Influence of the defect of carbonaceous surface on ammonium adsorption: A DFT study

Carbonaceous material can be used as efficient adsorbent to remove ammonium from water. The effect of the defect of carbonaceous material on the adsorption of ammonium ion is essential for the insight of the adsorption mechanism. In this study, the adsorption properties of ammonium ions on the defective carbonaceous surfaces were studied by density functional theory (DFT). The Atomic Dipole Moment Corrected Hirshfeld (ADCH) charge, Density-of-states (DOS), Mayer bond order (MBO), bond distance, and adsorption energy were analyzed. In addition, the effect of the co-existence of defect sites and functional groups on the adsorption of ammonium ions was also considered. The location and number of the defect sites are important for the adsorption of ammonium ion on carbonaceous surface. Positive effect and negative effect of defect on the adsorption of ammonium ion were found on the armchair and zigzag carbonaceous surfaces, respectively. Oxygen functional groups showed different effects on the adsorption of ammonium ions to the defective and non-defective carbonaceous surfaces. It provides an important theoretical basis for the precise and targeted modification of carbon materials for adsorption of ammonium ions from water.