Nanofiltration (NF) membranes with ultrahigh permeance and high rejection are highly beneficial for efficient desalination and wastewater treatment. Improving water permeance while maintaining the high rejection of state-of-the-art thin film composite (TFC) NF membranes remains a great challenge. Herein, we report the fabrication of a TFC NF membrane with a crumpled polyamide (PA) layer via interfacial polymerization on a single-walled carbon nanotubes/polyether sulfone composite support loaded with nanoparticles as a sacrificial templating material, using metal-organic framework nanoparticles (ZIF-8) as an example. The nanoparticles, which can be removed by water dissolution after interfacial polymerization, facilitate the formation of a rough PA active layer with crumpled nanostructure. The NF membrane obtained thereby exhibits high permeance up to 53.5 l m−2h−1 bar−1 with a rejection above 95% for Na2SO4, yielding an overall desalination performance superior to state-of-the-art NF membranes reported so far. Our work provides a simple avenue to fabricate advanced PA NF membranes with outstanding performance. Nanofiltration membranes are important for water desalination technologies, but designing membranes that achieve both high permeance and high salt rejection remains challenging. Here, the authors use sacrificial nanoparticles in the membrane fabrication process, leading to crumpled structures with ultrahigh permeance.

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Nanoparticle-templated nanofiltration membranes for ultrahigh performance desalination

Biomimetic nanosurfaces with distinct wettability and versatility have found special enthusiasm in both fundamental research and industrial applications. With the advent of nanotechnology, it is doable to acclimate surface architecture and surface chemistry to attain superhydrophobicity. The uniqueness of superhydrophobic surfaces arises from various phenomenal advances, and its progress is expected to continue for decades in the future. In this Review Article, we discuss recent progress made in defining physical aspects of numerical modeling, experimental practices adopted, and applications of superhydrophobic surfaces. First, we revisit various classical models of superhydrophobicity and recent theoretical advances achieved related to the wetting phenomena. Subsequently, we emphasize various precursors and advance fabrication strategies adopted to fabricate superhydrophobic surfaces. In the following section, we take up various potential applications and appropriate working principles to explain wettability phenomena. Finally, some general conclusions are drawn along with proposed guidelines for designing robust superhydrophobic coatings.

Superhydrophobic Surfaces: Insights from Theory and Experiment.

Nanofiltration membranes are of great interest in brackish water desalination and drinking water purification. Improving the permeation and separation performance remains a big challenge in advanced nanofiltration membranes. Herein, we report triple-layered composite nanofiltration membranes constructed by the interfacial polymerization of diamine and acyl chloride on a cellulose nanocrystal interlayer supported by a microporous substrate. The cellulose nano-crystal interlayer plays a crucial role in the polyamide skin layer formation and the following nanofiltration process. It can store aqueous diamine monomers and slow down the interfacial polymerization for a relatively low cross-linking degree of the skin layer. This hydrophilic interlayer also facilitates water permeation through a “dragging effect”. The constructed membranes exhibit an ultra-high permeation flux up to 204 L m−2 h−1 under 0.6 MPa with a Na2SO4 rejection above 97%, which is the highest reported result to our knowledge. The ultra-high water permeation flux enables nanofiltration at low operating pressure, making it an energy-saving process. Moreover, the low cross-linking degree of the skin layer results in a high monovalent/divalent ion separation ratio.

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Nanofiltration membranes with cellulose nanocrystals as an interlayer for unprecedented performance

Metal/covalent–organic framework (MOF/COF) membranes have attracted increasing research interest and have been considered as state-of-the-art platforms applied in various environment- and energy-related separation/transportation processes. To break the trade-off between permeability and selectivity to achieve ultimate separation, recent studies have been oriented towards how to design and exploit ultrathin MOF/COF membranes (i.e. sub-1 μm-thick). Given great advances made in the past five years, it is valuable to timely and systematically summarize the recent development and shed light on the future trend in this multidisciplinary field. In this review, we first present the advanced strategies in fabricating ultrathin defect-free MOF/COF membranes such as in situ growth, contra-diffusion method, layer-by-layer (LBL) assembly, metal-based precursor as the pre-functionalized layer, interface-assisted strategy, and laminated assembly of MOF/COF nanosheets. Then, the recent progress in some emerging applications of ultrathin MOF/COF membranes beyond gas separation is highlighted, including water treatment and seawater desalination, organic solvent nanofiltration, and energy-related separation/transportation (i.e. lithium ion separation and proton conductivity). Finally, some unsolved scientific and technical challenges associated with future perspectives in this field are discussed, inspiring the development of next-generation separation membranes.

Ultrathin metal/covalent-organic framework membranes towards ultimate separation.

Mussel-inspired chemistry, owing to its unique and versatile functions to manipulate dynamic molecular-scale interactions, has emerged as a powerful tool for the rational design and synthesis of new hydrogels. In particular, possessing a myriad of unique advantages that are otherwise impossible by conventional counterparts, mussel-inspired hydrogels have been widely explored in numerous fields such as biomedical engineering, soft electronics and actuators, and wearable sensors. Despite great excitement and vigor, a comprehensive and timely review on this emerging topic is missing. In this review, we discuss (1) the fundamental interaction mechanisms underpinning the spectacular wet adhesion in natural mussels and mussel-inspired materials; (2) the key routes to engineering hydrogels by leveraging on the interactions of mussel-inspired building blocks; (3) the emerging applications of mussel-inspired hydrogels, especially in the areas of flexible electronics and biomedical engineering; (4) the future perspectives and unsolved challenges of this multidisciplinary field. We envision that this review will provide an insightful perspective to stimulate new thinking and innovation in the development of next-generation hydrogels and beyond.

