Thin film composite nanofiltration membranes fabricated from polymeric amine polyethylenimine imbedded with monomeric amine piperazine for enhanced salt separations

Combining phthalimide innate of a positive-charge nanofiltration membrane for high selectivity and rejection for bivalent cations

A positively charged nanofiltration (NF) membrane is known to have exceptional separation performance for bivalent cations in aqueous solutions. In this study, a new NF activity layer was created using interfacial polymerization (IP) on a polysulfone (PSF) ultrafiltration substrate membrane. The aqueous phase combines the two monomers of polyethyleneimine (PEI) and phthalimide, while successfully producing a highly efficient and accurate NF membrane. The conditions of the NF membrane were studied and further optimized. The aqueous phase crosslinking process enhances the polymer interaction, resulting in an excellent pure water flux of 7.09 L·m^-2·h^-1·bar^-1 under a pressure of 0.4 MPa. Additionally, the NF membrane shows excellent selectivity toward inorganic salts, with a rejection order of MgCl₂ > CaCl₂ > MgSO₄ > Na₂SO₄ > NaCl. Under optimal conditions, the membrane was able to reject up to 94.33% of 1,000 mg/L of MgCl₂ solution at an ambient temperature. Further to assess the antifouling properties of the membrane with bovine serum albumin (BSA), the flux recovery ratio (FRR) was calculated to be 81.64% after 6 h of filtration. This paper presents an efficient and straightforward approach to customize a positively charged NF membrane. We achieve this by introducing phthalimide, which enhances the membrane's stability and rejection performance.

One-Step Construction of the Positively/Negatively Charged Ultrathin Janus Nanofiltration Membrane for the Separation of Li+ and Mg2

To coordinate the trade-off between the separation and permeation of the nanofiltration membrane for the separation of Mg²⁺/Li⁺, we regulated poly(ethyleneimine)/piperazine interface polymerization parameters to construct a positively/negatively charged ultrathin Janus nanofiltration membrane at a free aqueous-organic interface. At the optimized interfacial polymerization parameters, 0.03 wt % of piperazine reacted with trimethylbenzene chloride prior to poly(ethyleneimine), forming a primary polyamide layer with fewer defects or limiting large-scale defects of the polyamide layer. The controlled subsequent reaction of poly(ethyleneimine) and trimethylbenzene chloride results in a Janus nanofiltration membrane, with one side enriched with the carboxyl groups, the other side enriched with the amine groups, and a dense polyamide structure in the middle. Under the optimum conditions, the positive potential of the rear surface of the prepared membrane was 14.57 mV, and the water contact angle reached 71.31°, while the negative potential of the front surface was -25.48 mV, and the water contact angle was 12.93°, confirming a Janus membrane with opposite charges and large hydrophilicity differences in the front and rear surfaces. With a high cross-linking degree, a 40 nm thick polyamide layer is 29.09% more thinner than the traditional polyamide membrane. The ultrathin Janus nanofiltration membrane showed an excellent separation factor (S_Li,Mg of 18.26), stability, and water permeability flux (10.6 L·m^-2·h^-1·bar^-1). The rejections to MgCl₂, CaCl₂, MgSO₄, and Na₂SO₄ are measured above 90% at a nearly constant permeability of 10.6 L·m^-2·h^-1·bar^-1, particularly stable rejections to MgCl₂ and Na₂SO₄.

A Comprehensive Membrane Process for Preparing Lithium Carbonate from High Mg/Li Brine

The preparation of Li2CO3 from brine with a high mass ratio of Mg/Li is a worldwide technology problem. Membrane separation is considered as a green and efficient method. In this paper, a comprehensive Li2CO3 preparation process, which involves electrochemical intercalation-deintercalation, nanofiltration, reverse osmosis, evaporation, and precipitation, was constructed. Concretely, the electrochemical intercalation-deintercalation method shows excellent separation performance of lithium and magnesium, and the mass ratio of Mg/Li decreased from the initial 58.5 in the brine to 0.93 in the obtained lithium-containing anolyte. Subsequently, the purification and concentration are performed based on nanofiltration and reverse osmosis technologies, which remove mass magnesium and enrich lithium, respectively. After further evaporation and purification, industrial-grade Li2CO3 can be prepared directly. The direct recovery of lithium from the high Mg/Li brine to the production of Li2CO3 can reach 68.7%, considering that most of the solutions are cycled in the system, the total recovery of lithium will be greater than 85%. In general, this new integrated lithium extraction system provides a new perspective for preparing lithium carbonate from high Mg/Li brine.

