Special Issue "Transport of Fluids in Nanoporous Materials"

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Materials Processes".

Deadline for manuscript submissions: closed (31 October 2018)

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Guest Editor
Prof. Dr. Suresh K. Bhatia

FTSE, FASc, FIChemE, School of Chemical Engineering, The University of Queensland, St. Lucia, QLD 4072, Australia
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Phone: +61 7 3365 4263
Fax: +61 7 3365 4199
Interests: adsorption and transport in porous materials; chemical engineering; simulation of carbon structure; reaction engineering; fluid solid reactions
Guest Editor
Prof. Dr. David Nicholson

School of Chemical Engineering, Faculty of Engineering, Architecture and Information Technology, University of Queensland, Australia
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Interests: adsorption and transport in nanoporous materials
Guest Editor
Dr. Xuechao Gao

College of Chemical Engineering, Nanjing Tech University, Nanjing, China
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Interests: nanomaterials synthesis; adsorption; membrane science and technology
Guest Editor
Dr. Guozhao Ji

School of Environmental Science & Technology, Dalian University of Technology, Dalian 116024, China
Website | E-Mail
Interests: fluid mechanics; modelling and simulation; computational fluid dynamics; membrane science and technology; CO2 capture

Special Issue Information

Dear Colleagues,

The infiltration and transport of fluids in nanoporous materials are central to a vast array of existing and emerging processes for gas separation and energy storage. These include adsorption and catalysis, membrane separations, nanofluidics, electrochemical supercapacitors and batteries, all of which exploit features of fluid adsorption and transport in the narrow confinement characteristic of nanoporous materials. Numerous biological processes in living systems are also critically dependent on these phenomena. Modelling of the complex interplay between the molecules of the confined fluid, and between the fluid and the confining matrix is fundamental to the understanding of these processes and ultimately to their design and control. Although transport in confined spaces has been an active area of research for more than a century, the last two decades have seen an increasing interest because of the explosive growth of new nanomaterials and their applications, which has revealed significant shortcomings in existing transport theory. 

Conventional models for flow have proved to be inadequate when fluids are confined within spaces of nanometer dimensions.  Two considerations stand out:  First, that it is no longer possible to ignore the effects of the potential energy fields generated by the solid surrounding the fluid phase.  Second, the “no slip” boundary condition applied in the traditional treatment of viscous flow is not generally applicable. The no-slip condition is closely related to an assumption of random (or diffuse) reflection of fluid molecules at the solid boundaries, and therefore dependent on the atomic level configuration of the boundary and the intimate interaction between solid atoms and fluid phase molecules.

Progress has indeed been made in constructing molecular-level models of transport in highly confined spaces; however challenges remain in developing mechanical models of many particle systems that retain the key physics and are nevertheless tractable.  Molecular dynamics simulation has now emerged as the method of choice for predicting transport coefficients at the nanoscale but the interpretation of experimental transport coefficients on the basis of simulation requires an accurate atomistic model of both the confining material, including internal defects and imperfections which can significantly affect internal barriers, and also of the fluid itself.

Additional complexities arise from the multiscale nature of most porous materials, such as disordered carbons and the hierarchical materials developed to circumvent macroscale transport resistances that might exist in purely nanoporous solids. While effective medium theory offers an attractive route for modelling local or sub-microscale transport, the complex multiscale architecture of such materials often requires approaches that are more specialized and tailored specifically to suit the material structure. An example is the established 2-equation modelling of transport in bidisperse structures, which has long been used to model adsorbate transport in nanoporous carbons and other materials that comprise distinct pore networks at two different length scales. Further, many transport processes of practical interest involve a fluid phase of more than one molecular species.  It is now well established that transport of mixtures cannot be reliably predicted from knowledge of single phase properties.  Methods of predicting fluxes in mixture transport in confined spaces are therefore of considerable importance to this field.