Mussel-inspired hydrogels: from design principles to promising applications

Janus membranes (JMs) with opposite wettability have brought about new opportunities to tackle the challenging issues encountered in oil/water separation. However, these achievements suffer from empirical availability for the separation of oil-in-water emulsions, lacking a controllable way to tune the synergistic effect of asymmetric configurations, which is the “inner” driving force for practical performance. Herein, the role of the asymmetric configuration is theoretically and experimentally demonstrated in the Janus structural design, membrane fabrication, and separation performance for oil-in-water emulsions. These significant insights are particularly gained by analyzing Young–Laplace capillary pressures, measuring the adhesive forces between the oil and membrane surface, and monitoring the demulsification and oil transportation processes. Fluorescence imaging has been used to in situ visualize the separation process and then a mechanism is firstly proposed as demulsification followed by rapid unidirectional oil transportation for surfactant-stabilized oil-in-water emulsions. The two successive processes are strongly governed by the controllable asymmetric configuration of the JMs. An efficient oil separation can, therefore, be achieved from surfactant-stabilized oil-in-water emulsions with a wide size distribution (from nanometers to microns) by optimizing these two stages via tuning the hydrophilic/hydrophobic configuration and surface charge property of the JMs. Therefore, this work is expected to yield a design principle and guideline for developing JMs with applicability in the practical separation of oil-in-water emulsions.

Janus membranes with controllable asymmetric configurations for highly efficient separation of oil-in-water emulsions

Hybrid conformal coatings, such as metal-phenolic networks (MPNs) that are constructed from the coordination-driven assembly of natural phenolic ligands, are of interest in areas including biomedicine, separations, and energy To date, most MPN coatings have been prepared by immersing substrates in solutions containing the phenolic ligands and metal ions, which is a suitable method for coating small or flexible objects In contrast, more industrially relevant methods for coating and patterning large substrates, such as spray assembly, have been explored to a lesser extent toward the fabrication of MPNs, particularly regarding the effect of process variables on MPN growth Herein, a spray assembly method was used to fabricate MPN coatings with various phenolic building blocks and metal ions and their formation and patterning were explored for different applications Different process parameters including solvent, pH, and metal-ligand pair allowed for control over the film properties such as thickness and roughness On the basis of these investigations, a potential route for the formation of spray-assembled MPN films was proposed Conditions favoring the formation of bis complexes could produce thicker coatings than those favoring the formation of mono or tris complexes Finally, the spray-assembled MPNs were used to generate superhydrophilic membranes for oil-water separation and colorless films for UV shielding The present study provides insights into the chemistry of MPN assembly and holds promise for advancing the fabrication of multifunctional hybrid materials

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Spray Assembly of Metal-Phenolic Networks: Formation, Growth, and Applications

Enzyme-triggered coatings of tea catechins/chitosan for nanofiltration membranes with high performance

The tunable growth of metal-organic materials has implications for engineering particles and surfaces for diverse applications. Specifically, controlling the self-assembly of metal-phenolic networks (MPNs), an emerging class of metal-organic materials, is challenging, as previous studies suggest that growth often terminates through kinetic trapping. Herein, kinetic strategies were used to temporally and spatially control MPN growth by promoting self-correction of the coordinating building blocks through oxidation-mediated MPN assembly. The formation and growth mechanisms were investigated and used to engineer films with microporous structures and continuous gradients. Moreover, reactive oxygen species generated by ultrasonication expedite oxidation and result in faster (ca. 30 times) film growth than that achieved by other MPN assembly methods. This study expands our understanding of metal-phenolic chemistry towards engineering metal-phenolic materials for various applications.

https://minerva-access.unimelb.edu.au/bitstream/handle/11343/227180/accepted version.pdf

Oxidation-Mediated Kinetic Strategies for Engineering Metal–Phenolic Networks

The manipulation of interfacial properties has broad implications for the development of high-performance coatings. Metal-phenolic networks (MPNs) are an emerging class of responsive, adherent materials. Herein, host-guest chemistry is integrated with MPNs to modulate their surface chemistry and interfacial properties. Macrocyclic cyclodextrins (host) are conjugated to catechol or galloyl groups and subsequently used as components for the assembly of functional MPNs. The assembled cyclodextrin-based MPNs are highly permeable (even to high molecular weight polymers: 250-500 kDa), yet they specifically and noncovalently interact with various functional guests (including small molecules, polymers, and carbon nanomaterials), allowing for modular and reversible control over interfacial properties. Specifically, by using either hydrophobic or hydrophilic guest molecules, the wettability of the MPNs can be readily tuned between superrepellency (>150°) and superwetting (ca. 0°).

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Qi-Zhi Zhong

Papers

Janus membranes with controllable asymmetric configurations for highly efficient separation of oil-in-water emulsions

Spray Assembly of Metal-Phenolic Networks: Formation, Growth, and Applications

Enzyme-triggered coatings of tea catechins/chitosan for nanofiltration membranes with high performance

Oxidation-Mediated Kinetic Strategies for Engineering Metal–Phenolic Networks

Modular Assembly of Host–Guest Metal–Phenolic Networks Using Macrocyclic Building Blocks