Porous organic cage supramolecular membrane showing superior monovalent/divalent salts separation

Crystalline Porous Organic Cage Membranes Constructed Using Fortified Intermolecular Interactions for Molecular Sieving

Among the various types of materials with intrinsic porosity, porous organic cages (POCs) are distinctive as discrete molecules that possess intrinsic cavities and extrinsic channels capable of facilitating molecular sieving. However, the fabrication of POC membranes remains highly challenging due to the weak noncovalent intermolecular interactions and most reported POCs are powders. In this study, we constructed crystalline free-standing porous organic cage membranes by fortifying intermolecular interactions through the induction of intramolecular hydrogen bonds, which was confirmed by single-crystal X-ray analysis. To elucidate the driving forces behind, a series of terephthaldehyde building blocks containing different substitutions were reacted with flexible triamine under different conditions via interfacial polymerization (IP). Furthermore, density functional theory (DFT) calculations suggest that intramolecular hydrogen bonding can significantly boost the intermolecular interactions. The resulting membranes exhibited fast solvent permeance and high rejection of dyes not only in water, but also in organic solvents. In addition, the membrane demonstrated excellent performance in precise molecular sieving in organic solvents. This work opens an avenue to designing and fabricating free-standing membranes composed of porous organic materials for efficient molecular sieving.

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.

Ti3C2Tx MXene@MOF decorated polyvinylidene fluoride membrane for the remediation of heavy metals ions and desalination

Nowadays, the evolution of two-dimensional materials like transition metal carbides (MXene) prepares a novel path to surpass the "trade-off" between the membrane permeation and rejection rates. Based on water swelling and oxidation vulnerability, MXene membranes showed vivid defects such as inadequate stability, detrimental adsorption, and haphazardly stacked nanosheets. Here, we prepared Ti3C2Tx MXene@metal-organic frameworks nanosheets from aminated metal-organic framework-101 (NH2-MIL-101(Al)) via the in-situ growth method and incorporated them into the thin-film polymer to acquire desirable MXene nanosheets with tailor-made structures. The earned modified thin-film nanocomposite membrane showed high salt rejection for Na2SO4 (98.6 ± 0.5%), MgSO4 (96.9 ± 0.7%), MgCl2 (84.5 ± 0.8%), and NaCl (82.5 ± 0.8%), and also showed an improved permeation rate by three times (17.1 ± 0.2 L m-2. h-1. bar-1). Concurrently, the rejection rate of five different types of heavy metal ions (Ni2+, Cd2+, Mn2+, Cu2+, and Zn2+) was tested and denoted more than a 95.2 ± 0.5% rejection rate for all of them, notably high for Mn2+ (97.6 ± 0.4%). After modification, the flux recovery rate was as high as 95.3 ± 0.4%, denoting more than 30% improvement; besides, anti-compactness features enhanced by nearly 34 ± 0.7%. The long-term water permeation kept 91.5 ± 0.9% of its initial rate indicating almost 40 ± 0.8% enhancement. In addition, the rejection performance of Na2SO4 for the optimized membrane was more than 97% even after two weeks.