Sulfhydryl-modified zeolite A with exceptional strontium adsorption selectivity

Abstract

Efficient removal of trace radiostrontium from contaminated highly saline wastewater, such as seawater, remains a critical but challenging task due to the coexistence of large excess of hard cations like Na⁺, K⁺, Mg²⁺ and particularly Ca²⁺, which shares similar physicochemical properties with Sr²⁺. Herein, we successfully boosted the selectivity by a sulfhydryl-functionalized NaA zeolite (SH-NaA) via ion exchange coupled with reinforced soft-soft interactions between sulfhydryl groups and Sr²⁺. Remarkably, SH-NaA achieved a 99.8% removal efficiency of Sr²⁺ in the presence of a tenfold excess of Ca²⁺, with a distribution coefficient (K_d) of 4.98×10⁵ mL/g. The effectiveness of SH-NaA in accurately capturing Sr²⁺ was further validated by its superior dynamic adsorption performance in natural seawater compared to pristine NaA zeolite. Batch experiments highlighted SH-NaA’s exceptional Sr²⁺ removal efficiency (q_m = 233.36 mg/g), rapid adsorption kinetics (1 min), superior decontamination depth (K_d = 6.71×10⁵ mL/g), and robust irradiation stability (400 kGy γ-ray). X-ray photoelectron spectroscopy (XPS) and in situ Fourier-transform infrared (FTIR) analyses underscored the pivotal role of sulfhydryl groups in Sr²⁺ capture. Density functional theory (DFT) calculations revealed that the sulfhydryl-functionalized NaA zeolite exhibits the best selectivity toward Sr²⁺, with an interaction energy of −2.55 eV. These findings demonstrate that organic group functionalized zeolites hold significant promise for environmental remediation applications.