Efficient removal of organic dyes from aqueous solution by rapid adsorption onto polypyrrole-based composites

In order to improve the adsorption capacity of polypyrrole, two inexpensive and renewable biological resources containing abundant functional groups were used to achieve novel polypyrrole-based composites. Three low-cost polypyrrole-based composites, polypyrrole-chitosan-lignosulfonate (PPY-CS-LS), polypyrrole-chitosan (PPY-CS) and polypyrrole-lignosulfonate (PPY-LS) were prepared via an in-situ polymerization of pyrrole monomers with chitosan (CS) and/or lignosulfonate (LS) as dispersants. PPY-CS-LS, PPY-CS and PPY-LS nanoparticles with average diameters of 50 nm, 73 nm and 213 nm, respectively, were obtained with pyrrole/oxidant molar ratio of 1:1, and the contents of CS and/or LS of 10 wt%. Selective adsorption properties of the three composites for six dyes were investigated. Results showed that PPY-CS-LS and PPY-CS composites possessed much higher selectivity for acid (anion) dyes, especially for Congo red (CR); the removal efficiencies of PPY-CS-LS and PPY-CS composites for CR were up to 99.3% and 95.4%, respectively, when the initial concentration of CR was 60 mg L−1 at the adsorption temperature of 30 °C. The adsorption equilibrium time for CR was 30 min, which was more rapid than those of other reported PPY-based adsorbents. The results suggested that the PPY-CS-LS composite exhibited a high adsorption performance for dyes because of the synergistic effects of amino/hydroxyl-containing functional groups from CS, sulfonic groups from LS, and nitrogen-containing functional groups from PPY chains. Furthermore, the adsorption processes were feasible and spontaneous. Therefore, a productive route to fabrication of low-cost PPY-based composite nanoparticles with controllable size and high dye adsorption ability was achieved.