Novel thin-film composite nanofiltration membranes consisting of a zwitterionic co-polymer for selenium and arsenic removal

Grafting Buffer Layer Strategy onto the Nanofiltration Membrane to Enhance Antifouling Properties toward Highly Efficient Desalination

Water treatment and seawater desalination are two areas in which nanofiltration (NF) membranes have gained significant attention. The permeability and contamination resistance of NF membranes are crucial for their application in ion separation. Herein, a zwitterion monomeric N-sulfobutylpiperazine (PIPBS) was designed and synthesized through an in situ ring-opening reaction between 1,4-butylsulfonic acid lactone and piperazine. A new hydrophilic structure is formed when PIPBS is chemically grafted with piperazine-trimesoyl chloride (PIP-TMC) onto the surface of the NF membrane, increasing the water flux and improving antifouling properties. NF performance was systematically investigated with respect to both the PIPBS concentration and reaction time. In addition to higher salt retention for NaSO4 (97.3%) and MgSO4 (94.1%), the optimized PTPM also displayed better ion selectivity for Na2SO4/NaCl. Sulfonic acid groups make membranes more hydrophilic, reducing contamination, deposition, and membrane pore plugging by direct contact with contaminants. In comparison to untreated NF membranes, due to the hydration of PIPBS on the membrane surface, the water flux increased by 2.3 times with a 13.6% grafting ratio for PTPM-1. Furthermore, PTPM had superior protein fouling resistance and an excellent ability to recover flux after contamination experiments and could withstand continuous filtration operations for 60 h with a stable flux of 10.98 L m-2 h-1 bar-1. The as-prepared NF membrane's excellent water flux, selective rejection of salts, and outstanding fouling resistance make it ideal for efficient desalination, and it also provides novel insights into the design of antifouling membranes.

Zwitterionic Nanochannels in Covalent Organic Framework Membranes for Improved Flux and Antifouling Property

Zwitterionic membranes demonstrate excellent antifouling property in water purification. The covalent organic frameworks (COFs), due to the ordered channels and abundant organic functional groups, have distinct superiority in constructing zwitterionic surfaces.Here, the zwitterionic COF membrane is prepared with precise framework structures and uniform charge distribution. The negatively charged 4,4'-diaminobiphenyl-2,2'-sisulphonic acid sodium (SA) and positively charged ethidium bromide (EB) fragments are used to react with 1,3,5-triformylphloroglucinol (TP) at the gas-liquid interface to prepare zwitterionic COF membrane. The complementary charged fragments in the inter-layer and inner-layer facilitate the formation of continuous and tight hydration layer on the membrane surface and pore walls to resist the adsorption of pollutants. The zwitterionic COF membrane effectively resists both negatively charged bovine serum albumin and positively charged lysozyme pollutants with flux recovery ratio (FRR) of 97% and 85%, respectively. Furthermore, the regular nano-channels and balanced interactions between water and surface/pore walls of the zwitterionic membrane result in outstanding permeability of up to 146 L m-2 h-1 bar-1 and excellent dye/salt separation selectivity. The water permeation and antifouling mechanism of membranes are elucidated by experimental and molecular dynamics calculation. Zwitterionic COF membranes can find promising applications in preparing high-performance antifouling membranes.

Elimination of hazardous Se(IV) through adsorption-coupled reduction by iron nanoparticles embedded on mesopores of chitin obtained from waste shrimp shells

Selenium is an essential nutrient for biological function. However, there is a detrimental effect on the aquatic environment associated with higher concentrations of > 40 µg/L. The utilization of waste shrimp shells for the removal of high-concentrated selenium from wastewater is a commendable strategy in both the pollution control and waste management sectors. In the present study, a chitin-iron polymer complex hybrid material (Fe@SHC) was prepared from shrimp shell-derived hydrochar (SHC), and the synthesized composite was successfully employed to uptake selenium from wastewater. The highest removal performance of 79.18 mg/g was attained by Fe@SHC, whereas the capacity of SHC was 15.30 mg/g. It was found that the calcium content of Fe@SHC (1.98%) was lower than that of SHC (25.20%) and pHzpc of Fe@SHC was extended to 7.78 compared with that of SHC (2.00). The abundance of protonated hydroxyl (-OH2+) and amine (-NH3+) functional groups that developed through the iron co-precipitations resulted in the improved adsorption performance of Fe@SHC. XPS analysis demonstrated that the captured Se(IV) species were converted into less hazardous Se(0), which is accompanied by the electron transfer with both N-C = O (acetyl amine) and -NH2 (amine) functional groups. Adsorption kinetics disclosed that the adsorption process was governed by chemical sorption, and the Sips isotherm model provided the most accurate description of the isotherm equilibrium. This study proposed an inexpensive and environmentally friendly method for effective decontamination of Se from wastewater.