This Special Issue on “Transport of Fluids in Nanoporous Materials” aims to present novel theoretical and experimental advances that address key challenges in the area, as well as those which contribute to enhanced understanding of transport-related issues in specific applications. Topics include, but are not limited to:

  • Developments in theoretical and simulation-based modelling of transport in nanopores and nanopoprous materials
  • Relation between multiscale structure and transport properties of hierarchical porous materials
  • Transport in membranes, including composite mixed matrix membranes
  • Modelling and simulation of transport in electrochemical supercapacitors and batteries
  • Simulation and characterisation of nanoporous material structure and its influence on transport
  • Modelling of reaction-diffusion processes in porous materials and catalysts

Prof. Suresh K. Bhatia
Prof. Dr. David Nicholson
Dr. Xuechao Gao
Dr. Guozhao Ji
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1100 CHF (Swiss Francs). Please note that for papers submitted after 30 June 2019 an APC of 1200 CHF applies. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Molecular dynamics
  • Modeling of transport
  • Mixed matrix membranes
  • Nanoporous materials
  • Electrochemical systems

Published Papers (15 papers)

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Editorial

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Open AccessEditorial Special Issue on “Transport of Fluids in Nanoporous Materials”
Processes 2019, 7(1), 14; https://doi.org/10.3390/pr7010014
Received: 26 November 2018 / Accepted: 26 November 2018 / Published: 1 January 2019
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Abstract
Understanding the transport behavior of fluid molecules in confined spaces is central to the design of innovative processes involving porous materials and is indispensable to the correlation of process behavior with the material structure and properties typically used for structural characterizations such as [...] Read more.
Understanding the transport behavior of fluid molecules in confined spaces is central to the design of innovative processes involving porous materials and is indispensable to the correlation of process behavior with the material structure and properties typically used for structural characterizations such as pore dimension, surface texture, and tortuosity. [...] Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available

