HCl guided morphology and conductivity of chiral PPy nanostructures toward efficient electromagnetic wave absorption

To solve the severe electromagnetic (EM) radiation from the widespread application of electronic equipment, we developed a simple template-guided oxypolymerization strategy to synthesize polypyrrole (PPy) planar helixes as an efficient EM wave (EMW) absorber, and systematically investigated the morphology-dependent chirality, conductivity, and microwave absorption properties. As HCl concentration [HCl] varied from 0 to 2.0 M, the morphology evolved from planar helix to 3D cross-linking network structures, the conductivity increased from 0.0019 to 0.0302 S/cm, and the EM parameters peaked at [HCl]=0.5 M. Compared to other absorbers, the PPy planar helix formed at [HCl]=0 M possessed wider absorption band (5.84 GHz), smaller matching thickness (1.6 mm), lower loading (25 wt.%), and intenser absorption (-48.17 dB). The reason lies in the strong attenuation capability, multiple resonances, multiple scattering, and good impedance matching generated by chiral PPy planar helixes with a distinctive helical configuration, doped heteroatoms (O,S), and a local conductive network. Our results suggest that PPy planar helixes offer great promise for fields such as chiral sensors, electronics, optics, chiral catalysis, and EMW absorption and shielding due to their distinctive morphology, tunable conductivity, and outstanding EMW absorption properties (EMWAPs).