Large Area Self-Assembled Ultrathin Polyimine Nanofilms Formed at the Liquid-Liquid Interface Used for Molecular Separation

Separation membranes with higher molecular weight cut-offs are needed to separate ions and small molecules from a mixed feed. The molecular sieving phenomenon can be utilized to separate smaller species with well-defined dimensions from a mixture. Here, the formation of freestanding polyimine nanofilms with thicknesses down to ≈14 nm synthesized via self-assembly of pre-synthesized imine oligomers is reported. Nanofilms are fabricated at the water-xylene interface followed by reversible condensation of polymerization according to the Pieranski theory. Polyimine nanofilm composite membranes are made via transferring the freestanding nanofilm onto ultrafiltration supports. High water permeance of 49.5 L m^-2 h^-1 bar^-1 is achieved with a complete rejection of brilliant blue-R (BBR; molecular weight = 825 g mol^-1 ) and no more than 10% rejection of monovalent and divalent salts. However, for a mixed feed of BBR dye and monovalent salt, the salt rejection is increased to ≈18%. Membranes are also capable of separating small dyes (e.g., methyl orange; MO; molecular weight = 327 g mol^-1 ) from a mixed feed of BBR and MO. Considering a thickness of ≈14 nm and its separation efficiency, the present membrane has significance in separation processes.

Ultrathin Nanofiltration Membrane from Confined Polymerization within the Nanowire Network for High Efficiency Divalent Cation Removal

Membranes with high permeance and high rejection for di- and multivalent cation removal are highly desired for efficient brackish water and industrial water treatment. In this work, we report a facile strategy for constructing ultrathin nanofiltration (NF) membranes by in situ cross-linking of amine which is confined in a network film. The network made of single-walled carbon nanotubes (SWCNTs) serves as a framework for poly(ethylene imine) (PEI) to attach and stay, facilitating the formation of a polyamine (PA) layer with high quality and controlled thickness. Benefiting from the ultrathin thickness of the SWCNT network (∼31 nm), an active layer (∼34 nm thick) comes with a high permeance of 27 L m^-2 h^-1 bar^-1 along with a high rejection of 97% to MgCl₂, 2-5 times higher than the NF membranes with the same high rejection for MgCl₂ reported so far. In addition, the SWCNT-interpenetrated PA structure endows the ultrathin NF membrane with good operational stability. This work demonstrates the capability to control the position, thickness, and even quality of the PA layer by using a confined framework and provides a feasible strategy for the fabrication of highly permeable ultrathin NF membranes with a reinforced active layer.

Efficient removal of heavy metal ions by forward osmosis membrane with a polydopamine modified zeolitic imidazolate framework incorporated selective layer

A novel thin film nanocomposite (TFN) forward osmosis (FO) membrane with a positively charged and nano-functional selective layer has been developed for effective heavy metal ions removal. The selective layer is constructed by penetrating the polydopamine modified zeolitic imidazolate framework (ZIF-8@PDA) in the poly(ethyleneimine)/1,3,5-benzenetricarboxylic acid chloride (PEI/TMC) crosslinked matrix. Compared with the pristine thin film composite (TFC) membrane, the thin film nanocomposite membrane (0.05 wt % nanofillers loading) exhibits a higher water flux (20.8 vs12.8 LMH) without losing of selectivity in terms of J_s/J_w ratio (0.25 vs 0.20 g L^-1) in FO mode. This improvement of the permeability is mainly attributed to the optimized selective layer with good wettability and loose structure. Besides, the modified PDA layer facilitates the affinity between the nanofillers and selective layer, which results in an ideal selectivity. In addition, this modified membrane shows a high heavy metal ion (Cu²⁺, and Ni²⁺ and Pb²⁺) rejection (>96%) in FO mode. Our finding offers a simple and efficient method to enhance the FO performance of membrane by designing the selective layer for treating heavy metal wastewater.