Research

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Open AccessFeature PaperArticle Estimation of Pore Size Distribution of Amorphous Silica-Based Membrane by the Activation Energies of Gas Permeation
Processes 2018, 6(12), 239; https://doi.org/10.3390/pr6120239
Received: 31 October 2018 / Revised: 16 November 2018 / Accepted: 21 November 2018 / Published: 23 November 2018
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Abstract
Cobalt oxide silica membranes were prepared and tested to separate small molecular gases, such as He (dk = 2.6 Å) and H2 (dk = 2.89 Å), from other gases with larger kinetic diameters, such as CO2 ( [...] Read more.
Cobalt oxide silica membranes were prepared and tested to separate small molecular gases, such as He (dk = 2.6 Å) and H2 (dk = 2.89 Å), from other gases with larger kinetic diameters, such as CO2 (dk = 3.47 Å) and Ar (dk = 3.41 Å). In view of the amorphous nature of silica membranes, pore sizes are generally distributed in the ultra-microporous range. However, it is difficult to determine the pore size of silica derived membranes by conventional characterization methods, such as N2 physisorption-desorption or high-resolution electron microscopy. Therefore, this work endeavors to determine the pore size of the membranes based on transport phenomena and computer modelling. This was carried out by using the oscillator model and correlating with experimental results, such as gas permeance (i.e., normalized pressure flux), apparent activation energy for gas permeation. Based on the oscillator model, He and H2 can diffuse through constrictions narrower than their gas kinetic diameters at high temperatures, and this was possibly due to the high kinetic energy promoted by the increase in external temperature. It was interesting to observe changes in transport phenomena for the cobalt oxide doped membranes exposed to H2 at high temperatures up to 500 °C. This was attributed to the reduction of cobalt oxide, and this redox effect gave different apparent activation energy. The reduced membrane showed lower apparent activation energy and higher gas permeance than the oxidized membrane, due to the enlargement of pores. These results together with effective medium theory (EMT) suggest that the pore size distribution is changed and the peak of the distribution is slightly shifted to a larger value. Hence, this work showed for the first time that the oscillator model with EMT is a potential tool to determine the pore size of silica derived membranes from experimental gas permeation data. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessArticle Dispersion Performance of Carbon Nanotubes on Ultra-Light Foamed Concrete
Processes 2018, 6(10), 194; https://doi.org/10.3390/pr6100194
Received: 29 September 2018 / Revised: 10 October 2018 / Accepted: 12 October 2018 / Published: 17 October 2018
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Abstract
This study investigates the effect of carbon nanotube (CNT) dispersion on the mechanical properties and microstructures of ultra-light foamed concrete. A type of uniform and stable CNT dispersion solution is obtained by adding nano-Ce(SO4)2. Results show that CNT dispersion [...] Read more.
This study investigates the effect of carbon nanotube (CNT) dispersion on the mechanical properties and microstructures of ultra-light foamed concrete. A type of uniform and stable CNT dispersion solution is obtained by adding nano-Ce(SO4)2. Results show that CNT dispersion increases the compressive and breaking strengths of foamed concrete. CNTs play a nuclear role in the crystallization of C–S–H, and CNT dispersion effectively promotes the grain growth of C–S–H. The effect of CNT dispersion on the compressive and breaking strengths of foamed concrete is predicted through simulation. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessArticle Seepage and Damage Evolution Characteristics of Gas-Bearing Coal under Different Cyclic Loading–Unloading Stress Paths
Processes 2018, 6(10), 190; https://doi.org/10.3390/pr6100190
Received: 19 September 2018 / Revised: 10 October 2018 / Accepted: 12 October 2018 / Published: 15 October 2018
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Abstract
The mechanical properties and seepage characteristics of gas-bearing coal evolve with changes in the loading pattern, which could reveal the evolution of permeability in a protected coal seam and allow gas extraction engineering work to be designed by using the effect of mining [...] Read more.
