Synthesis of Polyaniline Nanoparticles With High Surface Area for CO ₂ and N ₂ Sorption

ABSTRACT Polyaniline nanoparticles (PANI NPs) in emeraldine salt (ES) and emeraldine base (EB) forms were synthesized via oxidative polymerization, with and without HCl stabilization, to investigate how subtle synthetic modifications affect structural, morphological, and gas sorption properties. Fourier‐transform infrared (FTIR) analysis confirmed the expected chemical structures and demonstrated that HCl acts as a protonic dopant and a morphological modifier. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) measurements showed that HCl stabilization results in smaller, more uniform NPs and improved dispersion, particularly in the protonated (ES) form. Nitrogen (N 2 ) and carbon dioxide (CO 2 ) sorption studies revealed that PANI EB naturally exhibits a higher surface area and porosity due to its open‐chain structure. The addition of HCl has a stronger effect on PANI ES, increasing its pore volume and gas adsorption capacity by disrupting interchain interactions. Notably, CO 2 uptake increased from 24.6 ± 1.2 to 30.6 ± 2.1 cm 3 /g upon stabilization, and the N 2 uptake for native PANI EB was 144.4 ± 1.3 cm 3 /g. This work highlights the structure–function relationship between protonation state, morphology, and gas sorption behavior. By fine tuning synthesis parameters, PANI NPs with exceptional surface areas (up to 70.8 ± 2.1 m 2 /g) were achieved, positioning them as promising candidates for gas sorption and related environmental applications.