Performance Of Thin Film Nanocomposite Membranes Research Articles

Boosted performance of thin-film nanocomposite membranes based on phytic acid functionalized Zr-MOF for nanofiltration

Endowed with designable pore structure and intrinsically interconnected channels, metal-organic frameworks (MOFs) offer immense potential as functional nanofillers to boost the performance of nanocomposite membranes. However, achieving optimal pore size matching between MOFs and the polymer matrix while maintaining robust interfacial affinity remains a significant challenge in fabricating high-performance nanocomposite membranes. Herein, natural organic polyphosphate phytic acid was utilized to functionalize PCN-224 to narrow its pore size and enhance the polymer affinity. Thin-film nanocomposites containing mPCN-224 were afterward synthesized on the polysulfone support through a combined approach of anodic electrophoretic deposition (EPD) and vacuum filtration-assisted interfacial polymerization (VF-IP). The incorporation of mPCN-224 nanoparticles not only enhanced the hydrophilicity and electronegativity of the polyamide film but also led to a substantial reduction in film thickness. This is likely attributed to lessened piperazine supply at the interface, related to its limited diffusion at the presence of negatively charged mPCN-224. The additional nanochannels provided by mPCN-224, coupled with the loose PA layer, resulted in a substantial 56.3 % increase in the water permeance of the TFN-mPCN-224 membrane, reaching 20.0 L m−2 h−1 bar−1. Additionally, the post-synthesis modification with phytic acid led to an improved Cl−/SO42− selectivity coefficient of 44, substantially higher than that of the TFN-PCN-224 membrane. This improvement was primarily attributed to the narrowed pore size of mPCN-224 and the enhanced surface electronegativity. This study introduces a pathway for developing high-performance TFN membranes based on post-synthetic modification of MOF nanofillers with phytic acid molecules.

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.

Effect of Positively Charged Lipids (DOTAP) on the Insertion of Carbon Nanotubes into Liposomes and the Separation Performance of Thin-Film Nanocomposite Membranes

A liposome vesicle is an ideal carrier for carbon nanotubes (CNTs) serving as the water channel that allows for the fast transport of water molecules, thus enhancing membrane permeability. However, a low quantity of CNTs inserted into the liposome vesicle is an important factor that limits the further improvement of the membrane flux. In the present study, a positively charged lipid, (2,3-dioleoyloxy-propyl)-trimethylammonium-chloride (DOTAP), was introduced to 1,2-dioleoyl-sn-glycero-3-phosphoethanolamineon (DOPE) liposome vesicles to tailor the vesicle charge so as to evaluate the effect of positively charged DOTAP on the insertion of CNTs into liposomes and the separation performance of thin-film nanocomposite (TFN) membranes. The results show that the addition of DOTAP increased the quantity of CNTs inserted into the liposome vesicles, as the shrinkage rate (k) and permeability (Pf) of the liposome vesicles presented an obvious increase with the increased content of DOTAP in the liposome vesicles. Moreover, it contributed to a 252.3% higher water flux for TFN membranes containing DOPE/DOTAP2:1-CNT liposomes (the mass ratio between DOPE and DOTAP was 2:1) than thin-film composite (TFC) membranes. More importantly, it presented a 106.7% higher water flux for TFN membranes containing DOPE/DOTAP4:1-CNT liposomes (the mass ratio between DOPE and DOTAP was 4:1), which originated from the greater number of water channels that the CNTs provided in the liposome vesicles. Overall, positively charged DOTAP effectively tailored the vesicle charge, which provided a better carrier for the insertion of a greater quantity of CNTs and contributed to the higher permeability of the TFN membranes.

Thin Film Nanocomposite Membranes Based on Zeolitic Imidazolate Framework-8/Halloysite Nanotube Composites.

Thin film nanocomposite (TFN) membranes have proven their unrivaled value, as they can combine the advantages of different materials and furnish membranes with improved selectivity and permeability. The development of TFN membranes has been severely limited by the poor dispersion of the nanoparticles and the weak adhesion between the nanoparticles and the polymer matrix. In this study, to address the poor dispersion of nanoparticles in TFN membranes, we proposed a new combination of m-ZIF-8 and m-HNTs, wherein the ZIF-8 and HNTs were modified with poly (sodium p-styrenesulfonate) to enhance their dispersion in water. Furthermore, the hydropathic properties of the membranes can be well controlled by adjusting the content of m-ZIF-8 and m-HNTs. A series of modified m-ZIF-8/m-HNT/PAN membranes were prepared to modulate the dye/salt separation performance of TFN membranes. The experimental results showed that our m-ZIF-8/m-HNT/PAN membranes can elevate the water flux significantly up to 42.6 L m-2 h-1 MPa-1, together with a high rejection of Reactive Red 49 (more than 80%). In particular, the optimized NFM-7.5 membrane that contained 7.5 mg of HNTs and 2.5 mg of ZIF-8 showed a 97.1% rejection of Reactive Red 49 and 21.3% retention of NaCl.

