Accessing greater thickness and new morphology features in polyamide active layers of thin-film composite membranes by reducing restrictions in amine monomer supply

Grzebyk, Kasia; Armstrong, Mikayla D.; Coronell, Orlando

doi:10.1016/j.memsci.2021.120112

Cited by 39 publications

(23 citation statements)

References 43 publications

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“…The water permeance appeared to be strongly dependent on the membrane surface morphology. For example, the SEM images of TFCmethanol and TFC-acetone exhibited high surface coverage of flattened PA features (which are often referred as exterior PA layers, 20,39,45 also see Section Tuning Membrane Morphology and Performance). These membranes also had the highest water permeances, resulting in a correlation coefficient R 2 of 0.99.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

“…20,39 According to some recent studies, 33,39 forceful degassing and vapor generation during the IP reaction can potentially drive more MPD convection into the TMC solution, promoting the formation of more extensive exterior PA layers and defects. Recently, Grzebyk et al 45 also reported that continuous MPD supply during the IP reaction could result in the formation of multiple exterior PA layers as a result of the faster reaction rate and more extensive degassing. In addition, the multilayer structured PA (TEM in Figure 3) together with the smaller and less backside pore openings (SEM in Figure 3) may cause greater accumulation of rejected salts, potentially resulting in more severe concentration polarization and thus compromised rejection.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

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Cosolvent-Assisted Interfacial Polymerization toward Regulating the Morphology and Performance of Polyamide Reverse Osmosis Membranes: Increased m-Phenylenediamine Solubility or Enhanced Interfacial Vaporization?

Gan

Peng

Guo

et al. 2022

Environ. Sci. Technol.

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Cosolvent-assisted interfacial polymerization (IP) can effectively enhance the separation performance of thin film composite (TFC) reverse osmosis (RO) membranes. However, the underlying mechanisms regulating the formation of their polyamide (PA) rejection films remain controversial. The current study reveals two essential roles of cosolvents in the IP reaction: (1) directly promoting interfacial vaporization with their lower boiling points and (2) increasing the solubility of m-phenylenediamine (MPD) in the organic phase, thereby indirectly promoting the IP reaction. Using a series of systematically chosen cosolvents (i.e., diethyl ether, acetone, methanol, and toluene) with different boiling points and MPD solubilities, we show that the surface morphologies of TFC RO membranes were regulated by the combined direct and indirect effects. A cosolvent favoring interfacial vaporization (e.g., lower boiling point, greater MPD solubility, and/or higher concentration) tends to create greater apparent thickness of the rejection layer, larger nanovoids within the layer, and more extensive exterior PA layers, leading to significantly improved membrane water permeance. We further demonstrate the potential to achieve better antifouling performance for the cosolvent-assisted TFC membranes. The current study provides mechanistic insights into the critical roles of cosolvents in IP reactions, providing new tools for tailoring membrane morphology and separation properties toward more efficient desalination and water reuse.

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Section: ■ Materials and Methodsmentioning

confidence: 99%

Section: ■ Materials and Methodsmentioning

confidence: 99%

Cosolvent-Assisted Interfacial Polymerization toward Regulating the Morphology and Performance of Polyamide Reverse Osmosis Membranes: Increased m-Phenylenediamine Solubility or Enhanced Interfacial Vaporization?

Gan

Peng

Guo

et al. 2022

Environ. Sci. Technol.

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“…Furthermore, Song et al reported that the formation of these nanovoids is largely dependent on the confinement effect by the substrate. For IP reactions without a substrate, the bubbles can escape from the “free interface”, resulting in a smooth polyamide morphology with few nanovoids. ,, Recently, Grzebyk et al fabricated an additional polyamide layer atop existing TFC polyamide membranes by supplying MPD through the existing polyamide film. In this case, the existing polyamide film acted as a substrate with a strong confinement effect, atop which the subsequently formed additional polyamide layer exhibited more prominent nanovoids.…”

