Abstract
Single phase CeO
2
nanocrystals were bio-synthesized using Hoodia
gordonii
natural extract as an effective chelating agent. The nanocrystals with an average diameter of 〈Ø〉 ~ 5–26 nm with 4
...+
electronic valence of Ce displayed a remarkable UV selectivity and an exceptional photostability. The diffuse reflectivity profile of such CeO
2
exhibited a unique UV selectivity, in a form of a Heaviside function-like type profile in the solar spectrum. While the UV reflectivity is significantly low; within the range of 0.7%, it reaches 63% in the VIS and NIR. Their relative Reactive Oxygen Species (ROS) production was found to be < 1 within a wide range of concentration (0.5–1000 μg/ml). This exceptional photostability conjugated to a sound UV selectivity opens a potential horizon to a novel family of green nano-cosmetics by green nano-processing.
Abstract
This contribution reports on the physical properties of the natural Namibian red Ochre used by the Himba Community in a form of a formulation, so called Otjize as a skin protective and ...beauty cream. The morphological and crystallographic studies of this red ochre validated its nano-scaled dominating phase of rhombohedral α-Fe
2
O
3
nanocrystals with an additional hydrolized oxide component in a form of γ-FeOOH. The optical investigations showed that such a red ochre exhibits an exceptional UV filtration and a significant IR reflectivity substantiating its effectiveness as an effective UV-blocking & solar heat IR reflector in support of the low skin cancer rate within the Namibian Himba community. In addition, such nanocrystals exhibited a non-negligible antibacterial response against E. Coli & S. Aurus. This study seems confirming the effectiveness of the indigenous Otjize as an effective skin UV protection cream with a sound antimicrobial efficacy against e-Coli & S-Aurus.
Coccolithophores of the Noëlaerhabdaceae family are covered by imbricated coccoliths, each composed of multiple calcite crystals radially distributed around the periphery of a grid. The factors ...that determine coccolith size remain obscure. Here, we used synchrotron-based three-dimensional Coherent X-ray Diffraction Imaging to study coccoliths of 7 species of Gephyrocapsa, Emiliania and Reticulofenestra with a resolution close to 30 nm. Segmentation of 45 coccoliths revealed remarkable size, mass and segment number variations, even within single coccospheres. In particular, we observed that coccolith mass correlates with grid perimeter which scales linearly with crystal number. Our results indirectly support the idea that coccolith mass is determined in the coccolith vesicle by the size of the organic base plate scale (OBPS) around which R-unit nucleation occurs every 110-120 nm. The curvation of coccoliths allows inference of a positive correlation between cell nucleus, OBPS and coccolith sizes.
Ellipsometry and X-ray reflectivity were used to characterize the mass density and the glass transition temperature of supported polystyrene (PS) thin films as a function of their thickness. By ...measuring the critical wave vector (q c) on the plateau of total external reflection, we evidence that PS films get denser in a confined state when the film thickness is below 50 nm. Refractive indices (n) and electron density profiles measurements confirm this statement. The density of a 6 nm (0.4 gyration radius, R g) thick film is 30% greater than that of a 150 nm (10R g) film. A depression of 25 °C in glass transition temperature (T g) was revealed as the film thickness is reduced. In the context of the free volume theory, this result seems to be in apparent contradiction with the fact that thinner films are denser. However, as the thermal expansion of thinner films is found to be greater than the one of thicker films, the increase in free volume is larger for thin films when temperature is raised. Therefore, the free volume reaches a critical value at a lower T g for thinner films. This critical value corresponds to the onset of large cooperative movements of polymer chains. The link between the densification of ultrathin films and the drop in their T g is thus reconciled. We finally show that at their respective T g(h) all films exhibit a critical mass density of about 1.05 g/cm3 whatever their thickness. The thickness dependent thermal expansion related to the free volume is consequently a key factor to understand the drop in the T g of ultrathin films.
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•Microcellular natural rubber is prepared using supercritical CO2 technology.•Cell size and size distribution drop with increasing saturation pressure and time.•Increment of ...saturation temperature enhances cell size and size distribution.•Crosslinking level of rubber affects on reducing cell size and size distribution.
Microcellular natural rubber (NR) prepared using a supercritical CO2 technology is a promising alternative to replace traditional foaming agent due to environmental concern. Crucial parameters for the foaming process including CO2 saturation time (30, 60, 90, 120, 180) min, pressure (0, 8.5, 10.5, 12.5) MPa, temperature (45, 55, 65, 85) °C, and crosslinking characteristics of NR (pre-vulcanized time at 15 min and 30 min) were orderly conducted. The results obtained showed a decrement of average cell size (less than 10 μm), cell size distribution, and expansion ratio depending on an enhancement of saturation time and pressure. However, the increment of saturation temperature affected the increase in average cell size, cell size distribution, and expansion ratio. In case of the crosslinking behavior, an escalation of the pre-vulcanized time of rubber influenced the decrement in average cell size, cell size distribution and expansion ratio resulting from an elevation of matrix crosslinking.
Smart materials with reversible tunable optical constants from visible to near-infrared wavelengths could enable excellent control over the resonant response in metamaterials, tunable plasmonic ...nanostructures, optical memory based on phase transition and thermally tunable optical devices. Vanadium dioxide (VO
2) is a promising candidate that exhibits a dramatic change in its complex refraction index or complex dielectric function arising from a structural phase transition from semiconductor to metal at a critical temperature of 70
°C. We demonstrated the thermal controllable reversible tunability of optical constants of VO
2 thin films. The optical/dielectric constants showed an abrupt thermal hysteresis which confirms clearly the electronic structural changes. Temperature dependence of dielectric constants as well as optical conductivity of sputtered VO
2 thin films was also reported and compared to previous theoretical and experimental reports.
