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We investigated the radiolytic hydrogen production of geopolymers that are a candidate material for solidifying radioactive waste. The effects of water content and solid properties on the hydrogen production were evaluated by 60Co γ-ray irradiation using geopolymers with and without boric acid, which controls the setting time of the geopolymer. We also constructed a preliminary model of the geopolymer pore structure and calculated the dose to water on the pore surface using Monte Carlo simulation. Hydrogen production was influenced by water content, specific surface area, and electron density of elements in the solid, and increased as these values increased. Simulation results suggested that the amount of hydrogen was affected by the dose of Compton electrons generated by γ-ray irradiation on the geopolymer solid to water on the pore surface. The apparent hydrogen production yield of the geopolymer containing boric acid was 1.1 × 10−8 mol/J, less than 1/4 of that of water. When this sample was heated over 800°C, it decreased to 1.0 × 10−9 mol/J. In contrast, the apparent hydrogen production yield based on the energy absorbed by water in the geopolymer was larger than that of water and increased with a decrease in water content. Furthermore, it decreased below 0.2 wt.% water content. [ABSTRACT FROM AUTHOR]

Recently, doped organic semiconductors with high work functions have been studied for opto-electronic device applications. However, a higher work function commonly results in poorer stability due to redox reactions with water in air, limiting device processing and applications. In this study, combinations of bulky anions and a semicrystalline polythiophene derivative were explored for chemical doping under ambient conditions. The use of tetrakis(pentafluorophenyl)borate (TFPB) anions resulted in a high work function over 5.5 eV with remarkably improved stability, with 90% of the conductivity retained after storage in air for 20 days. The stability at elevated temperatures of 100 °C and 125 °C was also dramatically improved compared with the use of other dopant ions. X-ray diffraction measurements suggest that intercalation of the TFPB anion occurs in the lamellar structure of the polymer, while in-plane π-stacking structures are present. Dedoping reactions including self-degradation at high temperatures seemed to be suppressed for this inert dopant anion, which contributed to the observed exceptional stability. Our findings provide promising insights into the design of combinations of polymers and dopants to achieve highly stable doped organic semiconductors. [ABSTRACT FROM AUTHOR]

The efficiency with which polymeric semiconductors can be chemically doped--and the charge carrier densities that can thereby be achieved--is determined primarily by the electrochemical redox potential between the [pi]-conjugated polymer and the dopant species.sup.1,2. Thus, matching the electron affinity of one with the ionization potential of the other can allow effective doping.sup.3,4. Here we describe a different process--which we term 'anion exchange'--that might offer improved doping levels. This process is mediated by an ionic liquid solvent and can be pictured as the effective instantaneous exchange of a conventional small p-type dopant anion with a second anion provided by an ionic liquid. The introduction of optimized ionic salt (the ionic liquid solvent) into a conventional binary donor-acceptor system can overcome the redox potential limitations described by Marcus theory.sup.5, and allows an anion-exchange efficiency of nearly 100 per cent. As a result, doping levels of up to almost one charge per monomer unit can be achieved. This demonstration of increased doping levels, increased stability and excellent transport properties shows that anion-exchange doping, which can use an almost infinite selection of ionic salts, could be a powerful tool for the realization of advanced molecular electronics. The limitations of conventional chemical doping of polymeric semiconductors can be overcome by adding a second ionic species into the system, leading to enhanced doping, electrical conductivity and stability., Author(s): Yu Yamashita [sup.1] [sup.2] [sup.3] , Junto Tsurumi [sup.1] [sup.2] [sup.3] , Masahiro Ohno [sup.1] [sup.2] , Ryo Fujimoto [sup.1] [sup.2] , Shohei Kumagai [sup.1] [sup.2] , Tadanori Kurosawa [...]