Synthesis of a robust layered metal sulfide for rapid and effective removal of Sr2+ from aqueous solutions

Abstract

A novel robust metal sulfide (NaTS) was synthesized via a simple one-step hydrothermal reaction for the first time. SEM, TEM, EDS, and XPS analyses indicated that NaTS has a sheet-like structure stacked by hexagonal thin flakes with the formula Na2Sn3S7. PXRD and TG results indicated that NaTS was chemically and thermally stable. The rapid kinetic studies showed that NaTS can rapidly remove Sr2+, with a rate of 98.71% in the first minute, and can reach adsorption equilibrium within 5 min. A pseudo-second-order model and intraparticle diffusion model were found to be good fits for the NaTS adsorption data. The adsorption isotherms were well described by the Langmuir model and NaTS exhibited high adsorption capacity for Sr2+ (80.0 mg/g at 298 K). They also displayed a high distribution coefficient (Kd = 3.43 × 107 mL/g) and excellent removal efficiency of 99.98% with 0.5 g/L dosage in 5 mg/L Sr2+ solutions. In particular, NaTS exhibited outstanding affinity (Kd ≥ 1.31 × 105 mL/g) for Sr2+ over a broad pH range of 3–13. In addition, the adsorption mechanism of NaTS towards Sr2+ was ion exchange and Sr⋯S binding, as confirmed by EDS, XPS and ICP-OES. Furthermore, NaTS had significant advantages for Sr2+ removal compared with other adsorbents. In general, these adsorption advantages combined with facile synthesis, as well as structural stability, make NaTS promising for removal of radioactive Sr2+ from strongly acidic or alkaline radioactive wastewaters easily and efficiently.