First-principles study of adsorption mechanism of NH3 on different ZnO surfaces on organics photocatalytic degradation purpose

ZnO nano-materials present excellent performance in catalysis and their different surfaces have different catalytic properties. In this work, the adsorption activities of NH3 and H2O on different crystal faces of ZnO are investigated by DFT theory, and the results show that the surface of (1 0 0) has absorbability of NH3 as well as the repellency of H2O. Meanwhile, its relatively low adsorption energy is good for the desorption of organics after the photocatalytic degradation process, which makes the ZnO nano materials easily reused and recycled. According to the calculation results, the adsorption energy value of (0 0 1)-a O-terminal surface is higher than that of other surfaces. Based on the electron density and density of state analysis, the NH3 loses electrons, leading to the N-H bond's weakening when the NH3 is adsorbed on the highest-energy-adsorption site. On the contrary, the adsorption energy is negative on all adsorption sites of (0 0 1)-b Zn-terminal surface, which may explain why the O-terminal surface is the most likely to be formed in the experiment by hydrothermal method. (C) 2017 Elsevier B.V. All rights reserved.