Boosting cesium retention efficiency with polyoxometalate-ionic liquid composites: Insights into {WO6} octahedral affinity

• Published in: Journal of cleaner production 2024-11, Vol.478, p.143922, Article 143922
• Main Authors: Sun, Qina, Wang, Mengzhou, Yang, Yujia, Song, Jinshan, Li, Junfeng, Zhang, Qingrui
• Format: Article
• Language: English
• Subjects: Adsorption; Cesium; Ionic liquid; Phosphotungstate; Polyoxometalate; Retention
• ISSN: 0959-6526
• DOI: 10.1016/j.jclepro.2024.143922

Commonly used polyoxometalate (POM) adsorbents exhibit high cesium (Cs) adsorption capacity. However, its impotent ability to sequester adsorbates poses a risk of Cs migration in radioactive waste decontamination and disposal. By leveraging the cesium affinity of POMs and the regulatory properties of ionic liquids (ILs), POM-IL composites hold promise for mitigating the risk of cesium migration through efficient adsorption and retention. Herein, we designed two POM-ILs composed of the phosphotungstate anion (PW) and tetrabutylammonium cation (TBA), i.e., the {WO6}-saturated TBA-PW12 and mono-lacunary TBA-PW11, for the capture and retention of aqueous Cs. The composites were then characterized, and the performance and mechanism of Cs uptake were investigated. TBA-PW12 exhibited ∼300 nm aggregate of particles around 20–60 nm. TBA-PW12 retained the Keggin structural features of PW12O403−, which was proven essential for the binding of Cs+. With a retention efficiency of 97.3% in an NH4Cl eluent and a maximum adsorption capacity of 400.9 mg/g at 338 K, TBA-PW12 exhibited superior Cs capture and retention compared to the POM-IL derived from common Cs adsorbent phosphomolybdate. The Cs adsorption onto TBA-PWs achieved equilibrium within 180 min. Cs uptake by TBA-PWs was monolayer chemisorption of Cs+ accompanied by H+ release, and the removal efficiencies stabilized around initial pH 5–10. Due to intense affinity between {WO6} and Cs+, TBA-PW12 efficiently sequestered Cs + through {WO6} octahedra so that the {WO6}-saturated TBA-PW12 presented better Cs uptake performance than the mono-lacunary TBA-PW11. The IL anion [N(C4H9)4]+ provided a composite-water biphasic interface for aqueous Cs adsorption, while retaining the ability of POM cation PW12O403− to form a stable structure with Cs via its affinity to {WO6} octahedra. These findings support the design of POM-IL composites as efficient adsorbents for capturing and retaining Cs, aiding in the decontamination and safe disposal of radioactive waste, thereby minimizing the risk of nuclide leakage into the environment. Cesium capture and retention by polyoxometalate-ionic liquid composites TBA-PW12 under the affinity of {WO6}. [Display omitted] •Tetrabutylammonium phosphotungstate (TBA-PW) had efficient Cs capture and retention performance.•The {WO6}-saturated TBA-PW12 exhibited superior Cs uptake than the mono-lacunary TBA-PW11.•After elution with 3 mol/L NH4Cl, 97.3% of the adsorbed Cs was retained on TBA-PW12.•A