Polyamide Chains Research Articles

Construction of low-resistance nano-transport channels with UiO-66-(NH2)2 “transmembrane” in polyamide layer structure for efficient nanofiltration

Metal-organic frameworks (MOFs) is always a research hotspot as the modifier for fabrication of thin-film nanocomposite (TFN) membrane due to their excellent chemical tunability and suitable pore size. However, the traditional strategy for the involvement of MOFs into interfacial polymerization (IP) process has its limitations, as the addition of MOFs only serve to modulate the structure of the polyamide (PA) layer and to optimize the transport path of water molecules, rather than play an important role in selectively sieving solutes. To solve the problem that MOF embedded under the PA layer cannot directly participate in solute sieving, this study designed a “transmembrane” structure of MOF in the PA layer. Here, the feasibility of 1,3,5-Benzenetricarbonyl chloride modified UiO-66-(NH2)2 was verified based on Gibbs free energy calculations. By adding chlorinated UiO-66-(NH2)2 nanomaterials in the dual IP process, a high-throughput nanofiltration membrane was innovatively constructed. In contrast to conventional thin-film composite membrane prepared by only one IP process, the sieving mechanism no longer relied solely on the free volume of the PA chain segments. Instead, it was determined by the combination of the pore channels of UiO-66-(NH2)2 and the matrix gaps. Based on density functional theory (DFT), the calculated diffusion energy barriers of H2O and Na2SO4 in UiO-66-(NH2)2 and PA matrices reveal the reasons for the improvement of water flux and changes in retention rate of TFN membranes. In addition, the gap size between PA-MOFs was determined by comparing the solvation and de-solvation structures of dye molecules. This work provides a new theoretical basis for explaining the changes in the separation performance of TFN membranes, and offers new ideas for the development of novel TFN membrane structures.

A Theoretical Investigation into the Oligomer Structure of Carbon Dots Formed from Small-Molecule Precursors.

In-depth insights into the oligomers of carbon dots (CDs) prepared from small-molecule precursors are important in the study of the carbonization mechanism of CDs and for our knowledge of their complex structure. Herein, citric acid (CA) and ethylenediamine (EDA) were used as small-molecule precursors to prepare CDs in an aqueous solution. The structure of oligomers acquired from CA and EDA in different molar ratios and their formation process were first studied using density functional theory, including the dispersion correction (DFT-D3) method. The results showed that the energy barrier of dimer cyclization was higher than that of its linear polymerization, but the free energy of the cyclized product was much lower than that of its reactant, and IPCA (5-oxo-1,-2,3,5-tetrahydroimidazo [1,2-a]pyridine-7-carboxylic acid) could therefore be obtained under certain conditions. The oligomers obtained from different molar ratios of EDA and CA were molecular clusters formed by short polyamide chains through intermolecular forces; with the exception of when the molar ratio of EDA to CA was 0.5, excessive CA did not undergo an amidation reaction but rather attained molecular clusters directly through intermolecular forces. These oligomers exhibited significant differences in their surface functional groups, which would affect the carbonization process and the surface structure of CDs.

Functionalization of zinc ferrites nanoparticles by cyclic aromatic polyimide chains as a novel star polymer with antibacterial activity and low toxicity

The creation and development of biocompatible nanostructures pose significant challenges for biomedical purposes. This study presents a novel magnetic star polymer structure composed of cyclic polyimide chains as grown arms and a central ZnFe2O4 core with low toxicity and antibacterial activity for use in biological applications such as Targeted drug delivery, hyperthermia therapy and wound healing. To preparate this structure, the surface of MNPs was activated with anchor molecules, and then cyclic aromatic polyamide chains were polymerized using pyromellitic dianhydride and phenylenediamine derivatives on the surface-functionalized ZnFe2O4 MNPs. The cytotoxicity of this nanocomposite was evaluated using MTT tests on MCF10A cells, showing low cytotoxicity against healthy cells. Additionally, the MIC/MBC tests of the prepared star polymer were assessed against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and showed that this has antibacterial effect against these bacterial strains. From the results, it can be concluded that the prepared nanocomposite can be introduced as a new biological structure for biomedical applications.

