Radionuclide 106Ru behavior in aqueous solutions by ion exchange, ultrafiltration, and centrifugation methods

The paper presents the results of 106Ru radionuclide behavior regularities study in aqueous solutions in a wide pH range by ultrafiltration, ion exchange and centrifugation methods. The regions of 106Ru various species existence in solution have been established: cationic 106Ru species at pH < 3.5; the transition region of non-ionic species formation in the range of pH 3.5–4.2 and the region of non-ionic species predominant formation at pH > 4.2. A characteristic feature of the studied solutions is the formation of non-ionic particles by microconcentrations of 106Ru via pseudocolloids at lower pH values as compared to ruthenium solutions with a concentration of 10-6–10-4 mol/dm3. The established regularities of the behavior of ruthenium radionuclides can be utilized to increase the efficiency of ion exchange and membrane separation methods at nuclear and radiation facilities for technological solutions and liquid radioactive waste treatment.

A Facile and Versatile Approach for the Synthesis of Degradable Polymers via Controlled Ring-Opening Metathesis Copolymerization

Norbornene derivatives (NBEs) are the most common monomers for ring-opening metathesis polymerization (ROMP) because they undergo living polymerization, yielding polymers with low dispersities and diverse functionalities. However, the all-carbon backbone of polyNBEs cannot be degraded. Polymer degradation is highly desired for many applications and has been a major limitation in ROMP chemistry. Here, we report a simple yet powerful method to synthesize controlled, degradable polymers by copolymerizing 2,3-dihydrofuran (DHF) with NBEs. DHF rapidly reacts with the Grubbs catalyst to form a thermodynamically stable Ru Fischer carbene, which is the only detectable active Ru species during the copolymerization, and the addition of NBEs becomes rate determining. This unique Ru Fischer carbene reactivity attenuates NBE homoaddition, which presented a significant challenge to previous copolymerization approaches, allows even incorporation of DHF units (acid-degradable enol ether bonds) throughout the copolymers, and thus enables complete polymer degradation while maintaining the favorable characteristics of living ROMP. We demonstrate the effective copolymerization of DHF with several types of NBEs to synthesize narrow-disperse polymers with tunable solubility, glass transition temperature, and mechanical properties. These polymers can all be fully degraded into small molecule or oligomeric species under mildly acidic conditions. This method can be readily adapted to traditional ROMP of widely used NBEs to synthesize new degradable polymers with tunable properties and facile degradation for various applications and environmental sustainability.

Direct probing of atomically dispersed Ru species over multi-edged TiO2 for highly efficient photocatalytic hydrogen evolution

A cocatalyst is necessary for boosting the electron-hole separation efficiency and accelerating the reaction kinetics of semiconductors. As a result, it is of critical importance to in situ track the structural evolution of the cocatalyst during the photocatalytic process, but it remains very challenging. Here, atomically dispersed Ru atoms are decorated over multi-edged TiO2 spheres for photocatalytic hydrogen evolution. Experimental results not only demonstrate that the photogenerated electrons can be effectively transferred to the isolated Ru atoms for hydrogen evolution but also imply that the TiO2 architecture with multi-edges might facilitate the charge separation and transport. The change in valence and the evolution of electronic structure of Ru sites are well probed during the photocatalytic process. Specifically, the optimized catalyst produces the hydrogen evolution rate of 7.2 mmol g−1 hour−1, which is much higher than that of Pt-based cocatalyst systems and among the highest reported values.

Synthesis and Evaluation of PtNi Electrocatalysts for CO and Methanol Oxidation in Low Temperature Fuel Cells

Pt(Ni)/C and PtRu(Ni)/C catalysts were synthesized by electroless deposition of Ni on a carbon dispersion followed by sequenced Pt deposition and spontaneous deposition of Ru species. The structural analyses of the catalysts with 88:12 and 98:2 Pt:Ni atomic ratios pointed out to the formation of small hexagonal Ni crystallites covered by thin cubic Pt surface structures with no evidence about PtNi alloy formation. The onset potentials for CO oxidation on Pt(Ni)/C and PtRu(Ni)/C were about 0.10 and 0.24 V more negative than those of Pt/C, thus indicating their better CO tolerance. The surface Ru species appeared to have the major effect by facilitating the CO removal by the bifunctional mechanism. The onset potential for the methanol oxidation reaction (MOR) of Pt(Ni)/C was about 0.15 V lower than that of Pt/C. The mass and specific activities together with the exchange current densities of the Pt(Ni)/C catalysts were also higher than those of Pt/C, making in evidence their higher activity in front of the MOR. The Tafel slopes for the MOR on Pt(Ni)/C suggested different reaction mechanism than on Pt/C. The electronic (ligand) effect of Ni on Pt was considered the main reason to explain the higher activity of Pt(Ni)/C in front of the CO oxidation and the MOR.