Advanced Membranes最新文献

Inspired by biological systems in nature, smart membranes with stimuli responsiveness exhibit advantages over traditional membranes with stationary structures and have shown the potential in breaking the thresholds of traditional membrane technologies. Unfortunately, responsive polymeric membranes suffer from inevitable fouling and the trade-off effect between permeability and selectivity, seriously hindering further applications. Recently, smart membranes based on two-dimensional (2D) nanomaterials with regulated nanochannel sizes and surface charges triggered by external stimuli have attracted increasing attention and are highly suitable for membrane technologies due to their promising properties. In this review, we summarize the state-of-art progress on the 2D smart membranes (2DSMs) including the general design strategies for fabricating 2DSMs, recent advances in responsive mechanisms under various stimuli and diverse applications such as gas separation, water treatment, ion rectification and osmotic energy harvest. To conclude, we propose a brief perspective on the challenges and opportunities in this fast-growing field.

The Hansen solubility parameter (HSP) theory, which includes the Hansen dispersion (D), polar (P), and hydrogen (H) components and a derivative ‘solubility parameter distance, Ra’ parameter, was adopted to evaluate the interaction between different polymers and their various diluents, so as to obtain a valuable and feasible criterion for the diluent selection of the thermally induced phase separation (TIPS) process for the preparation of polymeric membranes. Firstly, a full-scale database of the four HSP parameters of typical polymer-diluent systems was obtained based on a complete literature review about the phase separation process of all the polymer/diluents systems that have been applied to prepare polymeric membranes via TIPS and our additional exploratory experiments for membrane formation mechanism, in which two different phase separation processes including solid to liquid and liquid to liquid were distinguished. Relationships between the Ra parameter and the phase separation behavior were figured out to get a criterion for selecting the single diluent for the typical polymers. Moreover, the diluent selection was extended by adding a second diluent, and a schematic three-dimensional phase diagram was drawn to provide a feasible understanding of the TIPS process of the polymer-binary diluent system. Taking polypropylene (PP) as the representative example, plenty of exploratory experiments for the membrane formation mechanism based on a literature review were conducted to propose a guide based on the Hansen polar and hydrogen solubility component parameters to help select a proper binary diluent system.

Membrane separation is a promising alternative for gas purification. Facilitated transport (FT) membranes, with reversible reactions to promote CO₂ transport, can simultaneously obtain high CO₂ permeability and selectivity of CO₂ over other gases, such as CH₄, making FT membranes particularly interesting for CO₂/CH₄ separation. An overview of the state-of-the-art FT membranes used for CO₂/CH₄ separation is desired for the R&D of industrial membrane applications. This paper has reviewed the development progress and advances in various FT membranes for CO₂/CH₄ separation, including mobile carrier FT membranes, fixed site carrier FT membranes, and mixed matrix FT membranes. Over 100 different kinds of membrane materials with over 500 gas separation data have been summarized with performance data collected and analyzed. Perspectives of FT membranes for CO₂/CH₄ separation are also proposed.

Anti-fouling property is of vital significance and remains a challenge in the membrane separation field. In this work, N-diethylethylenediamine (DEEDA) was incorporated into the polyamide matrix first. Then, an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge was fabricated by the grafting of p-xylylene dichloride (XDC) on the membrane surface. The resulting nanofiltration membrane possessed zwitterionic groups of positively charged N⁺ and negatively charged COO^-. Meanwhile, the surface charge could be tuned precisely by the concentration of XDC. A neutrally charged nanofiltration membrane was obtained when the concentration of XDC was 1.0 ​wt% and the preparing membrane showed permeance of 9.1 ​L·m^-2·h^-1·bar^-1 with high rejection of CaCl₂ (90.8%) and Na₂SO₄ (91.3%) at pH ​= ​6.5. This membrane exhibited excellent anti-fouling properties towards not only negatively charged bovine serum albumin but also positively charged lysozyme. The optimum membrane, PA-XDC-1.0, had flux recovery rates of 95.0% and 94.0% for bovine serum albumin and lysozyme, respectively, which was higher than those of PA-DEEDA-0 (86.1% and 80.7%). This work offered a facile way to fabricate an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge, which had wide applications in water purification.

