Just add this stuff, nanofiltration membrane selectively direct 1Å less!
Membrane material capable of accurately separating small molecules and ions would have a revolutionary impact energy, water, chemicals and pharmaceutical industries. This separation membrane material is required to have a highly uniform pore size to achieve precise molecular sieving and separation of solutes, it is technically difficult to achieve. In recent years, researchers have attempted to produce a film with high precision by a method of stacking two-dimensional material, synthesis or biological integration oriented channels, etc., but so far no studies have reported separation wrong application of pressure and flow sub-angstrom accuracy achieved by membrane filtration under sub-nanometer solute. In addition, these approaches face significant technical challenges in terms of large-scale preparation of defect-free films. Small solutes in the art based composite polyamide (TFC-PA) nanofiltration membrane (NF) is a mature technology, efficient separation of the liquid from the solvent. Traditional selection layer is a polyamide-based NF membranes on a porous support by interfacial polymerization (IP) is formed. In a typical IP process, diffusion of the amine aqueous monomer solution into the organic solvent phase in the aqueous / organic interface vigorous reaction with an acid chloride by Schotten-Baumann. This uncontrolled proliferation and rapid polymerization formed polyamide (PA) layer having a multi-scale non-uniformity and non-uniform pore size. Since TFC-PA film is widely used in the purification and desalination of water, and the lack of in-depth understanding of the IP process, the mechanism of IP has been the subject of considerable attention. Although recent studies have explored various ways to improve the selectivity through, but with precise separation membrane PA claim ions and small molecules to improve the uniformity of the pore size of the membrane PA, which requires changing the design of the active layer pattern PA. In this case, the Chinese Academy of Sciences Suzhou Institute of Nano Jin Jian researcher and Vanderbilt University research group Professor Lin Shihong research group Cooperation prove the polymeric polyamide film (SARIP) is formed by a surfactant interface allows accurate adjustment assembly solute – separation of solutes. Sodium dodecyl sulfate (SDS) was added in a water / n-hexane to build a self-assembled network interface amphiphilic molecules, the amine monomers contribute interfacial polymerization process faster and more evenly in the water / n-hexane diffusion interface. A polyamide obtained with the conventional interfacial polymerization active layer compared to the more uniform sub-nanometer hole. SARIP polyamide film formed by high solute exhibits size dependent sieved, less than half the size of the solute in AngstromsWithin the range generated from stepwise transition to a low cut-off near complete interception of the first time sub-Angstrom level precision solute by adding a surfactant – separation of solutes. Traditional SARIP TFC-PA preparation changes required minimum NF membrane technology is a method of preparing an ultra-large-scale-selective membrane having a uniform nanopores can be used for precise separation of ions and small solutes. Related research \”Polyamide nanofiltration membrane with highly uniform sub-nanometre pores for sub-1 Å precision separation\” was published in Nature communications.
First, the performance and properties of the film produced by PA SARIP
PA is formed by an active layer having a uniform regular IPPorosity (free volume) distribution, and in the presence of SDS SARIP network interface promotes a more uniform PA network, leading to more accurate discrimination between similarly sized solutes. TFC-PA film and comparing IP SARIP synthesis of different rejection of small solute, the solute can be seen that a significant impact on the accuracy of screening or PA selective adjustment layer SDS web interface. TFC-PA film formed by a conventional IP Stokes radius rs of having a wide range of solute rejection rate between 2.5 Å to 5.0 Å. In contrast, in the presence of SARIP SDS network interface is significantly alter the behavior of the final separation of the solute PA film, wherein the entrapped solutes strongly dependent on the ionic size, measured rejection showed a sharp curve at rs ~ 2.7Å stepped transition, the accuracy of separation in a significant monovalent and divalent cations. By comparing the use of rejection curves PA films IP and SARIP prepared found SARIP not only reduces the molecular weight cutoff MWCO (i.e., 90% rejection of the corresponding molecular weight), but also reduced the scope of the transition zone rejection curve, so that the solute 1Å achieve the selective separation (i.e. difference in particle size is smaller than the rejection of both ions 1Å difference above 60%). For example, PA film is formed by SARIP obtained retention of Li + (rs = 2.4 Å) and Ba2 + (rs = 2.9Å) was 30% and 93% respectively, while for the PA film obtained by a conventional IP their rejection is very similar (19% and 17%). Distribution precise separation membrane SARIP TFC-PA preparation is attributable to the implementation of the active layer SARIP PA derived more uniform pore size, positron annihilation lifetime spectroscopy (PALS) and characterized using neutral solutes pore size distribution have confirmed this. Specifically, S-parameters TFC-PA films were prepared using two different methods showed that the distribution of holes generated SARIP both smaller and more uniform. These results are consistent with from PALS by fitting neural organic molecules of different molecular weight retention obtained. From the two measurement results, the PA layer sharp pore size distribution obtained by SARIP still provided with a pore size distribution of a conventional IP layer PA obtained. Accordingly, the main role is to SARIP sharpening a pore size distribution, pore size distribution rather than just moved to a smaller range. By XPS analysis of the live PAElemental composition layer, the results show that the degree of crosslinking, and conventional IP PA SARIP active layer formed was 76% and 81%, respectively.
two, SARIP uniform pore size distribution of the theoretical simulation
Researchers in the presence of SDS molecular dynamics (MD) simulation of the diffusion of water transport through the PIP monomer / n-hexane interface. The results show that electrostatic interactions between negatively charged sulfonic acid group by SDS-band and a small amount of positively charged molecules attract PIP, presence of SDS monomers to promote aggregation PIP near water / hexane interface. Second, a density functional theory and a PIP SDS molecules in the water molecule interactions (DFT) simulations indicate, SARIP the network interface by reducing SDS-related Gibbs free energy barrier, promoting the PIP across the interface from water to n-hexane transmission. Monte Carlo (MC) simulations show that the method, reduced barrier transfer interface not only accelerates the PIP, PIP and such that a more spatially uniform diffusion across the interface, which has a uniform pore size distribution of the PA membrane is essential for the formation. Further, in the water – a self-assembled network on SDS-hexane may also be applied to the interface PA fragment diffusion of water into newly formed steric hindrance, reducing the competing hydrolysis reaction, thereby increasing the degree of crosslinking. Thus, inhibition of proliferation and enhanced PIP adversely synergistically hydrolysis degree of crosslinking result in higher and more uniform pore size distribution. Table 1: DifferentNF membrane water permeability distribution, retention selected salt, MWCO and pore size. define: MWCO: molecular weight cut off, 2b neutral solute rejection is determined by the graph of FIG, : The average pore diameter, [sigma] p: geometric standard deviation. ⊥ no additives. This film is used as a reference. * Additives for each multi-concentration test (Supplementary Information), in this report the best performance results. # In addition to this (or p-toluene sulfonate TsNA), all other additives are surfactants.
In general, SARIP represent a generally applicable process, in this process, the amine monomer on the diffusive transport of water / n-hexane by an organized interface , anionic surfactants flexible network adjustment. This dynamic networks facilitate amine monomers faster and more uniformly by the water / hexane interface, it is a necessary condition for a more uniform active layer PA is formed. Effect SARIP amine monomer entire IP interface and diffusion process provides a new method for utterly a surfactant. Notably, SARIP TFC-PA changes to conventional techniques NF membrane preparation requirement extremely small, can be easily realized for precisely solute – scale preparation of super-selective separation of solutes NF membranes.