Investigating the local structure of silver in different chemical environments using TDPAC spectroscopy

Nanomaterials have been the topic of notable research for various applications due to its different properties than exhibited by bulk materials. To find suitable structure property correlations of different nanostructures, understanding their local electronic structure is important. Time differential perturbed angular correlation (TDPAC) is a potential spectroscopic technique used to investigate the local structures of different materials. In this work, the local structure of silver, hosted in Nafion-117 membrane as Ag⁺ ions and after in situ chemical reduction with NaBH₄ and tri-sodium citrate was studied using ¹¹¹Ag (t_1/2 = 7.5 d) as TDPAC probe and compared with the BH₄ - reduced silver precipitate at bulk. The ¹¹¹Ag probe was prepared by nuclear reaction: ¹¹⁰Pd(n, γ)¹¹¹Pd(β-)¹¹¹Ag by irradiating natPd metal powder at Dhruva reactor. Separation of ¹¹¹Ag from the irradiated ^natPd was carried out following the protocol of Khalid et. al. TDPAC spectra of the as prepared samples were acquired to investigate the change in local structure of silver as ions and in the reduced Ag⁰ form in Nafion-117 membrane. It can be seen that, the TDPAC response of silver in Nafion-117 membrane before and after chemical reduction is noticeably different. The amplitude of oscillations in case of the reduced silver is higher compared to Ag⁺ ions, suggesting the formation of silver nanoparticles in the membrane as a result of chemical reduction. The amplitude is highest in case of the BH₄^- reduced sample, suggesting smaller particle size in case of the BH₄^- reduction compared to the citrate reduction. The presence of oscillations in the TDPAC response of the BH₄^- reduced silver in bulk points to the formation of nano-silver even in absence of Nafion, suggesting the role of BH₄^- ions as capping agent in addition to its reducing properties. The lesser oscillation amplitude suggests larger NPs compared to that in Nafion. The results of the present study open up the possibility of using in-situ TDPAC spectroscopy to explore the structure-property relations of nanomaterials. (author)