The mechanical properties and seepage characteristics of gas-bearing coal evolve with changes in the loading pattern, which could reveal the evolution of permeability in a protected coal seam and allow gas extraction engineering work to be designed by using the effect of mining multiple protective seams. Tests on gas seepage in raw coal under three paths (stepped-cyclic, stepped-increasing-cyclic, and crossed-cyclic loading and unloading) were carried out with a seepage tester under triaxial stress conditions. The permeability was subjected to the dual influence of stress and damage accumulation. After being subjected to stress unloading and loading, the permeability of coal samples gradually decreased and the permeability did not increase before the stress exceeded the yield stage of the coal samples. The mining-enhanced permeability of the coal samples in the loading stage showed a three-phase increase with the growth of stress and the number of cycles and exhibited an N-shaped increase under the stepped-cyclic loading while it linearly increased under the other two paths in the unloading stage. With the increase of peak stress and the accumulation of damage in coal samples, the sensitivity of the permeability of coal samples to stress gradually declined. The relationship between the damage variable and the number of cycles conformed to the Boltzmann function. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessArticle Numerical Simulation of a New Porous Medium Burner with Two Sections and Double Decks
Processes 2018, 6(10), 185; https://doi.org/10.3390/pr6100185
Received: 11 July 2018 / Revised: 14 September 2018 / Accepted: 26 September 2018 / Published: 6 October 2018
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Abstract
Porous medium burners are characterized by high efficiency and good stability. In this study, a new burner was proposed based on the combustion mechanism of the methane-air mixture in the porous medium and the preheating effect. The new burner is a two-section and [...] Read more.
Porous medium burners are characterized by high efficiency and good stability. In this study, a new burner was proposed based on the combustion mechanism of the methane-air mixture in the porous medium and the preheating effect. The new burner is a two-section and double-deck porous medium with gas inlets at both ends. A mathematical model for the gas mixture combustion in the porous medium was established. The combustion performance of the burner was simulated under different equivalence ratios and inlet velocities of premixed gas. The methane combustion degree, as well as the temperature and pressure distribution, was estimated. In addition, the concentrations of emissions of NOx for different equivalence ratios were investigated. The results show that the new burner can not only realize sufficient combustion but also save energy. Furthermore, the emission concentration of NOx is very low. This study provides new insights into the industrial development and application of porous medium combustion devices. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessFeature PaperArticle Effects of Pulse Interval and Dosing Flux on Cells Varying the Relative Velocity of Micro Droplets and Culture Solution
Processes 2018, 6(8), 119; https://doi.org/10.3390/pr6080119
Received: 28 June 2018 / Revised: 2 August 2018 / Accepted: 3 August 2018 / Published: 7 August 2018
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Abstract
Microdroplet dosing to cell on a chip could meet the demand of narrow diffusion distance, controllable pulse dosing and less impact to cells. In this work, we studied the diffusion process of microdroplet cell pulse dosing in the three-layer sandwich structure of PDMS [...] Read more.
Microdroplet dosing to cell on a chip could meet the demand of narrow diffusion distance, controllable pulse dosing and less impact to cells. In this work, we studied the diffusion process of microdroplet cell pulse dosing in the three-layer sandwich structure of PDMS (polydimethylsiloxane)/PCTE (polycarbonate) microporous membrane/PDMS chip. The mathematical model is established to solve the diffusion process and the process of rhodamine transfer to micro-traps is simulated. The rhodamine mass fraction distribution, pressure field and velocity field around the microdroplet and cell surfaces are analyzed for further study of interdiffusion and convective diffusion effect. The cell pulse dosing time and drug delivery efficiency could be controlled by adjusting microdroplet and culture solution velocity without impairing cells at micro-traps. Furthermore, the accuracy and controllability of the cell dosing pulse time and maximum drug mass fraction on cell surfaces are achieved and the drug effect on cells could be analyzed more precisely especially for neuron cell dosing. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessFeature PaperArticle The Influence of Cation Treatments on the Pervaporation Dehydration of NaA Zeolite Membranes Prepared on Hollow Fibers
Processes 2018, 6(6), 70; https://doi.org/10.3390/pr6060070
Received: 21 April 2018 / Revised: 13 May 2018 / Accepted: 23 May 2018 / Published: 1 June 2018
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Abstract
NaA zeolite membrane is an ideal hydrophilic candidate for organic dehydrations; however, its instability in salt solutions limits its application in industries as the membrane intactness was greatly affected due to the replacement of cation ions. In order to explore the relationship between [...] Read more.
