Progress toward Zeolite-Based Self-Luminous Sensors for Radioactive Isotopes such as ²⁰¹Tl and ¹³⁷Cs: Structures and Luminescence of Hf,Cl,Tl-A and Hf,Cl,Cs,Na-A

Abstract

Smart materials that both sorb and announce the presence of radioactive isotopes such as 201Tl and 137Cs are needed for human safety in environmental catastrophies. This study reports progress toward zeolite-based self-luminous sensors for radioactive isotopes. Hf4+ was introduced into zeolite A by treating Tl-A and Cs,Na-A with HfCl4(g) under anhydrous conditions. The crystal structures of the products, Hf,Cl,Tl-A and Hf,Cl,Cs,Na-A, were determined by single-crystal crystallography using synchrotron X-radiation, with compositional confirmation by SEM-EDX analysis. Their luminescence properties upon X-ray, UV, and proton beam irradiation were studied. In Hf,Cl,Tl-A, some Hf4+ ions are 3-coordinate with three framework oxygen atoms of 6-rings; octahedral HfCl6 2– ions are at the very centers of 7% of the large cavities within Tl14HfCl6 12+ clusters. HfCl6 2– ions are also seen in Hf,Cl,Cs,Na-A; they similarly occupy 7% of the large cavities and are members of a Cs11HfCl6 9+ continuum. The X-ray-induced luminescence spectra of Hf,Cl,Tl-A and Hf,Cl,Cs,Na-A, and that of Hf,Cl,Tl-A induced by UV, are all broad bands from 300 to 720 nm, peaking near 400 nm. By comparisons with the corresponding spectra of Zr,Cl,Tl-A, Zr,Cl,Cs,Na-A, Cs2HfCl6, and Cs2ZrCl6, several luminescence mechanisms are proposed. These zeolite-based materials can be expected to emit light (be self-luminous) as radioactive isotopes exchange into them.

Crystal Structure of Zeolite LTA Containing Extraframework Tungsten(VI) Ions

“…It can be seen in reactions and that no TlCl exited the zeolite, and therefore, that TIE did not occur. Perhaps this is because this crystal was prepared at a lower temperature (453 K) than that used in previous work with Zr,Cl,Tl-A (553 and 623 K) and Hf,Cl,Tl-A (523 K). Perhaps also TlCl is simply more firmly held (Figures b and b) in this crystal.…”