Synthesis and Characterization of Flower-Like Cobalt-Doped ZnO Nanostructures for Ammonia Sensing Applications

The future trajectory of gas sensor development focuses mainly on two key aspects: minimizing power consumption and enhancing the capability to detect hazardous gases at lower concentrations under ambient conditions. The present study used the co-precipitation method to explore the synthesis of zinc oxide and cobalt-doped ZnO sensors, encompassing a range of cobalt concentrations from 1 wt% to 4 wt%. The synthesized samples undergo comprehensive analysis to evaluate their structural, morphological, optical, and gas-sensing properties. X-ray Diffraction (XRD) revealed a hexagonal Wurtzite structure, and the crystallite size decreased from 16.92 to 15.39 nm. Energy-Dispersive X-ray spectroscopy (EDX) and Fourier-Transform Infrared (FTIR) Spectroscopy collectively affirmed the presence of cobalt. Scanning Electron Microscopy (SEM) was used to analyze the morphological characteristics. The Tauc-plot was used to determine the optical bandgap via diffuse reflectance spectroscopy. As cobalt doping increased, the band gap increased from 3.18 to 3.23 eV. Further, Atomic Force Microscopy (AFM) and Brunauer–Emmett–Teller (BET) analysis were used to assess the surface topography and pore size distribution. The AFM measurements indicated roughness increased from 435 to 700 nm. The BET analysis revealed mesoporous properties, with surface area increased from 18.657 to 21.962 m 2 /g and pore sizes varying from 3.67 to 3.72 nm. Subsequently, the gas-sensing capabilities of the Co-doped ZnO sensors were examined for various volatile organic compounds (VOCs) at room temperature. The experimental results demonstrated excellent performance in detecting NH 3 gas precisely. The sensor with 4% cobalt doping exhibited a fast response and recovery time of 21 and 20 s towards 2 ppm of NH 3 .