Selenite Removal from Aqueous Solution Using Silica-Iron Oxide Nanocomposite Adsorbents

In recent years, during industrial development, the expanding discharge of harmful metallic ions from different industrial wastes (such as arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, or zinc) into different water bodies has caused serious concern, with one of the problematic elements being represented by selenium (Se) ions. Selenium represents an essential microelement for human life and plays a vital role in human metabolism. In the human body, this element acts as a powerful antioxidant, being able to reduce the risk of the development of some cancers. Selenium is distributed in the environment in the form of selenate (SeO₄^2-) and selenite (SeO₃^2-), which are the result of natural/anthropogenic activities. Experimental data proved that both forms present some toxicity. In this context, in the last decade, only several studies regarding selenium's removal from aqueous solutions have been conducted. Therefore, in the present study, we aim to use the sol-gel synthesis method to prepare a nanocomposite adsorbent material starting from sodium fluoride, silica, and iron oxide matrices (SiO₂/Fe(acac)₃/NaF), and to further test it for selenite adsorption. After preparation, the adsorbent material was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The mechanism associated with the selenium adsorption process has been established based on kinetic, thermodynamic, and equilibrium studies. Pseudo second order is the kinetic model that best describes the obtained experimental data. Also, from the intraparticle diffusion study, it was observed that with increasing temperature the value of the diffusion constant, K_diff, also increases. Sips isotherm was found to best describe the experimental data obtained, the maximum adsorption capacity being ~6.00 mg Se(IV) per g of adsorbent material. From a thermodynamic point of view, parameters such as ΔG⁰, ΔH⁰, and ΔS⁰ were evaluated, proving that the process studied is a physical one.

A single functionalized graphene nanocomposite in cross flow module for removal of multiple toxic anionic contaminants from drinking water

Polyether sulfone (PES)-based thin-film nanofiltration (TFN) membranes embedded with ferric hydroxide (Fe^III(OH)_x) functionalized graphene oxide (GO) nanoparticles were fabricated through interfacial polymerization for a generalized application in removal of a plethora of anionic and toxic water contaminants. Following the most relevant characterization, the newly synthesized membranes were fitted in a novel flat sheet cross-flow module, for experimental investigation on purification of live contaminated groundwater collected from different affected areas. The separation performances of the membranes in the flat sheet cross-flow module demonstrated that GOF membranes had higher selectivity for monovalent and divalent salt rejections than pristine GO membranes. Furthermore, both membranes were tested for simultaneously removing widely occurring hazardous ions of heavy metals and metalloids in groundwater, such as arsenic, selenium, chromium, and fluoride. Compared to the pristine GO and the reported membranes in the literature, the GOF membrane exhibited remarkable performance in terms of rejection efficiency (Cr (VI): 97.2%, Se (IV): 96.6%, As(V): 96.3%, F^- 88.4%) and sustained flux of 184 LMH (Lm^-2 h^-1) at an optimum transmembrane pressure of 16 bar. The investigated membrane module equipped with the GOF membrane proved to be a low-cost system with higher anionic rejection and sustained high flux at a comprehensive pH range, as evident over long hours of study vis-à-vis reported systems.

Single-Molecule Imaging in Commercial Stationary Phase Particles Using Highly Inclined and Laminated Optical Sheet Microscopy

We resolve the three-dimensional, nanoscale locations of single-molecule analytes within commercial stationary phase materials using highly inclined and laminated optical sheet (HILO) microscopy. Single-molecule fluorescence microscopy of chromatography can reveal the molecular heterogeneities that lead to peak broadening, but past work has focused on surfaces designed to mimic stationary phases, which have different physical and chemical properties than the three-dimensional materials used in real columns and membranes. To extend single-molecule measurements to commercial stationary phases, we immobilize individual stationary phase particles and modify our microscope for imaging at further depths with HILO, a method which was originally developed to resolve single molecules in cells of comparable size to column packing materials (∼5-10 μm). We describe and characterize how to change the angle of incidence to achieve HILO so that other researchers can easily incorporate this method onto their existing epi- or total internal reflection fluorescence microscopes. We show improvements up to a 32% in signal-to-background ratio and 118% in the number of single molecules detected within stationary phase particles when using HILO compared to epifluorescence. By controlling the objective position relative to the sample, we produce three-dimensional maps of molecule locations throughout entire stationary phase particles at nanoscale lateral and axial resolutions. The number of localized molecules remains constant axially throughout isolated stationary phase particles and between different particles, indicating that heterogeneity in a separation would not be caused by such affinity differences at microscales but instead kinetic differences at nanoscales on identifiable and distinct adsorption sites.

Recovery of Metals from Wastewater-State-of-the-Art Solutions with the Support of Membrane Technology

This paper discusses the most important research trends in the recovery of metals from industrial wastewater using membrane techniques in recent years. Particular attention is paid to the preparation of new membranes with the required filtration and separation properties. At the same time, possible future applications are highlighted. The aspects discussed are divided into metals in order to clearly and comprehensibly list the most optimal solutions depending on the composition of the wastewater and the possibility of recovering valuable components (metalloids, heavy metals, and platinum group metals). It is shown that it is possible to effectively remove metals from industrial wastewater by appropriate membrane preparation (up to ~100%), including the incorporation of functional groups, nanoparticles on the membrane surface. However, it is also worth noting the development of hybrid techniques, in which membrane techniques are one of the elements of an effective purification procedure.

