Advanced desalination of dye/NaCl mixtures by a loose nanofiltration membrane for digital ink-jet printing

Construction of PDA-PEI/ZIF-L@PE tight ultra-filtration (TUF) membranes on porous polyethylene (PE) substrates for efficient dye/salt separation

Tight ultra-filtration (TUF) membranes were constructed by in situ growing zinc imidazole frameworks micro-crystalline leaves (ZIF-L) in polyethylene imine (PEI) and polydopamine (PDA) deposit layers on porous polyethylene (PE) substrates. The effects of preparation conditions on the surface physical and chemical structures as well as on the dye/salt separation performance of the formed TUF membranes were systematically investigated. By inserting selective water permeation channels and increasing contacting surface areas, in situ-grown ZIF-L arrays tightly cross-linked in the coating matrix greatly increased water permeation without trading off dye/salt retention selectivity. The morphology of the included ZIF-L particles could be varied by adjusting the ligand/Zn molar ratio (α) in the preparation processes. Optimized PDA-PEI/ZIF-L@PE TUF membranes containing ZIF-L of cross-cross block morphology showed very high pure water permeability of 180 ± 20 L·m-2·h-1·bar-1 (LMHB) and retention selectivity (SCR/Na2SO4 and SMB/Na2SO4) of 267 and 43, respectively, as well as excellent stability and anti-fouling properties.

Membrane-based technology in water and resources recovery from the perspective of water social circulation: A review

In this review, the application of membrane-based technology in water social circulation was summarized. Water social circulation encompassed the entire process from the acquirement to discharge of water from natural environment for human living and development. The focus of this review was primarily on the membrane-based technology in recovery of water and other valuable resources such as mineral ions, nitrogen and phosphorus. The main text was divided into four main sections according to water flow in the social circulation: drinking water treatment, agricultural utilization, industrial waste recycling, and urban wastewater reuse. In drinking water treatment, the acquirement of water resources was of the most importance. Pressure-driven membranes, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were considered suitable in natural surface water treatment. Additionally, electrodialysis (ED) and membrane capacitive deionization (MCDI) were also effective in brackish water desalination. Agriculture required abundant water with relative low quality for irrigation. Therefore, the recovery of water from other stages of the social circulation has become a reasonable solution. Membrane bioreactor (MBR) was a typical technique attributed to low-toxicity effluent. In industrial waste reuse, the osmosis membranes (FO and PRO) were utilized due to the complex physical and chemical properties of industrial wastewater. Especially, membrane distillation (MD) might be promising when the wastewater was preheated. Resources recovery in urban wastewater was mainly divided into recovery of bioenergy (via anaerobic membrane bioreactors, AnMBR), nitrogen (utilizing MD and gas-permeable membrane), and phosphorus (through MBR with chemical precipitation). Furthermore, hybrid/integrated systems with membranes as the core component enhanced their performance and long-term working ability in utilization. Generally, concentrate management and energy consumption control might be the key areas for future advancements of membrane-based technology.

Ionic Hyperbranched Poly(amido-amine)-Incorporated Nanofiltration Membranes for High-Efficiency Dye Desalination

High-efficiency dye desalination is crucial in the textile industry, considering its importance for human health, safe aquatic ecological systems, and resource recovery. In order to solve the problem of effective separation of univalent salt and ionic dye under the condition of high salt, ionic hyperbranched poly(amido-amine) (HBPs) were synthesized based on a simple and scalable one-step polycondensation method and then incorporated into the polyamide (PA) selective layers to construct charged nanochannels through interfacial polymerization (IP) on the surface of a polyvinyl chloride ultrafiltration (PVC-UF) hollow fiber membrane. Both the internal nanopores of HBPs (internal nanochannels) and the interfacial voids between HBPs and the PA matrix (external nanochannels) can be regarded as a fast water molecule transport pathway, while the terminal ionic groups of ionic HBPs endow the nanochannels with charge characteristics for improving ionic dye/salt selectivities. The permeate fluxes and dye/salt selectivities of HBP-TAC/PIP (57.3 L m-2 h-1 and rhodamine B (RB)/NaCl selectivity of 224.0) and HBP-PS/PIP (63.7 L m-2 h-1 and lemon yellow (LY)/NaCl selectivity of 664.0) membranes under 0.4 MPa operation pressure are much higher than PIP-only and HBP-NH2/PIP membranes. At the same time, this project also studied the membrane desalination process in a simulated high-salinity dye/salt mixture system to provide a theoretical basis and technical support for the actual dye desalination process.

