Mechanism of surface effect and selective catalytic performance of MnO2 nanorod: DFT+U study

The mechanism of surface effect and selective catalytic performance of MnO2 nanorods remain mysterious at present. Using first-principles pseudo-potential plane wave method, the surface energy, cohesive energy, geometrical and electronic structure for MnO2 in the evolution of crystal → bulk surface → nanorod morphologies have been systematically calculated and analyzed. The results show that the surface energy is increased along with the decrease of geometry configuration in crystal → bulk surface → nanorod as a whole. However in three nanorod morphologies, the surface energy is increased along with the additional geometry configuration, wherein the largest nano(III) has the largest surface energy and lowest cohesive energy. These characters are originated from their changes in geometry structure and lost in Mulliken charges of atoms along surface planes. Electronic structure shows that the selective catalytic activity of MnO2 nanorods is originated from their unique states of valence electrons, which occupying the highest occupied molecular orbital (HOMO) only appears on (110) Miller surface layers and the lowest unoccupied molecular orbital (LUMO) only on (100) Miller surface layers, respectively. Such attracting phenomenon has significantly difference with that of MnO2 bulk surface. Thereinto, a transitional model of [(100 × 110)] microfacet model is found to exhibit much more approaching surface performance to MnO2 nanometer structure somewhere. Thus, our findings open an avenue for detailed and comprehensive studies on the growth and catalysis of MnO2 nanomaterials.