Nanoscale assembly of MoS2/CoS2/Ni3S2 grown on Ni foam for synergistic capture of iodine

We report a series of MoS2/CoS2/Ni3S2/NF heterogeneous interfaces with multiple types of adsorption sites which exhibit excellent iodine capture performance. The optimized MoS2/CoS2/Ni3S2/NF-13 obtained at Mo:Co molar ratio of 1:3 exhibits an extremely large maximum iodine capture of 1804 mg/g. For the including component of Ni3S2/NF, REDOX reaction between Ni0/S2- and I2 offers the main driving force of chemisorption toward iodine (forming NiI2 and S8), while for MoS2, electrostatic adsorption makes the main contribution to the iodine capture, and for CoS2, interfacial interactions promote the uptake capability of iodine. We perform density functional theory (DFT) calculations to determine the iodine adsorption energies (Ead), which show that in Ni3S2 the Ni and S both serve as iodine sorption sites and Ni site binds more tightly to I2 than S site does, while for MoS2, the S site (rather than Mo) prefers to adsorb the I2. X-ray absorption fine structures (XAFS) indicate that after iodine capture, oxidation states of Mo and Ni are increased more than that of Co, verifying Ni3S2 and MoS2 act more significantly than CoS2 on I2. Though CoS2 component does not directly adsorb I2, the interfacial electron transfers of Co → Ni and Co → Mo significantly promote iodine sorption capability by Ni3S2 and MoS2. Synergistic effect of the multiple components/sites in the MoS2/CoS2/Ni3S2/NF assembly offers the wonderful iodine capture. This work provides a novel perspective and theoretical reference for tailoring effective metal sulfides-based sorbents to trap iodine from radioactive wastes.