Three-Dimensional Assemblies of Edge-Enriched WSe₂Nanoflowers for Selectively Detecting Ammonia or Nitrogen Dioxide

Herein, we present, for the first time, a chemoresistive-type gas sensor composed of two-dimensional WSe2, fabricated by a simple selenization of tungsten trioxide (WO3) nanowires at atmospheric pressure. The morphological, structural, and chemical composition investigation shows the growth of vertically oriented three-dimensional (3D) assemblies of edge-enriched WSe2 nanoplatelets arrayed in a nanoflower shape. The gas sensing properties of flowered nanoplatelets (2H-WSe2) are investigated thoroughly toward specific gases (NH3 and NO2) at different operating temperatures. The integration of 3D WSe2 with unique structural arrangements resulted in exceptional gas sensing characteristics with dual selectivity toward NH3 and NO2 gases. Selectivity can be tuned by selecting its operating temperature (150 °C for NH3 and 100 °C for NO2). For instance, the sensor has shown stable and reproducible responses (24.5%) toward 40 ppm NH3 vapor detection with an experimental LoD < 2 ppm at moderate temperatures. The gas detecting capabilities for CO, H2, C6H6, and NO2 were also investigated to better comprehend the selectivity of the nanoflower sensor. Sensors showed repeatable responses with high sensitivity to NO2 molecules at a substantially lower operating temperature (100 °C) (even at room temperature) and LoD < 0.1 ppm. However, the gas sensing properties reveal high selectivity toward NH3 gas at moderate operating temperatures. Moreover, the sensor demonstrated high resilience against ambient humidity (Rh = 50%), demonstrating its remarkable stability toward NH3 gas detection. Considering the detection of NO2 in a humid ambient atmosphere, there was a modest increase in the sensor response (5.5%). Furthermore, four-month long-term stability assessments were also taken toward NH3 gas detection, and sensors showed excellent response stability. Therefore, this study highlights the practical application of the 2H variant of WSe2 nanoflower gas sensors for NH3 vapor detection.