Here we report on the spontaneous assembly of Ti
3
C
2
T
x
MXene flakes into monolayer films at the liquid-air interface. According to X-ray reflectivity and grazing incidence X-ray fluorescence both ...the structure of the layers and assembly kinetics depends on the pH value of the solution. At pH > 4 MXene flakes form a single ∼1.5 nm thick layer carrying a negative charge, while in the acidic medium the layer contains coordinated anions with the formation of the Br
aq
−
/Ti
3
C
2
T
x
/subphase interface. The surface layer compression allows the assembling of MXene flakes into a dense monolayer films with the surface coverage of up to 96% and surface pressure exceeding 40 mN m
−1
in the case of the acidic subphase. The films can readily be transferred onto solid substrates by the conventional Langmuir-Blodgett approach or modified by surfactants to form MXene/surfactant composite films.
Here we report on the spontaneous assembly of Ti
3
C
2
T
x
MXene flakes into monolayer films at the liquid-air interface.
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•Membrane contactor performance with alkali absorbent was studied.•Removing of CO2 and H2S from gaseous stream with NaOH solution was studied.•In-liquid diffusion and gas/membrane ...contact time are key factor influence on performance.•Utilization of membrane contactor allows to reduce H2S content down to 7 ppm.•Conditions for selective H2S removing in presence of CO2 was found, allowing to attain H2S/CO2 selectivity >1500.
The paper reports a comprehensive review of the performance of nanoporous gas-liquid polypropylene membrane contactor with NaOH absorbents for removal of H2S and CO2 components from the gas streams. The experiments at different operation conditions, including variation of acid gas content in a feed stream, alkali concentration in absorbent, gas and liquid absorbent volume flow rates, absolute and gas-liquid differential pressures are discussed as a function of the absorbent saturation levels. In-liquid diffusion of components and gas/membrane contact times were determined as main governing factors limiting contactor efficiency. Mass transfer rates of acid gas removal on the membrane contactor over 3 × 10−3 mol/(m2 × s) for CO2 and 7.5 × 10−3 mol/(m2 × s) for H2S were attained. Ultimate processed gas quality with H2S content below 5 ppm and CO2 content below 0.01% was achieved at the contactor performance over 7 m3/(m2 × h) and initial acidic gas content of 2%, while achieving a membrane packing density in the contactor over 3000 m2/m3. The paper also provides an experimentally-proven theoretical model for calculating removal efficiency and residual acid gas partial pressures depending on the membrane parameters and operation conditions. It is shown, the mass transfer coefficient and removal efficiency differ significantly for H2S and CO2 due to the difference in dissolution mechanism involving kinetically limited deprotonation reaction of solvated water in case of CO2(aq) while engaging direct deprotonation of H2S. This allows to attain residual partial pressure of H2S in retentate stream equal to the equilibrium pressure above the absorbent solution, while CO2 residual pressure exceeds an equilibrium value few orders of magnitude. The effect has been successfully utilized for the selective removal of H2S from both CO2 and H2S-containing mixtures with H2S/CO2 selectivity exceeding 1500.
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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This study reports on experimental evidence for large mass flux difference in opposite flow directions through asymmetric membranes in capillary condensation regime. Anodic alumina membranes with ...pore diameters of 10–80 nm in the selective layer and 40–80 nm in the supporting layer were inspected for permeance variation depending on the feed and permeate pressure conditions. Starting pressure of capillary condensation was found to follow the Thompson–Kelvin equation for pore diameters at the upstream side of a membrane. The experimental ratio between the permeances in the upstream and downstream membrane orientations attained ∼2 at the feed pressure close to condensation pressure for membranes containing pores of small diameters. The experimental data were treated assuming Knudsen and viscous vapor transport in the gaseous state and Poiseuille flow in liquid condensate. It is shown that condensate transport through the nanochannels in the capillary condensation regime is mostly governed by the condensing/evaporating menisci curvatures deviating from the thermodynamic equilibrium value and gradually changing with pressure conditions. Coincidently, the curvature of meniscus is controlled by the liquid influx velocity and velocity distribution in nanochannels, giving rise to a self-regulating regime of flow. At high liquid intake velocities, the curvature radius of meniscus significantly increases, being accompanied by a serious drop of liquid evaporation efficiency. The effect is ascribed to a sequential evaporation of liquid in the pore center and vapor condensation close to the pore walls, generating gas–liquid rotating flow.
We report on the specific properties of O- and OH-terminated Ti3C2Tx nanosheets contributing the permeance of MXene membranes with sorption type selectivity. Thin MXene selective layers on porous ...support demonstrated separation factor for NH3/H2 pair over 50 with ammonia permeance up to 5.0 m3(STP)∙m−2∙bar−1∙h−1 facilitated for humid medium and separation factor for H2O/N2 over 1000 with water permeance over 30 m3(STP)∙m−2∙bar−1∙h−1 close to P0(H2O). According to QCM and GIWAXS studies, high permeance and selectivity of membranes towards ammonia and water vapors are attributed both to ultimate sorption capacity for “basic” vapors and condensation-induced expansion of the interlayer space. Sorption capacity of MXene over 0.045 g∙g(MXene)−1 at 0.3P0 for both NH3 and H2O, significantly exceeds the sorption capacity for permanent gases. Calculations of the diffusion coefficient suggest labyrinthine transport of vapors. For permanent gases no variation of diffusion coefficients was observed with feed pressure, indicating Knudsen diffusion mechanism. Diffusion coefficient of strongly absorbed gases significantly increases with pressure. According to GIWAXS the effect was attributed to the increase of the interlayer distance with saturation of membrane with vapors and reduction of activation barriers for hopping diffusion. Demonstrated characteristics of Ti3C2Tx nanosheets makes it a promising candidate for developing of ammonia selective membranes for Haber-Bosch process membrane extractors.
