A sustainable waterproof temperature sensor made with single-use-packets and enhancement of its sensing performance by depositing the g-C3N4/BiOBr composite on its surface

Abstract

Currently, flexible temperature sensors are highly demanded for processes in the food industry. However, they have a high cost and most of them detect temperatures only below 80 °C. To fabricate temperature sensors at lower cost, temperature sensors were fabricated by printing graphene ink on recycled plastics (obtained from single-use-packets). Firstly, sensors made exclusively with graphene were tested for the temperature detection, but no detection signal was obtained. Subsequently, the sensors were coated with g-C3N4 (gCN)/BiBrO composite microparticles and those ones produced response times of 8–12.2 s when they are detecting temperatures of 60–120 °C in air. For this same detection range, the recovery times varied from 19 to 27.6 s. The sensors were also tested in hot water and detected temperatures of 60–92 °C. Interestingly, lower response/recovery times of 5–7.8/7–14.7 s were obtained in comparison with the sensors used in air. The surface of the sensors exposed to different temperatures was also analyzed by Raman and XPS techniques. After this, we found that the highest amount of defects (oxygen vacancies) are present in the sensor used for the temperature detection of 90 °C. If the temperature detection is increased to 120 °C, graphene oxide is formed on the sensor's surface as well as Bi-O-C and Br-C bonds. Those ones indicate a better chemical linking between the gCN/BiBrO and the graphene layer, which in turn, favored the electron transport through the sensor and lowered the response time at high temperatures. In general, the results of this research indicate that recycled plastics can be used for the fabrication of inexpensive waterproof temperature sensors, which can operate in air or underwater. The sensors studied here could be of interest for the food industry or for the monitoring of temperatures under rain.