer Nature Singapore Pte Ltd. doi: 10.1007/978-981-15-4810-9

[4] Nirav Joshi, Luís F. da Silva, Harsharaj S. Jadhav, Flavio M. Shimizu, Pedro H. Suman, Jean-Claude M'Peko, Marcelo Ornaghi Orlandi, Valmor R. Mastelaro, Osvaldo N. Oliveira Jr, Yolk-shelled ZnCo2O4 microspheres: Surface properties and gas sensing application, Sensors and Actuators B 257 (2018) 906–915. doi: 10.1016/j.snb.2017.11.041.