Novel polyaniline-polyethersulfone nanofiltration membranes: effect of in situ polymerization time on structure and desalination performance

In this research, novel polyaniline-layered nanofiltration membranes were prepared by phase inversion of base polyethersulfone (PES) membranes and subsequent in situ solution-phase deposition of polyaniline as a thin surface layer. In these composite membranes, the impact of the polyaniline deposition time on steric hindrance and electrostatic interactions during permeation was elucidated. The chemical structure, thermal stability, and mechanical properties of the PES and PANI-PES membranes were investigated using Fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA), respectively. The membranes' porosity and pore size decreased as PANI deposition time increased. As PANI deposition time increased, PANI layered nanofiltration membranes exhibited improved thermal stability but deteriorated mechanical characteristics due to free radical destruction from prolonged exposure to the oxidant. These PANI-PES membranes showed 43% rejection (NaCl) at 1.7 bar coupled with a flux of 11.59 L h-1 m2 that is quite promising when comparing with similar Nanofilteration (NF) membranes in the literature and commercial NF membranes, as well. As the deposited layer, PANI is partially doped; hence, permeation results have been interpreted in terms of steric hindrance and electrostatic repulsion by electrochemical PANI layering.

Nanofiltration Membranes with Crumpled Polyamide Films: A Critical Review on Mechanisms, Performances, and Environmental Applications

Nanofiltration (NF) membranes have been widely applied in many important environmental applications, including water softening, surface/groundwater purification, wastewater treatment, and water reuse. In recent years, a new class of piperazine (PIP)-based NF membranes featuring a crumpled polyamide layer has received considerable attention because of their great potential for achieving dramatic improvements in membrane separation performance. Since the report of novel crumpled Turing structures that exhibited an order of magnitude enhancement in water permeance ( Science 2018, 360 (6388), 518-521), the number of published research papers on this emerging topic has grown exponentially to approximately 200. In this critical review, we provide a systematic framework to classify the crumpled NF morphologies. The fundamental mechanisms and fabrication methods involved in the formation of these crumpled morphologies are summarized. We then discuss the transport of water and solutes in crumpled NF membranes and how these transport phenomena could simultaneously improve membrane water permeance, selectivity, and antifouling performance. The environmental applications of these emerging NF membranes are highlighted, and future research opportunities/needs are identified. The fundamental insights in this review provide critical guidance on the further development of high-performance NF membranes tailored for a wide range of environmental applications.

Performance and Mechanism of As(III/V) Removal from Aqueous Solution by Fe3O4-Sunflower Straw Biochar

Humans and ecosystems are severely damaged by the existence of As(III/V) in the aquatic environment. Herein, an advanced Fe₃O₄@SFBC (Fe₃O₄-sunflower straw biochar) adsorbent was fabricated by co-precipitation method with sunflower straw biochar (SFBC) prepared at different calcination temperatures and different SFBC/Fe mass ratios as templates. The optimal pH for As(III/V) removal was investigated, and Fe₃O₄@SFBC shows removal efficiency of 86.43% and 95.94% for As(III) and As(V), respectively, at pH 6 and 4. The adsorption effect of calcining and casting the biochar-bound Fe₃O₄ obtained at different temperatures and different SFBC/Fe mass ratios were analyzed by batch experiments. The results show that when the SFBC biochar is calcined at 450 °C with an SFBC/Fe mass ratio of 1:5, the adsorption of As(III) and As(V) reaches the maximum, which are 121.347 and 188.753 mg/g, respectively. Fe₃O₄@SFBC morphology, structure, surface functional groups, magnetic moment, and internal morphology were observed by XRD, FTIR, SEM, TEM, and VSM under optimal working conditions. The material shows a small particle size in the range of 12-14 nm with better magnetic properties (54.52 emu/g), which is suitable for arsenic removal. The adsorption mechanism of As(III/V) by Fe₃O₄@SFBC indicates the presence of chemisorption, electrostatic, and complexation. Finally, the material was used for five consecutive cycles of adsorption-desorption experiments, and no significant decrease in removal efficiency was observed. Therefore, the new adsorbent Fe₃O₄@SFBC can be efficiently used for arsenic removal in the aqueous system.

