The effect of cesium content on the thermodynamic stability and chemical durability of (Ba,Cs)1.33(Al,Ti)8O16 hollandite

Titanate-based hollandite ceramics are promising nuclear waste forms for Cs immobilization. In this work, a series of Al-substituted hollandite (Ba_,Cs)_1.33(Al,Ti)₈O₁₆ was investigated across a broad compositional range with varying Cs content. Powder X-ray diffraction showed that all samples exhibited a tetragonal hollandite phase. Enthalpies of formation determined by high-temperature melt solution calorimetry indicated enhanced thermodynamic stability with increased Cs content, which generally agreed with sublattice-based thermodynamic calculations. Moreover, enthalpies of formation of the samples were primarily affected by three factors: (a) relative sizes of cations on the A-sites and B-sites, (b) tolerance factor, and (c) optical basicity. Fractional element release revealed that Cs retention was significantly improved for the high Cs-containing hollandite compositions, which were supported by the evolution of microstructure of the pre and postleach particles. Elution studies of Al-substituted hollandite spiked with radioactive ¹³⁷Cs indicated that transmutation of Cs to Ba in the hollandite was accompanied by an increase in the retention of the Cs decay product, suggesting long-term stability of Al-substituted hollandite phase.     

Volumetric Electron Transfer from Metabolites to Chemically Doped Polymer Electrodes

The development of sensor electrode materials for the detection of metabolites will enable point-of-care diagnostic devices for the monitoring and treatment of metabolic diseases such as diabetes. Current state-of-the-art glucose sensing electrodes employ the organic salt tetrathiafulvene tetracyanoquinodimethane (TTF TCNQ) to receive electrons directly from enzymatic reactions of glucose. However, TTF TCNQ is insoluble in most solvents, making it challenging to deposit high-quality electrodes. Furthermore, its hydrophobicity hinders its interface with aqueous solutions in physiological environments. To overcome these issues, TCNQ derivatives are introduced into an electron-rich and hydrophilic conjugated polymer. Thus, a polymeric electrode is demonstrated that is easily solution processible and can undergo volumetric direct electron transfer with glucose reactions throughout its bulk. This study further elucidates the electron transfer mechanism during chemical doping and metabolite sensing reactions to inform general design rules for this new class of glucose sensing materials.