Here, we report on the synthesis of tungsten diselenide (WSe₂) nanosheets using an atmospheric pressure chemical vapor deposition technique via the rapid selenization of thin tungsten films. The morphology and the structure, as well as the optical properties, of the so-produced material have been studied using electron microscopies, X-ray photoelectron spectroscopy, photoluminescence, UV–visible and Raman spectroscopies, and X-ray diffraction. These studies confirmed the high crystallinity, quality, purity, and orientation of the WSe₂ nanosheets, in addition to the unexpected presence of mixed phases, instead of only the most thermodynamically stable 2H phase. The synthesized material might be useful for applications such as gas sensing or for hydrogen evolution reaction catalysis.

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.