A highly sensitive and biodegradable NO2 sensor made with CNTs and Ni (OH)2/NiO:Yb microparticles

This work reports the fabrication of flexible and biodegradable sensors for NO2 detection. The sensors were fabricated by depositing Yb doped Nickel oxides (or hydroxides) on a flexible and biodegradable support of algae-sheets/CNTs. According to the analysis by X-ray diffraction, the Ni(OH)(2):Yb and the NiO:Yb employed to make the sensors presented hexagonal and cubic phases, respectively. The Ni(OH)(2):Yb and the NiO:Yb were synthesized at 200 and 400 degrees C, therefore, they are named as NiYe200-OH and NiYe400-0, respectively. In addition, the analysis by scanning electron microscopy revealed that the Ni(OH)(2):Yb and the NiO:Yb consisted in porous microparticles with sizes of 25-47 mu m and 1-25 mu m, respectively. Those microparticles were the sensitive material for the gas detection, since the gas detection was not possible without them. The gas detection tests for NO2 (100 ppm at room temperature) were firstly achieved in the unbent state and the sensors made with NiYe200-OH and NiYe400-0 powders presented the lowest response/recovery times of 16/252 s and 19/361 s, respectively. Surprisingly, the values of response/recovery times decreased by 37%/16% and by 26%/32% for the AS-CNT/NiYe200-OH and AS-CNT/NiYe400-0 sensors, respectively, after bending them (at a radius of curvature of 0.8 cm). The sensors were able to detect NO2 gas because they had on their surface oxygen vacancy defects, which acted as active sites for the adsorption of NO2 molecules. The presence of such defects was demonstrated by the XPS, absorbance and Raman measurements. Some advantages of the sensors were: 1) their capacity to operate with very low power (200-300 mu W) and 2) their ability to be recovered for the next cycle of detection without the use of UV radiation or heating, which is normally used to recover the capacity of the sensor for gas detection. Hence, the results showed this work indicate that our gas sensor could be used for the detection of noxious gases and can be used in portable applications due to their compact size and light-weight. Most importantly, most of their mass (approximate to 92%) is biodegradable, making them eco-friendly. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This work presents the fabrication of flexible and biodegradable sensors for NO2 detection. The sensors show active sites on their surface for gas detection and exhibit advantages of low power consumption and recoverability.