Adsorptive removal of cationic dyes from water with polypyrrole-derived porous carbons

Polypyrrole-derived carbons (PpDCs) were obtained via pyrolysis of polypyrrole under various preparation conditions. After characterization, PpDCs were used for the adsorptive purification of water contaminated with organic dyes. One PpDC (PpDC-800) exhibited the highest adsorption capacity (Q_o) for cationic dyes (e.g., methylene blue and crystal violet) compared to other adsorbents. The adsorption capacity of PpDC-800 for methylene blue and crystal violet was approximately seven times higher than that of activated carbon. The effective adsorption of cationic dyes (200 mg/L) over PpDC-800 was also observed in water with very low concentrations of methylene blue or crystal violet (1 mg/L), which causes toxicity and affects aesthetics. PpDC-800 showed high selectivity for methylene blue adsorption from an equivalent-weight mixture of anionic methyl orange and cationic methylene blue. Plausible adsorption mechanisms of methylene blue removal, such as electrostatic and π–π interactions, have been suggested. Structural characterization and adsorption mechanism were confirmed using XRD, N₂ adsorption, Raman spectroscopy, SEM, XPS, zeta potential analysis, and other techniques. The facile regeneration of PpDC-800 was confirmed through successive adsorption/reactivation cycles using FT-IR, N₂ adsorption, Raman, and SEM analyses. PpDC-800 is one of the most promising adsorbents for the effective and selective removal of cationic dyes from water.