We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future.
Pt NPs were in situ synthesised on poly(sodium styrene sulfonate) functionalized graphene supports (PSS-G) in aqueous solution. We investigate the reduction of graphene oxide, PSS adsorption on reduced graphene, and Pt NP functionalization by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure studies (XAFS), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. The as-prepared Pt on PSS-G sample (Pt-PSS-G) was used directly as a catalyst ink without further treatment. The use of PSS as a stabilizer prevents stacking of reduced graphene sheets, binds Pt NPs, and promotes mass transport of reaction species. The as-prepared Pt-PSS-G exhibits higher activity and stability for methanol oxidation reaction than Pt NPs supported on pristine graphene sheets (Pt-G). The higher activity is due to the presence of Pt NPs on the surface of the PSS-G support, which provides an integrated electron and mass transport pathway for every Pt NP. This work realizes both scalable and greener production of highly efficient catalysts, and would be valuable for practical applications of graphene based fuel cell catalysts.
Fabrication of highly ordered arrays of single-walled carbon nanotubes (SWNTs) has been of great interest for a wide range of potential applications. Here, we report thermally switchable one- and two-dimensional arrays of individually isolated SWNTs formed by cooperative self-assembly of functionalized SWNTs and a block copolymer/water system. Small-angle X-ray scattering measurements reveal that when the block copolymer/water system is in an isotropic phase, two-dimensional hexagonal arrays of SWNTs are formed by depletion attraction, and when the block copolymer/water system is in a lamellar phase, one-dimensional lattices of SWNTs intercalated in the polar regions of the polymeric lamellar structure are formed by entropically driven segregation and two-dimensional depletion attraction. These two SWNT arrays are thermally interchangeable, following the temperature-dependent phase behavior of the block copolymer/water system.
A new dispersant for stabilization of single wall carbon nanotubes (SWNTs) in water that simultaneously utilizes three different dispersion or stabilization mechanisms: surfactant adsorption, polymeric wrapping, and Coulomb repulsive interaction, has been demonstrated. The new dispersant, a charged rod‐like nanoparticle (cROD), is a cylindrical micelle wrapped by negatively charged polymers which is fabricated by the aqueous free radical polymerization of a polymerizable cationic surfactant, cetyltrimethylammonium 4‐vinylbenzoate (CTVB), in the presence of sodium 4‐styrenesulfonate (NaSS). The surface charge density of the cRODs is controlled by varying the concentration of NaSS. Dispersions of SWNTs are obtained by sonicating a mixture of SWNTs and cROD in water, followed by ultra‐centrifugation and decanting. While the cRODs with neutral or low surface change densities (0 and 5 mol % NaSS) result in very low dispersion power and poor stability, the cRODs with high surface charge densities (15, 25, and 40 mol % NaSS) produce excellent dispersions with SWNT concentration as high as 437 mg L−1 and long term stability. The sharp van Hove transition peaks of the cROD assisted SWNT dispersions indicate the presence of individually isolated SWNTs. Atomic force microscopy and small angle neutron scattering analysis show that the dominant encapsulation structure of the cROD assisted SWNTs is surfactant assisted polymeric wrapping. SWNTs dispersed by the cRODs can be fully dried and easily re‐dispersed in water, providing enhanced processibility of SWNTs.
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