Hierarchical assemblies of SnS microflowers and Ni3S2 nanofibers grown in situ on nickel foam for highly efficient capture of iodine vapor

Abstract

Developing cost-effective iodine sorbents is crucial for managing nuclear waste. Herein, hierarchical polymetallic sulfide assemblies of n-SnS/Ni₃S₂ (n is the millimolar number (0.2, 0.6 and 1.2) of the SnCl₄·5H₂O added) are fabricated in situ on nickel foam (NF) via a facile one-step method. The NF serves not only as a Ni source but also as a reducing agent to reduce the Sn⁴⁺ (in SnCl₄) to Sn²⁺, leading to formation of SnS/Ni₃S₂/NF. The Ni⁰ (of Ni₃S₂ and NF), Sn²⁺ and S²⁻ ions all work as reducing reagents to reduce I₂ molecules to I⁻ ions, while themselves are oxidized to Ni²⁺, Sn⁴⁺ and S₈, respectively. The Ni/Sn ions bind to I⁻ ions forming NiI₂ and SnI₄, achieving stable immobilization toward gaseous iodine. The optimized 0.6-SnS/Ni₃S₂/NF material exhibits a desirable morphology of microflowers and nanofibers well exposing sorption sites, leading to an extremely large iodine sorption capacity of 3412 mg g⁻¹. Density functional theory (DFT) calculations exhibit negative values of iodine adsorption energies (E_ad) for Sn, Ni and S sites, demonstrating rich and effective sorption sites in the polymetallic sulfide. The most elongated I–I bond (3.057 Å) bound to a Ni atom of Ni₃S₂ and the lowest E_ad (−4.67 eV) at the Ni site indicate that it is the most effective active site for trapping iodine. The density of state (DOS) and charge density difference calculations verify the electron transfer from SnS/Ni₃S₂ to I₂, and the interfacial effect of SnS and Ni₃S₂ significantly promotes the iodine capture. This study offers an important reference to develop new sorbent materials applied for controlling nuclear pollution.