Use of atomic force microscopy and solid-state NMR spectroscopy to characterize structure-property-performance correlation in high-flux reverse osmosis (RO) membranes

Kwak, Seung‐Yeop; Ihm, Dae Woo

doi:10.1016/s0376-7388(99)00039-3

Cited by 122 publications

(68 citation statements)

References 9 publications

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“…However, this was also the case for polymeric membranes [40][41][42][43][44][45][46][47][48][49][50] years ago and these scale-up issues can be resolved if the performance enhancements promised by these exiting materials prove practically achievable.…”

Section: Discussionmentioning

confidence: 99%

A review of water treatment membrane nanotechnologies

Pendergast

Hoek

2011

Energy Environ. Sci.

1,850

917

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We thank the reviewers for their insightful comments and we have revised the above referenced manuscript in response. In addition, we addressed each reviewer comment in an itemized fashion in the attached "Response to Reviewer Comments."We have uploaded high resolution (600 dpi minimum) TIF files for each image in the article. We have kept the images in color for the online version, but please convert these to grey-scale for the print version. We have ensured that no information is lost from the figure upon conversion.We feel we have adequately addressed all reviewer comments and hope that you will accept our review paper for publication in Energy & Environmental Science without further revision. Figure 6. Percolation Threshold was removed because it also seemed to provide superfluous detail. Section 3.2.1. Mixed Matrix MembranesSelections have been deleted due to excessive explanation of mixed matrix theory; the detail of background theory here appeared to be out of proportion with that in other sections. The important points from the deleted paragraphs have, however, been shortened and inserted into the present introduction so that major points are not lost. Also, it was re-emphasized that details about gas separation membranes were included only to show the past application and strength of these materials now being re-engineered for water treatment purposes. Section 3.3.3. Isoporous Block Copolymer MembranesSelections have been deleted, again when out of proportion detail in background explanation was found. Within the particular works cited and described, some specific details have been removed or minimized in order to highlight the most important achievement of each work. Lengthy block copolymer names have also been removed in most cases, in lieu of the type (i.e., tri-block, homopolymer) so that the individual methods described can be seen in a more general system framework. Some of the extensive deleted sections have been shortened/rewritten and inserted in the section so that significant points are not lost, but only the excess detail. DiscussionThe discussion section has been significantly lengthened and clarified. Each technology is summarized to shed light upon the benefits and hurdles of each material that led to its individual ranking in our system. Each score is justified and explained within our metric.Throughout the text, an effort was made to reduce excess detail and highlight the major hurdles achieved by each researcher cited. Primary accomplishments and future needs for each material were further emphasized throughout the body of this paper.Specific responses to the referees follows. RESPONSES TO REVIEWER COMMENTS REFEREE 1Within their extensive review the authors state that in their review "… the published literature describing … membrane technologies (i.e. nanotechnologies) is critically reviewed and discussed within the context of conventional membrane materials used in the relevant water treatment applications" and "a ranking system was developed …" (all citations from the Abstract) Yet...

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Section: Discussionmentioning

confidence: 99%

A review of water treatment membrane nanotechnologies

Pendergast

Hoek

2011

Energy Environ. Sci.

1,850

917

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“…Surface roughness and the appearance of multi-level structures increased up to a certain co-solvent concentration, after which membranes became flatter and performance worsened. The effects of other additives that work as surfactants, catalysts or acid acceptors, such as triethylamine (TEA) and camphor sulfonic acid (CSA), have also been evaluated [18,[23][24][25]. Furthermore, physicochemical properties of the porous support such as porosity and hydrophobicity play a role in shaping the morphology of the polyamide thin film by influencing the way in which the MPD aqueous solution impregnates the support [8,[26][27][28].…”

Section: Introductionmentioning

confidence: 99%

3D visualization of the internal nanostructure of polyamide thin films in RO membranes

Pacheco

Sougrat

Reinhard

et al. 2016

Journal of Membrane Science

165

123

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The front and back surfaces of fully aromatic polyamide thin films isolated from reverse osmosis (RO) membranes were characterized by TEM, SEM and AFM. The front surfaces were relatively rough showing polyamide protuberances of different sizes and shapes; the back surfaces were all consistently smoother with very similar granular textures formed by polyamide nodules of 20-50 nm. Occasional pore openings of approximately the same size as the nodules were observed on the back surfaces.Because traditional microscopic imaging techniques provide limited information about the internal morphology of the thin films, TEM tomography was used to create detailed 3D visualizations that allowed the examination of any section of the thin film volume. These tomograms confirmed the existence of numerous voids within the thin films and revealed structural characteristics that support the water permeance difference between brackish water (BWRO) and seawater (SWRO) RO membranes.Consistent with a higher water permeance, the thin film of the BWRO membrane ESPA3 contained relatively more voids and thinner sections of polyamide than the SWRO membrane SWC3. According to the tomograms, most voids originate near the back surface and many extend all the way to the front surface shaping the polyamide protuberances. Although it is possible for the internal voids to be connected to the outside through the pore openings on the back surface, it was verified that some of these voids comprise nanobubbles that are completely encapsulated by polyamide. TEM tomography is a powerful technique for investigating the internal nanostructure of polyamide thin films. A comprehensive knowledge of the nanostructural distribution of voids and polyamide sections within the thin film may lead to a better understanding of mass transport and rejection mechanisms in RO membranes.3

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“…Recent studies have shown that membrane surface morphology and structure influence performance characteristics of membranes [1][2][3][4][5][6][7][8][9]. Hirose et al [9] suggested an approximately linear relationship between membrane surface roughness and permeate flux for crosslinked aromatic polyamide reverse osmosis (RO) membranes, where permeability increased with increasing surface roughness.…”

Section: Introductionmentioning

confidence: 99%

“…Higher flux and lower rejection were associated with the smoother membrane surfaces obtained from methyl substitution, while lower flux and higher rejection were associated with the rougher membrane surfaces resulting from halogen substitution. Additional work by Kwak and Ihm [5] coupling nuclear magnetic resonance (NMR) spectroscopy and atomic force microscopy (AFM) has shown an important relationship between proton spin-lattice relaxation times and RO permeability, regardless of surface morphological features. The latter two studies suggest that membrane performance (flux and rejection) is strongly influenced by the structure of the polymer network which constitutes the thin-film active layer.…”

Section: Introductionmentioning

confidence: 99%

“…Various analytical techniques have been employed for elucidating specific physical and chemical surface properties of membranes, including Raman spectroscopy (structure) [1], electron spin resonance (solute mobility in membrane polymer matrix and pores) [1], AFM (surface morphology, structure, and pore size) [1][2][3][4][5][6][7][8][9], streaming potential (membrane surface zeta potential) [10,11], NMR spectroscopy (permeability) [5], contact angle [12], and X-ray photoelectron spectroscopy (XPS) for surface chemical functional groups [13,14]. Despite these efforts, however, the role of membrane surface properties in colloidal fouling of RO/NF membranes is still not well understood.…”

Section: Introductionmentioning

confidence: 99%

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