Resistive gas sensors based on precisely size-controlled polypyrrole nanoparticles: Effects of particle size and deposition method

Polypyrrole nanoparticles (PPyNPs) with uniform diameters of 20, 60, and 100 nm were fabricated by chemical oxidation polymerization. The synthesized PPyNPs provided higher conductivity and surface-to-volume ratio value in the order of 20 nm > 60 nm > 100 nm. The conductivities and BET surface areas were measured to be ca. 10¹ S cm^-1/144 m² g^-1 (20 nm in diameter), ca. 10A° S cm^-1/104 m ² g^-1 (60 nm in diameter), and ca. 10^-1 S cm^-1/68 m² g^-1 (100 nm in diameter). To minimize the contact resistance between internanoparticles, the uniform PPyNPs were deposited on the sensor substrate by spin-coating, and the loading amount of PPyNPs was also controlled. The sensitivity of PPyNP gas sensors increased with decreasing diameter of PPyNPs. Minimum detectable limits (MDL) of uniformly dispersed PPyNP gas sensors were ca. 5 ppm (NH₃ gas), ca. 50 ppm (methanol gas), ca. 100 ppm (acetonitrile gas), and ca. 100 ppm (acetic acid gas). Moreover, the response and recovery time of the gas sensor based on 20 nm-diameter particles were less than 1 and 30 s at 5 ppm of NH₃ gas. PPyNP gas sensors provide the enhanced sensing performance compared to chemical sensors based on the conventional one-dimensional (1D) conducting polymer nanomaterials in detecting ammonia gas and volatile organic compounds (VOCs).