scholarly journals Comment on “Enhanced water permeability and tunable ion selectivity in subnanometer carbon nanotube porins”

Science ◽  
2018 ◽  
Vol 359 (6383) ◽  
pp. eaap9173 ◽  
Author(s):  
Andreas Horner ◽  
Peter Pohl
Keyword(s):  
Activation Energy ◽  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Water Transport ◽  
Water Permeability ◽  
Ion Selectivity ◽  
Membrane Interface ◽  
Single File ◽  
Lower Activation ◽  
Lower Activation Energy

Tunuguntla et al. (Reports, 25 August 2017, p. 792) report that permeation of single-file water occurs faster through carbon nanotubes than through aquaporins. We show that this conclusion violates fundamental thermodynamic laws: Because of its much lower activation energy, aquaporin-mediated water transport must be orders of magnitude faster. Leakage at the nanotube-membrane interface may explain the discrepancy.

scholarly journals Response to Comment on “Enhanced water permeability and tunable ion selectivity in subnanometer carbon nanotube porins”

Science ◽  
2018 ◽  
Vol 359 (6383) ◽  
pp. eaaq1241 ◽  
Author(s):  
Ramya H. Tunuguntla ◽  
Yuliang Zhang ◽  
Robert Y. Henley ◽  
Yun-Chiao Yao ◽  
T. Anh Pham ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Experimental Evidence ◽  
Water Transport ◽  
Water Permeability ◽  
Transport Mechanism ◽  
Ion Selectivity ◽  
High Water ◽  
Arrhenius Factor ◽  
Rule Out

Horner and Pohl argue that high water transport rates reported for carbon nanotube porins (CNTPs) originate from leakage at the nanotube-bilayer interface. Our results and new experimental evidence are consistent with transport through the nanotube pores and rule out a defect-mediated transport mechanism. Mechanistic origins of the high Arrhenius factor that we reported for narrow CNTPs at pH 8 require further investigation.

scholarly journals Development of a PtSn bimetallic catalyst for direct fuel cells using bio-butanol fuel

2015 ◽  
Vol 51 (69) ◽  
pp. 13412-13415 ◽  
Author(s):  
V. K. Puthiyapura ◽  
D. J. L. Brett ◽  
A. E. Russell ◽  
W. F. Lin ◽  
C. Hardacre
Keyword(s):  
Activation Energy ◽  
Fuel Cells ◽  
Bimetallic Catalyst ◽  
Lower Activation ◽  
Lower Activation Energy

PtSn showed a higher activity and lower activation energy towards butanol electrooxidation compared to pure Pt.

The diffusion of Fe2+ ions in spinels with relevance to the process of maghemitization

1980 ◽  
Vol 43 (331) ◽  
pp. 889-899 ◽  
Author(s):  
W. Freer ◽  
R. O'Reilly
Keyword(s):  
Activation Energy ◽  
Spinel Structure ◽  
Single Phase ◽  
Sea Water ◽  
Magnetic Minerals ◽  
Magnetic Studies ◽  
Water Leaching ◽  
Lower Activation ◽  
Diffusion Activation ◽  
Lower Activation Energy

SummaryThe maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe2+ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe2+ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe2+-containing spinels FeAl2O4, FeCr2O4, FeGa2O4, and Fe2GeO4, in which Fe2+ is predominantly in either A or B sites were prepared, and the diffusion of Fe2+ was studied by (1) interdiffusion experiments with the Mg2+ counterparts and (2) oxidation experiments in air. Fe2GeO4 (Fe2+ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl2O4 (75% Fe2+ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe2+ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe2+ in B sites is preferentially oxidized.

One, two, and three-dimensional metal–organic coordination polymers derived from enantiopure organic phosphorate: homochirality, water stability and proton conduction

CrystEngComm ◽  
2017 ◽  
Vol 19 (42) ◽  
pp. 6325-6332 ◽  
Author(s):  
Xiaoqiang Liang ◽  
Kun Cai ◽  
Feng Zhang ◽  
Jia Liu ◽  
Guangshan Zhu
Keyword(s):  
Activation Energy ◽  
Metal Ions ◽  
Coordination Polymers ◽  
Three Dimensional ◽  
High Water ◽  
Water Stability ◽  
Lower Activation ◽  
Metal Organic ◽  
Lower Activation Energy ◽  
Multifunctional Ligand

A multifunctional ligand reacts with metal ions to generate three new coordination polymers, where 3 has a high water stability, a moderate proton conductivity and a lower activation energy.

