Specific Hydrogen Spillover Pathways Generated on Graphene Oxide Enabling the Formation of Non-Equilibrium Alloy Nanoparticles

The phenomenon of hydrogen spillover is investigated as a means of realizing a hydrogen-based society for over half a century. Herein, a graphene oxide having a precisely tuned architecture via calcination in air to introduce ether groups onto basal planes along with carbon defects is reported. This material provides specific pathways for the spillover of atomic hydrogen and has practical applications with regard to the synthesis of non-equilibrium solid-solution alloy nanoparticles. A combination of experimental work and simulations confirmed that the presence of ether groups associated with carbon defects facilitated hydrogen spillover within the basal planes of this graphene oxide. This enhanced hydrogen spillover ability, in turn, enables the simultaneous reduction of Ru3+ and Ni2+ ions to form RuNi alloy nanoparticles under hydrogen reduction conditions. Energy dispersive X-ray and X-ray absorption near edge structure simulations establish that this strategy forms unique alloy nanoparticles each comprising a Ru core with a RuNi solid-solution shell having a hexagonal close-packed structure. These non-equilibrium RuNi alloy nanoparticles exhibit greater catalytic activity than monometallic Ru nanoparticles during the hydrolysis of ammonia borane.

Revealing hydrogen spillover pathways in reducible metal oxides

Hydrogen spillover, the migration of dissociated hydrogen atoms from noble metals to their support materials, is a ubiquitous phenomenon and is widely utilized in heterogeneous catalysis and hydrogen storage materials. However, in-depth understanding of the migration of spilled hydrogen over different types of supports is still lacking. Herein, hydrogen spillover in typical reducible metal oxides, such as TiO₂, CeO₂, and WO₃, was elucidated by combining systematic characterization methods involving various in situ techniques, kinetic analysis, and density functional theory calculations. TiO₂ and CeO₂ were proven to be promising platforms for the synthesis of non-equilibrium RuNi binary solid solution alloy nanoparticles displaying a synergistic promotional effect in the hydrolysis of ammonia borane. Such behaviour was driven by the simultaneous reduction of both metal cations under a H₂ atmosphere over TiO₂ and CeO₂, in which hydrogen spillover favorably occurred over their surfaces rather than within their bulk phases. Conversely, hydrogen atoms were found to preferentially migrate within the bulk prior to the surface over WO₃. Thus, the reductions of both metal cations occurred individually on WO₃, which resulted in the formation of segregated NPs with no activity enhancement.

The hydrogen spillover pathway in typical reducible metal oxides, such as TiO₂, CeO₂, and WO₃, was investigated by combining various in situ characterization techniques, kinetic analysis, and density functional theory calculations.

Synthesis of a binary alloy nanoparticle catalyst with an immiscible combination of Rh and Cu assisted by hydrogen spillover on a TiO2 support

This work demonstrated the use of TiO2 as a promising platform for the synthesis of non-equilibrium RhCu binary alloy nanoparticles (NPs). These metals are regarded as immiscible based on their phase diagram but form NPs with the aid of the significant hydrogen spillover on TiO2 with concurrent proton-electron transfer. The resulting RhCu/TiO2 exhibited 2.6 times higher catalytic activity than Rh/TiO2 during hydrogen production from the hydrolysis of ammonia borane (AB), due to a synergistic effect. Theoretical simulations showed a higher energy value for the adsorption of AB on the RhCu alloy and a lower activation energy for the rate determining N-B bond dissociation by the attack of H2O during AB hydrolysis compared to monometallic Rh. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the formation of RhCu alloy NPs with a mean diameter of 2.0 nm on the TiO2. H2-temperature programmed reduction and in situ X-ray absorption fine structure analyses at elevated temperature under H2 demonstrated that Rh3+ and Cu2+ precursors were simultaneously reduced only on the TiO2 support. This effect resulted from the improved and limited reducibility of Cu2+ and Rh3+, respectively. The rate of hydrogen spillover of TiO2 is faster as compared to γ-Al2O3 and MgO as evidenced by sequential H2/D2 exchanges during in situ Fourier transform infrared analyses. Density functional theory calculations also showed that the migration of H atoms on TiO2 proceeds with a lower energy barrier than that on Al2O3, and the reduction of Cu2+ species is facilitated by H spillover on the support rather than by direct reduction by H2. These results confirm the vital role of TiO2 in the formation of the alloy and may represent a new strategy for the synthesis of different non-equilibrium solid solution alloys.

Colocalisation of CD9 and mortalin in CD9-induced mitotic catastrophe in human prostate cancer cells

CD9, a member of the tetraspanin family of proteins, is involved in a variety of cellular interactions with many other proteins and molecules. Although CD9 has been implicated in cell fusion, migration and cancer progression, the detailed function of this protein is not completely understood and likely depends on interactions with different protein partners, which are not yet all known. Using co-immunoprecipitation and mass-spectrometric protein sequencing, we have identified in prostate cancer cells, a novel CD9 partner, the 75-kDa protein HSPA9B, also known as mortalin. We further show that introduction and overexpression of wild-type CD9 into human PC-3 prostate cancer cells induces mitotic catastrophe. We also demonstrate, by immunocolocalisation studies, the interaction of CD9 and mortalin in PC-3 cells undergoing mitotic catastrophe. Our results not only identified mortalin as a new CD9 partner, but also clarify the mechanisms by which CD9 may control prostate cancer progression.

[Anatomic analysis of canine ureteral smooth muscle structure]

We have investigated the structure of canine middle ureteral smooth muscle anatomically. In a transverse section inner fibers appeared to be longitudinal and outer fibers appeared to be circular. In the parallel sections with the wall of longitudinal ureteral muscle, inner and outer fibers appeared to be oblique in a mesh structure. In parallel sections with the wall of helical ureteral muscle, fibers appeared to be longitudinal. Anatomical analysis showed that canine ureteral smooth muscle is entirely composed of spinal fibers in a mesh structure and that the helical muscle strip have continuous fibers though the inner fibers have a tendency to run longitudinally and the outer fibers circularly.