Chitosan-modified magnetic sepiolite composite for simultaneous efficient removal of Sb(III/V) from wastewater: investigation of bifunctional active site recognition and adsorption mechanisms.

In view of the multiple valence states, high toxicity, carcinogenicity, and persistence of antimony (Sb) in aquatic environments, the efficient removal of Sb is crucial. The effective screening, grafting, and density regulation of functional groups (like -NH2 and -OH) on material surfaces are key to removing and adsorbing Sb. This study used a cross-linked grafting method to load chitosan onto the surface of magnetic sepiolite, aiming at the characteristics of Sb(III) and Sb(V). The characterization results demonstrated that the MSep@CTS material was successfully synthesized, exhibiting a stable structure and rich active sites. Under 298 K and pH=3, the Langmuir model fitted maximum adsorption capacities reached 306.11 mg/g (Sb(III)) and 471.80 mg/g (Sb(V)), respectively. Encouragingly, compared to systems containing only a single-valence antimony state, even when both valence states of Sb coexist, MSep@CTS could simultaneously adsorb multivalent antimony, with efficiency increasing from 67% to 71%. Density functional theory calculation results showed that the -NH2/-NH- and -OH groups on the chitosan surface serve as the optimal adsorption sites for Sb(V), while the -C=N group acts as the main adsorption site for Sb(III). Furthermore, the MSep@CTS adsorbent demonstrated excellent recyclability, maintaining removal efficiencies exceeding 80% for antimony after five cycles. In summary, this study provides a sustainable and cost-effective remediation strategy for antimony-contaminated water bodies, with a specific focus on the simultaneous adsorption of multivalent antimony species, offering high removal efficiency, low secondary solid waste generation, and excellent reusability, thereby effectively addressing the key environmental challenges in heavy metal pollution control.