Screening of MnO2 with desired facet and its behavior in highly selective adsorption of aqueous Pb (II): Theoretical and experimental studies.

In this study, Density Functional Theory (DFT) calculations and experimental methods were adopted to evaluate MnO2 with 5 different facets for their selective adsorption of Pb (II) from wastewater containing Cd (II), Cu (II), Pb (II), and Zn (II). The DFT calculations were performed to screen the selective adsorption capability of the facets and demonstrated that the MnO2 (3 1 0) facet has an excellent performance in selective adsorption of Pb (II) among all facets. The validity of DFT calculations was verified by comparing with the experimental results. MnO2 with different facets was prepared in a controlled manner and the characterizations confirmed that the lattice indices of the fabricated MnO2 have the desired facets. Adsorption performance experiments illustrated a high adsorption capacity (320.0 mg/g) on the (3 1 0) facet MnO2. The selectivity of adsorption of Pb (II) was 3-32 times greater than that of the other coexisting ions, i.e., Cd (II), Cu (II), and Zn (II)), which is consistent with results of the DFT calculations. Furthermore, results of DFT calculations on adsorption energy, charge density difference, and projected density of states (PDOS) showed that the adsorption of Pb (II) on the MnO2 (3 1 0) facet is non-activated chemisorption. This study shows that it is feasible to use DFT calculations to quickly screen suitable adsorbents for environmental applications.