Reduced graphene oxide decorated with SnO2:Fe nanoparticles as humidity sensors
Authors: Dana Toloman, Adriana Paula Popa, Manuela Stan, Ioan Ovidiu Pană, Crina Socaci
Keywords: composite nanoparticles, humidity sensors
Applications
The development of humidity sensors is a continuous challenge for the scientific community. These devices are essential for maintaining a healthy and comfortable living environment with applications in various sectors such as hospitals, museums, textile and food processing industries.
The use of nanostructured materials has been a particularly important step in the accelerated development of new classes of simple but reliable sensors.
Innovative aspects
State-of-the-art humidity sensors are made of nanostructured semiconductor oxides such as ZnO, SnO2. The detection process is based on the adsorption of water molecules on the surface of the oxide, which causes a change in the material conductivity.
The characteristics that a humidity sensor must fulfill – in order to be economically attractive – are: high sensitivity, fast response time, chemical and physical stability, wide sensing range and low cost.
There are several methods of improving the sensitivity of the humidity sensors, such as: doping the semiconductor material with transition metal ions, realization of composite materials by coupling with another semiconductor material or with carbon-based materials.
The use of graphene oxide (GO) as a support for the semiconductor material ensures better dispersion of the nanoparticles, facilitating their contact with water molecules. Moreover, its presence can lead to increased sensor sensitivity, as water molecules integrate more efficiently into the graphene structure even at low humidity.
The technological solution provided by our group is the following: decoration of reduced graphene oxide (rGO) with Fe-ion doped SnO2 nanoparticles, optimizing the ratio between the two components to obtained a high humidity sensing sensitivity.
The obtained composite material exhibits 5 times higher sensitivity than Fe-ion doped SnO2 nanoparticles. The relative humidity (RH) range in which the composite material can be used is 25-100% RH.
Technology
SnO2 nanoparticles doped with Fe3+ ions (1%) were prepared by precipitation method. The nanoparticles mean size is 17 nm. The SnO2:Fe-rGO nanocomposite was obtained by the electrostatic interaction between positively charged doped SnO2 nanoparticles and negatively charged rGO.
The formation of the composite can be easily confirmed by X-ray diffraction and transmission electron microscopy. The testing of the material as a humidity sensor was done by measuring the electrical resistivity at a given frequency as a function of relative humidity.
Advantages
- Narrow nanoparticle size distribution (10-20nm) ensures a large contact surface area with water molecules
- The use of rGO as a nanoparticles support facilitates the adsorption of water molecules due to its porous structure and by ensuring a high degree of nanoparticles dispersion
- The preparation method does not involve sophisticated infrastructure and can be done with low production costs