Naturally Extracted Hydrophobic Solvent and Self-Assembly in Interfacial Polymerization

Interfacial Polymerization of Aromatic Polyamide Reverse Osmosis Membranes

Polyamide membranes are widely used in reverse osmosis (RO) water treatment, yet the mechanism of interfacial polymerization during membrane formation is not fully understood. In this work, we perform atomistic molecular dynamics simulations to explore the cross-linking of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) monomers at the aqueous-organic interface. Our studies show that the solution interface provides a function of "concentration and dispersion" of monomers for cross-linking. The process starts with rapid cross-linking, followed by slower kinetics. Initially, amphiphilic MPD monomers diffuse in water and accumulate at the solution interface to interact with TMC monomers from the organic phase. As cross-linking progresses, a precross-linked thin film forms, reducing monomer diffusion and reaction rates. However, the structural flexibility of the amphiphilic film, influenced by interfacial fluctuations and mixed interactions with water and the organic solvent at the solution interface, promotes further cross-linking. The solubility of MPD and TMC monomers in different organic solvents (cyclohexane versus n-hexane) affects the cross-linking rate and surface homogeneity, leading to slight variations in the structure and size distribution of subnanopores. Our study of the interfacial polymerization process in explicit solvents is essential for understanding membrane formation in various solvents, which will be crucial for optimal polyamide membrane design.

Interfacially Cross-Linked Polydopamine/Polybenzimidazole Composite Membranes for Organic Solvent Nanofiltration

Interfacial cross-linking was used to prepare composite organic solvent nanofiltration (OSN) membranes comprising a polydopamine (PDA) active layer formed on a polybenzimidazole (PBI) substrate. Dibromo-p-xylene (DBX) was employed as a cross-linking agent to make the composite membranes chemically stable against harsh polar aprotic solvents. The interfacial cross-linking of PDA/PBI allowed for finely tuning the molecular weight cutoff (MWCO) of the membrane, resulting in a membrane with precise molecular separation capabilities for OSN. The morphology and surface properties of the membranes were characterized, and a membrane with a MWCO of 286 Da was investigated for OSN of a series of solvents. The membrane permeance was in the order of acetonitrile (MeCN) > methanol (MeOH) > acetone > toluene > dimethylformamide (DMF) > heptane > ethanol (EtOH) > isopropanol (IPA) > tetrahydrofuran (THF). The membranes displayed a sharp pore size distribution, yielding a rejection rate of over 99% for Rose Bengal (RB, MW 1020 g/mol) and Remazol brilliant blue (RBB, MW 626.5 g/mol) from DMF and EtOH solutions. When it came to methyl orange (MO, MW 327.3 g/mol) that had a molecular weight closer to the MWCO of the membrane, the membrane still displayed a high rejection rate of 95% and 99% in nanofiltrating solvents DMF and EtOH, respectively. In addition, it was demonstrated that the membrane was able to effectively fractionate mixed solutes having molecular weights appropriate for the MWCO rating of the membrane during OSN.

Synthesis of tunable thickness-to-diameter ratio microcapsules via a diffusion-controlled process for temperature-responsive release

Designing microcapsules with a complicated functionalized shell to respond to an external stimulus has attracted much attention for triggered release; however, simplifying the synthesis process remains a significant challenge. Herein, we initially propose a novel, simple synthesis strategy that utilizes a mixed solvent as the organic phase to control the diffusion of common monomers during interfacial polymerization, resulting in the successful preparation of microcapsules with tunable thickness-to-diameter ratios (T/D). The morphology of microcapsules is confirmed by scanning electron microscopy. We also observe that the T/D of the designed microcapsules progressively increases as the diffusion of monomers occurs, and the glass transition temperature of microcapsules is controlled. Furthermore, microcapsule-based crosslinking agents are applied to investigate the crosslinking reaction of poly(vinyl chloride). Rotational rheometer results indicate that the microcapsules exhibit an excellent external stimulus response, precisely triggering release at the predetermined temperature. This simple approach for the preparation of microcapsules with tunable physical properties has great potential for triggered release in diverse applications.

Additive-optimized micro-structure in cellulose acetate butyrate-based reverse osmosis membrane for desalination

Progress toward the high water flux of cellulose acetate butyrate (CAB)-based reverse osmosis (RO) membrane is a bottleneck for desalination and mitigation of fresh water shortage. Here, we develop an "optimization of formulation-induced structure" strategy using acetone (solvent), triethyl phosphate (pore-inducing agent), glycerin and n-propanol (boosters), which achieves a state-of-the-art salt rejection of 97.1% and permeate flux of 8.73 L m^-2·h^-1, ranking top among CAB-based RO membrane. Compared with reported literatures, it represents high separation performance for different concentrations (20-100 mg L^-1) of Rhodamine B and Congo red, different ion types (NaCl and MgCl₂), different time (600 min), and resistance to feed pressure changes. The key is the appropriate viscosity of the casting solution (995.52 mPa s), the synergy between the components and additives, contributing to the formation of "jellyfish"-like microscopic pore structure with the lowest surface roughness (Ra = 16.3) and good hydrophilicity. The proposed correlation mechanism between additive-optimized micro-structure and desalination provides a promising prospect for CAB-based RO membrane.

Loosely Sandwich-Structured Membranes Decorated with UiO-66-NH2 for Efficient Antibiotic Separation and Organic Solvent Resistance

Thin-film nanocomposite (TFN) membranes with efficient molecular separation and organic solvent resistance are active in demand in wastewater treatment and resource reclamation, meeting the goal of emission peaks and carbon neutrality. In this work, a simple and rational design strategy has been employed to construct a sandwich-structured membrane for removing fluoroquinolone antibiotics and recycling organic solvents. The sandwich-structured membrane is composed of a porous substrate, a hydrophilic tannic acid-polyethyleneimine (TA-PEI) interlayer, and a polyamide (PA) selective layer decorated with metal-organic framework (PA-MOF). Results manifest that the hydrophilic TA-PEI interlayer played a bridging and gutter effect to achieve effective control in amide storage, amine diffusion, and nanomaterial downward leakage at the immiscible interface. The PA-MOF selective layer has been changed to a loosely crumpled surface, endowing functionalities on the sandwich-structured membrane that included limited pores, strengthened electronegativity, and stronger hydrophilicity. Thus, an enhanced water flux of 87.23 ± 7.43 LMH was achieved by the TFN-2 membrane (0.04 mg·mL^-1 UiO-66-NH₂), which is more than five times that of the thin-film composite membrane (17.46 ± 3.88 LMH). The rejection against norfloxacin, ciprofloxacin, and levofloxacin is 92.94 ± 1.60%, 94.62 ± 1.29%, and 96.92 ± 1.05%, respectively, effectively breaking through the "trade-off" effect between membrane permeability and rejection efficiency. Further antifouling results showed that the sandwich-structured membrane had lower flux decay ratios (3.36∼7.07%) and higher flux recovery ratios (93.40∼98.40%), as well as superior long-term stability after 30 days of filtration. Moreover, organic solvent resistance testing confirms that the sandwich-structured membrane maintained stable solvent flux and better recovery rates in ethanol, acetone, isopropanol, and N,N-dimethylformamide. Detailed nanofiltration mechanism studies revealed that these outstanding performances are based on the joint effect of the TA-PEI interlayer and PA-MOF selective layer, proposing a new perspective to break through the bottleneck of nanofiltration application in a complex environment.