Mechanism of Ion Exclusion by Sub-2nm Carbon Nanotube Membranes

2008 ◽  
Vol 1106 ◽  
Author(s):  
Francesco Fornasiero ◽  
Hyung Gyu Park ◽  
Jason K Holt ◽  
Michael Stadermann ◽  
Costas P Grigoropoulos ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Electrostatic Interactions ◽  
Ion Selectivity ◽  
Molecular Transport ◽  
Water Desalination ◽  
Oxygen Plasma Treatment ◽  
Nanotube Membranes ◽  
Ion Exclusion ◽  
Carbon Nanotube Membranes

AbstractCarbon nanotubes offer an outstanding platform for studying molecular transport at nanoscale, and have become promising materials for nanofluidics and membrane technology due to their unique combination of physical, chemical, mechanical, and electronic properties. In particular, both simulations and experiments have proved that fluid flow through carbon nanotubes of nanometer size diameter is exceptionally fast compared to what continuum hydrodynamic theories would predict when applied on this length scale, and also, compared to conventional membranes with pores of similar size, such as zeolites. For a variety of applications such as separation technology, molecular sensing, drug delivery, and biomimetics, selectivity is required together with fast flow. In particular, for water desalination, coupling the enhancement of the water flux with selective ion transport could drastically reduce the cost of brackish and seawater desalting. In this work, we study the ion selectivity of membranes made of aligned double-walled carbon nanotubes with sub-2 nm diameter. Negatively charged groups are introduced at the opening of the carbon nanotubes by oxygen plasma treatment. Reverse osmosis experiments coupled with capillary electrophoresis analysis of permeate and feed show significant anion and cation rejection. Ion exclusion declines by increasing ionic strength (concentration) of the feed and by lowering solution pH; also, the highest rejection is observed for the salts (A=anion, C=cation, z= valence) with the greatest zA/zC ratio. Our results strongly support a Donnan-type rejection mechanism, dominated by electrostatic interactions between fixed membrane charges and mobile ions, while steric and hydrodynamic effects appear to be less important. Comparison with commercial nanofiltration membranes for water softening reveals that our carbon nanotube membranes provides far superior water fluxes for similar ion rejection capabilities.

scholarly journals Differential Activation Energy and NBO Interaction Approaches to Torquoselectivity and Its Dependence on the Conformational Profile of the Substituent

2021 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Activation Energy ◽  
Ring Opening ◽  
Energy Approach ◽  
Differential Activation ◽  
Distinct Level ◽  
Lower Activation ◽  
Secondary Reactions ◽  
The Subject ◽  
Interaction Approach ◽  
Lower Activation Energy

The torquoselectivity of ring opening of 3-CF<sub>3</sub>-cyclobutene, 3-CHF<sub>2</sub>-cyclobutene, 3-CH<sub>2</sub>F-cyclobutene, 3-CF<sub>3</sub>-oxetene and perfluoro-3-CH<sub>3</sub>-cyclobutene have been studied at the MP2/cc-pVTZ level of theory and the results analysed by using the differential activation energy approach and also differential NBO interactions of the breaking ring bond with the substituent bonds. The outward or inward ring opening that has lower activation energy in the differential activation energy approach or larger interaction in the differential NBO interaction approach constitutes the preferred mode. The predictions from the two approaches are largely found to be contradicting each other, specifically when the substituent is electron-deficient. The CHF<sub>2</sub> and CH<sub>2</sub>F substituents on cyclobutene and oxetene can adopt three distinct conformations with respect to the cleaving ring bond. It has been discovered that each conformer exhibits a distinct level of torquoselectivity and some may even contribute to the overall selectivity substantially. The conformational profile of the substituent, therefore, is recommended to be taken into account in any serious treatment of the subject. The experimental torquoselectivity, if otherwise, is a likely consequence of secondary reactions, specifically equilibration through reaction reversal while honouring the relative thermodynamic stabilities of the ring opened products.

scholarly journals Differential Activation Energy and NBO Interaction Approaches to Torquoselectivity and Its Dependence on the Conformational Profile of the Substituent

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Activation Energy ◽  
Ring Opening ◽  
Energy Approach ◽  
Differential Activation ◽  
Distinct Level ◽  
Lower Activation ◽  
Secondary Reactions ◽  
The Subject ◽  
Interaction Approach ◽  
Lower Activation Energy

The torquoselectivity of ring opening of 3-CF<sub>3</sub>-cyclobutene, 3-CHF<sub>2</sub>-cyclobutene, 3-CH<sub>2</sub>F-cyclobutene, 3-CF<sub>3</sub>-oxetene and perfluoro-3-CH<sub>3</sub>-cyclobutene have been studied at the MP2/cc-pVTZ level of theory and the results analysed by using the differential activation energy approach and also differential NBO interactions of the breaking ring bond with the substituent bonds. The outward or inward ring opening that has lower activation energy in the differential activation energy approach or larger interaction in the differential NBO interaction approach constitutes the preferred mode. The predictions from the two approaches are largely found to be contradicting each other, specifically when the substituent is electron-deficient. The CHF<sub>2</sub> and CH<sub>2</sub>F substituents on cyclobutene and oxetene can adopt three distinct conformations with respect to the cleaving ring bond. It has been discovered that each conformer exhibits a distinct level of torquoselectivity and some may even contribute to the overall selectivity substantially. The conformational profile of the substituent, therefore, is recommended to be taken into account in any serious treatment of the subject. The experimental torquoselectivity, if otherwise, is a likely consequence of secondary reactions, specifically equilibration through reaction reversal while honouring the relative thermodynamic stabilities of the ring opened products.

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