A pH-stable positively charged composite nanofiltration membrane with excellent rejection performance

A novel kind of pH-stable positively charged composite nanofiltration (NF) membrane with excellent rejection performance was developed via interfacial polymerization on the surface of a polysulfone (PSF) ultrafiltration (UF) membrane, using a mixture of polyethyleneimine (PEI) and piperazine (PIP) as the monomers of the aqueous phase, and cyanuric chloride (CC) as the monomer of the organic phase. The strong electron withdrawing and steric hindrance effects of the chloride group in the molecules of CC could protect the amido bond from the attack of hydrogen ions (H⁺) or hydroxyl ions (OH⁻) under acidic or alkaline conditions, thus the resultant polyamide composite membranes could be stable in acidic or alkali aqueous solution. A more compact PA active layer could be developed via mixing PIP into the PEI aqueous solution, where the PIP molecules could fill the pores of the polymer networks. There was no obvious change in the surface morphologies, the chemical structures, and the rejection performances after immersing the resultant polyamine composite NF membranes in the strong acidic solution (pH 1) and the strong alkaline solution (pH 13) for 30 days, respectively. The rejection performances of this kind of polyamine composite NF membranes could be adjusted through adjusting the mass ratio of PEI to PIP in the aqueous phase.

A pH-stable positively charged composite nanofiltration (NF) membrane was developed via the interfacial polymerization (IP) between polyethyleneimine (PEI), piperazine (PIP), and cyanuric chloride (CC).

A novel positively charged composite nanofiltration membrane based on polyethyleneimine with a tunable active layer structure developed via interfacial polymerization

A novel positively charged composite nanofiltration (NF) membrane with tunable active layer structure was successfully developed via interfacial polymerization on a polysulfone (PSF) ultrafiltration (UF) membrane surface, using polyethyleneimine (PEI) as the monomer of the aqueous phase, and a mixture of isophthaloyl dichloride (IPC) and tri-mesoyl chloride (TMC) as the monomer of the organic phase. Interestingly, a synergetic effect of the mass ratio of IPC and TMC was observed on the pore size and the structure of the active layer of the resultant polyamide (PA)/polysulfone (PSF) composite NF membrane. The rejection (R) to the inorganic electrolytes increased with the mass ratio of IPC to TMC, while the permeate flux (F) escalated up to a 1 : 1 mixing ratio of IPC to TMC and dropped at higher mixing ratios. The rejection to different inorganic electrolytes decreased in the order of ZnCl₂, MgCl₂, CaCl₂, CuCl₂, MgSO₄, NaCl, and Na₂SO₄. At ambient temperature and 0.4 MPa, the optimized membrane demonstrated R and F to 1 g L⁻¹ MgCl₂ aqueous solution as 98.1% and 27.6 L m⁻² h⁻¹, respectively. Its rejection to various dyes reduced significantly in the order of cationic red X-GTL (100%), rhodamine B (94.2%), cationic gold yellow X-GL (93.5%), and brilliant blue KN-R (43.9%), in agreement with the decrease in the molecular weight (M_w) and the overall charges of the dye.

The tunable active layer structure was developed via interfacial polymerization, using polyethyleneimine as the monomer of the aqueous phase, and a mixture of isophthaloyl dichloride and tri-mesoyl chloride as the monomer of the organic phase.

Tannic Acid/Fe3+ Nanoscaffold for Interfacial Polymerization: Toward Enhanced Nanofiltration Performance

Conventional thin-film composite (TFC) membranes suffer from the trade-off relationship between permeability and selectivity, known as the "upper bound". In this work, we report a high performance thin-film composite membrane prepared on a tannic acid (TA)-Fe nanoscaffold (TFC_n) to overcome such upper bound. Specifically, a TA-Fe nanoscaffold was first coated onto a polysulfone substrate, followed by performing an interfacial polymerization reaction between trimesoyl chloride (TMC) and piperazine (PIP). The TA-Fe nanoscaffold enhanced the uptake of amine monomers and provided a platform for their controlled release. The smaller surface pore size of the TA-Fe coated substrate further eliminated the intrusion of polyamide into the substrate pores. The resulting membrane TFC_n showed a water permeability of 19.6 ± 0.5 L m^2- h^-1 bar^-1, which was an order of magnitude higher than that of control TFC membrane (2.2 ± 0.3 L m^-2 h^-1 bar^-1). The formation of a more order polyamide rejection layer also significantly enhanced salt rejection (e.g., NaCl, MgCl₂, Na₂SO₄, and MgSO₄) and divalent to monovalent ion selectivity (e.g., NaCl/MgSO₄). Compared to conventional TFC nanofiltration membranes, the novel TFC_n membrane successfully overcame the longstanding permeability and selectivity trade-off. The current work paves a new avenue for fabricating high performance TFC membranes.

