A computational study on the adsorption of arsenic pollutants on graphene-based single-atom iron adsorbents

Integrated gasification combined cycle (IGCC) is a promising clean technology for coal power generation; however, the high volatility and toxicity of arsenic pollutants (As2, As4, AsO and AsH3) released from an IGCC coal plant cause serious damage to human health and the ecological environment. Therefore, highly efficient adsorbents for simultaneous treatment of multiple arsenic pollutants are urgently needed. In this work, the adsorption characteristics and competitive adsorption behaviors of As2, As4, AsO, and AsH3 on four kinds of graphene-based single-atom iron adsorbents (Fe/GA) were systematically investigated through density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The results suggest that single-vacancy Fe/GA doped with three nitrogen atoms has the largest adsorption ability for As2, As4, AsO and AsH3. The adsorption energies of As2, AsO and As4 on Fe/GA depend on both charge transfer and orbital hybridization, while the adsorption energy of AsH3 is mainly decided by electronic transfer. The adsorption differences of As2, As4, AsO and AsH3 on four Fe/GA adsorbents can be explained through the obvious linear relationship between the adsorption energy and Fermi softness. As2, As4, AsO and AsH3 will compete for adsorption sites when they exist on the same adsorbent surface simultaneously, and the adsorption capacities of AsO and As2 are relatively stronger. After the competitive adsorption between AsO and As2, AsO occupies the adsorption site at 300-900 K. This theoretical work suggests that Fe/GA is a promising adsorbent for the simultaneous removal of multiple arsenic pollutants with high adsorption capacity and low cost.