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.

Mechanistic insights into the role of nanoparticles towards the enhanced performance of thin-film nanocomposite membranes

Thin-film nanocomposite (TFN) membranes are promising in improving water treatment due to their high permeability and selectivity. However, little is known about the mechanism by which nanoparticles enhance their performance. In this study, we prepared two series of TFN membranes containing ∼40 nm-sized zeolitic imidazolate framework (ZIF-8) nanoparticles, one with a hydrophobic porous form and the other with a nonporous amorphous form (aZIF-8). The TFN membranes containing 0.15 w/v% ZIF-8 exhibited a 100% increase in water permeance while maintaining a similar NaCl rejection (98.38%) compared to thin-film composite (TFC) membranes used in brackish water reverse osmosis (BWRO). In contrast, adding the same amount of aZIF-8 resulted in almost no water permeance enhancement. By comparing the physicochemical properties of the two materials and the two series of membranes, we found that the only difference was the presence or absence of internal hydrophobic pore structures. We proposed that the hydrophobic internal pores of nanoparticles served as extra water channels while preventing the passage of NaCl during BWRO.

Flower-like MnO2 nanoparticles modified thin film nanocomposite membranes for efficient organic solvent nanofiltration

Novel thin film nanocomposite (TFN) membranes comprised of polyimide (PI) supporting layer and polyamide (PA) skin layer were prepared for efficient organic solvent nanofiltration (OSN) by doping flower-like MnO2 nanomaterials in PA skin layer through interfacial polymerization (IP). The OSN performance of TFN membranes doped with flower-like MnO2 nanomaterials was significantly improved compared to pristine thin film composite (TFC) and spherical MnO2 nanoparticle-doped (TFN-S) membranes. The synthesized optimal sample (TFN-0.50 membrane) exhibits the optimum methanol permeability of 11.88 L m−2 h−1 bar−1 (1.54 times more than the TFC membrane and 1.20 times more than the TFN-S membrane). This excellent OSN performance is due to the large spatial site resistance effect present in the flower-like MnO2 nanoparticles themselves which make the diffusion rate of MPD monomer from the aqueous phase to the oil phase unstable, resulting in unstable interfacial polymerization reactions. The unstable interfacial polymerization confers a ridge-valley surface morphology that allows the TFN membrane to have an increased contact area with the solvent. Meanwhile, the special flower-like structure of MnO2 nanomaterials provides additional transport channels for solvent transport. In addition, the prepared TFN-0.50 membrane has good long-term operability and organic solvent nanofiltration even after immersion in strongly polar DMF solvent at 80 °C for 5 days.

Enhanced performance of thin-film nanocomposite membranes achieved by hierarchical zeolites for nanofiltration

Nanosized zeolite molecular sieves are increasingly explored for developing high-performance nanocomposite membranes, mainly because of their ordered pore structures and remarkable thermal stability. In this study, hierarchical nanosized aluminophosphate molecular sieves [AlPO-5 (AFI)] were synthesized as functional fillers to construct thin-film nanocomposite (TFN) membranes. Nanosized AlPO-5 was effectively positioned onto porous polysulfone supports via a filtration-assisted method, followed by in situ interfacial polymerization to construct a polyamide layer atop the modified supports. The synthesized nanosized AlPO-5 crystals have both intrinsic micropores and abundant intracrystalline mesopores. SEM and AFM analyses reveal that the introduction of AlPO-5 not only enhanced the surface roughness of TFN membranes with valley-shaped surface but also substantially decreased the thickness of a polyamide layer compared to nodular-shaped TFC membranes. These differences are mainly ascribed to retarded piperazine diffusion and positioned AlPO-5 nanoaggregates. The role of AlPO-5 loading in overall separation performance of TFN membranes was studied. The best-performing TFN membranes showed the highest water permeability of 23.2 L m−2 h−1 bar−1, nearly twice that of unmodified TFC membranes, while maintaining a high salt rejection of 97.5%. The thickened and roughened polyamide layer with reduced transport resistance as well as intrinsic abundant mesopores of AlPO-5 fillers mainly contribute to the enhanced water transport. This study highlights the usage of hierarchical zeolite molecular sieves to fabricate high-permeable polyamide membranes for elevated nanofiltration performance.

