Adsorption behaviors and atomistic mechanisms of iodate and iodide on hollow spherical allophane nanoparticles

• Published in: Applied clay science Vol. 250; p. 107293
• Main Authors: Wang, Shun, Zhang, Yanjun, Liu, Dong, Yuan, Peng, Li, Mengyuan, Du, Peixin, Zhao, Jinkui, Yu, Wenbin, Wang, Howard
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.03.2024
• Subjects: Adsorption behavior; Adsorption mechanism; Allophane; Iodate; Iodide; Surface-interface interaction; Iodate; Iodide; Adsorption behavior; Surface-interface interaction; Adsorption mechanism; Allophane
• ISSN: 0169-1317
• DOI: 10.1016/j.clay.2024.107293

The adsorption of radioactive iodate (IO3−) and iodide (I−) anions on natural minerals is critical for nuclear environmental safety. Allophane, a nanosized clay mineral, is considered to adsorb IO3− and I−, but the essential interactions between both anions and allophane remain unknown, due to the challenges of characterizing extremely small allophane nanoparticles in complex soils and obtaining high-purity natural allophane. In this work, neat allophane (Allo) nanoparticles were synthesized and used to study their adsorption for IO3− and I− anions. The adsorption kinetics, adsorption thermodynamics, pH-dependent adsorption-desorption, and competitive adsorption (Cl− and SO42−) were quantitatively investigated. Moreover, combined with advanced spectroscopic analyses of X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS), the atomistic adsorption mechanisms were illustrated. The adsorption capacities of Allo can be about 0.22 mmol/g for IO3− and 0.077 mmol/g for I−, which are at least one order of magnitude and 2.6-fold higher than those of other clay minerals, respectively. The IO3− adsorption involved the ligand exchange and electrostatic attraction interactions, while the I− adsorption involved the Lewis acid-base and hydrogen-bond interactions. The inner-sphere adsorption mainly occurred in the wedge-shaped nanopores within Allo. The findings will improve the understanding of IO3− and I− adsorption on allophane, promote the practical applications of natural allophane in the management of nuclear wastes, and provide foundations for revealing the geochemical behaviors of iodine. [Display omitted] •Allophane (Allo) has high adsorption capacities to I− and particularly IO3−.•Adsorption behaviors of IO3− and I− on Allo were quantitatively evaluated.•Firstly revealing the local chemical environments of adsorbed iodine on Allo surface.•Illustrating multiple surface-interface interactions between Allo and IO3−/I− at an atomistic scale.