CVD growth of self-assembled 2D and 1D WS2 nanomaterials for the ultrasensitive detection of NO2

Herein, we report for the first time on the facile synthesis of 2D layered WS ₂ nanosheets assembled on 1D WS ₂ nanostructures by combining the aerosol assisted chemical vapor deposition (AA-CVD) method with H ₂-free atmospheric pressure CVD, for an ultrasensitive detection of NO ₂. This synthesis strategy allows us a direct integration of the sensing material onto the sensor transducer with high growth yield and uniform coverage. Two different WS ₂ morphologies (nanotriangles and nanoflakes) were prepared and investigated. The results show that the assembly of layered WS ₂ nanosheets on a 3D architecture leads to an improvement in sensing performance by maintaining a high surface area in an accessible porous network. The sensors fabricated show stable, reproducible and remarkable responses towards NO ₂ at ppb concentration levels. The highest sensitivity was recorded for WS ₂ NT sensors, with an unprecedented ultra-low detection limit under 5 ppb. Additionally, this material has demonstrated its ability to detect 800 ppb of NO ₂ even when operated at room temperature (25 °C). Regarding humidity cross-sensitivity, our WS ₂ sensors remain stable and functional for detecting NO ₂ at ppb levels (i.e., a moderate response decrease is observed) when ambient humidity is raised to 50%. An 8-month long-term stability study has been conducted, which indicates that WS ₂-NT sensors show a very stable response to NO ₂ over time.