Design of a new polyethersulfone nanofiltration membrane with anti-fouling properties using supported protic ionic liquid modification for dye/salt removal

Facile techniques to fabricate the nanofiltration membranes with ideal molecular sieving is one of the most interesting subjects in membrane separation technology. In this study, the application of modified graphene oxide (GO) with triethylenetetramine (TETA), CuFe₂ O₄ , and acetic acid (AC) (supported GO-TETA-CuFe₂ O₄ @AC) as a supported protic ionic liquid (PIL) modifier for polyethersulfone (PES) membrane was evaluated to approve the improvement of anti-fouling properties and wastewater rejection of the fabricated membranes. To enhance the key properties of graphene oxide, it was modified by hydrophilic nanomaterials (TETA-CuFe₂ O₄ ). High flux and promising flux recovery ratio (up to 95% compared to the unmodified membrane) can be observed in the modified membranes. The modified membranes by GO-TETA-CuFe₂ O₄ @AC were studied at optimum concentrations (0.5 wt.%) for salt rejection and different dyes. The obtained data indicated that the modified membranes by GO-TETA-CuFe₂ O₄ @AC indicated higher salt removal (up to 97% for BaCl₂ than the unmodified membrane), which was related to the efficient modification. The obtained pure water flux (PWF) for bare and optimal modified membrane from 13.11 to 27.87 kg/m² ·h, respectively. To exact evaluate the effect of membrane modification on performance examination, the modified membranes were evaluated for chlorine resistance testing. This study aimed to develop cost-effective nanofiltration (NF) membranes with high anti-fouling properties and to determine the maximum filtration capacity of in-time dyes and salts in effluents. PRACTITIONER POINTS: A GO-TETA-CuFe2O4 mixed matrix membrane was prepared for removal of salts and dyes. The effect of GO-TETA-CuFe2O4 enhanced the hydrophilicity and porosity. The membrane exhibited superior antifouling properties and ions rejection.

Simultaneous phosphate recovery and sodium removal from brackish aquaculture effluent via diafiltration-nanofiltration process

Expansion of the aquaculture industry has been accompanied by environmental impact as the discharged effluent contains excess nutrients such as phosphorus compounds. Recovery of such nutrients is not economically feasible as it presents in trace amounts. Furthermore, brackish aquaculture effluent which contains high sodium chloride (NaCl) content makes the treated solution inappropriate for fertilizer production. Herein, this study proposed a diafiltration-nanofiltration route to perform a simultaneous phosphate concentrating and osmotion (sodium) removal from brackish aquaculture effluent. Effects of operating pressure, phosphate, and sodium content on membrane performance were first determined using Desal-5 DK membrane with three types of solutions namely (i) freshwater without NaCl, (ii) dilute brackish water with 1,500 mg/L NaCl, and (iii) brackish water with 10,000 mg/L NaCl. It was found that at 4 bar operating pressure, it could achieve higher phosphate rejection and sodium permeance. The presence of NaCl negatively influenced both phosphate rejection and concentrating factor (CF) due to the salt screening effect. It was noteworthy that negative sodium rejection (up to -16%, CF <1) could be attained, indicating the concentrating effect for sodium was negligible. The concentrating process was effective to concentrate phosphate by 2-fold but less effective in removing sodium. Diafiltration was then introduced and resulted in about 76% of sodium removal. Diafiltration-nanofiltration (DF-NF) mode was shown to be a more efficient method than nanofiltration-diafiltration (NF-DF) mode as phosphate could be concentrated up to 2 factors with 99 wt% of sodium being removed from the real brackish aquaculture effluent. These findings showed that DF-NF is a feasible approach for concentrating phosphate while removing sodium ions from aquaculture effluent and the recovered nutrient solution has huge potential to be applied as liquid fertilizer for hydroponic plants.

