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[en] Nano-materials are materials with at least one nano-phase. A nano-phase is a phase with at least one of its dimensions below 100 nm. It is shown here that nano-phases have at least 1% of their atoms along their surface layer. The ratio of surface atoms is proportional to the specific surface area of the phase, defined as the ratio of its surface area to its volume. Each specific/molar property has its bulk value and its surface value for the given phase, being always different, as the energetic states of the atoms in the bulk and in the surface layer of a phase are different. The average specific/molar property of a nano-phase is modeled here as a linear combination of the bulk and surface values of the same property, scaled with the ratio of the surface atoms. That makes the performance of all nano-phases proportional to their specific surface area. As the characteristic size of the nano-phase is inversely proportional to its specific surface area, all specific/molar properties of nano-phases are inversely proportional to the characteristic size of the phase. This is applied to the size dependence of the molar Gibbs energy of the nano-phase, which appears to be in agreement with the thermodynamics of Gibbs. This agreement proves the general validity of the present model on the size dependence of the specific/molar properties of independent nano-phases. It is shown that the properties of nano-phases are different for independent nano-phases (surrounded only by their equilibrium vapor phase) and for nano-phases in multi-phase situations, such as a liquid nano-droplet in the sessile drop configuration.
[en] Hierarchically porous carbon monoliths with high specific surface areas have been fabricated by removing nano-sized silica phase from carbon/silica composites pyrolyzed from bridged poly(silsesquioxane). This activation method improves the homogeneity between inner and outer parts of the monoliths compared to the conventional thermal activation methods.
[en] In the EU regulation, a material containing particles is considered as nano if, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1–100 nm. Due to the difficulty to measure in a reliable way the number particle size distribution, it is suggested to use the volume-specific surface area (VSSA) >60 m"2/cm"3 as simple screening criterion to identify nanomaterials. This threshold corresponds to monodispersed spherical particles with a size of 100 nm. In this paper, a theoretical study is carried out to identify the effect of the particle shape, polydispersity, agglomeration and aggregation on the VSSA threshold. It appears that the VSSA approach is overprotective because a lot of samples are identified as nanomaterials even if less than 50 % of the particles have a size lower than 100 nm, this 50 % in number criterion being the main identification criterion in the EU definition. Even if the VSSA is leading to many false positive results, it can be used to identify non-nanomaterials as soon as its value is lower than the threshold at the condition to take into account the shape of the particles and their external surface area. This conclusion is true for monomodal distributions of particles but is subject to some restrictions for bimodal distributions
[en] Based on the biomimetic route the metal material with tree-like fractal structure was prepared, which showed a rough surface observed by scanning electron microscopy. According to the electrochemical experiments, the formed material exhibited the strong catalytic capability as an electrode in hydrogen evolution reaction, comparing with other conventional structure materials under comparable scales. We suggested this promotion of property arose from the contribution of the great surface area and the excellent connectivity offered from the fractal structure
[en] Understanding the effects of structural properties on the lithium storage behavior of mesoporous TiO2 is crucial for further optimizing its performance through rational structure design. To achieve this, herein, the surface area and the grain size of the prepared mesoporous TiO2 are intentionally adjusted by controlling the calcination temperatures. It is found that the capacities of the mesoporous TiO2 contain both the lithium-ion insertion into the bulk phase ( Q in) and the additional surface lithium storage ( Q as). The Q in gradually increases with grain sizes to a steady level and then slightly drops. By contrast, the Q as is directly proportional to the specific surface area of the mesoporous TiO2 and is ascribed to the capacity originated from the lithium-ion insertion into the surface layer. The experimental comparison and analysis demonstrate that the fast kinetics of the Q as ensure both the better rate performance and capacity retention of mesoporous TiO2 than bulk ones. Specially, the mesoporous TiO2 calcinated at 350 °C shows the highest reversible specific capacity of 250.2 mA h g−1, the best rate capability (132.5 mA h g−1 at 2C) and good cycling stability. Our findings shed great light on the design of high-performance nanostructured TiO2 with surface lithium storage. (paper)
[en] The dependence of the perimeter-area relation on the size of Koch Island is discussed. It is found that in general the fractal ratio between Koch perimeter and the square root of the enclosed area is not independent of the size of the Island; though in some cases, this relation may approximately hold. Therefore, this relation should be used carefully for determination of the fractal dimension of Koch Island. (author). 17 refs, 3 figs
[en] Highlights: • Electrodeposition of PEDOT polymers with alkyne groups toward platform surfaces • Use of the Huisgen reaction as post-functionalization • Different hydrophobic substituents tested • Influence of the grafting of nanoparticles before post-functionalization • The nanoparticles allow reaching superhydrophobic properties. Surface post-functionalization is one of the key modification pathways leading to superhydrophobic surfaces. The functionalization is deeply linked to the functionalizable area and the number of functionalizable groups. By grafting functional nanoparticles onto surfaces it is possible to dramatically increase both the area and the number of functionalizable groups. In this work, we report the elaboration of platform surfaces for direct functionalization by grafting nanoparticles and functionalization using the Huisgen reaction. The surfaces were functionalized with various hydrophobic side chain including alkyl, aryl and perfluorinated chains. The modified surfaces have enhanced hydrophobic, parahydrophobic or superhydrophobic properties. The surfaces were investigated for their wettability, morphology and roughness. This work shows that the use of nanoparticles to increase functionalizable surface area can highly enhance surface hydrophobic properties.