Constructing hydrophobic microenvironment in the separation layer by a small molecule for improving reverse osmosis membrane performance

The development of reverse osmosis (RO) membranes with both high permeability and selectivity is a key goal for RO technology, the leading water treatment technology. This work presents a simple and cost-effective method for improving RO membrane performance obviously via introducing a hydrophobic small molecule, benzoic acid (BA), in the polyamide (PA) separation layer. The introduction of BA is achieved by adding it in the oil phase of the interfacial polymerization technology because of its oil solubility, which is pretty simple. The hydrophobicity and self-assembly characteristic of BA could establish hydrophobic microenvironments within the PA separation layer. The hydrophobicity of this microenvironment can reduce the number of hydrogen bonds between water molecules, accelerating the rapid transport of water and thereby enhancing membrane performance. Concurrently, BA as a small molecule could moderately increase the space between PA chains and thus enlarge the free volume of hydrophobic microenvironment region, which is also in favour of the improvement of membrane flux. The as-developed RO membrane possessed both high rejection rate (with a NaCl rejection rate of 98.9 %) and high flux (91.7 L m−2 h−1) under the brackish water testing condition, surpassing the performance of many previously reported membranes, and noticeably, a flux increase of 113 % was achieved by utilizing BA. Besides, the performance showed a good long-term stability. It is worth mentioning that small molecules are generally purchasable and cheap, which is beneficial to the large-scale production. This work showcased the great potential of hydrophobic small molecules in improving PA water treatment membrane performance, paving the way for diverse small molecules to develop PA water treatment membrane with both high permeability and selectivity.

Adjustable free volume of polyamide membrane medicated by confined organic alkane molecules for efficient hydrogen separation

Rational design of polyamide cross-linked network is of vital significance for fabricating advanced separation membranes. Herein, polyamide membranes with tunable free volume cavity are constructed utilizing an in-situ confinement strategy during interfacial polymerization process, where organic alkane molecules with different alkyl chain such as n-octane, n-dodecane, and n-hexadecane are confined in stiff polyamide skeleton and entangled with nearby polyamide chains. The efficient confinement of organic alkane molecules is confirmed by thermogravimetric coupled with mass spectrometry analysis, and corresponding variations in chain architecture of polyamide network are verified by X-ray diffraction and positron annihilation lifetime spectroscopy techniques. Upon thermal stimulation, the inherent flexibility of confined organic alkane molecules along with stiffness of polyamide skeleton, allow enlargement of chain d-spacing and dynamic regulation of membrane microstructure for fascinating H2 permeation separation. The optimized modified membrane exhibits a H2 permeance of 116.1 GPU and a H2/CH4 selectivity of 70.8, which can be stably operated at 100 °C for over 400 h. This study provides a deep understanding of polyamide membranes with confinement of organic molecules and thermally induced separation performances, advancing the design of novel membranes with promising H2 separation performances at elevated temperatures.

Thermodynamic characteristics of the aliphatic polyamide crystal structures: Enhancement of nylon 66α, 610α and 77γ polymers

Despite the polymer industry's reliance on nylon polymers, numerous questions remain about their crystal structures, modeling, and other features. This work discusses the thermodynamic properties and molecular modeling of a polyamides nylon 66α, 610α, and 77γ crystal structure systems for use in various electronics and Nano-devices that feature distinct properties such as exceptional optoelectronic properties at a low cost compared to other structures. This study looked at the crystal structure of a linear polyamide chain made up of repeating units. The influence of the thermal expansion coefficient and thermodynamic parameters on crystal structures' characteristics at different temperatures has previously been explored. The findings of this study demonstrate, on the one hand, the influence of the amorphous phase on the final thermodynamic characteristics of semi-crystalline polymers and, on the other hand, pave the way for greater improvement in the durability of these polymers by increasing their crystalline features. The values of the thermodynamic parameters for nylon 66α, 610α and 77γ such as enthalpy (ΔHExp.) were 35.08, 40.25, and 1.44 kJ/mol, entropy (ΔSExp.) 113.75, 128.84, and 15.10 J/mol-K, free energy (ΔGExp.) was −44.57, −46.62, and −6.86 kJ/mol, respectively. When the nylon data is compared, the nylon 610α exhibits a significantly higher free energy, at high temperatures, the process is spontaneous and exergonic, making it a potentially viable material for use as fibers and engineering thermoplastics.

