Advanced Covalent Organic Framework‐Based Membranes for Recovery of Ionic Resources

Abstract

metal ions have strong chemical toxicity including carcinogenicity, mutagenicity and teratogenicity, which can cause danger threat to the natural ecosystem and public health. [2] These heavy metal ions, unlike organic pollutants, are nonbiodegradable, highly soluble, and mobile, and remain in the environment. [3] This water contamination has further aggravated water scarcity, causing a new and unprecedented challenge for mankind. On the other hand, pure ions such as lithium, heavy metal ions, and radionuclides are important resources for industrial applications. [4] For example, lithium has rising demand for various applications especially the recent burgeoning of lithium-ion batteries for electric equipment and energy storage devices. [5] Consequently, the efficient recovery of these ion resources with high purity is becoming an urgent issue.Many technologies have been implemented for water treatment, among which membrane technology attracted much attention because of its low energy consumption, small carbon footprint, convenient operation, and good scalability. [6] Recently, novel membranes constructed from advanced materials such as porous carbons, [7] layered double hydroxides, [8] graphene, [9] molybdenum disulfide nanosheet, [10] and metal organic frameworks (MOFs) [11] have attracted extensive attention for their high surface area and porous structures. These unique physical structures have an excellent separation performance over conventional polymer membranes. [12] Recently, a new class of crystalline material-covalent organic frameworks (COFs) has been put forward and applied in membrane fabrication. COFs have crystalline porous network structures with regular and periodical assembly covalent bonds synthesized from reversible reactions, and were first reported by Yaghi and co-workers in 2005. [13] After that, various COF materials including bromo-based COFs, imine-based COFs, and amine-based COFs were reported. [14] The geometry of the COF depends on the size, symmetry, and connectivity of the connecting bonds, enabling a precise fine-tuning of the COF-based membrane channels to separate molecules or ions with different sizes. Varieties of synthesis methods have been developed to produce novel COFs, [15] such as the hydrothermal method, [16] the ion thermal method, [17] the mechanochemical method, [18] and the microwave method. [19] The unique structure endows COFs with superior properties like orderly assembled channels, tunable pore size and miscibility with organics, [20] Membrane technology has shown a viable potential in conversion of liquidwaste or high-salt streams to fresh waters and resources. However, the nonadjustability pore size of traditional membranes limits the application of ion capture due to their low selectivity for target ions. Recently, covalent organic frameworks ( COFs) have become a promising candidate for construction of advanced ion separation membranes for ion resource recovery due to their low density, large surface area, tunable channel structure, and tailored functionality...

Recent advances of pure/independent covalent organic framework membrane materials: preparation, properties and separation applications

“…The amorphous polymers prepare conventional membranes with disordered and inconsistent apertures. 15 It is difficult to achieve beyond the current Robeson upper limit. COF with abundant and well-organized in-plane pores are particularly promising for achieving ultrafast and highly selective molecular sieving.…”

“…13,14 Traditional amorphous polymer membranes, such as polyamide, polyimide, polyethersulfone, polyvinylidene fluoride, etc ., have disadvantages such as the lack of an ordered pore structure, non-uniform pore size as well as fewer pores, limiting their practical applications. 15–17 In contrast to conventional polymer membranes, the organic fragments of COF form thermodynamically stable covalent bonds through dynamic and reversible chemical processes. This property acts as a self-healing and error-correcting agent during the synthesis of COF, resulting in a long-range ordered, periodic crystal structure of COF.…”

Water/Vapor Assisted Fabrication of Large‐Area Superprotonic Conductive Covalent Organic Framework Membranes

“…[28] In recent years, iCOMs employed in fuel cells as proton exchange membranes to harvest clean energy have gained tremendous interest. [29][30][31][32][33][34] Compared with non-ionic COMs, fabrication of iCOMs is much more difficult due to the presence of charged groups such as the sulfonic acid groups with dense electron clouds, leading to strong Coulombic repulsion, steric hindrance and weaker 𝜋-𝜋 interactions, often yielding nanoparticles or nanosheets rather than membranes. [27,35] Till now, four strategies for the fabrication of iCOMs as proton exchange membranes have been explored: i) doping of non-ionic COF powders with proton carriers, [36,37] ii) synthesis of ionic COF powder and their subsequent pressing into pellets, [38][39][40] iii) assembling ionic COF nanosheets into membranes, [2,27] and iv) direct fabrication of iCOMs by reacting monomers with ionic groups using interfacial polymerization [35] or in situ solvothermal [41] methods.…”

Exploring Cation-Exchange Membranes: Synthesis, Characterization, and Real-World Applications in a Multidisciplinary Laboratory

“…This technology has played a pivotal role in addressing critical societal challenges, including clean water and air, public health, climate change, waste reduction, and energy generation. − At the heart of this technology lies the membrane material itself. − Covalent organic frameworks (COFs) are a distinct class of crystalline porous polymers constructed via a bottom-up method, utilizing molecular units with pre-established geometries that are interlinked through covalent bonds. − The hallmark of COFs is their inherent ability to maintain precise positioning of their constituent building blocks in both two and three dimensions, allowing them to synthesize stable porous structures characterized by regularity. This property enables meticulous modulation of both the chemical and the physical attributes of the constructed network. − Since the very first publication by Omar M. Yaghi in 2005, research on COFs has advanced beyond the synthesis and characterization of diverse structures and has extended into the realm of applied science. − Because of their unique attributes, COFs have emerged as promising candidates for membrane construction, and membranes made from COFs have showcased groundbreaking results in fields such as desalination, resource element extraction, and energy conversion. − …”