Graphene oxide membrane chemically modified by electron-transfer diazonium chemistry for efficient dye separation

By chemical modification of the graphene oxide (GO) surface via diazonium chemistry, we introduce nitrobenzene groups as new interlayer pillars to GO memebranes like the surface oxygen-containing functional groups. The larger pillar can finely enlarge the interlayer space of the GO membrane. The filtration performance of modified GO membranes with different mass ratios of nitrobenzene diazonium tetrafluoroborate (NDT) were tested for EB, DR81, and MB. Notably, when the GO : NDT ratio is 1 : 1, it is found that the water flux can be enhanced by more than twice and by nearly 1.4 times its value for EB and DR81, respectively, while maintaining a high rejection (92% for EB and 95% for DR81). In conclusion, the chemical modification of GO through the dediazonization reaction of NDT can indeed improve the separation efficiency of the dye.

A novel synergistic effect of TiO2 and ZnO incorporation in PES-based thin-film nanocomposite nanofiltration membrane for treatment of textile wastewater

A novel synergistic effect of TiO₂ and ZnO incorporation in the PES-based thin-film nanocomposite nanofiltration membranes was developed for the treatment of common effluent treatment plant (CETP) textile wastewater. PES@TiO₂ membranes were developed by phase inversion via the immersion precipitation method followed by the addition of zinc oxide nanoparticles prepared by the rapid microwave-assisted hydrothermal process via interfacial polymerization. p-Phenylenediamine was used as a monomer for the IP process that was coated on the PES@TiO₂ support layer. Various techniques have been applied to characterize the developed thin-film nanocomposite membranes such as Fourier transform infrared (FTIR) microscopy, field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), and contact angle measurement to examine the presence of vibrational modes, surface morphology, the crystal structure of nanoparticles, and hydrophilicity of the membrane, respectively. Membrane properties include porosity, salt rejection, mean pore radius, pure water flux, and industrial effluent rejection efficiency that were studied. The thin-film nanocomposite membrane T5-PES@TiO₂(2%)-ZnO(0.3%) was prepared with a combination of 17 wt% PES, 78 wt% DMF, 3 wt% PVP K30, 2% TiO₂, 2.5 wt% PPD, 0.3 wt% ZnO, and 1.0 wt% TMC that exhibited high water permeability, porosity, higher industrial effluent rejection, and salt rejection efficiency compared to the neat PES membrane.

Confining Nano-Fe3O4 in the Superhydrophilic Membrane Skin Layer to Minimize Internal Fouling

Membrane surface fouling is often reversible as it can be mitigated by enhancing the crossflow shear force. However, membrane internal fouling is often irreversible and thus more challenging. In this study, we developed a new superhydrophilic poly(vinylidene fluoride) (P-PVDF) membrane confined with nano-Fe₃O₄ in the top skin layer via reverse filtration to reduce internal fouling. The surface of the P-PVDF membrane confined with nano-Fe₃O₄ had superwetting properties (water contact angle reaching 0° within 1 s), increased roughness (from 182 to 239 nm), and enhanced water affinity. The Fe₃O₄@P-PVDF membrane surface showed a thicker and enhanced hydration layer, which prevented foulants from approaching membrane surfaces and pores, thereby improving the rejection. For example, when 50 ppm humic acid (HA) solution was used as the feed, the removal efficiency of the Fe₃O₄@P-PVDF membrane was ∼67%, while the HA removal of the P-PVDF membrane was only ∼20%. The results from the resistance-in-series model showed that nanoconfinement of Fe₃O₄ in the top skin layer of the membrane allowed foulants to accumulate on the membrane surface (i.e., surface fouling) rather than within the internal pores (i.e., internal fouling). The filtration results under crossflow fouling and cleaning confirmed that the Fe₃O₄@P-PVDF membrane had higher surface fouling but it was much more reversible and much lower internal fouling compared with the control membrane. Our fouling analysis offers new insights into mass transfer mechanisms of the membrane with a nanoconfinement-enhanced hydration layer. This study provides an effective strategy to develop membranes with low internal fouling propensities.