Correlating the role of nanofillers with active layer properties and performance of thin-film nanocomposite membranes

Thin-film nanocomposite (TFN) membranes are emerging water-purification membranes that could provide enhanced water permeance with similar solute removal over traditional thin-film composite (TFC) membranes. However, the effects of nanofiller incorporation on active layer physico-chemical properties have not been comprehensively studied. Accordingly, we aimed to understand the correlation between nanofillers, active layer physico-chemical properties, and membrane performance by investigating whether observed performance differences between TFN and control TFC membranes correlated with observed differences in physico-chemical properties. The effects of nanofiller loading, surface area, and size on membrane performance, along with active layer physico-chemical properties, were characterized in TFN membranes incorporated with Linde Type A (LTA) zeolite and zeolitic imidazole framework-8 (ZIF-8). Results show that nanofiller incorporation up to ~0.15 wt% resulted in higher water permeance and unchanged salt rejection, above which salt rejection decreased 0.9–25.6 % and 26.1–48.3 % for LTA-TFN and ZIF-8-TFN membranes, respectively. Observed changes in active layer physico-chemical properties were generally unsubstantial and did not explain observed changes in TFN membrane performance. Therefore, increased water permeance in TFN membranes could be due to preferential water transport through porous structures of nanofillers or along polymer-nanofiller interfaces. These findings offer new insights into the development of high-performance TFN membranes for water/ion separations.

Building rapid water transport channels within thin-film nanocomposite membranes based on 2D mesoporous nanosheets

The fabrication of novel thin-film nanocomposite (TFN) membranes with superior flux, rejection as well as prolonged stability is being requested by membrane industries for saving energy and cost. In this regard, in the present research work we developed novel TFN membranes using amine-rich synthetic talc (NHST) nanosheets within diethylenetriamine (DETA) and trimesoyl chloride (TMC) monomers over a polydopamine (PDA) coating layer. Different concentrations (0.2–1 %) of NHST nanosheets are applied for the fabrication of TFN membranes and comparatively examined with a thin-film composite (TFC) membrane. In-situ synthesized NHST nanosheet phases are confirmed by several characterization techniques and results are explored in depth. All prepared membranes are well investigated to confirm the incorporation of NHST by several characterization techniques, like FE-SEM, ATR-FTIR, HR-TEM, XPS, PXRD, TGA, and contact angle. It is found that a small amount of NHST doping in the TFN layer considerably improved the performance in the form of permeability and rejection. The developed TFN membranes showed hydrophilic characteristics as confirmed by the contact angle. Water flux performance of TFN membranes was also observed comparatively higher than TFC membranes. Optimized NHST-PDT-TFN2 membrane with NHST concentration 0.5 % resulted in 98.96, 95.35, 93.83 and 21.66 % rejection for Na2SO4, MgSO4, CuSO4 and NaCl salts, respectively together with permeance up to 24.45, 22.72, 26.45 and 30.75 Lm−2h−1b−1. The present research finding concludes that the incorporation of a little quantity of NHST nanosheets in the TFN layer plays a unique potential role in the enhancement of flux and rejection of targeted mineral salts. Additionally, the NHST-PDT-TFN membranes revealed outstanding antibacterial properties signifying that contact with microorganisms does not affect the performance and sustains the fouling resistance. The antifouling study of the membranes concluded that the addition of nanomaterials has led to enhanced antifouling tendency and low irreversible fouling, improving the longevity of the membranes.

Probing the influence of shape and loading of CeO2 nanoparticles on the separation performance of thin-film nanocomposite membranes with an interlayer

