A volatile organic compound sensor using porous Co₃O₄ spheres

Porous Co₃O₄ spheres with bimodal pore distribution (size: 2-3 nm and ∼ 30 nm) were prepared by ultrasonic spray pyrolysis of aqueous droplets containing Co-acetate and polyethylene glycol (PEG), while dense Co₃O₄ secondary particles with monomodal pore distribution (size: 2-3 nm) were prepared from the spray solution without PEG. The formation of mesopores (∼ 30 nm) was attributed to the decomposition of PEG. The responses of a porous Co₃O₄ sensor to various indoor air pollutants such as 5 ppm C₂H₅OH, xylene, toluene, benzene, and HCHO at 200°C were found to be significantly higher than those of a commercial sensor using Co₃O₄ and dense Co₃O₄ secondary particles. Enhanced gas response of porous Co₃O₄ sensor was attributed to high surface area and the effective diffusion of analyte gas through mesopores (∼ 30 nm). Highly sensitive porous Co₃O₄ sensor can be used to monitor various indoor air pollutants.