MXene-regulation polyamide membrane featuring with bubble-like nodule for efficient dye/salt separation and antifouling performance

Removing salt from dye/salt mixtures using nanofiltration (NF) membranes needs to be improved to ensure high permeability, high selectivity, and antifouling performance. In this study, we used an interfacial polymerization (IP) technique to create a novel thin-film nanocomposite NF membrane by introducing two-dimensional MXene Ti₃C₂T_x into the polyamide (PA) layer. Enhanced IP reaction rate facilitated the overflow of residual solvent from the fresh PA layer's edge due to the MXene-mediated IP strategy, resulting considerable bubble-like nodules on the membrane surface. The unique nanostructure of PA effective layer could be tuned by controlling the MXene concentration in aqueous phase solution, which finally promoted the obtained membranes with superb permselectivity. In this way, the water permeability was elevated to a maximum value of 45.12 L m⁻¹ h⁻¹, nearly 1.58-fold compared to the PA-pristine membrane. Moreover, the Ti₃C₂T_x/NF membrane exhibited a superior dye/monovalent salt separation coefficient of 820, outperforming the pristine PA membrane and other NF membranes in the literature. Additionally, the MXene-assisted IP strategy designed an effective dye anti-fouling hydration layer, which played a crucial role in fouling resistance. This work illustrates a novel use of Ti₃C₂T_x to successfully regulate high-performance TFN PA membranes for potential application in dye/salt separation.

A novel thin-film nanocomposite NF membrane with efficient dye/salt separation and antifouling performance was designed by introducing different amounts of MXene into the PA layer.

POM-based metal–organic compounds: Assembly, structures and properties

Four POM-based inorganic-organic hybrid compounds, which are {[(Cu·L1’·H2O)·(α-Mo8O26)0.5]·H2O}n (1), {(Cu·L2’·H2O)·(α-Mo8O26)0.5}n (2), {[(Cu·L3’·H2O)·(β-Mo8O26)0.5]·5H2O}n (3), {(Cu·L4’·H2O)·(β-Mo8O26)}n (4)[L1’ = 1,5-bis (4-carboxylpyridine) pentane dibromide, L2’ = 1,7-bis (4-carboxylpyridine) heptane dibromide, L3’ = 1,2-bis [(4-carboxylpyridine) - N-methylene] benzene dibromide, L4’ = 1,4-bis [(4-carboxylpyridine) - N-methylene] benzene dibromide] have been successfully synthesized under hydrothermal conditions by tuning ligands. Compounds 1–4 were characterized by single crystal X-ray diffraction, infrared spectrum (IR), powder X-ray diffraction (PXRD), and thermogravimetric (TG). The transformation of ligands have a momentous effect on the [Mo8O26]4 - structures of this series. In addition, the adsorption and photocatalytic properties of organic dyes for compounds 1–4 have been investigated.

Design, characterization, and adsorption properties of Padina gymnospora/zeolite nanocomposite for Congo red dye removal from wastewater

A comprehensive study combined experimental, computational and field experiments was conducted to find out the most appropriate adsorbent system for industrial elimination of congo red (CR) dye from simulated industrial wastewater. Modification of the zeolite (Z) by the Padina gymnospora algae (PG) (Egyptian marine algae) was evaluated in terms of the adsorption capability of the zeolite (Z) to remove CR dye from aqueous solutions. The zeolite/algae composite (ZPG) was fabricated using the wet impregnation technique. Various techniques were used to characterize the PG, Z, and the produced ZPG nanocomposite. Batch experiments were performed to study the influence of various practical variables on adsorption processes. The isotherms and kinetics of dye adsorption were also studied. The newly synthesized ZPG nanocomposite exhibits much higher adsorption capacity, especially at low CR concentrations than that of Z. The computational calculations have shown that owing to the presence of intermolecular interactions, the adsorption of the CR molecule on zeolite surfaces is exothermic, energetically favorable, and spontaneous. For all configurations, increasing the zeolite size does not have a noticeable impact on the adsorption energies. The experimental results revealed that the ZPG nanocomposite can be applied as an economical nanoadsorbent to eliminate anionic dyes from simulated industrial wastewater at low CR dye concentrations. The adsorption isotherm of dye onto Z, PG, and ZPG almost agreed with Langmuir isotherm and pseudo-second-order kinetics. The sorption mechanism was also evaluated using Weber's intra-particle diffusion module. Finally, the field experiments revealed optimistic results for the newly synthesized adsorbent in removing dyes from industrial wastewater with 82.1% efficiency, which in turn confirmed the foundation of new eco-friendly materials that aid in the reuse of industrial wastewater.

