Superb adsorption capacity and mechanism of poly(1-amino-5-chloroanthraquinone) nanofibrils for lead and trivalent chromium ions

Poly(1-amino-5-chloroanthraquinone) (PACA) nanofibrils were applied as new nano-adsorbents for heavy metal removal from aqueous solutions. Adsorption properties including adsorption capacity, selectivity, kinetics, mechanism, and isotherm of PACA nanofibrils were studied in detail. The competitive adsorption of the nanofibrils for Pb(II) and Cr(III) in binary mixture systems was investigated. The results showed that Pb(II) and Cr(III) were adsorbed preferentially over the other metal ions including Hg(II), Cr(VI), Zn(II), Cd(II), Fe(III) and Cu(II), under competitive conditions. Kinetic data indicated that the adsorption process of PACA nanofibrils for Pb(II) and Cr(III) achieved equilibrium within 2 h following a pseudo-second-order rate equation and exhibiting a three-stage intraparticle diffusion mode. The adsorption mechanism of PACA nanofibrils for Pb(II) and Cr(III) was investigated by Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses. The adsorption isotherms of Pb(II) and Cr(III) fitted well with the Langmuir model, exhibiting superb adsorption capacity of 4.27 and 4.22 mmol of metal per gram of adsorbent, respectively. Furthermore, adsorption-desorption experiments demonstrated that the PACA nano-adsorbents could be easily recycled without considerable changes in the adsorption capacity.