Tuning composite nanofiltration membranes with γ-cyclodextrin for improved Mg2+/Li+ selectivity

As a new frontier method, nanofiltration (NF) membranes still face challenges in achieving a balance between selectivity and permeability, especially in the field of extracting lithium from brines. In the study, we addressed this issue by incorporating γ-cyclodextrins (CDs) with amphipathic cavities onto the polyamide chains using interfacial polymerization (IP) reaction, employing polyethyleneimine (PEI) and trimesoyl chloride (TMC). The addition of γ-cyclodextrin (γ-CD) enhances the hydrophilicity and water flux of NF membrane on account of its remarkable structural properties. The outer surface of γ-CD exhibits hydrophilic characteristics, while its inner cavity possesses hydrophobic properties. Benefiting from its water-attracting surface and water-repellent cavity, γ-CD could enhance the overall water affinity and water permeability of the NF membrane. Furthermore, the dimensions of the γ-CD cavity allowed for effective screening Mg2+ / Li+ to a certain extent. Notably, γ-CD exhibited a superior capability to accommodate and encapsulate Mg2+ ions, indicating a higher binding affinity compared to Li+. Thus, Li+ was easier to pass through the NF membrane grafted by γ-CDs than Mg2+. The optimized NF membrane demonstrated an enhanced magnesium-lithium separation coefficient of 23.61, 237 % better than that of the TFC-control membrane. This work introduces a novel approach for designing and constructing of high-permselectivity NF membranes for Mg2+ / Li+ separation utilization.

Ultralow Coefficient of Thermal Expansion and a High Colorless Transparent Polyimide Film Realized Through a Reinforced Hydrogen-Bond Network by In Situ Polymerization of Aromatic Polyamide in Colorless Polyimide.

Colorless polyimides (CPIs) are a key substrate material for flexible organic light-emitting diode (OLED) displays and have attracted worldwide attention. Here, in this paper, the dispersion and interfacial interaction of aromatic polyamide (PA) in CPI (synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB)) were significantly improved by in situ polymerization, and colorless transparent macromolecular polyimide composites (CPI-PAx) were successfully prepared by PA and CPI. By adjusting the ratio of PA to CPI, a high-performance engineering plastic with excellent film-forming properties was obtained. Molecular simulations confirmed the uniform distribution of PA in CPI and its interaction in polymers. In CPI-PAx, the CPI was locked by the PA chain, and numerous molecular chains were mutually entangled to form a hydrogen-bond network structure. Due to the strong interaction between the chains imparted by the hydrogen bonds of the PA, they do not slide under external forces and heating. In addition, the additive PA has excellent dimensional stability, thermal, and mechanical properties, and CPI has outstanding optical properties, so the synthesized CPI-PAx combines the comprehensive properties of PA and CPI. The CPI-PAx has excellent thermal and mechanical properties, with a thermal decomposition temperature of 499 °C, a glass transition temperature of 385 °C, a coefficient of thermal expansion of 0.8 ppm K-1, a tensile strength of 50.9 MPa, and an elastic modulus of 3.9 GPa. Particularly, CPI-PAx has a 90% transmittance in the visible region. These data prove that the strategy of combining PA and CPI by in situ polymerization is an effective method to circumvent the bottleneck of CPI in the current flexible window application, and this design strategy is universal.

Physicochemical Characterization of Chitosan/Poly-γ-Glutamic Acid Glass-like Materials.

This paper sets up a new route for producing non-covalently crosslinked bio-composites by blending poly-γ-glutamic acid (γ-PGA) of microbial origin and chitosan (CH) through poly-electrolyte complexation under specific experimental conditions. CH and two different molecular weight γ-PGA fractions have been blended at different mass ratios (1/9, 2/8 and 3/7) under acidic pH. The developed materials seemed to behave like moldable hydrogels with a soft rubbery consistency. However, after dehydration, they became exceedingly hard, glass-like materials completely insoluble in water and organic solvents. The native biopolymers and their blends underwent comprehensive structural, physicochemical, and thermal analyses. The study confirmed strong physical interactions between polysaccharide and polyamide chains, facilitated by electrostatic attraction and hydrogen bonding. The materials exhibited both crystalline and amorphous structures and demonstrated good thermal stability and degradability. Described as thermoplastic and saloplastic, these bio-composites offer vast opportunities in the realm of polyelectrolyte complexes (PECs). This unique combination of properties allowed the bio-composites to function as glass-like materials, making them highly versatile for potential applications in various fields. They hold potential for use in regenerative medicine, biomedical devices, food packaging, and 3D printing. Their environmentally friendly properties make them attractive candidates for sustainable material development in various industries.

