NixSy/NF composites assembled by sulfidation of nickel foam (NF) for highly effective capture of iodine

Under a facile one-step hydrothermal reaction by changing thiourea dosage to regulate sulfidation degree of nickel foam (NF), a variety of nickel sulfide composites of n-NixSy/NF (1-Ni3S2/NF, 3-Ni3S2 and 6-Ni3S2/Ni9S8) were prepared and utilized to capture iodine for the first time. The compositions and structures of the composites and their influence on iodine adsorption performance were elaborated in detail. During adsorption, Ni0 in NF and Ni0/S2− in Ni3S2/Ni9S8 both served as reducing agents to achieve the chemisorption for iodine, where the Ni0 and S2− were oxidized to Ni2+ and elemental S0 (S8), and the I2 molecules were reduced to I− which then reacted with the Ni2+ to form NiI2. The 1-Ni3S2/NF, 3-Ni3S2 and 6-Ni3S2/Ni9S8 exhibited different iodine adsorption capacities (qmI) of 1442, 1109 and 420 mg/g for iodine vapor, and 1191, 869 and 296 mg/g for iodine in solutions, respectively, giving the largest qmI of 1442 (for I2 vapor) and 1191 mg/g (for I2 in solution) by 1-Ni3S2/NF. The capture mechanism for iodine in solution was mainly by chemisorption, while for iodine vapor, profiting from the three-dimensional skeleton of NF, besides the chemisorption, physical sorption also played a role. After γ irradiation, the structures of n-NixSy/NF were well-maintained and iodine adsorption performance did not deteriorate, indicating the good radiation resistance. This work provides an important reference for tailoring new kinds of cost-effective sorbents to trap iodine from radioactive nuclear wastes.