AuPt Bimetal-Functionalized SnSe₂ Microflower-Based Sensors for Detecting Sub-ppm NO₂ at Low Temperatures

A novel chemiresistive-type sensor for detecting sub-ppm NO₂ has been fabricated using AuPt bimetal-decorated SnSe₂ microflowers, which was synthesized by the hydrothermal treatment followed by in situ chemical reduction of the bimetal precursors on the surface of the petals of the microflowers. The as-prepared sensor registers a superior performance in detection of sub-ppm concentration of NO₂. Functionalized by the AuPt bimetal, the SnSe₂ microflower-based sensor shows a response of approximately 4.62 to 8 ppm NO₂ at 130 °C. It is significantly higher than those of the sensors using the pristine SnSe₂ (∼2.29) and the modified SnSe₂ samples by a single metal, either Au (∼3.03) or Pt (∼3.97). The sensor demonstrates excellent long-term stability, signal repeatability, and selectivity to some typical interfering gaseous species including ammonia, acetone, formaldehyde, ethanol, methanol, benzene, CO₂, SO₂, and CO. The remarkable improvement of the sensitive characteristics could be induced by the electronic and chemical sensitization and the synergistic effect of the AuPt bimetal. Density functional theory (DFT) is implemented to calculate the adsorption states of NO₂ on the sensing materials and thus to possibly reveal the sensing mechanism. The significantly enhanced response of the SnSe₂-based sensor decorated with AuPt bimetallic nanoparticles has been found to be possibly caused by the orbital hybridization of O, Au, and Pt atoms leading to the redistribution of electrons, which is beneficial for NO₂ molecules to obtain more electrons from the composite material.