Here we report on gas and vapor transport properties of ultra-thin graphene oxide (GO) membranes, with various C:O ratios. Graphene oxide nanosheets with an average lateral size of 800 nm and C:O ...ratio ranging from 2.11 to 1.81 have been obtained using improved Hummers’ method by variation of graphite:KMnO4 ratio. Thin-film selective layers based on the obtained graphene oxide have been spin-coated onto porous substrates. To extend the C:O range to 2.60, thermal reduction of GO membranes was applied. A decrease in C:O ratio leads to significant water vapor permeance growth to over 60 m3(STP)·m−2·bar−1·h−1 while the permeance towards permanent gases reduces slightly. According to the permeation and sorption measurements, a decisive role of H2O diffusivity has been established, while the water sorption capacity of the graphene oxide stays nearly independent of C:O ratio in GO. The result is supported by semi-empirical modeling which reveals diminution of H2O jump activation barriers with both increasing GO interlayer spacing and its oxidation degree. The height of the activation barriers was found to vary up to an order of magnitude within the entire range of relative humidity (0–100% RH), lowering significantly for strongly oxidized GO. Our results evidence the necessity of attaining maximum GO oxidation degree for improving water transport in GO, especially at low partial pressures.
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•Anodic alumina membranes modification performed using octadecylphosphonic acid.•Surface modification was proved by IR- and Raman spectroscopy and thermal analysis.•Modification ...allows to control molecule residence time in adsorbed stage.•For hydrocarbons TMAC coefficients depend on surface saturation of grafted layer.•Modification allows to achieve n-C4H10/CH4 separation factors up to 32.3.
Here we report evidence for substantial changes in the separation efficiency of nanoporous anodic alumina membranes with nanochannel diameters ranging from 10–100 nm modified with octadecylphosphonic acid in the transitional flow regime. Softening of surface by alkyl groups with a surface density ∼2 groups/nm2 leads to a general permeance decrease in 3–500 times, depending strongly on the penetrant gas nature and the channels diameter. The divergence of the permeance, for different gases, increases with the decreasing diameter of the pores. For a surface-functionalized membrane, with 10-nm channel diameters, it results in n-C4H10/CH4 ideal and mixed gas separation factors up to 32.3 and 9.0 respectively at a n-C4H10 permeance up to 3.5 m3/(m2·bar·h). The effect is related to the changes of the ratio of molecule travelling time to residence time in the adsorbed state, as well as a strong influence of surface saturation by the absorbed molecules on the tangential momentum accommodation coefficient, which is supported by the derived model. Synergetic contribution of these two factors allows to enhance the separation factor of permanent and condensable gases strongly beyond the Knudsen limit, while maintaining a high permeance of porous membranes.
Here we report on tunable ammonia transport through ultrathin Prussian Blue (PB) membranes facilitated with protonic carrier. Continuous gas-tight 15–50 nm Prussian Blue layers were prepared by ...cyclic electrodeposition on porous gold/anodic aluminum oxide supports. The membranes reveal fast ammonium transport with NH3 permeance exceeding 0.3 m3(STP) m-2 bar-1 h-1, ultimate ideal NH3/H2 selectivity attaining 40 and NH3/N2 selectivity over 100. In mixed-gas separation thermodynamically-favored sorption leads to additional NH3/H2 selectivity rise to ~70. Facilitation of NH3 transport occurs upon its conversion to NH4+ maintaining the electroactivity of the selective layer and reversibly tuned by electrochemical framework loading. Engagement of the protonation step is supported with Raman spectroscopy and close values of NH3 diffusion coefficients measured in gas permeation experiments and NH4+ diffusion coefficient determined by electrochemical impedance spectroscopy in liquid phase. The impact of water vapors partial pressure as backward protonic carrier on NH3 transport efficiency is exposed and discussed.
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•Dense Prussian Blue (PB) layer was electrochemically deposed on anodic alumina support.•PB membranes demonstrate NH3/H2 mixed-gas selectivity up to 70 and NH3 permeance >0.3 m3/(m2·bar·h).•Ammoina facilitated transport is realized due to transformation NH3 into NH4+ form.•Gas transport properties of membrane can be tuned by PB loading with NH4+ cations.
Thin laminar CdTe nanoflake membranes grafted by oleic acid were investigated for sorption characteristics and permeation of permanent gases and hydrocarbons depending on the process temperature. A ...huge influence of temperature was revealed, enabling enhancement of the ideal selectivity for butane-methane separation from 28 to over 100 with the change of process conditions from 25 °C to 10 °C. The separation factor attains 26 in mixed-gas CH4/C4H10 separation experiments. Both sorption enthalpy and activation energy of diffusion were evaluated for penetrants, exhibiting the role of low activation barriers in fast transport of condensable hydrocarbons. The experimental results were proved by a semi-empirical calculation, illustrating swelling of grafted layer with heavy hydrocarbons. The effect was proved experimentally with in situ diffraction experiment. The low activation energy for the transport of condensable hydrocarbons, strong temperature dependence of permeance, and huge extinction coefficient of CdTe nanoflakes enable modulating the membrane permeance with laser irradiation, demonstrated with permeance photoswitching.
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•Sorption enthalpy and activation energy of diffusion were evaluated for penetrants.•Fast transport of heavy hydrocarbons governed by low activation barriers of diffusion.•Low activation energy of heavy hydrocarbons governed by swelling of the grafted layer.•Swelling of the grafted layer with heavy hydrocarbons was proved by in situ X-ray diffraction.•The permeance photoswitching was demonstrated under laser irradiation.
Calcium phosphate ceramics, with the phase composition represented by β-calcium pyrophosphate β-Ca
2
P
2
O
7
, was obtained from a powder mixture of calcium hydroxyapatite Ca
10
(PO
4
)
6
(OH)
2
, ...monocalcium phosphate monohydrate Ca(H
2
PO
4
)
2
· H
2
O, and sodium hydrogen phosphate Na
2
HPO
4
. The powder mixture was preliminarily homogenized in acetone using a planetary mill. This treatment resulted in the chemical reaction between the starting components to form monetite, calcium hydrogen phosphate CaHPO
4
(precursor of calcium pyrophosphate Ca
2
P
2
O
7
). According to the XRD data, sodium hydrogen phosphate Na
2
HPO
4
when present in an amount of 5 wt % in the starting mixture had no effect on the phase composition of the powder after homogenization and of the ceramics after annealing. Sodium pyrophosphate Na
4
P
2
O
7
formed from sodium hydrogen phosphate Na
2
HPO
4
as a result of thermal conversion had a significant effect on sintering mechanism and the microstructure of the ceramics. A ceramics with a low sintering temperature based on β-calcium pyrophosphate β-Ca
2
P
2
O
7
was obtained for the first time from a powder system, upon preparation of which under mechanical activation conditions homogenization of components and synthesis of the main crystal phase precursor were combined.
A powder of monetite СаНРО
4
with a particle size of 100–300 nm was synthesized from monocalcium phosphate monohydrate Ca(H
2
PO
4
)
2
⋅ H
2
O and calcium hydroxyapatite Ca
10
(PO
4
)
6
(OH)
2
in an ...acetone medium upon mechanical activation in a planetary mill. According to X-ray powder diffraction data, after heat treatment in the range 900–1100°С, the phase composition of the samples was represented by calcium β-pyrophosphate β-Ca
2
P
2
O
7
. The synthesized powder can be used for producing resorbable calcium phosphate ceramic materials.