Novel triazine-based cationic covalent organic polymers for highly efficient and selective removal of selenate from contaminated water

Selenium (Se) removal from contaminated water has become a major environmental problem in recent years. Designing efficient and selective materials for selenium adsorption is urgent and still represents a great challenge. Herein, two novel cationic covalent triazine frameworks (CTFS-Cl and CTFL-Cl) are developed for the first time and employed as a new class of Se adsorbents. The results from systematic adsorption experiments indicate that these materials can adsorb SeO₄^2- in a wide range of pH values (2-11) with fast kinetics (5 min), outstanding adsorption capacity, and excellent selectivity over other competing anions. The maximum adsorption capacity achieved (149.3 mg/g by CTFS-Cl) constitutes one of the highest values among the organic polymeric materials. More importantly, after a single step adsorption, these materials can reduce the Se concentrations to lower than 10 μg/L, the lowest drinking water standard in the world. The adsorption mechanism was probed by XPS technique, EDS analysis, adsorption experiments, and DFT calculations, which reveals that anion exchange between Cl^- and SeO₄^2- is the main driving force for Se adsorption. Additionally, CTFS-Cl and CTFL-Cl perform well toward real contaminated river water sample with the residual Se being less than 8.49 μg/L. This work demonstrates the excellent performance of CTFs-based materials with great application prospect for Se removal in contaminated water treatment.

Advanced Polymeric Nanocomposites for Water Treatment Applications: A Holistic Perspective

Water pollution remains one of the greatest challenges in the modern era, and water treatment strategies have continually been improved to meet the increasing demand for safe water. In the last few decades, tremendous research has been carried out toward developing selective and efficient polymeric adsorbents and membranes. However, developing non-toxic, biocompatible, cost-effective, and efficient polymeric nanocomposites is still being explored. In polymer nanocomposites, nanofillers and/or nanoparticles are dispersed in polymeric matrices such as dendrimer, cellulose, resins, etc., to improve their mechanical, thermophysical, and physicochemical properties. Several techniques can be used to develop polymer nanocomposites, and the most prevalent methods include mixing, melt-mixing, in-situ polymerization, electrospinning, and selective laser sintering techniques. Emerging technologies for polymer nanocomposite development include selective laser sintering and microwave-assisted techniques, proffering solutions to aggregation challenges and other morphological defects. Available and emerging techniques aim to produce efficient, durable, and cost-effective polymer nanocomposites with uniform dispersion and minimal defects. Polymer nanocomposites are utilized as filtering membranes and adsorbents to remove chemical contaminants from aqueous media. This study covers the synthesis and usage of various polymeric nanocomposites in water treatment, as well as the major criteria that influence their performance, and highlights challenges and considerations for future research.

A Bibliometric Analysis of Research on Selenium in Drinking Water during the 1990-2021 Period: Treatment Options for Selenium Removal

A bibliometric analysis based on the Scopus database was carried out to summarize the global research related to selenium in drinking water from 1990 to 2021 and identify the quantitative characteristics of the research in this period. The results from the analysis revealed that the number of accumulated publications followed a quadratic growth, which confirmed the relevance this research topic is gaining during the last years. High research efforts have been invested to define safe selenium content in drinking water, since the insufficient or excessive intake of selenium and the corresponding effects on human health are only separated by a narrow margin. Some important research features of the four main technologies most frequently used to remove selenium from drinking water (coagulation, flocculation and precipitation followed by filtration; adsorption and ion exchange; membrane-based processes and biological treatments) were compiled in this work. Although the search of technological options to remove selenium from drinking water is less intensive than the search of solutions to reduce and eliminate the presence of other pollutants, adsorption was the alternative that has received the most attention according to the research trends during the studied period, followed by membrane technologies, while biological methods require further research efforts to promote their implementation.

The occurrence, transformation and control of selenium in coal-fired power plants: Status quo and development

As a trace element, selenium can cause serious harm to organisms when the concentration is too high. Coal-fired power plants are the main source of man-made selenium emissions. How to control the selenium pollution of coal-fired power plants to realize the renewable selenium and the sustainability of coal has not attracted enough attention from the whole world. This paper outlines the conversion and occurrence of selenium in coal-fired power plants. A small part of the selenium produced by combustion can be removed by selective catalytic reduction (SCR) and electrostatic precipitator (ESP) after the gas phase undergoes physical condensation and chemical adsorption to combine with the particulate matter in the flue gas.Because the chemical precipitation method has poor selenium removal effect, the remaining part enters the flue gas desulfurization absorption tower and can be enriched in the desulfurization slurry. The occurrence situation and conversion pathway of selenium in desulfurization slurry are introduced subsequently, the research progress of selenium removal from wet desulfurization wastewater is reviewed from three aspects: physics, biology and chemistry. We believe that the coupling application of oxidation-reduction potential (ORP) and pH can optimize selenium removal in the desulfurization system by improving the oxidation control. As a technology for wet desulfurization system to treat selenium pollution, it has a good development prospect in near future.Implications: Selenium is a trace element present in coal. It is not only of great significance to the life activities of organisms, but also a kind of rare resource. As the most important source of man-made emissions, coal-fired power plants will cause waste of selenium resources and selenium pollution in the surrounding environment. In this study, the occurrence, conversion and control of selenium in coal-fired power plants were systematically sorted out and analyzed. It is helpful for scholars to study the selenium transformation process more deeply. It is of great significance for policy formulation of recommended control technologies and emission limits. It is of great value for the formulation of recommended control technology and the in-depth study of the selenium transformation process.