Three-channel capillary NF membrane with PAMAM-MWCNT-embedded inner polyamide skin layer for heavy metals removal

Nanofiltration (NF) membranes with simultaneous high rejection of divalent cations and anions and high water permeation were designed and fabricated via interfacial polymerization (IP) on three-channel capillary ultrafiltration (UF) membranes. MWCNTs-COOH were modified with poly(amidoamine) (PAMAM) and the as-synthesized MWCNTs-PAMAM were embedded into the inner polyamide skin-layer of the NF membranes by incorporating them into a piperazine (PIP) aqueous solution, followed by IP with trimesoyl chloride (TMC). The rigid MWCNTs and the dendrimer PAMAM molecules endow the as-fabricated NF membranes with high porosity and good hydrophilicity. Additionally, the -NH2 groups of PAMAM introduce some positive sites into the polyamide layer. The as-prepared NF membranes with incorporated MWCNTs-PAMAM exhibit a pure water flux of 48.7 L m-2 h-1 and 92.6% and 88.5% rejection for Na2SO4 and MgCl2, respectively, at 4 bar. Moreover, the NF membranes display high rejection for sulfates and metal cations, including heavy metal ions. The practicability of the membranes for mine-wastewater treatment was tested, and the membranes showed above 80% rejection of heavy metals and solution flux of about 30 L m-2 h-1. In addition, their separation performance and stability were satisfactory during the long-term run. The high rejection of the membranes for metal cations is ascribed to the positive sites offered by MWCNTs-PAMAM and the narrow membrane pores since both electrostatic repulsion and size exclusion play a role during membrane filtration. The good separation performance of the membranes for multivalent anions and heavy metal cations illustrates their potential for applications in heavy metal wastewater treatment.

Preparation and characterization of a novel nanofiltration membrane with chlorine-tolerant property and good separation performance

High water flux, good separation property and excellent chlorine resistance are crucial factors affecting the development of nanofiltration (NF) membranes. To obtain these properties, NF membranes were fabricated via interfacial polymerization using m-xylylenediamine (m-XDA) and polyethyleneimine (PEI) as aqueous monomers. By controlling the concentration ratio of m-XDA and PEI in the aqueous solution, it was found that the addition of PEI to the aqueous solution can increase the rejection of the NF membrane to magnesium chloride (MgCl₂) and magnesium sulfate (MgSO₄) from 18.3%, 54.5% to 84.4%, 94.1%, respectively. Meanwhile, the rejection to sodium sulphate (Na₂SO₄) and sodium chloride (NaCl) remain essentially unchanged. On the other hand, the addition of m-XDA to the aqueous solution can improve the chlorine resistance of the NF membrane, but it decreased the water flux of NF membrane. Sodium hypochlorite (NaClO) solution was used to evaluate chlorine resistance of NF membranes. After 10 000 ppm h NaClO immersion, the rejections to Na₂SO₄ of NF membranes prepared from the pure m-XDA and the blend of m-XDA and PEI were basically unchanged and the water flux increased. In conclusion, the obtained membranes not only exhibited good separation performance but also had good chlorine resistance.

High water flux, good separation property and excellent chlorine resistance are crucial factors affecting the development of nanofiltration (NF) membranes.

Antifouling sulfonated polyamide nanofiltration hollow fiber membrane prepared with mixed diamine monomers of BDSA and PIP

A novel high-flux sulfonated polyamide nanofiltration (NF) hollow fiber membrane was made from the mixed monomers of 2,2′-benzidinedisulfonic acid (BDSA) and piperazine (PIP).

Tailoring polyamide thin film composite nanofiltration membranes by polyethyleneimine and its conjugates for the enhancement of selectivity and antifouling property

Post modification of poly(piperazineamide) membrane with polyethyleneimine conjugates provides membranes with novel properties such as high monovalent to divalent ion selectivity and improved antifouling properties, suitable for water purification.