NaA zeolite membrane is an ideal hydrophilic candidate for organic dehydrations; however, its instability in salt solutions limits its application in industries as the membrane intactness was greatly affected due to the replacement of cation ions. In order to explore the relationship between the structural variation and the cation types, the obtained NaA zeolite membranes were treated by various monovalent and divalent cations like Ag+, K+, Li+, NH4+, Zn2+, Mg2+, Ba2+ and Ca2+. The obtained membranes were subsequently characterized by contact angle, scanning electron microscopy (SEM), pervaporation (PV), and vapor permeation (VP). The results showed that all of the hydrophilicities of the exchanged membrane were reduced, and the membrane performance varied with cation charges and sizes. For the monovalent cations, the membrane performance was largely determined by the cation sizes, where the membrane remained intact. On the contrary, for the divalent cation treatments, the membrane separation was generally reduced due to the presence of cation vacancies, resulting in some unbalanced stresses between the dispersive interaction and electrostatic forces, thereby damaging the membrane intactness. In the end, a set of gas permeation experiments were conducted for the two selected cation-treated membranes (K+ and Ag+) using H2, CO2, N2 and CH4, and a much higher decreasing percentage (90% for K+) occurred in comparison with the permeation drop (10%) in the PV dehydration, suggesting that the vaporization resistance of phase changing for the PV process was more influential than the water vapor transport in the pore channel. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessArticle A Facile Synthesis of Hexagonal Spinel λ-MnO2 Ion-Sieves for Highly Selective Li+ Adsorption
Processes 2018, 6(5), 59; https://doi.org/10.3390/pr6050059
Received: 28 April 2018 / Revised: 8 May 2018 / Accepted: 14 May 2018 / Published: 17 May 2018
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Abstract
Ion-sieves are a class of green adsorbent for extraction Li+ from salt lakes. Here, we propose a facile synthesis of hexagonal spinel LiMn2O4 (LMO) precursor under mild condition which was first prepared via a modified one-pot reduction hydrothermal method [...] Read more.
Ion-sieves are a class of green adsorbent for extraction Li+ from salt lakes. Here, we propose a facile synthesis of hexagonal spinel LiMn2O4 (LMO) precursor under mild condition which was first prepared via a modified one-pot reduction hydrothermal method using KMnO4 and ethanol. Subsequently, the stable spinel structured λ-MnO2 (HMO) were prepared by acidification of LMO. The as-prepared HMO shows a unique hexagonal shape and can be used for rapid adsorption-desorption process for Li+ adsorption. It was found that Li+ adsorption capacity of HMO was 24.7 mg·g−1 in Li+ solution and the HMO also has a stable structure with manganese dissolution loss ratio of 3.9% during desorption process. Moreover, the lithium selectivity ( α Mg Li ) reaches to 1.35 × 103 in brine and the distribution coefficients ( K d ) of Li+ is much greater than that of Mg2+. The results implied that HMO can be used in extract lithium from brine or seawater containing high ratio of magnesium and lithium. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessArticle Structure Manipulation of Carbon Aerogels by Managing Solution Concentration of Precursor and Its Application for CO2 Capture
Processes 2018, 6(4), 35; https://doi.org/10.3390/pr6040035
Received: 2 February 2018 / Revised: 1 April 2018 / Accepted: 7 April 2018 / Published: 12 April 2018
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Abstract
A series of carbon aerogels were synthesized by polycondensation of resorcinol and formaldehyde, and their structure was adjusted by managing solution concentration of precursors. Carbon aerogels were characterized by X-ray diffraction (XRD), Raman, Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption and scanning [...] Read more.
A series of carbon aerogels were synthesized by polycondensation of resorcinol and formaldehyde, and their structure was adjusted by managing solution concentration of precursors. Carbon aerogels were characterized by X-ray diffraction (XRD), Raman, Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption and scanning electron microscope (SEM) technologies. It was found that the pore structure and morphology of carbon aerogels can be efficiently manipulated by managing solution concentration. The relative micropore volume of carbon aerogels, defined by Vmicro/Vtol, first increased and then decreased with the increase of solution concentration, leading to the same trend of CO2 adsorption capacity. Specifically, the CA-45 (the solution concentration of precursors is 45 wt%) sample had the highest CO2 adsorption capacity (83.71 cm3/g) and the highest selectivity of CO2/N2 (53) at 1 bar and 0 °C. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Review

