Microcrystalline hexagonal tungsten bronze. 1. Basis of ion exchange selectivity for cesium and strontium.

摘要: The structural basis of selectivity for cesium and strontium microcrystalline hexagonal tungsten bronze (HTB) phase NaxWO3+x/2 center dot zH(2)O has been studied using X-ray neutron diffraction techniques, 1D 2D Na-23 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, radiochemical ion exchange investigations. For the HTB system, this study shown that scattering techniques alone provide an incomplete description disorder rapid water (with tunnel cations) occurring in system. However, MAS NMR identified three sodium species within tunnels-species A, which is located at window devoid coordinated water, B C, are di- monohydrated variants, respectively, A. Although accords with traditional crystallographic model phase, work first to propose identify anhydrous A monohydrate C. population (total) C decreases comparison increasing either or strontium; is, appear more exchangeable than Moreover, a significant proportion redistributed by these cations. Multiple investigations radiotracers Cs-137 Sr-85 have there definite advantage ensuring any easily exchanged removed from tunnels prior exchange. decrease (wrt cesium) most probably due slightly smaller effective size Sr2+; namely, it less good fit window, site. framework unequivocally be defined structure Compromising geometry even slightest way (1) varying cell volume through changes hydration content (2) introducing a-b plane isomorphous substitution molybdenum sufficient reduce selectivity. Indeed, our hypothesis applies all cations strongly bound framework.