Section: Introductionmentioning

confidence: 99%

Deciphering the Role of Amine Concentration on Polyamide Formation toward Enhanced RO Performance

et al. 2022

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Polyamide surface morphology and its underneath nanosized voids have crucial influence on the separation performance of thin film composite (TFC) polyamide reverse osmosis membranes. Although there have been numerous studies reporting the impact of amine monomer concentration on polyamide formation and membrane performance, the observations and interpretations in the existing literature remain controversial. In this study, we performed interfacial polymerization (IP) of polyamide films over a wide range of m-phenylenediamine (MPD) concentration (0.05−8.0 w/w %). For the first time, we demonstrate that the water permeance of the resultant TFC membranes is governed by the competing effects of (1) promoted polyamide film growth for forming thicker polyamide films and (2) improved nanofoaming effect that results in more extensive nanovoids at higher MPD concentrations. To dissect these competing mechanisms, we further adopted a free-interface IP strategy to suppress the nanofoaming effect. The corresponding polyamide nanofilms had negligible nanovoids and monotonously increased film thickness, leading to decreased water permeance at high MPD concentrations. In contrast, the conventional TFC membranes exhibited optimal water permeance at the intermediate MPD concentration of 2.0 w/w %, which results from the trade-off between improved nanovoid formation (which promotes higher permeance) and increased film growth (which limits permeance). On the other hand, the better film growth at greater MPD concentration was generally beneficial for achieving better membrane rejection. The current study unveils the fundamental chemistry−morphology−performance relationship of TFC polyamide membranes and provides important implications on their synthesis and environmental applications.

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“…As shown in Figure , the polyamide films formed at longer IP reaction times achieved less passage for MPD monomers. Since the growth in the film thickness is dependent on the supply of MDP monomers, ,, the reduced transport rate of MPD at a longer IP reaction time explains the limited growth of film thickness over time. This “self-limit” nature of film growth is critical for the formation of ultrathin polyamide films, commonly in the range of 10–20 nm, as reported in the literature − for RO membranes.…”

Section: Resultsmentioning

confidence: 99%

“…This explanation is also consistent with Grzebyk et al's observation on the growth of additional roughness features over an existing polyamide film (e.g., a commercial RO membrane): the formation of an additional leaf-like roughness feature is well correlated to the transport of MPD across the existing layer. 62 Presumably, the presence of defects would allow a faster localized MPD supply, which would promote the further growth of polyamide near the defective regions.…”

Section: ■ Introductionmentioning

confidence: 99%

Unveiling the Growth of Polyamide Nanofilms at Water/Organic Free Interfaces: Toward Enhanced Water/Salt Selectivity

Zhou

Yang

et al. 2022

Environ. Sci. Technol.

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The permeance and selectivity of a reverse osmosis (RO) membrane are governed by its ultrathin polyamide film, yet the growth of this critical film during interfacial polymerization (IP) has not been fully understood. This study investigates the evolution of a polyamide nanofilm at the aqueous/organic interface over time. Despite its thickness remaining largely constant (∼15 nm) for the IP reaction time ranging from 0.5 to 60 min, the density of the polyamide nanofilm increased from 1.25 to 1.36 g cm–3 due to the continued reaction between diffused m-phenylenediamine and dangling acyl chloride groups within the formed polyamide film. This continued growth of the polyamide nanofilm led to a simultaneous increase in its crosslinking degree (from 50.1 to 94.3%) and the healing of nanosized defects, resulting in a greatly enhanced rejection of 99.2% for NaCl without sacrificing water permeance. Using humic acid as a molecular probe for sealing membrane defects, the relative contributions of the increased crosslinking and reduced defects toward better membrane selectivity were resolved, which supports our conceptual model involving both enhanced size exclusion and healed defects. The fundamental insights into the growth mechanisms and the structure–property relationship of the polyamide nanofilm provide crucial guidance for the further development and optimization of high-performance RO membranes.

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Accessing greater thickness and new morphology features in polyamide active layers of thin-film composite membranes by reducing restrictions in amine monomer supply

Cited by 39 publications

References 43 publications

Cosolvent-Assisted Interfacial Polymerization toward Regulating the Morphology and Performance of Polyamide Reverse Osmosis Membranes: Increased m-Phenylenediamine Solubility or Enhanced Interfacial Vaporization?

Cosolvent-Assisted Interfacial Polymerization toward Regulating the Morphology and Performance of Polyamide Reverse Osmosis Membranes: Increased m-Phenylenediamine Solubility or Enhanced Interfacial Vaporization?

Deciphering the Role of Amine Concentration on Polyamide Formation toward Enhanced RO Performance

Unveiling the Growth of Polyamide Nanofilms at Water/Organic Free Interfaces: Toward Enhanced Water/Salt Selectivity

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