Briefly iodized Ag foils: microstructure, structure, optical response and potential as iodine detectors

Abstract

Commercial silver foils—typically 10 µ thick—were subjected to a regulated flux of iodine (I₂) vapors produced in a “figure of eight” iodinator. The effect of iodization time, varied in steps from 0 to 720 s, on the microstructure, structure and optical response is reported. The uniodized Ag foil shows large clusters which transform into sub 100 nm sizes on exposure to iodine vapors up to a duration of 540 s, beyond which there is re-growth of large clusters. Crystallization of AgI is not observed up to an iodine exposure duration of 720 s. The foils continue to exhibit diffraction peaks corresponding to crystalline Ag up to this duration of iodine exposure. In the first 180 s, there is very little difference between the optical absorption spectra of the exposed and unexposed foils. At an exposure time of 360 s, a localized surface plasmon peak of Ag appears at a wavelength of 550 nm. The intensity of the plasmon peak increases with further increase in exposure time to 540 and 720 s. Interestingly, the intensity of the plasmon peak and the optical absorption value at 700 nm increase linearly beyond an exposure time of 180 s. The process was monitored gravimetrically to obtain a mass loss of I₂ versus iodination time profile. This profile is apparently linear for iodination times in the range 180–720 s, suggesting a linear uptake of I₂ by silver foil. This feature together with the gravimetry result makes the process applicable as detectors in situations where ppm levels of I₂ need to be detected.