Effects of MOFs size and functional group on the pore structure and performance of thin-film nanocomposite membranes

Incorporation of nanomaterials into the selective layer during the interfacial polymerization process was an effective way to improve the perm-selectivity of the membranes. In this study, the piperazine enriched templates assisted interfacial polymerization method was proposed to enhance the salts rejection of thin-film nanocomposite (TFN) membranes. The mono-dispersed UiO-66 type MOFs with high amine adsorption ability were utilized as templates to increase the reaction region and promote the participation of piperazine (PIP) during the interfacial polymerization reaction, resulting in a denser polyamide (PA) layer with weaker surface electronegativity and higher nitrogen-containing group contents. The TFN membranes prepared with 236 nm UiO-66-OH and PIP concentration of 0.35 w/v% exhibited smaller mean pore size (0.636 nm) and reduced surface zeta potential (−26.0 mV) compared to the pristine TFC membranes (0.667 nm and −31.1 mV). Consequently, the rejection of 10 mM MgCl2, MgSO4 and Na2SO4 was increased from 44.7%, 97.7% and 98.3% to 84.3%, 99.2% and 99.5%, respectively, while the pure water flux was slightly decreased from 53.5 L m−1 h−1 to 37.4 L m−1 h−1 at 0.3 MPa. In addition, the size and functional group of the MOFs were found to have significant impacts on the pore structure and performance of the TFN membranes. The increasing of reaction region with relatively large MOFs and higher absorption ability were beneficial to obtain a thicker PA layer, while strong interaction between MOFs and PA oligomers was unfavorable for PA chain packing. Therefore, the TFN membranes prepared with UiO-66-NO2 exhibited a much narrow size distribution and high rejection to all salts, whether by divalent cationic salt or divalent anion salts, i.e., MgCl2 of 95.5%, MgSO4 of 98.9% and Na2SO4 of 99.1%, and the pure water flux was 28.6 L m−1 h−1 at 0.3 MPa. These results illustrated the influences of MOFs size and functional group on the interfacial polymerization process, which was crucial for the TFN membranes preparation.

Synthesis and Properties of Polyamide 6 Random Copolymers Containing an Aromatic Imide Structure.

In order to adjust the properties of polyamide 6 (PA6) and expand its application, a new strategy of introducing an aromatic imide structure into the PA6 chain through the random copolymerization method is reported. The diimide diacid monomer was first synthesized by the dehydration and cyclization of pyromellitic dianhydride and 6-aminocaproic acid before it reacted with 1,6-hexamethylene diamine to form poly(amide imide) (PAI) salt, and finally synthesized PA6/PAI random copolymers containing an aromatic imide structure by the random copolymerization of ε-caprolactam and PAI salt. The introduction of an aromatic imide structural unit into the PA6 chain could have a great influence on its properties. As the content of PAI increases, the crystallinity (Xc) and melting temperature (Tm) of the PA6/PAI random copolymer gradually decrease, but its glass transition temperature (Tg) increases obviously. When the PAI content is 20 wt%, the copolymer PA6/PAI-20 has the best comprehensive performance and not only has high thermal stabilities but also excellent mechanical properties (high strength, high modulus, and good toughness) and dielectric properties (low dielectric constant and dielectric loss). Moreover, these properties are significantly superior to those of PA6. Such high-performance PA6 random copolymers can provide great promise for the wider applications of PA6 materials.

