Adsorption of toxic methyl iodide over Beta, ZSM-5 and SSZ-13 supported silver adsorbents

Abstract

The efficient capture of radioactive isotopes of iodine uranium fission reactions is a major issue for safe nuclear energy. To investigate the toxic methyl iodide (CH3I) retention performance of Ag/Beta, Ag/ZSM-5 and Ag/SSZ-13, these Ag zeolites with identical Ag loadings and close Si/Al were prepared. The limited pore volume of ZSM-5 makes a larger size of Ag particles (∼7 nm) than Ag/Beta and Ag/SSZ-13. Silver, in the form of Ag+ ions, enters the cages of the zeolites as Lewis acid sites. In terms of the CH3I retention performance, Ag/Beta rivals the currently reported Ag zeolites applied to capture of radioactive iodine compounds. The CH3I storage capacity of Ag/Beta reaches 1.76 g/gAg. The strong CH3I affinity on Ag/Beta is confirmed by DFT method. The CH3I adsorption energy reaches 121.24 kJ/mol. Kinetics analysis shows that CH3I adsorption on three Ag zeolites observes pseudo-second order model. Good fitting of intra-particle diffusion model on Ag/SSZ-13 also demonstrates that intragranular diffusion is the rate-determining step of CH3I adsorption. The mechanism of CH3I retention is CH3I diffusion within the zeolites and then the formation of AgI species. This work expands the research field of Ag zeolite and contributes to its promising application in the capture of radioactive iodine.