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Ordered mesoporous SiO 2 (KIT-6) was synthesized using triblock copolymer P123 as the structure template and tetraethyl orthosilicate (TEOS, C 8 H 20 O 4 Si) as silica source. Small-angle X-ray scattering and high resolution electron microscope measurements indicate the 3d cubic Ia3d symmetry of the pore structure of KIT-6 synthesized at 30–120  ° C. When the synthesis temperature increases to 180  ° C, the order of pores was deteriorated. The pore size was estimated by nitrogen adsorption/desorption measurements, which increases from 3.8 nm to 18.5 nm as the synthesis temperature increases from 30  ° C to 180  ° C. With the increase of mesopore size, the pore wall thickness shows continuous decrease. Positron annihilation lifetime spectra was measured for the synthesized KIT-6. The lifetime spectra can be resolved to two short and two long lifetime components. The two long lifetimes τ 3 and τ 4 correspond to o- Ps lifetime in micropore and mesopores, respectively. The size of mesopores was estimated from the o -Ps lifetime by using Goworeck’s model for cylindrical pores, which shows continuous increase with synthesis temperature, and is consistent with the N 2 adsorption/desorption measurements. The size of micropore has no change with increasing synthesis temperature. However due to the decrease in wall thickness, the number of micropores in the wall shows subsequent decrease. In addition, the second lifetime component τ 2 is also found to be a sensitive parameter for the pore size, which shows the same trend as lifetime τ 4 with increasing synthesis temperature. [ABSTRACT FROM AUTHOR]

Adsorption of small gas molecules (O 2 , NO, NO 2 and NH 3 ) on transition-metal Cu atom embedded monolayer MoS 2 was investigated by first-principles calculations based on the density-functional theory (DFT). The embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS 2 with a high diffusion barrier. The stable adsorption geometry, charge transfer and electronic structures of these gas molecules on monolayer MoS 2 embedded with transition-metal Cu atom are discussed in detail. It is found that the monolayer MoS 2 with embedded Cu atom can effectively capture these gas molecules with high adsorption energy. The NH 3 molecule acts as electron donor after adsorption, which is different from the other gas molecules (O 2 , NO, and NO 2 ). The results suggest that MoS 2 -Cu system may be promising for future applications in gas molecules sensing and catalysis, which is similar to those of the transition-metal embedded graphene. [ABSTRACT FROM AUTHOR]

Mesoporous silica with ordered pore structure was synthesized at various temperatures using TEOS as the silica source and P123 as the template. Both small angle X-ray scattering (SAXS) and high resolution transition electron microscopy (HRTEM) measurements verify the ordered pore structure of the synthesized SiO 2 . With synthesis temperature increasing, the pore structure has slight damage at 130 °C, while it shows ordered structure again at 150 °C. When the synthesis temperature increases to 180 °C, the ordered pore structure is severely destructed. The change of pore structure is further confirmed by scanning electron microscopy (SEM) measurements. Positron lifetime measurements reveal four lifetime components in the synthesized mesoporous SiO 2 , and the two long lifetimes τ 3 and τ 4 correspond to the annihilation of o-Ps in the micropores and large pores of the material, respectively. The longest lifetime τ 4 tends to increase slightly with increasing synthesis temperature. However, its intensity I 4 shows an overall decrease with exception at 150 °C. At the synthesis temperature of 180 °C, the intensity I 4 decreases drastically to about 17.5%. This indicates variation of the size and fraction of pores with increasing synthesis temperature, and the pore structure is seriously destructed at 180 °C. By comparing with the N 2 adsorption–desorption measurements, it was found that the Goworek's model is more suitable for the size estimation of cylindrical pores from the o-Ps lifetime, while Dull's and Ito's model is appropriate for the rectangular and spherical pores, respectively. [ABSTRACT FROM AUTHOR]

Abstract: NiO/γ-Al2O3 catalysts with NiO content of 9wt% and 24wt% were prepared by solid state reaction method. They are annealed in air at temperatures from 100°C to 1000°C. Positron lifetime spectra were measured to study the microstructure variation during annealing process. Four positron lifetime components were resolved with two long lifetime τ 3 and τ 4, which can be attributed to the ortho-positronium lifetime in microvoids and large pores, respectively. It was found that the longest lifetime τ 4 is rather sensitive to the chemical environment of the large pores. The NiO active centers in the catalysts cause decrease of both τ 4 and its intensity I 4, which is due to the spin-conversion of positronium induced by NiO. However, after heating the catalysts above 600°C, abnormal increase of the lifetime τ 4 is observed. This is due to the formation of NiAl2O4 spinel from the reaction of NiO and γ-Al2O3. The generated NiAl2O4 weakens the spin-conversion effect of positronium, thus leads to the increase of o-Ps lifetime τ 4. Formation of NiAl2O4 is further confirmed by both X-ray diffraction and X-ray photoelectron spectroscopy measurements. [Copyright &y& Elsevier]

[Display omitted] • Dopant Fe atom can be firmly embedded in γ-graphyne (GY-Fe) and break surface chemical inertness. • GY-Fe surface is beneficial to the adsorption of gas molecules (O 2 , CO, NO, NO 2 , and SO 2). • Gas molecules are firmly anchored on GY-Fe plane through the formation of chemical bonds. • Modified γ-graphyne sheet may be a potential substrate to design gas sensor and catalysts. The adsorption behaviors of gas molecules O 2 , CO, NO, NO 2 and SO 2 on the surface of γ-graphyne doped with Fe atom were explored in detailed by first principles calculations. It is found that dopant Fe atoms could be embedded stability into the γ-graphyne plane with the lower binding energy, the modified surface could significantly enhance the adsorption capacity for free gas molecules. Gas molecules are anchored firmly at the surfaces through the formation of chemical bonds with Fe dopant atoms, the typical chemisorption behaviors can be confirmed by the analysis of electronic properties. The O O bond is elongated to 1.412 Å because of the chemical interaction between adsorbed O 2 and dopant surface, the production of activated oxygen radicals maybe used for elimination of toxic gases. The sensing mechanism of GY-Fe was discussed by desorption properties of gas and band structure analysis, we obtained the recovery time about 7.89 s for SO 2 at 398 K. Therefore, this study, maybe provide some helpful informations for the design of graphyne-based gas sensors and catalysts. [ABSTRACT FROM AUTHOR]

Graphene-based catalyst is an important direction in development of the carbocatalysis, however, the low carrier density near the Fermi level limits graphene's surface activity. Here, we report a way to overcome this difficulty by constructing graphene heterojunction with reported two-dimensional (2D) electride, resulting in a significant improvement of graphene's reactivity. Employing first-principles density functional theory calculations, we demonstrate that 2D electride has the strong electron donation ability and makes the Van Hove Singularity (VHS) of graphene's π ∗ -band close to Fermi level, producing large density of states. We use CO oxidation on graphene/Y 2 C as a prototype example, and show that the states near VHS play a vital role in facilitating O 2 adsorption and CO oxidation by serving as an effective electron bath. Our researches demonstrate that the electron doping of graphene with a layered 2D electride is a promising alternative to turn the graphene into an excellent catalyst. [Display omitted] • The graphene heterojunction constructed with reported Y 2 C electride, results in a significant improvement of graphene's reactivity. • Y 2 C electride has strong electron donation ability and makes the Van Hove Singularity (VHS) of graphene's π *-band close to Fermi level, producing large density of states. • The states near VHS play a vital role in facilitating O 2 adsorption and CO oxidation. • Graphene/Y 2 C electride is a promising alternative to turn the graphene into an excellent catalyst. [ABSTRACT FROM AUTHOR]