Facile Synthesis of Co-BDC MOFs for Porous Co3O4 Nano-Assemblies for Gas Sensing Application

Under rapid industrialization, air pollution remains a significant topic in the society. Nitrogen dioxide (NO₂) is the most important among the primary atmospheric pollutants. It comes from vehicle emissions and coal, petroleum, and natural gas combustion in various industrial processes. NO₂ does not lead to environmental contamination and pollution of the soil and water but also poses a severe threat to human health. Prolonged exposure to nitrogen dioxide can result in conditions such as asthma, macular degeneration, heart failure, and pulmonary edema.<br/>Hence, having a detector for nitrogen dioxide is urgently needed. This research aims to enhance the gas sensing response of cobalt oxide by synthesizing a high surface area sensor using Metal-organic frameworks (MOFs) as a template. In this experiment, a conventional heating method was applied. By adjusting the molar ratio of cobalt ion to terephthalic acid, two Co-based MOFs, Co₂(OH)₂C₈H₄O₄and Co(H₂O)₂C₈H₄O₄, were successfully synthesized. We used BET to analyze the sample, and the molar ratio of cobalt ion and organic ligand was 2:1; the layered Co-based MOF exhibited the highest specific surface area (23.81 m²/g). We have successfully controlled the MOF structure and overcome the challenges with the conventional solvent-based method.<br/>Co-BDC undergoes calcination at 325 °C, resulting in a Co₃O₄ material with a remarkable specific area of 75.52 m²/g. In this study, we have also discussed the impact of different calcination temperatures. The accumulation of cobalt oxide nanoparticles led to a reduction in specific surface area and increased pore size. Finally, gas detection experiments were conducted at 150°C to detect 200 ppm of NO₂. The response value reached a high of 1.57. In comparison, it performs an outstanding selectivity to nitrogen dioxide compared to methane, ethane, and carbon dioxide.