Multirole Regulations of Interfacial Polymerization Using Poly(acrylic acid) for Nanofiltration Membrane Development

Effective control of monomer diffusion and reaction rate is the key to achieving a controlled interfacial polymerization (IP) and a high-performance nanofiltration (NF) membrane. Herein, an integration of multirole regulations was synchronously realized using poly(acrylic acid) (PAA) as an active additive in a piperazine (PIP) aqueous phase. Thanks to synergistic interactions, including hydrogen bonding, electrostatic interaction, and covalent bonding between PAA and PIP molecules, together with the increased viscosity of the solution, PIP diffusion was rationally controlled. Moreover, interfacial polycondensation was also restrained via the modestly reduced pH of the aqueous solution. These contribute to the formation of a thinner, looser, more hydrophilic, and higher negatively charged PAA-decorated polyamide selective layer with a unique nanostrand-nodule morphology. The harvested NF-PAA/PIP membrane showed an ∼70% rise in water permeability (up to 23.5 L·m-2·h-1·bar-1) while retaining high Na2SO4 and dye rejections. Furthermore, the optimized NF-PAA/PIP membrane presented a superior fouling resistance capability for typical pollutants, as well as long-term stability during successive filtration. Thus, this work offers a straightforward and impactful approach to regulating IP and promoting NF membrane properties.

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

Recent advances in technologies for removal and recovery of selenium from (waste)water: A systematic review

Selenium (Se) is distributed into different environmental compartments by natural and anthropogenic activities, and generally discharged in the form of selenate [SeO₄^2-] and selenite [SeO₃^2-], which are both toxic. Physical-chemical and biological treatment processes have been reported to exhibit good treatment efficiencies for Se from aqueous streams, only a few demonstrated to achieve effluent concentrations <5 μg/L. Moreover, there are only a few numbers of studies that describe the progress in technological developments over the last decade. Therefore, to unify the state of knowledge, identify ongoing research trends, and determine the challenges associated with available technologies, this systematic review critically analyses the published research on Se treatment. Specific topics covered in this review include (1) Se chemistry, toxicity, sources and legislation, (2) types of Se treatment technologies, (3) development in Se treatment approaches, (4) Se recovery and circular economy and (5) future prospects. The current research has been found to majorly focused on Se removal via adsorption techniques. However, the key challenges facing Se treatment technologies are related to the presence of competing ions in the solution and the persistence of selenate compared to selenite during their reduction.

The Use of Polymer Membranes to Counteract the Risk of Environmental of Soil and Water Contamination

Chemical, biological, radiological, or nuclear (CBRN) contamination of the environment is a significant threat to human health and life as well as environmental safety. It is then necessary to take actions aimed at minimizing and eliminating the threat. Depending on the type of contamination, various methods are used, including sorption, biodegradation, separation, or ion exchange processes in which membranes play an important role. The type of membrane is selected in respect of both the environment and the type of neutralized pollutants. Therefore, the production and modification of membranes are being adapted to the type of contamination and the purpose of the work. This article presents examples of membranes and their possible applications depending on the part of the environment subject to reclamation and the type of contamination.

Organic Nanobowls Modified Thin Film Composite Membrane for Enhanced Purification Performance toward Different Water Resources

The structure and composition of nanofillers have a significant influence on polyamide nanofiltration (NF) membranes. In this work, an asymmetric organic nanobowl containing a concave cavity was synthesized and incorporated into a polyamide layer to prepare thin film nanocomposite (TFN) membranes via an interfacial polymerization process. Benefiting from the hydrophilicity, hollow cavity and charge property of the compatible organic nanobowls, the separation performance of the developed TFN membrane was significantly improved. The corresponding water fluxes increased to 119.44 ± 5.56, 141.82 ± 3.24 and 130.27 ± 2.05 L/(m²·h) toward Na₂SO₄, MgCl₂ and NaCl solutions, respectively, with higher rejections, compared with the control thin film composite (TFC) and commercial (CM) membranes. Besides this, the modified TFN membrane presented a satisfying purification performance toward tap water, municipal effluent and heavy metal wastewater. More importantly, a better antifouling property of the TFN membrane than TFC and CM membranes was achieved with the assistance of organic nanobowls. These results indicate that the separation performance of the TFN membrane can be elevated by the incorporation of organic nanobowls.