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Open AccessFeature PaperReview Modeling Permeation through Mixed-Matrix Membranes: A Review
Processes 2018, 6(9), 172; https://doi.org/10.3390/pr6090172
Received: 30 August 2018 / Revised: 14 September 2018 / Accepted: 14 September 2018 / Published: 18 September 2018
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Abstract
Over the past three decades, mixed-matrix membranes (MMMs), comprising an inorganic filler phase embedded in a polymer matrix, have emerged as a promising alternative to overcome limitations of conventional polymer and inorganic membranes. However, while much effort has been devoted to MMMs in [...] Read more.
Over the past three decades, mixed-matrix membranes (MMMs), comprising an inorganic filler phase embedded in a polymer matrix, have emerged as a promising alternative to overcome limitations of conventional polymer and inorganic membranes. However, while much effort has been devoted to MMMs in practice, their modeling is largely based on early theories for transport in composites. These theories consider uniform transport properties and driving force, and thus models for the permeability in MMMs often perform unsatisfactorily when compared to experimental permeation data. In this work, we review existing theories for permeation in MMMs and discuss their fundamental assumptions and limitations with the aim of providing future directions permitting new models to consider realistic MMM operating conditions. Furthermore, we compare predictions of popular permeation models against available experimental and simulation-based permeation data, and discuss the suitability of these models for predicting MMM permeability under typical operating conditions. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessFeature PaperReview Diffusion in Nanoporous Materials: Novel Insights by Combining MAS and PFG NMR
Processes 2018, 6(9), 147; https://doi.org/10.3390/pr6090147
Received: 6 August 2018 / Revised: 15 August 2018 / Accepted: 21 August 2018 / Published: 1 September 2018
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Abstract
Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) allows recording of molecular diffusion paths (notably, the probability distribution of molecular displacements over typically micrometers, covered during an observation time of typically milliseconds) and has thus proven to serve as a most versatile means [...] Read more.
Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) allows recording of molecular diffusion paths (notably, the probability distribution of molecular displacements over typically micrometers, covered during an observation time of typically milliseconds) and has thus proven to serve as a most versatile means for the in-depth study of mass transfer in complex materials. This is particularly true with nanoporous host materials, where PFG NMR enabled the first direct measurement of intracrystalline diffusivities of guest molecules. Spatial resolution, i.e., the minimum diffusion path length experimentally observable, is limited by the time interval over which the pulsed field gradients may be applied. In “conventional” PFG NMR measurements, this time interval is determined by a characteristic quantity of the host-guest system under study, the so-called transverse nuclear magnetic relaxation time. This leads, notably when considering systems with low molecular mobilities, to severe restrictions in the applicability of PFG NMR. These restrictions may partially be released by performing PFG NMR measurements in combination with “magic-angle spinning” (MAS) of the NMR sample tube. The present review introduces the fundamentals of this technique and illustrates, via a number of recent cases, the gain in information thus attainable. Examples include diffusion measurements with nanoporous host-guest systems of low intrinsic mobility and selective diffusion measurement in multicomponent systems. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessFeature PaperReview Challenges in Nanofluidics—Beyond Navier–Stokes at the Molecular Scale
Processes 2018, 6(9), 144; https://doi.org/10.3390/pr6090144
Received: 18 July 2018 / Revised: 17 August 2018 / Accepted: 21 August 2018 / Published: 1 September 2018
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Abstract
The fluid dynamics of macroscopic and microscopic systems is well developed and has been extensively validated. Its extraordinary success makes it tempting to apply Navier–Stokes fluid dynamics without modification to systems of ever decreasing dimensions as studies of nanofluidics become more prevalent. However, [...] Read more.
The fluid dynamics of macroscopic and microscopic systems is well developed and has been extensively validated. Its extraordinary success makes it tempting to apply Navier–Stokes fluid dynamics without modification to systems of ever decreasing dimensions as studies of nanofluidics become more prevalent. However, this can result in serious error. In this paper, we discuss several ways in which nanoconfined fluid flow differs from macroscopic flow. We give particular attention to several topics that have recently received attention in the literature: slip, spin angular momentum coupling, nonlocal stress response and density inhomogeneity. In principle, all of these effects can now be accurately modelled using validated theories. Although the basic principles are now fairly well understood, much work remains to be done in their application. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessFeature PaperReview Computational Molecular Modeling of Transport Processes in Nanoporous Membranes
Processes 2018, 6(8), 124; https://doi.org/10.3390/pr6080124
Received: 19 July 2018 / Revised: 3 August 2018 / Accepted: 4 August 2018 / Published: 9 August 2018
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Abstract
In this report we have discussed the important role of molecular modeling, especially the use of the molecular dynamics method, in investigating transport processes in nanoporous materials such as membranes. With the availability of high performance computers, molecular modeling can now be used [...] Read more.