Biological membranes allow not only fast and selective ion permeation but also tunable ion transport, passively or actively on demands, in response to external stimuli such as light, voltage, temperature, etc. At the core of the membrane is the ultimate small ion channels approaching the dimension of a single ion and water molecule in the angstrom scale. To mimic and better understand the functioning of biological ion channels, artificial systems of similar sizes are developed recently. As novel platforms, these systems provide insights into many important problems such as mechanisms of non-continuum ion transport that are difficult to be investigated in larger structures. The unique couplings among ions, channels and various external stimuli at this spatial scale further inspire potential technologies where efficient and tunable ion transport is required. We review the main concepts of creating angstrom-scale channels and focus on discussing the tunable ion transport behavior inside. Permeability and selectivity of ion permeation controlled by light, electric field and solution environment variation are highlighted.

Over the past decades, fossil fuel combustion has emitted large quantities of CO₂ into the atmosphere, resulting in global climate change. Nowadays, it's considered a feasible strategy to capture CO₂ from some significant point sources. Three main strategies have been developed, namely post-combustion, pre-combustion, and oxy-fuel combustion. Recent research indicates that the membrane technology for CO₂ capture has become competitive compared with conventional technologies because of the improved separation performance in materials and process designs. This paper mainly reviews the progress and breakthroughs of membrane materials for the three gas separation systems corresponding to the CO₂ capture strategies. Besides, the CO₂ utilization by the membrane process has also been highlighted.

Mono-/multivalent ion-selective separation has become a common requirement at the water-energy nexus, including energy storage and conversion, water purification, and sustainable industrial processes. In this review, we summarize the theory of ion transport through membrane and mechanisms of selective ion separation in nanofiltration (NF) briefly. Recent advancing in improving the mono-/multivalent ion selectivity of thin-film composite (TFC) NF membrane via size sieving enhancement, electric charge property regulation and co-enhancement of size sieving and electric charge properties are concluded. What's more, three material classes—surface assembly materials, nanomaterials and biomimetic ion channels are highlighted as candidates for the preparation of ion-selective NF membranes. Lastly, design directions and critical challenges for developing high-selectivity nanofiltration membranes based on the ion-selective mechanisms are provided.

Oily wastewater poses a significant impact on both environments and human societies. Especially, the treatment of oil/water emulsions for separating oil from water is challenging due to the high stability of oil/water emulsions. Smart membranes, known as stimuli-responsive membranes, are one of the emerging technologies that have been paid wide attention for separating oil/water emulsions in recent years. Smart membranes possess the unique features of switchable wettability between hydrophilicity and hydrophobicity after being triggered by external stimuli and have desired anti-fouling properties. This review summarizes the development of smart membranes for oil/water emulsions separation during the past five years (2018 – present). It was found that solvent stimuli-responsive membranes are the most popular type of smart membranes for oil/water emulsions separation. For multi-stimuli-responsive membranes that can respond to more than one stimulus, future research should focus on developing appropriate fabrication strategies to increase the separation and anti-fouling performances of the membranes. Additionally, surface coating, surface grafting, and copolymer blending are the most popular methods for smart membranes fabrication. However, these methods might not be universally applicable to the different types of stimuli-responsive membranes.

Metal Organic Frameworks (MOFs) have been recently found to exist in a more processible liquid and glassy phase. These glassy MOFs have been shown to exhibit functional properties either in their native glassy form or when composited with other functional materials. The capability of MOF glass to be easily tailored similar to its crystalline form, while being able to form a continuous film with limited intergrain boundaries makes it a promising candidate for a selective membrane material. However, even with its high processibility, limited studies have been performed on this material in a thin film format. This perspective highlights the properties of currently studied MOF glass and its composite, as well as existing studies on MOF glass membranes. Views on possible future exploration pathways for this material in the form of membrane thin films, such as possible new MOF glass composite membrane configuration and new applications, are also provided.

The expansion of separation demands at molecular and ionic levels has triggered extensive research to explore new materials as promising practical membranes for separations. Owing to their dimension-related properties of two-dimensional (2D) porous organic polymers (POPs), promising research on the construction of 2D POPs into membranes has emerged and progressed rapidly, offering membranes with highly tunable pores/channels, robust frameworks/networks, intrinsic flexibility, and light weight for multiple separation purposes. In this review, up-to-date strategies for processing of 2D POPs into diverse continuous membranes and engineering of their nanochannels are highlighted. The 2D POPs materials discussed include the examples of 2D covalent organic frameworks (COFs), 2D covalent triazine frameworks (CTFs) and 2D conjugated microporous polymers (CMPs). Case studies on these materials for potential membrane applications including gas separation, water treatment, organic solvent nanofiltration (OSN), pervaporation are summarized. Finally, the critical challenges and futuristic upgrades of research directions and opportunities of 2D POPs based advanced membranes are outlined.