Constructing an interlayer in the thin-film nanocomposite (TFN) membranes has been proved to be an effective strategy to break the trade-off between permeability and selectivity. The interlayer plays an important role in the formation of polyamide (PA) layer. In this study, cerium oxide (CeO2) nanoparticles with three shapes, including sphere, rod and flake were used to fabricate the interlayers of TFN membranes. The effects of nanoparticle shape and loading on the morphologies and properties of the interlayers and resultant TFN membranes were systematically investigated. The results showed the morphologies and physicochemical properties of the PA layers could be regulated well by the shape and loading of CeO2 nanoparticles. The surface morphologies of the TFN membranes exhibited the transformation from nodule structure to ridge-valley structure. At the same time, the introduction of interlayer made PA layer coarser, the pore size smaller and the pore distribution more uniform. Under the same loading conditions, the rodlike CeO2 nanoparticles tended to form a homogeneous network-like interlayer due to the large specific surface area and good dispersion. The interlayer reduced the transport path of water molecules in the PA layer based on the “gutter” effect, thus improving the permeability of TFN membrane. The water permeability of the TFN membrane with rodlike CeO2 interlayer could be 124% higher than that of the control, while the rejection of salts did not significantly change. This study deepens our understanding on the role of nanoparticle in regulating the morphologies and properties of interlayer and TFN membrane, and provides an effective method to enhance separation performance of nanofiltration membrane.

Organo-Functionalization: An Effective Method in Enhancing the Separation and Antifouling Performance of Thin-Film Nanocomposite Membranes by Improving the Uniform Dispersion of Palygorskite Nanoparticles.

Recently, palygorskite (Pal) has become a promising new membrane additive in flux enhancement and fouling reduction, which is an environmentally friendly nanoclay material under the 2:1 layer composition with 1D tubular structure. However, the aggregation of Pal due to the intermolecular forces is still an obstacle to be solved in improving membrane performance. Herein, Pal nanoparticles were chemically modified by KH550 to weaken the aggregation and improve the dispersibility, and then incorporated into the organic phase to prepare thin-film nanocomposite (TFN) membranes. The results showed that the organo-functionalization could effectively improve the membrane hydrophilicity and dispersion of Pal nanoparticles in the polyamide layer, which contributed to the enhanced water flux (from 25 to 38 L/m2·h), unchanged salt rejection (98.0%) and better antifouling capacity (91% flux recovery rate), which suggested that the organo-functionalization of nanoparticles was an efficient method in further enhancing membrane performance

Thin-Film Nanocomposite Membrane Incorporated with Porous Zn-Based Metal-Organic Frameworks: Toward Enhancement of Desalination Performance and Chlorine Resistance.

Metal-organic framework (MOF) materials have received extensive attention for the design of advanced thin-film nanocomposite (TFN) membranes with excellent permselectivity. However, the relationship between the unique physicochemical properties and performance of engineered MOF-based membranes has yet to be extensively investigated. In this work, we investigate the incorporation of porous zinc-based MOFs (Zn-MOFs) into a polyamide active layer for the fabrication of TFN membranes on porous poly(phenylsulfone) (PPSU) support layers through an interfacial polymerization approach. The actual effects of varying the amount of Zn-MOF added as a nanofiller on the physicochemical properties and desalination performance of TFN membranes are studied. The presence and layout of Zn-MOFs on the top layer of the membranes were confirmed by X-ray photoelectron spectroscopy, scanning electron microscopy, and ζ potential analysis. The characterization results revealed that Zn-MOFs strongly bind with polyamide and significantly change the membrane chemistry and morphology. The results indicate that all four studied TFN membranes with incorporated Zn-MOFs enhanced the water permeability while retaining high salt rejection compared to a thin-film composite membrane. Moreover, the highest-performing membrane (50 mg/L Zn-MOF added nanofiller) not only exhibited a water permeability of 2.46 ± 0.12 LMH/bar but also maintained selectivity to reject NaCl (>90%) and Na2SO4 (>95%), similar to benchmark values. Furthermore, the membranes showed outstanding water stability throughout 72 h filtration and chlorine resistance after a 264 h chlorine-soaking test because of the better compatibility between the polyamide and Zn-MOF nanofiller. Therefore, the developed TFN membrane has potential to solve trade-off difficulties between permeability and selectivity. Our findings indicate that porous Zn-MOFs play a significant role in the development of a TFN membrane with high desalination performance and chlorine resistance.

