Abstract: Sn4+-containing LDH was prepared using the co-precipitation method at constant pH, and characterized using X-ray diffraction, UVvis diffuse reflectance spectroscopy and TG/DTG methods. The obtained product was further exposed to different thermal treatments in order to obtain nano-sized coupled ZnO/SnO2 systems with enhanced photocatalytic performances than the ones obtained by mixing the two semiconductor oxides. The formation of a well-defined ZnO/SnO2 system and the crystallite size, fully investigated using XRD, micro-Raman scattering and UVvis DR techniques, were found to be influenced by the nature of the precursors and the calcination temperature. The photocatalytic activity of the ZnO/SnO2 systems, evaluated for the photodegradation of methyl orange (MO) dye, was studied as a function of the initial pH, catalyst loading and the calcination temperature. The metal dispersion supplied by layered structures proved to be an advantage when preparing coupled ZnO/SnO2 systems, the photocatalytic activity being 2.3 times higher comparing with the physical mixtures performances. The maximum photocatalytic activity of the coupled ZnO/SnO2 system having a layered precursor was observed when using neutral pH, at a catalyst loading of 1 g/L calcined at 600 °C for 4 h.

Abstract: We have performed a first-principles density functional theory investigation of the penetration of helium atoms through a graphene monolayer with defects. The relaxation of the graphene layer caused by the incoming helium atoms does not have a strong influence on the height of the energy barriers for penetration. For defective graphene layers, the penetration barriers decrease exponentially with the size of the defects but they are still sufficiently high that very large defects are needed to make the graphene sheet permeable for small atoms and molecules. This makes graphene a very promising material for the construction of nanocages and nanomembranes.

Abstract: We study the effects of the rippling of a graphene sheet on quasiparticle dispersion. This is achieved using a generalization to the honeycomb lattice of the momentum average approximation, which is accurate for all coupling strengths and at all energies. We show that even though the position of the Dirac points may move and the Fermi speed can be renormalized significantly, quasiparticles with very long lifetimes survive near the Dirac points even for very strong couplings.