Coupling coloration of meta‐aramid fabric utilising diazonium salts from weakly basic aromatic amines

AbstractMeta‐aramid fibre exhibits poor dyeing performance when treated using conventional dyeing methods. In this study, coloration of meta‐aramid fabrics was performed at room temperature utilising diazonium salts from weakly basic aromatic amines and was achieved via in situ construction of azo chromophores on the meta‐phenylenediamine moiety. To promote diazonium‐salt penetration into the meta‐aramid fibre, the pretreatment of meta‐aramid fabrics with dimethyl sulfoxide at 55°C for 30 min and the utilisation of methanol were involved during the coloration process. As a result, the fabrics could be coloured with deep, levelled and firm shades of brown series. The azo chromophore is derived from the skeleton of the polyamide chain. Therefore, the coloured fabrics exhibit good resistance to organic solvents as well as good to excellent colour fastness to soaping, rubbing and sublimation. A study of the coloration mechanism revealed that the terminal and middle meta‐phenylenediamine moieties serve as the main coupling reaction sites. When treated with a diazonium salt, the highly reactive terminal meta‐phenylenediamine moiety reacted first and generated chromophores with an absorption peak in the long‐wavelength region. However, such chromophores only contributed a limited colour depth owing to the limited number of the terminals. If excess diazonium salts were used, the main hue can be attributed to the azo chromophores based on the massive middle meta‐phenylenediamine moieties, although these moieties are less reactive than the terminal meta‐phenylenediamine moieties.

In-situ compatibilization of polyamide 6/polycarbonate blends through interfacial localization of silica nanoparticles

Nanoparticles are used to compatibilize immiscible polymer blends. The key to success is to localize nanoparticles at polymer-polymer interfaces. This work aims to use silica nanoparticles (SiO2) to compatibilize polyamide 6 (PA6)/polycarbonate (PC) blends. The strategy to ensure the interfacial localization of the SiO2 in the blends is to graft a methacrylic monomer onto the SiO2 and then copolymerize this methacrylic monomer with styrene (St) and 3-isopropenyl-α,α′-dimethylbenzyl isocyanate (TMI). When PA6 and PC are blended in the melt in the presence of the above surface modified SiO2 (denoted as SiO2-PST), PA6 chains are grafted onto the SiO2-PST to form PA6-SiO2-PST through a coupling reaction between the terminal amine group of the PA6 and the isocyanate moieties of the PST grafts which are partially miscible with the PC. It is shown that an optimum TMI content allows for the SiO2-PST to be preferentially localized at the interfaces between the PA6 and PC. This leads to a significant decrease in the PC domain diameter from 1.6 μm to 0.6 μm without and with the SiO2-PST, respectively. The presence of the SiO2-PST (0.5 wt% with an optimum TMI content) increases the tensile strength of the PA6/PC (70/30 by weight) from 64.1 to 79.6 MPa, the elongation at break from 84.7 to 284.7%, and the notched Charpy impact strength from 10.3 to 29.4 kJ/m2.

Improving Mg2+/Li+ separation performance of polyamide nanofiltration membrane by swelling-embedding-shrinking strategy

Extraction of lithium from salt lakes is an important route for lithium sources. Due to the unique structure and separation mechanism, i.e., size exclusion and Donnan effect, nanofiltration (NF) is considered as a promising way to separate magnesium (Mg2+) and lithium (Li+) ions. However, the Mg2+/Li+ separation factor of NF membrane fabricated by traditional interfacial polymerization (IP) is usually dissatisfactory. Here, a swelling-embedding-shrinking strategy was proposed to modify polyethyleneimine (PEI)/trimesoyl chloride (TMC) NF membranes using diethylenetriamine (DETA) to improve the performance in Mg2+/Li+ separation. The pristine PEI/TMC NF membrane was swollen with methanol to increase the polyamide chain spacing followed by embedding electropositive DETA as a modifier. The charge properties and pore structure of the active layer could be regulated by optimizing the modification conditions. Within comparison to the pristine membrane (TFC-0), the pure water flux of modified NF membrane (TFC-3) increased by 63.6% because of the rougher surface and the larger pore size. Meanwhile, the embedding of electropositive DETA reduced the electronegative property of membrane surface. In consequence, TFC-3 membrane exhibited higher rejection of MgCl2 (93.9% against 88.4%) and lower rejection of LiCl (31.0% against 32.1%), thus showing a twofold improvement in Mg2+/Li+ separation factor (SLi, Mg = 11.38 against 5.87). The swelling-embedding-shrinking strategy in this article provided a good reference for the modification of NF membranes in the separation of multivalent and monovalent ions.

