Organic solvent reverse osmosis membranes for organic liquid mixture separation: A review

Dual-phase microporous polymer nanofilms by interfacial polymerization for ultrafast molecular separation

Fine-tuning microporosity in polymers with a scalable method has great potential for energy-efficient molecular separations. Here, we report a dual-phase molecular engineering approach to prepare microporous polymer nanofilms through interfacial polymerization. By integrating two micropore-generating units such as a water-soluble Tröger's base diamine (TBD) and a contorted spirobifluorene (SBF) motif, the resultant TBD-SBF polyamide shows an unprecedentedly high surface area. An ultrathin TBD-SBF membrane (~20 nm) exhibits up to 220 times improved solvent permeance with a moderate molecular weight cutoff (~640 g mol-1) compared to the control membrane prepared by conventional chemistry, which outperforms currently reported polymeric membranes. We also highlight the great potential of the SBF-based microporous polyamides for hydrocarbon separations by exploring the isomeric effects of aqueous phase monomers to manipulate microporosity.

Adsorption-driven reverse osmosis separation of ethanol/water using zeolite nanosheets

Developing more energy-efficient and cost-effective membrane processes for the separation of ethanol and water represents a strategically important direction to facilitate the production of renewable biofuels. In this study, by employing state-of-the-art molecular simulations, the potential of zeolite nanosheets as reverse osmosis (RO) membranes in ethanol/water separation is investigated. These materials are predicted to offer unprecedentedly high fluxes and more importantly, the ethanol-to-water separation factor can be as large as approximately 800 if the structure is meticulously selected. The separation achieved herein can in fact be considered counter-intuitive as the membrane allows the larger ethanol molecules to permeate through while blocking smaller water molecules. Further investigations reveal that the observed selectivity is strongly correlated with the adsorption selectivity of the bulk materials, suggesting an adsorption-driven mechanism. Promising candidates also appear to have the largest cavity diameter of approximately 6 Å, a size that can be commensurate with the dimensions of ethanol to facilitate its adsorption. The hydrophilicity on the membrane surfaces is as well found to play a non-negligible role. Overall, this study demonstrates the great promise of zeolite nanosheets as RO membranes for extracting anhydrous ethanol from its aqueous mixture and provides guidance toward the selection of promising membrane candidates.

Advancement of membrane separation technology for organic pollutant removal

In the face of growing global freshwater scarcity, the imperative to recycle and reuse water becomes increasingly apparent across industrial, agricultural, and domestic sectors. Eliminating a range of organic pollutants in wastewater, from pesticides to industrial byproducts, presents a formidable challenge. Among the potential solutions, membrane technologies emerge as promising contenders for treating diverse organic contaminants from industrial, agricultural, and household origins. This paper explores cutting-edge membrane-based approaches, including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, gas separation membranes, and pervaporation. Each technology's efficacy in removing distinct organic pollutants while producing purified water is scrutinized. This review delves into membrane fouling, discussing its influencing factors and preventative strategies. It sheds light on the merits, limitations, and prospects of these various membrane techniques, contributing to the advancement of wastewater treatment. It advocates for future research in membrane technology with a focus on fouling control and the development of energy-efficient devices. Interdisciplinary collaboration among researchers, engineers, policymakers, and industry players is vital for shaping water purification innovation. Ongoing research and collaboration position us to fulfill the promise of accessible, clean water for all.

Liquid- liquid (Cyclohexanone: Cyclohexanol) separation using augmented tight nanofiltration membrane: A sustainable approach

Organic solvent nanofiltration (OSN) is an incipient technology in the field of organic liquid-liquid separation. The incomplete separations and complexity involved in these, forces many organic liquids to be released as effluents and the adverse effects of these on environment is enormous and irreparable. The work prominences on the complete separation of industrially significant cyclohexanone: cyclohexanol (keto-alcohol oil) and heptane: toluene mixtures. The separations of these above-mentioned organic liquid mixtures were carried out using the fabricated Lewis acid modified graphitic carbon nitride (Cu2O@g-C3N4) incorporated polyvinylidene difluoride (PVDF) composite membranes. These fabricated membranes showed a separation factor of 18.16 and flux of 1.62 Lm-2h-1 for cyclohexanone: cyclohexanol mixture and separation of heptane and toluene mixture (with heptane flux of 1.52 Lm-2h-1) showed a separation factor of 9.9. The selectivity and productivity are based on the polarity and size of the organic liquids. The role of Cu2O@g-C3N4 is influencing the pore size distribution, increased divergence from solubility parameters, polarity, solvent uptake and porosity of the composite membranes. The developed composite membranes are thus envisioned to be apt for a wide range of liquid-liquid separations due to its implicit nature.