Metal ferrite incorporated polysulfone thin-film nanocomposite membranes for wastewater treatment

Effluents from food, fermentation, and sugar industries contain a large quantity of glucose which has to be removed to limit the chemical oxygen demand (COD) of the water discharged. This work proposes novel thin-film nanocomposite (TFN) membranes incorporated with MgFe₂O₄ and ZnFe₂O₄ nanoparticles to address this concern. The nanoparticles synthesized by the sol-gel method was extensively characterized and then incorporated into the active polyamide layer of the thin-film composite polysulfone membranes. The change in membrane morphology, wettability, chemical structure, and mechanical strength with the incorporation of nanoparticles was studied in detail. Membranes with 0.005 wt.% MgFe₂O₄ nanoparticle exhibited highest glucose rejection (96.52 ± 2.35%) at 10 bar, 25 °C, and sufficiently high pure water flux (50.54 ± 1.92 L/m²h). This membrane also displayed 69.1 ± 5.12% salt rejection when challenged with 2000 ppm synthetic NaCl solution.

Runge-Kutta Numerical Method Followed by Richardson's Extrapolation for Efficient Ion Rejection Reassessment of a Novel Defect-Free Synthesized Nanofiltration Membrane

A defect-free, loose, and strong layer consisting of zirconium (Zr) nanoparticles (NPs) has been successfully established on a polyacrylonitrile (PAN) ultrafiltration substrate by an in-situ formation process. The resulting organic–inorganic nanofiltration (NF) membrane, NF-PANZr, has been accurately characterized not only with regard to its properties but also its structure by the atomic force microscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy. A sophisticated computing model consisting of the Runge–Kutta method followed by Richardson extrapolation was applied in this investigation to solve the extended Nernst–Planck equations, which govern the solute particles’ transport across the active layer of NF-PANZr. A smart, adaptive step-size routine is chosen for this simple and robust method, also known as RK4 (fourth-order Runge–Kutta). The NF-PANZr membrane was less performant toward monovalent ions, and its rejection rate for multivalent ions reached 99.3%. The water flux of the NF-PANZr membrane was as high as 58 L · m⁻² · h⁻¹. Richardson’s extrapolation was then used to get a better approximation of Cl⁻ and Mg²⁺ rejection, the relative errors were, respectively, 0.09% and 0.01% for Cl⁻ and Mg²⁺. While waiting for the rise and expansion of machine learning in the prediction of rejection performance, we strongly recommend the development of better NF models and further validation of existing ones.

Poly(Homopiperazine-Amide) Thin-Film Composite Membrane for Nanofiltration of Heavy Metal Ions

The development of membrane-based technologies for the treatment of wastewater streams and resources containing heavy metal ions is in high demand. Among various technologies, nanofiltration (NF) membranes are attractive choices, and the continuous development of novel materials to improve the state-of-the-art NF membranes is highly desired. Here, we report on the synthesis of poly(homopiperazine-amide) thin-film composite (HTFC)-NF membranes, using homopiperazine (HP) as a monomer. The surface charge, hydrophilicity, morphology, cross-linking density, water permeation, solute rejection, and antifouling properties of the fabricated NF membranes were evaluated. The fabricated HTFC NF membranes demonstrated water permeability of 7.0 ± 0.3 L/(m2 h bar) and rejected Na2SO4, MgSO4, and NaCl with rejection values of 97.0 ± 0.6, 97.4 ± 0.5, and 23.3 ± 0.6%, respectively. The membranes exhibit high rejection values of 98.1 ± 0.3 and 96.3 ± 0.4% for Pb2+ and Cd2+ ions, respectively. The fouling experiment with humic acid followed by cross-flow washing of the membranes indicates that a flux recovery ratio (FRR) of 96.9 ± 0.4% can be obtained.

Effect of the Zwitterion, p(MAO-DMPA), on the Internal Structure, Fouling Characteristics, and Dye Rejection Mechanism of PVDF Membranes

The zwitterion poly-(maleic anhydride-alt-1-octadecene-3-(dimethylamino)-1-propylamine) (p(MAO-DMPA)) synthesized using a ring-opening reaction was used as a poly(vinylidene fluoride) (PVDF) membrane modifier/additive during phase inversion process. The zwitterion was characterized using proton nuclear magnetic resonance (¹HNMR) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Atomic force microscopy (AFM), field emission scanning electron microscope (SEM), FTIR, and contact angle measurements were taken for the membranes. The effect of the zwitterionization content on membrane performance indicators such as pure water flux, membrane fouling, and dye rejection was investigated. The morphology of the membranes showed that the increase in the zwitterion amount led to a general decrease in pore size with a concomitant increase in the number of membrane surface pores. The surface roughness was not particularly affected by the amount of the additive; however, the internal structure was greatly influenced, leading to varying rejection mechanisms for the larger dye molecule. On the other hand, the wettability of the membranes initially decreased with increasing content to a certain point and then increased as the membrane homogeneity changed at higher zwitterion percentages. Flux and fouling properties were enhanced through the addition of zwitterion compared to the pristine PVDF membrane. The high (>90%) rejection of anionic dye, Congo red, indicated that these membranes behaved as ultrafiltration (UF). In comparison, the cationic dye, rhodamine 6G, was only rejected to <70%, with rejection being predominantly electrostatic-based. This work shows that zwitterion addition imparted good membrane performance to PVDF membranes up to an optimum content whereby membrane homogeneity was compromised, leading to poor performance at its higher loading.