This contribution reports, for the first time, on an entirely green bio-engineering approach for the biosynthesis of single phase crystalline 1-D nano-scaled calcite CaCO3. This was validated using ...H2O as the universal solvent and natural extract of Hyphaene thebaica fruit as an effective chelating agent. In this room temperature green process, CaCl2 and CO2 are used as the unique source of Ca and CO3 respectively in view of forming nano-scaled CaCO3 with a significant shape anisotropy and an elevated surface to volume ratio. In terms of novelty, and relatively to the reported scientific and patented literature in relation to the fabrication of CaCO3 by green nano-chemistry, the current cost effective room temperature green process can be singled out as per the following specificities: only water as universal solvent is used, No additional base or acid chemicals for pH control, No additional catalyst, No critical or supercritical CO2 usage conditions, Only natural extract of thebaica as a green effective chelating agent through its phytochemicals and proper enzematic compounds, room Temperature processing, atmospheric pressure processing, Nanoscaled size particles, and Nanoparticles with a significant shape anisotropy (1-D like nanoparticles). Beyond and in addition to the validation of the 1-D synthesis aspect, the bio-engineered CaCO3 exhibited a wide-ranging functionalities in terms of highly reflecting pigment, an effective nanofertilizer as well as a potential binder in cement industry.
Solar heat management & green air-conditioning are among the major technologies that could mitigate heat islands phenomenon while minimizing significantly the CO
global foot-print within the building ...& automotive sectors. Chromogenic materials in general, and thermochromic smart coatings especially are promising candidates that consent a noteworthy dynamic solar radiation Infrared (NIR-IR) regulation and hence an efficient solar heat management especially with the expected increase of the global seasonal temperature. Within this contribution, two major challenging bottlenecks in vanadium oxide based smart coatings were addressed. It is validated for the first time that the NIR-IR modulation of the optical transmission (∆T
= T
- T
) of Vanadium oxide based smart coatings can be controlled & tuned. This upmost challenging bottle-neck controllability/tunability is confirmed via a genuine approach alongside to a simultaneous drastic reduction of the phase transition temperature T
from 68.8 °C to nearly room temperature. More precisely, a substantial thermochromism in multilayered V
O
/V/V
O
stacks equivalent to that of standard pure VO
thin films but with a far lower transition temperature, is reported. Such a multilayered V
O
/V/V
O
thermochromic system exhibited a net control & tunability of the optical transmission modulation in the NIR-IR (∆T
) via the nano-scaled thickness' control of the intermediate Vanadium layer. In addition, the control of ∆T
is accompanied by a tremendous diminution of the thermochromic transition temperature from the elevated bulk value of 68.8 °C to the range of 27.5-37.5 ºC. The observed remarkable and reversible thermochromism in such multilayered nano-scaled system of V
O
/V/V
O
is likely to be ascribed to a noteworthy interfacial diffusion, and an indirect doping by alkaline ions diffusing from the borosilicate substrate. It is hoped that the current findings would contribute in advancing thermochromic smart window technology and their applications for solar heat management in glass windows in general, skyscraper especially & in the automotive industry. If so, this would open a path to a sustainable green air-conditioning with zero-energy input.
Abstract
This contribution reports for the first time the possibility of using radiolysis to engineer stable efficient nanofluids which exhibit an enhanced thermal conductivity. The validation was ...confirmed on Ag-H
2
O and Ag-C
2
H
6
O
2
nanofluids fabricated via g-radiolysis within the mild dose range of 0.95 × 10
3
–2.45 × 10
3
Gray. The enhanced thermal conductivity of Ag-H
2
O and Ag-C
2
H
6
O
2
nanofluids, was found to be g-radiations dose dependent. In the latter case of Ag-C
2
H
6
O
2
nanofluid, the relative enhancement in the temperature range of 25–50 °C was found to be 8.89%, 11.54%, 18.69%, 23.57% and 18.45% for D
1
= 0.95 × 10
3
Gray, D
2
= 1.2 × 10
3
Gray, D
3
= 1.54 × 10
3
Gray, D
4
= 1.80 × 10
3
Gray and D
5
= 2.45 × 10
3
Gray respectively. Yet not optimized, an enhancement of the effective thermal conductivity as much as 23.57% relatively to pure C
2
H
6
O
2
was observed in stable Ag-C
2
H
6
O
2
nanofluids. Equivalent results were obtained with Ag-H
2
O.
While room temperature bulk mercury is liquid, it is solid in its nano-configuration (Ø
≤ 2.5 nm). Conjugating the nano-scale size effect and the Laplace driven surface excess pressure, Hg ...nanoparticles of Ø
≤ 2.4 nm embedded in a 2-D turbostratic Boron Nitride (BN) host matrix exhibited a net crystallization at room temperature via the experimentally observed (101) and (003) diffraction Bragg peaks of the solid Hg rhombohedral α-phase. The observed crystallization is correlated to a surface atomic ordering of 7 to 8 reticular atomic plans of the rhombohedral α-phase. Such a novelty of size effect on phase transition phenomena in Hg is conjugated to a potential Hg waste storage technology. Considering the vapor pressure of bulk Hg, Room Temperature (RT) Solid nano-Hg confinement could represent a potential green approach of Hg waste storage derived from modern halogen efficient light technology.
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