Polyamide nanofiltration membranes with rigid–flexible microstructures for high-efficiency Mg2+/Li+ separation

Lithium extraction from salt-lake brine with a high Mg2+/Li+ ratio is crucial for mitigating lithium supply shortage. Positively charged polyamide nanofiltration membranes, which are often prepared by performing interfacial polymerization (IP) using polyethyleneimine and trimesoyl chloride, are considered to be promising candidates for Mg2+/Li+ separation owing to their high energy efficiency and low environmental impact. However, the performance of these membranes is severely hindered by “useless pores” and “defects” present in the flexible polyamide layer. Herein, we provide a facile strategy for modifying flexible semi-aromatic polyamide chains by intercalating a rigid electropositive monomer, histamine, to remold the internal pores and positive charge density at a molecular level. Two routes, namely, “swelling-embedding-reacting-shrinking (SERS)” and “in-situ interposition (SIP)” were used to construct a new polyamide layer with rigid–flexible microstructures. The fabricated SERS-0.50 membrane showed a 5-fold higher water flux and 2-fold increase in the Mg2+/Li+ separation factor compared with the IP membrane. Moreover, the SIP-0.15 membrane with an enhanced positive charge density exhibited a considerably higher Mg2+/Li+ separation factor (15.38, 500 % increase compared with that of the IP membrane) for brine with a Mg2+/Li+ ratio of 20. This study provides a reference for developing nanofiltration membranes used for high-efficiency Mg2+/Li+ separation.

Polyoxometalate-modified halloysite nanotubes-based thin-film nanocomposite membrane for efficient organic solvent nanofiltration

Polyoxometalate-modified halloysite nanotubes (POM@MHNTs) were synthesized and doped into the polyamide (PA) matrix by interfacial polymerization to prepare doped POM@MHNTs thin-film nanocomposite (TFN) membranes for organic solvent nanofiltration (OSN). Likewise, thin-film composite (TFC) and TFN membranes doped with HNTs were fabricated. It is worth noting that the methanol flux of the TFN can be efficiently enhanced by tuning the contents of POM@MHNTs. The as-synthesized optimal sample (TFN-0.10) exhibits superior methanol flux of TFN-0.10 membrane of 14.80 L m−2 h−1 bar−1 (1.76 times of that of undoped TFC membrane and 1.12 times of that of doped HNTs membrane (TFN-HNTs-0.10). These are mainly due to the tubular structure of POM@MHNTs providing additional solvent transfer channels and the ridge-valley morphology of the membrane surface increasing the contact area between the membrane and the solvent. Meanwhile, the POM@MHNTs nanohybrids are similarly electrostatically attracted by the amide groups on the polyamide chains produced by interfacial polymerization, improving the compatibility of POM@MHNTs with polyamide membranes. TFN-0.10 OSN membrane showed stable chemical properties in medium polar organic (methanol, ethanol, THF), acid polar organic (acetonitrile), and strong polar organic (DMF) solvents. Prepared TFN OSN membranes exhibited strong long-term operation capability and organic solvent resistance after 80 °C DMF immersion for 7 days with inconspicuous separation performance changes. This work offers the prospect of using organic-inorganic hybrid modified nanomaterials to improve OSN performance.

Facile fabrication of hydroxyl-rich polyamide TFC RO membranes for enhanced boron removal performance

The insufficient boron removal performance is a conspicuous infirmity of reverse osmosis (RO) membranes for seawater desalination. Herein, RO membranes with high boron removal performance were prepared by adding 2-hydroxyethyl acrylate (HEA) and acrylamide (AA) into the m-phenylenediamine (MPD) solution and employing ultraviolet (UV) irradiation during the interfacial polymerization (IP) process. During the UV-imported IP process, the radical polymerization between HEA and AA was triggered to produce hydroxyl-containing HEA-co-AA copolymers, while polyamide polymers were simultaneously generated. Attributed to the interspersion of hydroxyl-containing copolymers in the polyamide chain segments, the superior dense and tight structure of the hybrid separation layer was achieved. Crucially, the high electron density hydroxyl groups enriched in the hybrid separation layer could specifically interact with the electron-deficient boric acid via electrostatic interaction and hydrogen bond. Therefore, in the modified membrane, the diffusion of boric acid was inhibited. Consequently, for the modified membrane, the boric acid retention rate was dramatically increased from 84.42% to 92.80%. Additionally, NaCl retention rate and water flux were also promoted. The UV-imported IP process was neither process-intensive nor time-consuming, exhibiting high compatibility with the continuous membrane production. It was expected that this work would guide the innovation of high boron removal RO membranes and other types of IP-made membranes.

