Efficient NO2 detection and the sensing mechanism of stretchable/biodegradable MWCNT based sensors decorated with CeO2 nanoparticles

We report the performance of stretchable sensors for the NO2 detection, which were fabricated by depositing multi-walled carbon nanotubes (MWCNTs)/CeO2 composites on a silicon rubber. SEM images of the sensor’s surface revealed that the MWCNTs are interconnected forming long carbon fibers, while the CeO2 powders consisted in a mixture of nanorods and porous coalesced nanoparticles. The detection tests for the NO2 gas were carried out by using sensors stretched at 0%, 50% and 100% strain. The best performance for the NO2 detection (1, 100 and 1000 ppm) was observed for the sensor stretched at 100% strain, since it produced a detection response ≈ 3.25 times faster than that for the non-stretched sensor (0% strain). Moreover, the sensor elongated up to 100% strain presented the lowest response and recovery times of 25.6 and 383.9 s, respectively. The improvement of the detection response and the reduction of the response/recovery times were caused by the increase of the oxygen vacancy defects (active sites for the adsorption of NO2 molecules) on the sensor’s surface when the tensile strain is applied. The presence of these defects was confirmed by Raman, XPS and absorbance measurements. Additionally, MWCNTs/CeO2 composites were deposited on a jelly based substrate to construct a flexible and biodegradable sensor. Interestingly, this device had even lower response/recovery times (22.9/345.2 s) than the stretchable sensors for the detection of NO2 (100 ppm). The response times for the stretchable/biodegradable sensors are among the lowest reported so far and the sensors operate at low energy consumption (50–67 µW).