In this report we have discussed the important role of molecular modeling, especially the use of the molecular dynamics method, in investigating transport processes in nanoporous materials such as membranes. With the availability of high performance computers, molecular modeling can now be used to study rather complex systems at a fraction of the cost or time requirements of experimental studies. Molecular modeling techniques have the advantage of being able to access spatial and temporal resolution which are difficult to reach in experimental studies. For example, sub-Angstrom level spatial resolution is very accessible as is sub-femtosecond temporal resolution. Due to these advantages, simulation can play two important roles: Firstly because of the increased spatial and temporal resolution, it can help understand phenomena not well understood. As an example, we discuss the study of reverse osmosis processes. Before simulations were used it was thought the separation of water from salt was purely a coulombic phenomenon. However, by applying molecular simulation techniques, it was clearly demonstrated that the solvation of ions made the separation in effect a steric separation and it was the flux which was strongly affected by the coulombic interactions between water and the membrane surface. Additionally, because of their relatively low cost and quick turnaround (by using multiple processor systems now increasingly available) simulations can be a useful screening tool to identify membranes for a potential application. To this end, we have described our studies in determining the most suitable zeolite membrane for redox flow battery applications. As computing facilities become more widely available and new computational methods are developed, we believe molecular modeling will become a key tool in the study of transport processes in nanoporous materials. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessReview A Review on the Separation of Lithium Ion from Leach Liquors of Primary and Secondary Resources by Solvent Extraction with Commercial Extractants
Processes 2018, 6(5), 55; https://doi.org/10.3390/pr6050055
Received: 10 April 2018 / Revised: 1 May 2018 / Accepted: 9 May 2018 / Published: 12 May 2018
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Abstract
The growing demand for lithium necessitates the development of an efficient process to recover it from three kinds of solutions, namely brines as well as acid and alkaline leach liquors of primary and secondary resources. Therefore, the separation of lithium(I) from these solutions [...] Read more.
The growing demand for lithium necessitates the development of an efficient process to recover it from three kinds of solutions, namely brines as well as acid and alkaline leach liquors of primary and secondary resources. Therefore, the separation of lithium(I) from these solutions by solvent extraction was reviewed in this paper. Lithium ions in brines are concentrated by removing other metal salts by crystallization with solar evaporation. In the case of ores and secondary resources, roasting followed by acid/alkaline leaching is generally employed to dissolve the lithium. Since the compositions of brines, alkaline and acid solutions are different, different commercial extractants are employed to separate and recover lithium. The selective extraction of Li(I) over other metals from brines or alkaline solutions is accomplished using acidic extractants, their mixture with neutral extractants, and neutral extractants mixed with chelating extractants in the presence of ferric chloride (FeCl3). Among these systems, tri-n-butyl phosphate (TBP)- methyl isobutyl ketone (MIBK)-FeCl3 and tri-n-octyl phosphine oxide (TOPO)- benzoyltrifluoroacetone (HBTA) are considered to be promising for the selective extraction and recovery of Li(I) from brines and alkaline solutions. By contrast, in the acid leaching solutions of secondary resources, divalent and trivalent metal cations are selectively extracted by acidic extractants, leaving Li(I) in the raffinate. Therefore, bis-2,4,4-trimethyl pentyl phosphinic acid (Cyanex 272) and its mixtures are suggested for the extraction of metal ions other than Li(I). Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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Open AccessReview Preparation and Potential Applications of Super Paramagnetic Nano-Fe3O4
Processes 2018, 6(4), 33; https://doi.org/10.3390/pr6040033
Received: 14 February 2018 / Revised: 23 March 2018 / Accepted: 3 April 2018 / Published: 9 April 2018
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Abstract
Ferroferric oxide nanoparticle (denoted as Nano-Fe3O4) has low toxicity and is biocompatible, with a small particle size and a relatively high surface area. It has a wide range of applications in many fields such as biology, chemistry, environmental science [...] Read more.
Ferroferric oxide nanoparticle (denoted as Nano-Fe3O4) has low toxicity and is biocompatible, with a small particle size and a relatively high surface area. It has a wide range of applications in many fields such as biology, chemistry, environmental science and medicine. Because of its superparamagnetic properties, easy modification and function, it has become an important material for addressing a number of specific tasks. For example, it includes targeted drug delivery nuclear magnetic resonance (NMR) imaging in biomedical applications and in environmental remediation of pollutants. Few articles describe the preparation and modification of Nano-Fe3O4 in detail. We present an evaluation of preparation methodologies, as the quality of material produced plays an important role in its successful application. For example, with modification of Nano-Fe3O4, the surface activation energy is reduced and good dispersion is obtained. Full article
(This article belongs to the Special Issue Transport of Fluids in Nanoporous Materials) Printed Edition available
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