Carbodiimide-assisted zwitterionic modification of poly(piperazine amide) thin-film composite membrane for enhanced separation and anti-depositing performances to cationic/anionic dye aqueous solutions

In this work, a novel method of carbodiimide-assisted zwitterionic modification was proposed and implemented to incorporate zwitterionic moieties onto poly(piperazine amide) membrane for improved water permeability and anti-depositing property, which are crucial for highly efficient nanofiltration of dye-contained effluents. Carboxyl groups of polyamide layer were firstly transferred into N-acylurea using excess l-ethyl-3-(3-(dimethylamino)propyl)-carbodiimide. Zwitterions were then incorporated through ring-opening reaction between tertiary amine groups of N-acylurea and 1, 4-butanesultone. Carbodiimide-assisted zwitterionic modification was verified by ATR-IR and XPS analyses and was found to not affect membrane pore size but significantly enhance membrane's permeation and anti-dye-deposition performances. Compared with those of virgin membrane, water permeabilities of the desired zwitterionic membrane to pure water, Congo red aqueous solution and Victoria blue B aqueous solution were higher by 42.9, 62.3 and 95.2 %, respectively, hydraulic resistances from irreversible deposition of Congo red and Victoria blue B molecules were dramatically lowered by 68.4 and 91.8 %, respectively. Furthermore, the perm-selectivity performance of the desired zwitterionic membrane in terms of molecular weight cut-off and pure water permeability was better than most of the reported zwitterionic membranes, and the separation and anti-depositing performances to both anionic and cationic dye aqueous solutions were better than commercial membrane NF270.

Synthesis of Fe-impregnated biochar from food waste for Selenium(Ⅵ) removal from aqueous solution through adsorption: Process optimization and assessment

Iron-impregnated food waste biochar (Fe-FWB) was synthesized for Se(Ⅵ) removal from aqueous solution. The effect and interactive effects of different parameters including pyrolysis time, temperature, and Fe concentration were explored using response surface methodology (RSM) to enhance conditions to achieve the highest Se(Ⅵ) removal using Fe-FWB. Pyrolysis time was not significant for Se(Ⅵ) adsorption capacity of Fe-FWB, but temperature and Fe concentration were found to be significant. The highest adsorption was achieved at 3.47 h and 495.0 °C with an Fe concentration of 0.44 M. Fe-FWB synthesized under optimum conditions were used to investigate the kinetic, equilibrium, and thermodynamic adsorption of Se(Ⅵ). Se(Ⅵ) adsorption reached equilibrium within 6 h, and both pseudo-second order and pseudo-first order models were suitable for describing kinetic Se(Ⅵ) adsorption. The Freundlich model was found to suitably fit the equilibrium adsorption data than the Langmuir model. The highest adsorption capacity of Fe-FWB for Se(Ⅵ) was 11.7 mg g^-1. Se(Ⅵ) adsorption on Fe-FWB was endothermic and spontaneous. The enthalpy change for Se(Ⅵ) adsorption was 54.4 kJ mol^-1, and the entropy change was negative at 15-35 °C. The increment of solution pH from 3 to 11 decreased the Se(Ⅵ) adsorption from 19.2 to 7.4 mg g^-1. The impact of interfering anions on Se(Ⅵ) adsorption followed the lineup: HCO₃^- > HPO₄^2- > SO₄^2- > NO₃^-. When compared to some adsorbents, the adsorption capacity of Se(Ⅵ) onto Fe-FWB was comparable even at neutral pH and the Fe-FWB was granular. These results indicate that Fe-FWB has prospective application in the removal of Se(Ⅵ) from aqueous solutions.

One-dimensional graphene for efficient aqueous heavy metal adsorption: Rapid removal of arsenic and mercury ions by graphene oxide nanoribbons (GONRs)

There is a knowledge gap for the application of one-dimensional graphene in the adsorption process. Our hypothesis was based on the fact that graphene oxide nanoribbons (GONRs) as one-dimensional graphene with more desired edges and specific surface area than other carbonaceous nanomaterials have more oxygen containing functional groups (active sites) on their edges and basal planes and therefore are more capable in adsorption of pollutants. In this regard, we synthesized GONRs by unzipping of multi-walled carbon nanotubes (MWCNTs) and investigated the adsorption behavior of GONRs by ultrasonic-assisted adsorptive removal of As(V) and Hg(II) ions from aqueous solution. The obtained results showed that As(V) ions are more favorably adsorbed onto the GONRs than Hg(II) ions and with increasing initial As(V) and Hg(II) ions concentration to 300 ppm, the equilibrium adsorption uptake of the synthesized GONRs increases to 155.61 and 33.02 mg/g for As(V) and Hg(II) ions, respectively through a rapid separation process in just 12 min. Also, three kinetic models and Freundlich and Langmuir adsorption isotherms were applied to evaluate the obtained experimental results. Our findings highlight the potential application of GONRs as one-dimensional graphene adsorbent with more desired edges than MWCNTs and graphene oxide (GO) and high adsorption capacity for selective removal of heavy metals.