Polyamide@GO microporous membrane with enhanced permeability for the molecular sieving of nitrogen over VOC

Mixed matrix membranes (MMMs) are typically fabricated by mechanically mixing presynthesized polymers and fillers together in a solvent to form a membrane solution, which often causes poor filler dispersion in the polymer matrix. In this work, an in situ polymerization method was proposed by which 2,6,14-triaminotriptycene (Trip), octanedioyl chloride, and graphene oxide (GO) reacted in the polymerization to form a polyamide@GO mixed matrix polymer. Different characterization methods, such as Raman analysis, XRD (X-ray diffraction), and TGA (thermogravimetric analysis), were used to verify the chemical linking between GO and polyamide. The performance of the polyamide@GO membrane in the separation of cyclohexane/nitrogen mixtures was evaluated and compared with that of pure polyamide membranes and mechanically mixed polyamide + GO membranes. The polyamide@GO membrane with a GO content of 0.3 wt% exhibited the highest separation performance. The permeability increased from 427 Barrer to 1098 Barrer under the same rejection (99.4%) conditions compared with that of the pure polyamide membrane. Because incorporation of GO disrupted the efficient stacking of polyamide chains, more amorphous domains were formed, providing more transport channels. This work provides an alternative way to overcome the trade-off phenomenon in the synthesis of new MMMs.

Treatment of reverse osmosis membrane by sodium hypochlorite and alcohols for enhanced performance using the swelling-fastening effect

Chemicals soaking is generally acknowledged as a convenient and efficient method to improve the performance of reverse osmosis (RO) membranes. The conventional soaking of RO membranes in alkaline sodium hypochlorite (NaClO) usually promotes extensive hydrolysis and cleavage amide bonds, resulting in improved water flux but declined salt rejection. Here, alcohols were added into the NaClO solution to regulate the chlorination processes using their “swelling-fastening” effect. The alcohols could interact with polyamide chains, and thus swell the polyamide network. Due to this interaction, the NaClO has less probability of attacking the polyamide chains. Hence, the chlorine-promoted hydrolysis was partly eased, which could weaken the decrease of salt rejection. Besides, after removing alcohols as well as the dissolved small oligomers and fragments of polyamide, the network was compacted and the loosened sites were healed, which is also beneficial to increase the difficulty of salt penetration. The treatment of RO membrane by the NaClO and alcohols could produce a hydrophilic surface with increased water flux and high salt rejection. The membrane chloridized at 2000 ppm NaClO exhibited a water flux improvement of 20.28% and a salt rejection declination of 0.95%. When treated with 2000 ppm NaClO associated with 5% methanol, the water flux improved 20.13% with little declination in salt rejection.

How alginate monomers contribute to organic fouling on polyamide membrane surfaces?

Organic fouling of polyamide membrane surfaces with alginate molecules in an aqueous solution is studied through computer molecular simulations. Here, we focus on the molecular binding properties of β-d-mannuronic acid (M) and α-l-guluronic acid (G) alginate monomers on a polyamide membrane surface. Free energy calculations show that M alginate monomers exhibit significant hydrophobic attractions with certain types of benzene ring units in a polyamide chain, though such hydrophobic interactions are not as strong as the ionic bridge binding between the M monomer and the carboxylate group on a polyamide membrane surface. This is in contrast to the fouling behavior of G alginate monomers to which such hydrophobic interactions with a membrane surface do not exist, and the organic fouling is largely attributed to the ionic bridge binding between the G monomer and polyamide carboxylate groups mediated by divalent metal ions. Molecular dynamics simulations of different alginate oligomers near a polyamide surface show that hydrophobic interactions between the M-containing oligomers and polyamide membrane surface result in a much shorter pathway of fouling than that of pure G-oligomers. These hydrophobic interactions, together with the mobility of M monomers on a polyamide chain surface, further reduce the docking time of M-containing oligomers compared to pure G-oligomers, and thus enhance the surface fouling.