Integrated loose nanofiltration-electrodialysis process for sustainable resource extraction from high-salinity textile wastewater

Effective extraction of useful resources from high-salinity textile wastewater is a critical pathway for sustainable wastewater management. In this study, an integrated loose nanofiltration-electrodialysis process was explored for simultaneous recovery of dyes, NaCl and pure water from high-salinity textile wastewater, thus closing the material loop and minimizing waste emission. Specifically, a loose nanofiltration membrane (molecular weight cutoff of ~800 Da) was proposed to fractionate the dye and NaCl in the high-salinity textile wastewater. Through a nanofiltration-diafiltration unit, including a pre-concentration stage and a constant-volume diafiltration stage, the dye could be recovered from the high-salinity textile wastewater, being enriched at a factor of ~9.0, i.e., from 2.01 to 17.9 g·L^-1 with 98.4% purity. Assisted with the subsequent implementation of electrodialysis, the NaCl concentrate and pure water were effectively reclaimed from the salt-containing permeate coming from the loose nanofiltration-diafiltration. Simultaneously, the produced pure water was further recycled to the nanofiltration-diafiltration unit. This study shows the potential of the integration of loose nanofiltation-diafiltration with electrodialysis for sufficient resource extraction from high-salinity textile wastewater.

Construction of Loose Positively Charged NF Membrane by Layer-by-Layer Grafting of Polyphenol and Polyethyleneimine on the PES/Fe Substrate for Dye/Salt Separation

The effective separation of dyes and inorganic salts is highly desirable for recycling inorganic salts and water resource in printing and dyeing wastewater treatment. In this work, tannic acid (TA) and polyethyleneimine (PEI) were grafted on the PES/Fe ultrafiltration membrane via the coordination assembly and Michael addition strategy to fabricated a loose nanofiltration membrane (LNM). The effect of PEI concentration on membrane morphologies and properties was systematically investigated. The membrane surface becomes more hydrophilic and transforms into positive charge after the PEI grafting. The optimized PES/Fe-TA-PEI membrane possesses high pure water flux (124.6 L·m⁻²·h⁻¹) and excellent dye rejections (98.5%, 99.8%, 98.4%, and 86.4% for Congo red, Eriochrome black T, Alcian blue 8GX, and Bromophenol blue, respectively) under 2 bar operation pressure. Meanwhile, the LNM showed a high Alcian blue 8GX rejection (>98.4%) and low NaCl rejection (<5.3%) for the dye/salt mixed solutions separation. Moreover, the PES/Fe-TA-PEI LNM exhibited good antifouling performance and long-term performance stability. These results reveal that such LNM shows great potential for effective fractionation of dyes and salts and recycling of textile wastewater.

Biomimetic dynamic membrane (BDM): Fabrication method and roles of carriers and laccase

Biomimetic dynamic membrane (BDM) has been employed as a promising membrane separation technology regarding water/wastewater treatment (Model pollutant is methylene blue). Given its catalytic function on micro-pollutant removal and fouling control, detailed mechanism for impacts of fabrication method, carriers (CNT and GO) and laccase on the construction of biomimetic layer and enzyme immobilization have not been clear so far. In this work, the BDM performance with various fabrication methods, carriers and laccase were investigated and verified. The BDM fabrication tests demonstrated that BDM with mixed filtration method had better filtration performance (up to 120 L m^-2 h^-1 flux and 80% removal rate) than BDM with stepwise filtration method. Moreover, the laccases immobilized on GO exhibited a stronger laccase activity than those on CNT. Increasing CNT or GO dosage strengthened removal rate, but lowered flux, meanwhile flux and removal rate exhibited a significant fluctuation with certain laccase dosage. At 25 g m^-2 CNT or GO dosage and 50 g m^-2 laccase dosage, the optimized flux and removal rate values were obtained. Further study investigated the surface morphology and property of BDM, showing that BDM with mixed filtration method turned out to be the optimized enzyme immobilization mechanism and fabrication method. In addition, during multiple filtration cycles, with the optimized conditions, the removal rate, flux and laccase activity of BDM could maintain at high levels. On account of the finding of the present study, selecting a suitable fabrication method, appropriate CNT or GO dosage and laccase dosage can indeed optimize the structure of biomimetic layer and enzyme immobilization, expanding its possibility on sustainable operation.