Nanofiltration for Arsenic Removal: Challenges, Recent Developments, and Perspectives

Arsenic (As) removal is of major significance because inorganic arsenic is highly toxic to all life forms, is a confirmed carcinogen, and is of significant environmental concern. As contamination in drinking water alone threatens more than 150 million people all over the world. Therefore, several conventional methods such as oxidation, coagulation, adsorption, etc., have been implemented for As removal, but due to their cost-maintenance limitations; there is a drive for advanced, low cost nanofiltration membrane-based technology. Thus, in order to address the increasing demand of fresh and drinking water, this review focuses on advanced nanofiltration (NF) strategy for As removal to safeguard water security. The review concentrates on different types of NF membranes, membrane fabrication processes, and their mechanism and efficiency of performance for removing As from contaminated water. The article provides an overview of the current status of polymer-, polymer composite-, and polymer nanocomposite-based NF membranes, to assess the status of nanomaterial-facilitated NF membranes and to incite progress in this area. Finally, future perspectives and future trends are highlighted.

Polyamide nanofilms synthesized via controlled interfacial polymerization on a "jelly" surface

A thermal-sensitive "jelly" was used to control the diffusion of a diamine monomer for synthesizing polyamide free-standing nanofilms with an adjustable thickness of 5-35 nm. The reduced reaction rate of the interfacial polymerization at the hexane-"jelly" interface made the synthesized nanofilms show high water permeation flux and suitable salt rejection, and they also have highly negative surface charges and fairly smooth surfaces.

Superhydrophilicity and strong salt-affinity: Zwitterionic polymer grafted surfaces with significant potentials particularly in biological systems

In recent years, zwitterionic polymers have been frequently reported to modify various surfaces to enhance hydrophilicity, antifouling and antibacterial properties, which show significant potentials particularly in biological systems. This review focuses on the fabrication, properties and various applications of zwitterionic polymer grafted surfaces. The "graft-from" and "graft-to" strategies, surface grafting copolymerization and post zwitterionization methods were adopted to graft lots type of the zwitterionic polymers on different inorganic/organic surfaces. The inherent hydrophilicity and salt affinity of the zwitterionic polymers endow the modified surfaces with antifouling, antibacterial and lubricating properties, thus the obtained zwitterionic surfaces show potential applications in biosystems. The zwitterionic polymer grafted membranes or stationary phases can effectively separate plasma, water/oil, ions, biomolecules and polar substrates. The nanomedicines with zwitterionic polymer shells have "stealth" effect in the delivery of encapsulated drugs, siRNA or therapeutic proteins. Moreover, the zwitterionic surfaces can be utilized as wound dressing, self-healing or oil extraction materials. The zwitterionic surfaces are expected as excellent support materials for biosensors, they are facing the severe challenges in the surface protection of marine facilities, and the dense ion pair layers may take unexpected role in shielding the grafted surfaces from strong electromagnetic field.

Techno-Economic Evaluation of Iron and Aluminum Coagulants on Se(IV) Removal

Research on selenium pollution in natural waters is continuous and discouraging. In this study, coagulation/precipitation was applied with the use of Fe(II), Fe(III), and poly-aluminum chloride (PACl) salts for Se(IV) removal at concentration range 10–100 μg Se(IV)/L that is commonly found in drinking waters. Prehydrolyzed Fe(III)-FeCl3 delivered the best uptake capacity (Q10 = 8.9 mg Se(IV)/g Fe(III) at pH 6) at the residual concentration equal to the drinking water regulation limit of 10 μg/L. This was much higher than the efficiencies achieved when applying the other coagulants: i.e., Q10 = 7.3 mg Se(IV)/g Fe3+-FeClSO4, Q10 = 6.4 mg Se(IV)/g prehydrolyzed Fe(III)-Fe2(SO4)3 and 0.7 mg Se(IV)/g Al-PACl at pH 6, and Q10 = 0.45 mg Se(IV)/g Fe(II) at pH 7.2. Comparing the different sources of Fe(III), it is apparent that Se(IV) uptake capacity is inhibited by the presence of SO42− in crystal structure of prehydrolyzed Fe2(SO4)3, while prehydrolyzed FeCl3 favors Se(IV) uptake. Temperature effect data showed that coagulation/precipitation is exothermic. In techno-economic terms, the optimal conditions for Se(IV) removal are coagulation/precipitation at pH values lower than 7 using prehydrolyzed Fe(III)-FeCl3, which provides a combination of minimum sludge production and lower operating cost.

Defect-engineered UiO-66-NH2 modified thin film nanocomposite membrane with enhanced nanofiltration performance

Defect-engineered UiO-66-NH₂ was introduced into a polyamide layer to form a thin film nanocomposite (TFN) membrane.