Organic Solvent Nanofiltration in Pharmaceutical Applications

Separation and purification in organic solvents are indispensable procedures in pharmaceutical manufacturing. However, they still heavily rely on the conventional separation technologies of distillation and chromatography, resulting in high energy and massive solvent consumption. As an alternative, organic solvent nanofiltration (OSN) offers the benefits of low energy consumption, low solid waste generation, and easy scale-up and incorporation into continuous processes. Thus, there is a growing interest in employing membrane technology in the pharmaceutical area to improve process sustainability and energy efficiency. This Review comprehensively summarizes the recent progress (especially the last 10 years) of organic solvent nanofiltration and its applications in the pharmaceutical industry, including the concentration and purification of active pharmaceutical ingredients, homogeneous catalyst recovery, solvent exchange and recovery, and OSN-assisted peptide/oligonucleotide synthesis. Furthermore, the challenges and future perspectives of membrane technology in pharmaceutical applications are discussed in detail.

Recovery of Homogeneous Platinoid Catalysts from Pharmaceutical Media: Review on the Existing Treatments and the Perspectives of Membrane Processes

Catalyst recovery is a major challenge for reaching the objectives of green chemistry for industry. Indeed, catalysts enable quick and selective syntheses with high reaction yields. This is especially the case for homogeneous platinoid catalysts which are almost indispensable for cross-coupling reactions often used by the pharmaceutical industry. However, they are based on scarce, expensive, and toxic resources. In addition, they are quite sensitive and degrade over time at the end of the reaction. Once degraded, their regeneration is complex and hazardous to implement. Working on their recovery could lead to highly effective catalytic chemistries while limiting the environmental and economic impacts of their one-time uses. This review aims to describe and compare conventional processes for metal removal while discussing their advantages and drawbacks considering the objective of homogeneous catalyst recovery. Most of them lead to difficulty recycling active catalysts due to their ability to only treat metal ions or to chelate catalysts without the possibility to reverse the mechanism. However, membrane processes seem to offer some perspectives with limiting degradations. While membranes are not systematically the best option for recycling homogeneous catalysts, current development might help improve the separation between pharmaceutical active ingredients and catalysts and enable their recycling.

New Materials and Phenomena in Membrane Distillation

In recent decades, membrane-based processes have been extensively applied to a wide range of industrial processes, including gas separation, food industry, drug purification, and wastewater treatment. Membrane distillation is a thermally driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. At the operational level, the performance of membrane distillation is negatively affected by wetting and temperature polarization phenomena. In order to overcome these issues, advanced membranes have been developed in recent years. This review, which focuses specifically on membrane distillation presents the basic concepts associated with the mass and heat transfer through hydrophobic membranes, membrane properties, and advances in membrane materials. Photothermal materials for solar-driven membrane distillation applications are also presented and discussed.

Review on Liquid-Liquid Separation by Membrane Filtration

Liquid-liquid separation is crucial in the present circumstances. Substitution of the conventional types of separation like distillation and pervaporation is mandatory due to the high energy requirement of the two. The separation of organic mixtures has a huge potential in industries such as pharmaceutical, fine chemicals, fuels, textile, papers, and fertilizers. Membrane-affiliated separations are one of the prime techniques for liquid-liquid separations. Organic solvent nanofiltration, solvent-resistant nanofiltration, and ultrafiltration are a few methods through which organic liquid-liquid separation can be attained. Implementation of such a technology in chemical industries reduces the time consumption and is cost efficient. Even though a lot of research has been done, attention is needed in the field of organic-liquid separation aided by membranes. In this review, various membranes used for organic mixture separations such as polar-nonpolar, polar-polar, and nonpolar-nonpolar are discussed with a focus on membrane materials, additives, separation theory, separation type, experimental setup, fouling mitigation, surface modification, and major challenges. The review also offers insights and probable solutions for existing problems and also discusses the scope of research to be undertaken in the future.

