Integrating the (311) facet of MnO2 and the fuctional groups of poly(m-phenylenediamine) in core-shell MnO2@poly(m-phenylenediamine) adsorbent to remove Pb ions from water.

Exposed active facets and functional groups are critical for adsorbents obtaining excellent adsorption properties. In the present study, MnO2@PmPD with exposed active facets was successfully prepared. MnO2,which came from KMnO4 by the sacrificial reductant of PmPD, deposited on the surface of PmPD. Meanwhile, we combined experimental study and theoretical calculations to elucidate the distinct adsorption nature of MnO2@PmPD towards Pb. The surface adsorption of MnO2@PmPD toward Pb was achieved by the interaction between Pb and O atoms on the surface of MnO2. The DFT calculations revealed the facet-dependent adsorption of MnO2 toward Pb. The adsorption affinity of facets toward Pb was in the order of (311) > (111) > (400) > (440), and (311) facet was predominantly adsorption site for Pb. The analysis of partial density of state revealed the strong hybridization between the Pb-p state and O-p states of MnO2. Additionally, the pores of MnO2 provide the interstitial channels for the transportation of Pb into PmPD. The Pb entered the internal of MnO2@PmPD was bonded by the amine and newly formed carboxy groups on PmPD. This study not only develops an efficient adsorbent for heavy metals removing, but also throws light on exemplifying the interaction of Pb with MnO2 based materials.