Comparing adsorption of arsenic and antimony from single-solute and bi-solute aqueous systems onto ZIF-8

The coexistence of toxic arsenic (As) and antimony (Sb) due to anthropic activities in environments has arose great challenge for their simultaneous removal. In this study, the zeolitic imidazolate framework-8 (ZIF-8) with ultrahigh porosity were first proposed for the removal of arsenite [As(III)], arsenate [As(V)], and antimonite [Sb (V)]. The maximum adsorption capacity (Q(max)) in single-solute system is determined to be 2.02, 1.42, and 0.86 mmol/g for As(III), As(V), and Sb(V) at pH=8.6, respectively. In bi-solute systems, As(V) exhibits a stronger inhibition on Sb(V) adsorption than As(III) does although Q(As(III),max) is higher than Q(As(V),max). Additionally, after the adsorption of As(III) and As(V), their substitution by Sb(V) occurs only at pH of below 8.8. However, this undesired effect became insignificant at elevated pH and higher initial concentrations of arsenic. When As and Sb are introduced in sequence, the pre-adsorbed species forms stable complexes with ZIF-8 and inhibits the subsequent adsorption of the other one. FTIR and XPS analyses indicate that the zinc hydroxyl group on ZIF-8 dominates in their adsorption. This study advances the understanding of the competitive adsorption between As and Sb and the strategy for their simultaneous removal. Therefore, ZIF-8 could serve as a promising adsorbent for the simultaneous removal of As and Sb.