Adsorption of organic dyes on macroporous melamine sponge incorporating conducting polypyrrole nanotubes

The macropores of melamine sponge were coated with globular polypyrrole or polypyrrole nanotubes. The resulting materials have been tested for the adsorptive removal of organic dyes from aqueous medium. The nanotubes deposited on the sponge were able to remove Reactive Black 5 dye while the adsorption on analogous polypyrrole globules was marginal. For that reason, the macroporous open-cell melamine sponge with embedded nanotubes was tested for the adsorption of five anionic and five cationic dyes. The anionic dyes were adsorbed efficiently in the contrast to cationic ones. This can be explained by the electrostatic interaction of anionic dyes with polypyrrole polycation. The fast-starting adsorption occurred within a few minutes and was followed by a slower process extending for days. The nanotubes deposited on the sponge have always been more efficient adsorbents than free polypyrrole nanotubes or melamine sponge alone. Better organization of polymer chains in the polypyrrole nanotubes and especially those deposited on the melamine sponge is proposed to be responsible for this effect. Cationic dyes were adsorbed even by neat melamine sponge while the adsorption by polypyrrole was negligible. In this case, the indifferent role of polypyrrole can be assigned to the electrostatic repulsion of the dye.