Nanocomposite membranes for organic solvent nanofiltration: Recent advances, challenges, and prospects

Organic solvent nanofiltration (OSN) is an emerging technology for the separation of organic solvents that are relevant to the petrochemical, pharmaceutical, food and fine chemical industries. The separation performance of OSN membranes has continued to push the boundary up through advanced membrane fabrication techniques and novel materials for fabricating the membranes. Despite the many advantages, OSN membranes still face such challenges as low solvent permeability and durability in harsh organic solvent conditions. To overcome these limitations, attempts have been made to incorporate nanomaterial fillers into OSN membranes to improve their overall performance. This review analyzes the potential and use of nanomaterials for OSN membranes, including covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal oxides (MOs) and carbon-based materials (CBMs). Recent advances in the state-of-the-art nano-based OSN membranes, in the form of thin-film nanocomposite (TFN) membranes and mixed matrix membranes (MMMs), are reviewed. Moreover, the separation mechanisms of OSN with nano-based membranes are discussed. The challenges faced by these OSN membranes are also elaborated, and recommendations for further research in this field are provided.

Treatment of Wastewater from Thermal Desorption for Remediation of Oil-Contaminated Soil by the Combination of Multiple Processes

Thermal desorption (TD) is one of the methods commonly used to remediate contaminated soil. However, as water is the liquid adsorbent of the off-gas treatment system in the TD stage, the wastewater generated after multiple cycles in the TD stage has low biodegradability and contains complex organic pollutants. In addition to petroleum hydrocarbon, there are also a lot of ammonia, emulsified oil, phenols, aldehydes, and ketones. In this study, effective removal of contaminants was achieved using a combined process of demulsification and flocculation (DF), ammonia stripping (AS), Fenton oxidation (FO), and reverse osmosis (RO). The combined process was optimized, and the maximum chemical oxygen demand (COD), NH3-N, turbidity, and extractable petroleum hydrocarbons (EPH) removal efficiencies reached 93.3%, 79.8%, 97.6%, and 99.9%, respectively. The FO was the key process for the efficient removal of contaminants. Ultraviolet-visible (UV/Vis), excitation-emission matrix (EEM), fluorescence spectroscopy, and gas chromatography-mass spectroscopy (GC-MS) showed that refractory macromolecular organic pollutants in water were removed, especially aromatics, phenols, and conjugated aldehydes or conjugated ketones, and further ring cleavage of benzene rings and carbocycles with carbon double bonds was observed. The cost-benefit analysis of the combined process was also carried out. The operating cost was 8.73 US$/m3, indicating that the combined process involved moderate costs for recalcitrant wastewater treatment. No studies have been published on combined processes for the treatment of wastewater from TD for the remediation of oil-contaminated soils. Therefore, this study could provide fundamental information based on experimental results and guidelines for wastewater treatment in engineering applications.

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes.

Tunable organic solvent nanofiltration in self-assembled membranes at the sub-1 nm scale

Organic solvent-stable membranes exhibiting strong selectivity and high permeance have the potential to transform energy utilization in chemical separation processes. A key goal is developing materials with uniform, well-defined pores at the 1-nm scale, with sizes that can be tuned in small increments with high fidelity. Here, we demonstrate a class of organic solvent-stable nanoporous membranes derived from self-assembled liquid crystal mesophases that display such characteristics and elucidate their transport properties. The transport-regulating dimensions are defined by the mesophase geometry and can be controlled in increments of ~0.1 nm by modifying the chemical structure of the mesogen or the composition of the mesophase. The highly ordered nanostructure affords previously unidentified opportunities for the systematic design of organic solvent nanofiltration membranes with tailored selectivity and permeability and for understanding and modeling rejection in nanoscale flows. Hence, these membranes represent progress toward the goal of enabling precise organic solvent nanofiltration.

