A research team led by Juan Casanova and Eduard Llobet from the Departamento de IngenierÃa ElectrÃ³nica, Eléctrica y AutomÃ¡tica at the Universitat PolitÃ¨cnica de ValÃ¨ncia (URV), used graphene and perovskites to create a nanosensor that detects nitrogen dioxide with 300% improved sensitivity.
The team used graphene that is hydrophobic (water and moisture-resistant) and sensitive in gas detection, but with some limitations: it is not very selective and its sensitivity declines over time. In addition, the researchers used perovskites, a crystalline-structure material commonly used in the field of solar cells. However, they quickly deteriorate when they are exposed to the atmosphere. That's the reason why the team decided to combine perovskites with a hydrophobic material able to repel water molecules - in order to prove they can prevent or slow down their deterioration.
"This graphene and perovskites hybrid resulted in a material that can more sensitively detect these kinds of gas. Perovskite alone eventually deteriorates and we have proved that when we put it on top of graphene, their properties and the sensor response remain stable longer," explains Eduard Llobet.
Researchers have worked for years looking for alternatives to conventional sensors and the carbon nanomaterials field offers promising results in this area. Besides being tiny and needing very low energy for functioning, these materials have proven to have good responses and quick recovery at room temperature, unlike existing sensors.
"They are portable devices due to their sizeâthey can be even wearable. Work at room temperature is very important because they need very small batteries, an unthinkable feature with other materials," says Llobet.
This research has used graphene with perovskite nanocrystals as a toxic gas sensor for the first time and it has shown that this combination is a good alternative to detect these compounds due to its high sensitivity over time.
This study showed that perovskites can pose a good alternative to metals, metal oxides, polymers and other molecules frequently used to modify the surfaces of carbon nanomaterials such as graphene.
An ITQ (Instituto de TecnologÃa QuÃmica) research team has worked for years in several lines aimed at the synthesis and application of perovskites in fields such as solar cells and photocatalysts. However, their use as sensors is relatively new. ITQ carried out the size and composition control of nanocrystals to make them highly sensitive to nitrogen dioxide.
These materials present a high potential to develop new gas sensors, because here we take advantage of a limitation in the field of solar cells: "defects" that in the case of sensors play a significant role in the functioning mechanism. In addition, taking into account all the structural modification possibilities of perovskites, we have the opportunity to find a large family of sensors to detect other gases. Also, it is important to note that perovskites are easy to synthesize and they use abundant elements in nature," explains Pedro Atienzar, CSIC scientist at the Instituto de TecnologÃa QuÃmica.