Although graphene materials are recognized as one of the strongest materials in the world, and graphene oxide (GO) membranes have also shown great potential in separation science and technology, they are very prone to stacking due to electrostatic repulsion after encountering media such as water. The redispersion and peeling of the GO sheet layer greatly limits its practical application. To solve this international problem,
Recently, the team of Professor Zhang Guoliang from the Institute of Membrane Separation and Water Science and Technology of Zhejiang University of Technology used the natural principle of chiral amplification to innovatively research and develop a cooperative molecular polymerization method (Cooperative Molecular Polymerization), which introduced chiral polymer molecules into graphene oxide for the first time. Interlayer and self-assembly fabricated chiral graphene oxide nanofiltration composite membranes (rGO/PLDA) with ultra-stable performance and ultra-strong structure in liquid separation. Generally, ordinary graphene oxide membranes are easy to rupture or even collapse and disperse in acid or alkaline solutions, while chiral composite membranes are very stable in their overall structure in pH 3.0-10.0 solutions. The most important thing is that the chiral composite membrane can not only maintain an excellent selective separation function for a long time under the actual turbulent state, but also resist the extreme harsh environment such as the solution of partial acid, partial alkali, ultrasound, oscillation and other external forces. The other graphene-based film materials reported are simply unattainable and can be called the "king of the strongest graphene film."
Unlike the previous graphene oxide film, which is difficult to go up to the sky, the liquid stability is very different. The preparation of this chiral composite film material is very simple, and there is an unusual formula in its monomer-poly-levodopamine molecule ( The English abbreviation is PLDA).
The "generals and soldiers" rule of chiral amplification usually means that the local chirality of a small part of chiral materials can determine the chiral characteristics of the entire assembly, and with the amplification of the chiral signal, its essence is the general molecule in the polymer The chiral properties of the combined molecular system can be controlled. Therefore, biologically excited chiral compounds such as PLDA can not only adjust the interlayer spacing between graphene oxide nanosheets in the composite film, but also generate a large number of chiral sites, thereby inducing many chiral fragments to form highly stable nanostructures. Ensure its long-term stable permeation performance and high separation selectivity.
Researchers also found that due to the addition of chiral compounds such as polylevodopamine as anchors, it has a strong chemical cross-linking effect, giving it excellent properties in nanofiltration membrane formation. For example: ordinary graphene oxide film is brittle, easy to break, and not resistant to water immersion, while the chiral composite film can not only flip and fold, but also keep the structure unchanged for a long time in the aqueous solution, but also undamaged after 2 hours of ultrasonic vibration , Performance is very stable.
Comparison of ordinary GO film (brown) and chiral rGO/PLDA composite film (black) in water for a long time and resistance to ultrasonic treatment.
Due to the chemical cross-linking reaction between the chiral poly-L-dopamine and the adjacent rGO nanosheets and its strong health, the Young's modulus of the chiral composite film can reach 22.62±2.04 Gpa, which is currently the best of other polymer-based GO composite films. More than 5 times.
Unique nano-scale molecular sieve
Not only that, the swelling distance of the chiral synthetic rGO/PLDA composite membrane in water can be as low as 0.37 Å, and it has excellent ultra-low pressure (1.0 bar) molecular sieve performance. The chiral composite membrane can maintain a very high polymer rejection rate (above 99%) in nearly 170 hours of continuous turbulent operation. The magic is that the rejection of negatively charged molecules by ordinary GO membranes is much greater than that of positively charged molecules and neutral molecules, but The chiral composite film has a good retention effect on positive and negative dyes.
The swelling resistance and stability of the chiral rGO/PLDA composite membrane and the performance comparison with other GO based nanofiltration membranes.
The preparation of chiral composite membranes by synergistic molecular polymerization has universality. For example, dextro-dopamine and amino acid chiral substances can be used to prepare chiral GO nanofiltration membranes with stable structures. The greatest significance of this research is that nano-scale molecular sieve membranes with multiple functions can be obtained through convenient chiral amplification and preparation, and are inexpensive and easy to mass produce. This method can be further extended to other layered and two-dimensional The development of membrane functional materials has a very broad industrial application prospect.