Size effects of carboxylated magnetite nanoparticles on the membrane dehumidification performance

This study aims to understand the effects of different nanoparticle sizes on the dehumidification performance of thin-film nanocomposite membranes (TFN). Carboxylated magnetite (C-Fe3O4) nanoparticles of different sizes (5–30 nm) were embedded in a polyamide layer (PA) over the polysulfone (PSf) substrate. The structural and morphological characteristics of the nanoparticles and coated membranes were explored using various analytical techniques such as FT-IR, SEM, DLS, the zeta-potential, EDS, AFM, and the water contact angle. Mixed-gas permeation tests showed that there were performance peak points at specific nanoparticle concentrations. These performance peaks shifted toward a high concentration of nanoparticles with a decrease in the magnetite size. The M5(0.3) membrane with 0.3 w/w% of 5 nm magnetite particles showed the highest water vapor permeance of 1886 GPU and the highest water vapor/nitrogen gas selectivity of 688 at 30 °C and 70% relative humidity (RH). These results are in good agreement with data pertaining to the hydrophilicity of the TFN membrane. The amounts of C-Fe3O4 nanoparticles deposited on the surfaces of the M5(0.3), M15(0.3) and M25(0.3) membranes were found to be 6.95, 6.27 and 5.44 µg/cm2, respectively. The impact of the pressure, RH% and temperature on the water vapor permeation were also studied and discussed.

Morphological effect of ZnO nanostructures on desalination performance and antibacterial activity of thin-film nanocomposite (TFN) membrane

This study highlights the effect of shape-controlled nanostructures on the desalination efficiency of thin-film nanocomposite (TFN) membranes. ZnO nanostructures such as nanoflowers (F-ZnO), nanorods (R-ZnO), and spherical nanoparticles (S-ZnO) were synthesised using hydrothermal and sol-gel processes. The chemical and structural characteristics of nanoparticles and the TFN membranes were analysed using X-ray diffraction, Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, contact angle measurement, and atomic force microscopy. The desalination performance of TFN membranes was investigated after the incorporation of different concentrations of ZnO nanoparticles (S-ZnO, F-ZnO, and R-ZnO) ranging from 0– to 0.03 wt%. Irrespective of the ZnO morphology, the TFN membrane showed improved hydrophilicity with an increase in ZnO loading. The S-ZnO/0.02 TFN membrane exhibited the highest permeate flux (23.85 L/m2·h) and relatively better NaCl rejection (97%), which can be attributed to higher surface area and smaller size of S-ZnO compared to F-ZnO and R-ZnO nanostructures. Furthermore, antifouling study (with DH5-alpha strain, Escherichia coli) for S-ZnO/0.02 TFN membrane revealed a reduction in viable cells to 70% after 180 min of contact compared to the thin-film composite (TFC) membrane. The S-ZnO/0.02 TFN membrane displayed enhanced operational stability, which confirms the stable embedment of S-ZnO nanoparticles in the selective polyamide layer.

Nanoclays‐Incorporated Thin‐Film Nanocomposite Membranes for Reverse Osmosis Desalination

AbstractA series of thin‐film nanocomposite (TFN) membranes with incorporation of Laponite nanoclays (NC‐LAP) is prepared and demonstrated for brackish water and seawater desalination. It is the first attempt to use poly(ethylene glycol) 200 (PEG200) assisted Laponite as nanofillers to improve the performance of TFN membranes for reverse osmosis (RO) seawater desalination. The influence of NC‐LAP loading and PEG200 as the dispersant on membrane properties is investigated. An increase in NC‐LAP loading results in an increase in water permeability without sacrificing the salt rejection. At the loading of 0.3 wt%, the TFN membrane shows a water permeability of 2.7 L m−2 h−1 bar−1 (LMH bar−1) and a salt rejection of 98.18% for brackish water desalination at 20 bar and 25 ± 1 °C. This water permeability is 53% higher than the conventional thin‐film composite (TFC) membrane. A steady water flux above 35 LMH is obtained when using seawater as the feed at 50 bar and 25 ± 1 °C. The existence of PEG200 to effectively disperse NC‐LAP nanoparticles is essential to fabricate the NC‐LAP incorporated TFN membranes for brackish water and seawater desalination.

A facile and versatile strategy for fabricating thin-film nanocomposite membranes with polydopamine-piperazine nanoparticles generated in situ

We propose in this study a facile and versatile strategy for fabricating thin-film nanocomposite (TFN) membranes, wherein polydopamine-piperazine (PDP) nanoparticles were formed in situ from the oxidative polymerization reaction of dopamine and its subsequent reaction with piperazine. Accordingly, PDP nanoparticles were then directly used as nanofillers for TFN membranes fabricated through interfacial polymerization. The characteristics of PDP nanoparticles and the performance of TFN membranes were easily tailored by varying the water-ethanol ratio in the PIP solution, solution pH, dopamine concentration, and reaction time. The TFN-PDP membranes exhibited an optimum separation performance (high water permeability and high salt selectivity): JH2O = 59.1 ± 3.3 L m−2 h−1; RNa2SO4 = 98.0%; RNaCl = 44.1% (6 bar, 25 °C). Moreover, the TFN-PDP membranes demonstrated high water flux recovery and enhanced antifouling property during cycles of filtration tests, with bovine serum albumin protein used as model foulant.