Electrochemical cell recharging by solvent separation and transfer processes

Electrochemical conversion and storage of unutilized renewable energy will contribute to decarbonization. Here, we create the concept of a liquid electrochemical cell that discharges between the anodic and cathodic sides by reverse reactions of the same redox couple in different solvation states, which are created by differences in the mixture ratios of two solvents called the main solvent (MS) and the transferred solvent (TS). The cell can be charged by a transfer of the TS between the discharged anolyte and catholyte. As an example, we demonstrate a cell utilizing a ferro-/ferricyanide redox couple. Stable discharging and charging via the proposed method is achieved by utilizing water (MS) and acetone (TS). Additionally, dominating factors in the design of a high-performance system are discussed, focusing on the electron acceptability of the MS and the TS. The cell voltages are successfully tuned, and a cell voltage of 0.63 V is achieved by the combination of dimethyl sulfoxide (MS) and water (TS). Moreover, the cell can be customized by various electrochemical reaction systems, which can allow multiple options for the charging processes. This concept provides new approaches for the utilization of diverse energy sources as an input for the charging of electrochemical cells.

Preparation, characterization, and applications of Fe-based catalysts in advanced oxidation processes for organics removal: A review

Fe-based catalysts as low-cost, high-efficiency, and non-toxic materials display superior catalytic performances in activating hydrogen peroxide, persulfate (PS), peracetic acid (PAA), percarbonate (PC), and ozone to degrade organic contaminants in aqueous solutions. They mainly include ferrous salts, zero-valent iron, iron-metal composites, iron sulfides, iron oxyhydroxides, iron oxides, and supported iron-based catalysts, which have been widely applied in advanced oxidation processes (AOPs). However, there is lack of a comprehensive review systematically reporting their synthesis, characterization, and applications. It is imperative to evaluate the catalytic performances of various Fe-based catalysts in diverse AOPs systems and reveal the activation mechanisms of different oxidants by Fe-based catalysts. This work detailedly summarizes the synthesis methods and characterization technologies of Fe-based catalysts. This paper critically evaluates the catalytic performances of Fe-based catalysts in diverse AOPs systems. The effects of solution pH, reaction temperature, coexisting ions, oxidant concentration, catalyst dosage, and external energy on the degradation of organic contaminants in the Fe-based catalyst/oxidant systems and the stability of Fe-based catalysts are also discussed. The activation mechanisms of various oxidants and the degradation pathways of organic contaminants in the Fe-based catalyst/oxidant systems are revealed by a series of novel detection methods and characterization technologies. Future research prospects on the potential preparation means of Fe-based catalysts, practical applications, assistive technologies, and impact in AOPs are proposed.

Proton exchange membrane based on graphene oxide/polysulfone hybrid nano-composite for simultaneous generation of electricity and wastewater treatment

Microbial fuel cell (MFC) is a combined technology for simultaneous generation of electricity and wastewater treatment. In MFC, the proton exchange membrane (PEM) is an essential component affecting electricity generation. In the current study, two proton exchange membranes, namely sulfonated polyethersulfone (SPES) and graphene oxide/sulfonated -polyethersulfone hybrid nanocomposite (GO-SPES), were prepared and characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The collected information confirmed the successful preparation of the membranes. Moreover, contact angle measurements, ion exchange capacity and degree of sulfonation of the prepared membranes were determined. The results showed that the introduction of GO nanoparticles into SPES membrane improved its proton exchange capability and resulted in better performance. The power density and the current generated from SPES membrane were 60 mW/m² and 425 mA/m², respectively. For GO-SPES, the obtained power density was 101.2 mW/m² and the current was 613 mA/m². Both membranes showed comparable chemical oxygen demand (COD) removal efficiency of about 80%; suggesting that the prepared membranes are working efficiently in wastewater treatment as PEMs in MFCs. As a final point, the performance of GO-SPES membrane was compared to the performance of the well-known Nafion® 117 membrane and the results were promising. To conclude, the GO-SPES membrane is an outstanding membrane for use as PEM in MFCs for simultaneous generation of electricity and wastewater treatment.