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•Acidic properties of OH groups on MXene surface determine affinity to “basic” gases.•NH3 sorption coefficient attains 52 mmol/(m3·Pa), drastically exceed sorption for other gases.•Membranes with Ti3C2Tx selective layer were obtained by spin-coating technique.•Selectivity for a NH3/H2 exceeds 50 with ammonia permeance up to 3.91 m3 m−2 bar−1∙h−1.•The increase of interlayer distance with MXene saturation with vapors was founded.
The electrochemical activity of a new electrode material based on Pr
5
Mo
3
O
16 + δ
(РМО) within the composition of a symmetrical solid oxide fuel cell (S-SOFC) of the electrolyte-supported design ...is studied. The model S-SOFC of the РМО/Ce
0.9
Gd
0.1
O
1.95
(GDC)/Zr
0.84
Y
0.16
O
1.92
(YSZ)/GDC/PMO composition demonstrated the maximum power density of 28 mW/cm
2
at 900°С. To improve the power characteristics of S-SOFC, the porous buffer GDC layer is modified by the method of Pr
6
O
11
infiltration. It is found that the addition of electroactive Pr
6
O
11
into the GDC buffer layer provides the three-fold increase in the fuel-cell power density with the maximum of 90 mW/cm
2
at 900°С. The 10 h life-time test of the model S-SOFC with the РМО/GDC + Pr
6
O
11
/YSZ/GDC + Pr
6
O
11
/PMO composition carried out at a load of 0.7 V reveals the absence of any considerable degradation in fuel cell power characteristics. The results obtained suggest that the new electrode material based on PMO holds promise for the development of S-SOFC.
Separation of CO
2
/CH
4
and CO
2
/N
2
mixtures containing from 20 to 50% CO
2
on membranes based on polytricyclononenes with tri(n-alkoxy)silyl groups containing substituents with alkyl fragments of ...different lengths (one to four carbon atoms), prepared by vinyl-addition polymerization, was studied. The separation selectivity for these mixtures is close to the corresponding ideal selectivity. The gas transport characteristics slightly depend on the pressure of the gas feed flow. The best results are obtained for the polymer with methyl groups in pendant substituents. The parameters of this polymer are located above the 2015 upper bound in the Robeson diagram for CO
2
/CH
4
gas mixtures.
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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.
Five new complexes Ln(Q(C17))3(H2O)(Solv) (Ln = Y, Solv = H2O, Ln = Tb, Dy, Sm or Eu, Solv = EtOH) were synthesized with the acylpyrazolonato ligand Q(C17) bearing a long aliphatic C17H35 chain in ...the acyl moiety, and the crystal structure of Y(Q(C17))3(H2O)2 shows the three aliphatic chains from the coordinated ligands positioned in the same direction, affording plane layers built by Y(Q(C17))3(H2O)2 molecules connected through H-bonding interactions. The layers are stitched to each other like in "hook & loop" tapes. Luminescence of complexes was determined and the complex Tb(Q(C17))3(H2O)(EtOH) was immobilized on the surface of silica preprocessed using a C17H35CONH(CH2)3Si(OEt)3 reagent via hydrophobic interactions of long aliphatic chains. Luminescent properties and micromorphology of the obtained hybrid particles and hybrid films were investigated. Intensive green emission of the complex retains after grafting onto the silica surface. Inclusion of the complex on the surface of silica materials occurs as separate molecules, after the disruption of the H-bonding network present in the crystalline phase of the pure terbium sample.
The paper reports the performance of nanoporous polypropylene membrane contactors in water evaporative transfer processes, depending on membrane packing density, flow, and temperature conditions. The ...membrane evaporator's heat and mass transfer efficiency were evaluated in a wide range of partial pressure gradients and gas phase Reynolds numbers. A protocol for simple evaluation of evaporative heat flux to the heat exchange flux is introduced to reveal the efficiency of mass-to-heat transfer. It has been shown the evaporation efficiency significantly depends on gas flow conditions, increasing at Re ∼ 30 and exceeding 4.6 kg × m-2×h−1 (3.0 kW × m-2×h−1) at the temperature of inlet water of 60 °C. It is achieved by inducing convective flows in the gas phase, which enable the rise of effective heat transfer coefficient for membrane evaporator ∼250 W × m-2×K−1. The attained efficiency is confirmed to originate from heat extraction from the gaseous phase and the evaporation of water from the external surface of fibers. While exhibiting maximal heat flux the regime requires liquid phase penetration through the pores, leading to degradation of the membrane performance in desalination applications. To avoid penetration of ions thin (∼300 nm) graphene oxide coating was deposited onto the internal surface of the nanoporous evaporator, enabling to avoid liquid penetration through the pores and salts crystallization at the external surface, while exhibiting slightly lower performance of the membrane.
•The performance of nanoporous polypropylene membrane contactors in water evaporative transfer processes was studied•The evaporation efficiency significantly depends on flow conditions, increasing at Re ∼ 30 and exceeding 4.6 kg × m-2×h-1•To avoid penetration of ions thin (∼300 nm) graphene oxide coating was deposited onto the internal surface of the evaporator
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