Hydrophilic Hollow Nanocube-Functionalized Thin Film Nanocomposite Membrane with Enhanced Nanofiltration Performance.

The performance of thin film nanocomposite (TFN) membrane is significantly determined by the inherent structure and composition of the incorporated nanofillers. In this work, hydrophilic hollow nanocubes (HHNs) derived from zeolitic imidazolate framework 8 (ZIF-8) were incorporated into the polyamide layer via an interfacial polymerization approach. The HHNs with abundant hydroxyl groups on the surface were obtained by etching solid ZIF-8 using tannic acid. Benefiting from the hydrophilicity, hollow structure, and negative charge of HHNs, the outstanding nanofiltration performance of the composite membrane was achieved. With the assistance of HHNs, the permeance and Na2SO4 rejection of the TFN membrane increased up to 19.4 ± 0.6 L/(m2·h·bar) and 95.2 ± 1.4%, corresponding to an improvement of 190% of the permeance and 2.0% of the rejection compared to the pristine thin film composite membrane. Comparatively, the performance of TFN membranes prepared with solid ZIF-8 only shows 116% improvements of the permeance with slightly increased salt rejection. More importantly, the antifouling property of the TFN-4H membrane was also elevated. The flux recovery ratios of the TFN-4H membrane are 93.2 and 84.7% corresponding to humic acid and bovine serum albumin solutions, respectively. The results indicate that the nanofiltration performance of the composite membrane was significantly enhanced with the incorporation of HHNs.

ZIF-8 particle size effects on reverse osmosis performance of polyamide thin-film nanocomposite membranes: Importance of particle deposition

Thin-film nanocomposite (TFN) membranes based on nanomaterial-embedded ultrathin polyamide layers have been extensively studied as an energy-efficient material for reverse osmosis (RO) desalination. Although several studies have reported that TFN membranes with zeolitic imidazole frameworks (e.g., ZIF-8) showed improved RO performances, attributed to its intrinsic microporosity and high specific surface area, an in-depth study on the role of ZIF-8 nanoparticles in selective polyamide layers has not yet been published. Here we synthesized ZIF-8 nanoparticles with different average sizes (60, 150, and 250 nm) and investigated the effects of particle size on the separation performance of TFN membranes. Interestingly, it was found that the deposition of ZIF-8 nanoparticles on the microporous polysulfone (PSf) support prior to interfacial polymerization of the polyamide layer was influenced by ZIF-8 particle size. Small-sized ZIF-8 nanoparticles showed the highest surface coverage, which is consistent with the classical particle deposition theories. The interface area between ZIF-8 nanoparticles and polyamide matrix varied with particle size, ultimately affecting the RO performance of TFN membranes. Our results firstly reveal that the amount of particle deposition prior to interfacial polymerization could be strongly influenced by particle size, emphasizing the importance of particle deposition for the further studies on nanoparticle-embedded TFN membranes.

Nano-porous SAPO-34 enhanced thin-film nanocomposite polymeric membrane: Simultaneously high water permeation and complete removal of cationic/anionic dyes from water

Thin-film nanocomposite (TFN) membranes were prepared by embedding nano-porous SAPO-34 nanoparticles in a polypyrrole thin-film layer polymerized on PES substrate. SEM, EDX, AFM, hydrophilicity, zeta potential and MWCO measurements were applied to verify characteristics of membranes. TFN membranes presented considerably higher pure water permeability (by more than 300%) due to high hydrophilicity and also nano-channels created in thin-film. Performance of TFN membranes were also evaluated by removal of different anionic and cationic dyes (methyl violet 6B, reactive blue 4 and acid blue 193) from water. TFN membranes effectively removed 100% of all dyes from feed aqueous solutions with a low concentration (50 mg/l). Moreover, TFN membrane prepared with the highest amount of nano-filler presented an elevated water flux in filtration of solutions containing each dyes (e.g. more than 500% for reactive blue 4), a reduced flux decline ratio (36%) and also a higher flux recovery ratio (85%) in comparison with the pristine thin-film membrane, consequently indicating high performance of TFN membranes and potential of recovery just after a simple water washing. TFN membranes also revealed an efficient performance in filtration of high concentrations of dye solutions as well as in treatment of a real wastewater produced by a weaving company.