New insights into adsorption of As(V) and Sb(V) from aqueous by HCO–(Fe3O4)x adsorbent: Adsorption behaviors, competition and mechanisms

Arsenic and antimony removal technology have received significant attention due to their considerable danger to aquatic ecosystems. In this study, we designed HCO–(Fe 3 O 4 ) x adsorbents with substantial functional groups, ample pore spaces, and considerable surface area , specially tailored for the simultaneous adsorption of pentavalent arsenic (As( V )) and pentavalent antimony (Sb(V)). The adsorption performance of HCO–(Fe 3 O 4 ) x was subjected variably to the Ce/Fe molar ratio (CFMR), solution pH, and co-existing anions (SO 4 2− , PO 4 3− , SiO 3 2− ). The affinity order of As(V) and Sb(V) onto HCO–(Fe 3 O 4 ) x in binary systems was pH-dependent. At a pH of 2.0, Sb( V ) exhibited stronger adsorption than As(V), whereas the opposite trend occurred at pH levels above 4.0. Analysis of the kinetic data revealed the pseudo-second-order kinetic model was the most appropriate, indicating that chemical adsorption was the predominant mechanism. Notably, the formation of inner-sphere complexes led to a higher adsorption rate for As( V ) compared to Sb(V), attributed to a lower energy barrier of 0.863 eV, facilitating the breakdown of the Fe O bond in As(V)'s asymmetric tetrahedral structure. Various analyses (FTIR, XRD, and XPS) demonstrated that adsorption mechanisms involved multiple processes like hydrogen bonding , ligand exchange, electrostatic attraction, and complexation. The primary contributions for the adsorption of As( V ) and Sb(V) were the inner-sphere complex of cerium , oxygen and arsenic atoms (Ce O As) and the outer-sphere complex of iron, oxygen and antimony atoms (Fe O Sb), respectively, indicating significant differences in the mechanisms. These findings underscored the potential of HCO–(Fe 3 O 4 ) x in mitigating As( V ) and Sb(V) water pollution, emphasizing its considerable promise as an effective remediation agent.