[en] High surface area microporous carbon materials were synthesized using new, simple, and innovative approaches based on traditional template and chemical activation methods. The resulting surface area and porosity were characterized using Brunauer-Emmett-Teller (BET)-type measurements and analysis, and the hydrogen storage capacity was determined using excess hydrogen adsorption measurements at 77 K and up to 40 bar hydrogen pressure. For our direct one-step aerosol-assisted template-based synthesis method of mixing the template precursor and carbon precursor solutions, a specific surface area value of up to nearly 2000 m2 g-1 and an excess hydrogen storage capacity of 4.2 wt% was observed. For our chemical activation-based synthesis method of homogeneously mixing the chemical activation reagent into the carbon precursor solution, a specific surface area value of nearly 3000 m2 g-1 and an excess hydrogen adsorption capacity of nearly 5.8 wt% were observed. The surface area and hydrogen uptake results varied systematically with the synthesis parameters, and we observed a strong correlation between the BET values of the specific surface area and the excess hydrogen adsorption capacity.
[en] Highlights: • Novel ultrafine nanoporous Pt ribbons were fabricated by dealloying melt-spun Al-Pt-Ce alloys. • The as-dealloyed Pt ribbons exhibited a hierarchical nanoporous architecture. • The specific surface area of the NP-Pt reached up to 85.38 m2g−1. • Nanoporous Pt exhibited enhanced electro-catalytic performance and stability. - Abstract: Novel ultrafine nanoporous Pt (NP-Pt) ribbons were fabricated by dealloying melt-spun Al85Pt15 and Al85Pt8Ce7 alloys. The addtion of Ce to Al-Pt alloy changed the phase constituents and distribution of the alloy. During alkali-dealloying, CeOx nanorods formed and were distributed in NP-Pt. Sacrificial nanorods were then selectively removed during acid-dealloying, resulting in the formation of hierarchical NP-Pt ribbons with a ligament scale of approximately 3 nm. The specific surface area of the NP-Pt was 3 times greater than that of the Al85Pt15 alloy without Ce. NP-Pt with a high active surface area had remarkable electro-catalytic performance and stability towards methanol oxidation.
[en] Graphical abstract: CuKα X-ray diffraction patterns of the VP, VPOc, VPOcT, VPOcT200 and VPOcT500. Highlights: ► TEOS and octylamine incorporation into the VP was achieved by expanding the lamellar. ► The specific surface area increased from 15 m2 g−1 in VP to 237 m2 g−1 in VPOcT. ► The VPOcT exhibited thermal resistance up to 200 °C in air. ► Upon thermal treatment up to 500 °C, the surface area increased to 838 m2 g−1. -- Abstract: We have developed a vanadyl phosphate/tetraethylorthosilicate (VPO/TEOS) nanocomposite comprised of silicate chains interleaved with VPO layers, prepared by using an n-alkylamines such as octylamine as the structure directing agent. The nanocomposites were synthesized by reacting amine-intercalated vanadyl phosphate with tetraethylorthosilicate via the soft chemistry approach. The synthetic procedure encompassed the exfoliation of the layered vanadyl phosphate as well as the reorganization of this exfoliated solid into a mesostructured lamellar phase with the same V–P–O connectivity as in the original matrix. TEOS incorporation into the vanadyl phosphate was achieved by expanding the lamellar structure with n-alkylamine (Δd = 13 Å with n-octylamine). The specific surface area increased from 15 m2 g−1 in the vanadyl phosphate matrix to 237 m2 g−1 in VPOcT, and the isotherm curves revealed the characteristic hysteresis of mesoporous materials. Upon thermal treatment up to 500 °C, the surface area increased to 837 m2 g−1, which is suitable for catalytic purposes.