Researchers Dr. Zhiyong Tang and the team led by Dr. Lianshan Li at the National Center for Nanoscience and Technology have made significant progress in the field of organic small molecule separation membranes and single-molecule layer membranes. Their research on organic small molecule separation membranes has been published in German Applied Chemistry, while their work in the area of single-molecule layer membranes is now available in Nano Reports.
Separation membrane materials hold crucial application value in various fields. In aqueous systems, such as seawater desalination and wastewater treatment, commercial applications have already been achieved. However, compared to aqueous systems, the application of separation membrane materials in organic systems lags significantly behind.
In previous studies, the team explored the nano-fluid transport mechanism in separation membrane materials in aqueous systems and confined membrane channels, laying the groundwork for the application of separation membranes in organic systems. Membrane separation of aromatic and aliphatic hydrocarbons is a critical requirement in the petroleum industry. Researchers have utilized various organic small molecule mixtures for separation, ion separation and its derivatives, ion-electron devices, biological membrane channels, and neuromorphic devices for separation. However, the lack of membrane materials that can withstand organic solvents, exhibit molecular specificity, and are easy to process poses challenges.
To address this, the team employed a strategy of preparing covalent triazine frameworks (CTFs) membranes from mixed monomers. By copolymerizing a spatial monomer with a planar monomer, they were able to subtly adjust the pore size and membrane affinity, allowing aromatic hydrocarbons with lower molecular weights to permeate preferentially over aliphatic hydrocarbons, thus achieving the complete liquid-phase separation of mixtures of aromatic and aliphatic hydrocarbons.
"Further research revealed that molecular size sieving and the synergistic effect of affinity between permeating molecules and membranes play a crucial role in separating these similar organic small molecules," explained Dr. Cuijing Liu, co-first author of the paper and postdoctoral researcher at the National Center for Nanoscience and Technology. "The membrane exhibited excellent stability under practical operating conditions, including long-term operation, different feed compositions, different application pressures, and multiple feed components. This provides a pathway for the preparation of selective membranes for aromatic and aliphatic hydrocarbons, thus taking an important step towards addressing the challenges of membrane technology in separating organic small molecules."
In another study, the team employed an interface pre-assembly polymerization strategy to synthesize covalent organic framework (COF) thin films with single-molecule layer thickness for studying their ion transport behavior in organic solutions.
"Extracting osmotic energy from discarded organic solutions through reverse electrodialysis is a promising method for energy extraction," said Fang Munan, co-first author of the paper and doctoral student at the National Center for Nanoscience and Technology. "This can recycle industrial waste and help alleviate the growing energy demand."
Researchers found that these single-molecule layer thickness COF thin films exhibit charge-controlled ion transport behavior in organic solutions. Moreover, these ultrathin films also have high output power density, along with good conversion efficiency and stability, providing important theoretical guidance for the study of organic nanofluids and the conversion of salinity gradient energy in organic systems.
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