Improving the adsorption of poly(o-phenylenediamine) to heavy metal ions in aqueous solution through its composite with carbon dots

Because poly(o-phenylene diamine) (PoPD) has more free amino groups and imine groups than other conductive polymers, together with the functional groups on the surface of Carbon dots (CDs), it can provide more adsorption active sites for the adsorption of heavy metal ions, correspondingly. In this study, the novel adsorbent material composed of PoPD and CDs (CDs/PoPD) with high performance were prepared in order to investigate the synergetic effect of CDs in enhancing the adsorption properties of conductive polymer based adsorbent to heavy metal ions in water. The Cu2+ removal ratio of PoPD was 73.63% and that of CDs/PoPD was as high as 88.16%, which were higher than that of other reported conductive polymers. The removal ratios of Pb2+ and Cd2+ with CDs/PoPD were 98.97% and 77.48%, respectively. The maximum adsorption capacities of CDs/PoPD to Cu2+, Pb2+ and Cd2+ were 48.88 mg·g−1, 53.44 mg·g−1 and 36.20 mg·g−1, respectively. Results showed that Cu2+, Pb2+ and Cd2+ complexed with the amine and imine groups on the CDs/PoPD chain, and their adsorption processes could be explained with the quasi-second-order kinetic model and Langmuir adsorption isotherm model. The results of reusability test of adsorption for Cu2+ showed that the regeneration efficiency of CDs/PoPD was 85.95%, which was significantly higher than that of PoPD.