Journal of Membrane Science Letters最新文献

Three crystalline truxene-based β-ketoenamine COF membranes (TFP-HETTA, TFP-HBTTA and TFP-HHTTA) are fabricated via a de novo monomer design approach to understand the fundamental correlations between pore structure and molecular separation performance. By introducing bulky alkyl groups into the truxene framework, the pore size of TFP-HETTA, TFP-HBTTA, and TFP-HHTTA are systematically tuned from 1.08 to 0.72 nm. Accordingly, the TFP-HETTA showed good water permeance of 47 L m⁻² h⁻¹ bar⁻¹ along with a prominent rejection rate of Reactive Blue (RB, 800 Da) but less than 10% rejection rate of inorganic salts. In contrast, the TFP-HHTTA membrane with pore size of 0.72 nm can reject small dye molecules such as Safranin O (SO, 350 Da) and trivalent salts but with a moderate water permeance of 19 L m⁻² h⁻¹ bar⁻¹. The pore-flow model rooted from the viscous flow could well fit the observed organic solvent nanofiltration results of all three COF membranes.

The fractionation of complex liquid hydrocarbon mixtures is an important and emerging area of membrane science. Polymeric asymmetric hollow fiber membranes have the potential to be used for this purpose, especially if the size and number of defects in the membrane skin layer can be precisely engineered. Here, we fabricated various “defect-engineered” Torlon hollow fiber membranes by modifying hollow fiber spinning conditions and spin dopes to study the role of skin layer defects in the organic solvent reverse osmosis (OSRO) membranes. The quality of the membranes was investigated using several sets of pure gas permeation experiments, which provided input data for a permeation resistance model that estimates the pore size and surface porosity of the asymmetric hollow fiber membrane. We develop and experimentally validate a resistance permeation model for solvent permeation and utilize the surface properties derived from the gas permeation experiments to estimate the relative permeation rates of solvents in a mixture. The approach outlined here highlights the interconnection between gas permeation analysis and OSRO separation performance using Torlon hollow fiber membranes as an exemplar test case. The solvent permeation model is then utilized to provide quantitative insight on the differences between OSRO and organic solvent nanofiltration (OSN), and highlight the important transition region between these two modalities.

The separation of H₂/CH₄ or CO₂/CH₄ is critical to the purification of natural gas. Herein, we report on novel membranes with a metal-organic framework of CAU-10-PDC for the separation of these two mixtures. The dense CAU-10-PDC membranes are fabricated on a porous alumina support using the seeded growth method. An unexpected increase in selectivity was observed while testing mixed gas permeation with either H₂/CH₄ or CO₂/CH₄ at a molar ratio of 50:50. Steady-state selectivity reached 101 for H₂/CH₄ and 62 for CO₂/CH₄. Ideal selectivity measured from single gas permeation reached 475 for H₂/CH₄ and 288 for CO₂/CH₄. Molecular dynamics simulations and time-resolved X-ray diffraction with a synchrotron radiation source were used to probe conformational changes in CAU-10-PDC induced by exposure to CH₄. When exposed to an atmosphere containing CH₄, CAU-10-PDC presented a change in the space group (from I4₁/amd to I4₁), which drastically reduced the pore limiting diameter from 4.15 to 2.95 Å, rendering the channel nearly impermeable to CH₄.

Fabricating acid resistant nanofiltration (NF) membranes with precise solute separation performance is highly demanded for acidic wastewater treatment but remains a challenge. Herein, we propose a facile strategy for preparing dually charged acid resistant NF membranes with both high cations and anions rejections via a two-layer reverse interfacial polymerization (r-IP) process. Organic monomers of trimesoyl chloride (TMC) and 1,4-phenylene diisocyanate (PPDI) are firstly applied to react with 3-aminobenzenesulfonamide (ABSA) to construct a negatively charged loose intermediate layer, followed by the r-IP of TMC/PPDI and polyethyleneimine (PEI) to engineer a dense positively charged top layer. The highly cross-linked polyurea (PU) formed by isocyanate and amine leads to an enhanced size sieving effect, and the well-arranged dually charged layer endows the membrane stronger electrostatic exclusion. The resultant membrane has 97.7% rejection of Na₂SO₄ and 93.0% of MgCl₂, and it exhibits fairly high rejections to various heavy metals, as well as impressive long-term stability after exposure to strong acid (10 wt% of H₂SO₄ for 400 h).

Accounting for concentration-polarization (CP) is critical for modeling solute transport in membrane separation processes. In a mixed-electrolyte solution, ions' CP is affected not only by diffusion and advection but also by electromigration. Yet, the classic film model, lacking an electromigration term, is frequently used for modeling ion CP. Often, ion CP is altogether neglected to reduce the computational load. Here, we study the CP of trace ions in a dominant salt solution, a case relevant for many reverse-osmosis and nanofiltration processes. First, we revisit the solution-diffusion-electromigration-film theory to obtain an analytical solution for the CP and membrane-transport of trace-ions in a dominant salt solution. Secondly, we consider limiting conditions relevant to reverse-osmosis and nanofiltration, from which we derive two compact equations that emerge as a seamless extension to the classic film theory. These equations can be used to account for the effect of electromigration on CP with minimal effort. Thirdly, we use our theory to quantify the effect of electromigration on ion CP in different dominant salt solutions. Finally, by analyzing two environmental membrane processes, we demonstrate how our theory deviates from the conventional one and quantify the implications on membrane scaling potential and the transport of ionic contaminants.

Detrimental biofilms on RO membranes remain a crucial challenge for seawater desalination. Comparative analysis of 16S rRNA gene amplicon sequencing data revealed differences and commonalities of biofilm communities associated with unit operations in the two largest seawater desalination facilities in the U.S., the Claude "Bud" Lewis Carlsbad Desalination Plant and the Tampa Bay Seater Desalination facility. At both plants, feedwater collected at a single time point was a poor indicator of the RO membrane communities, which showed far greater taxa diversity. The analysis of prefilter cartridges from the Carlsbad plant revealed similarly high taxon diversity as the RO module biofilms, with relevant differences. Algal sequences were enriched on the prefilter cartridges as were sequences representing Bdellovibrionota, which are predatory bacteria. Sequences representing opportunistic Gammaproteobacteria (i.e., Shewanella, Woesia) were present in significantly higher relative abundance on the RO membranes than in the prefilter cartridges, suggesting growth of certain taxa in the RO modules. Untargeted metabolomics distinguished intra- and inter-desalination plant biofilm samples, highlighting the potential value of this tool for biofilm monitoring. These findings underscore the value of omics tools for effective microbial monitoring, to understand biofouling dynamics within RO desalination plants, and to provide insight for the development of ecologically-informed biofilm control measures.