Membrane modification with carbon nanomaterials for fouling mitigation: A review

This paper provides a comprehensive overview of recent advancements in membrane modification for fouling mitigation in various water treatment processes, employing carbon nanomaterials such as fullerenes, nanodiamonds, carbon quantum dots, carbon nanotubes, and graphene oxide. Currently, using different carbon nanomaterials for polymeric membrane fouling mitigation is at various stages: CNT-modified membranes have been studied for more than ten years and have already been tested in pilot-scale setups; tremendous attention has been paid to utilizing graphene oxide as a modifying agent, while the research on carbon quantum dots' influence on the membrane antifouling properties is in the early stages. Given the intricate nature of fouling as a colloidal phenomenon, the review initially delves into the factors influencing the fouling process and explores strategies to address it. The diverse chemistry and antibacterial properties of carbon nanomaterials make them valuable for mitigating scaling, colloidal, and biofouling. This review covers surface modification of existing membranes using different carbon materials, which can be implemented as a post-treatment procedure during membrane fabrication. Creating mixed-matrix membranes by incorporating carbon nanomaterials into the polymer matrix requires the development of new synthetic procedures. Additionally, it discusses promising strategies to actively suppress fouling through external influences on modified membranes. In the concluding section, the review compares the effectiveness of carbon materials of varying dimensions and identifies key characteristics influencing the antifouling properties of membranes modified with carbon nanomaterials.

Removal of pharmaceutically active compounds from water sources using nanofiltration and reverse osmosis membranes: Comparison of removal efficiencies and in-depth analysis of rejection mechanisms

Trace organic compounds from effluent streams are not completely removed by conventional purification techniques and hence, contaminating groundwater sources. Herein, we report the removal efficiency and rejection mechanisms of three common pharmaceutically active compounds (PhACs); caffeine (CFN), omeprazole (OMZ), and sulfamethoxazole (SMX), using commercial nanofiltration (NF) and reverse osmosis (RO) membranes with different surface characteristics. The RO membranes showed near-complete removal of all PhACs with rejection rates >99%. On the other hand, retention capabilities for the NF membranes varied and were influenced by the characteristics of the PhACs, membranes, and the feed solution. In general, during long-term testing, the rejection did not show much variation and followed a trend compatible with the size exclusion (steric hindrance) mechanism. When a real matrix was used, the rejection of CFN by the more tight NF membranes, HL TFC and NFW decreased by ∼10%, whereas the removal of SMX by the loose NF membrane, XN45, increased by the same ratio. In short-term testing, the rejection of negatively charged SMX increased significantly (∼20-40%) at a higher pH of ∼8 and in the presence of salts. Fouling by the PhACs was more severe on the high-flux NF membranes, HL TFC and XN45, as witnessed by the significant change in Contact angle (CA) values (∼25-50°) as well as the flux decline (∼15%) during long-term testing. To summarize, the removal of PhACs by membranes is a complex phenomenon and depends upon a combination of several factors.

Removal of chloride from water and wastewater: Removal mechanisms and recent trends

Increased chloride concentration can cause salinization, which has become a serious and widespread environmental problem nowadays. This review aims at providing comprehensive and state-of-the-art knowledge and insights of technologies for chloride removal. Mechanisms for chloride removal mainly include chemical precipitation, adsorption, oxidation and membrane separation. In chemical precipitation, chloride removal by forming CuCl, AgCl, BiOCl and Friedel's salt. Adsorbents used in chloride removal mainly include ion exchangers, bimetal oxides and carbon-based electrodes. Oxidation for chloride removal contains ozone-based, electrochemical and sulfate radical-based oxidation. Membrane separation for chloride removal consists of diffusion dialysis, nanofiltration, reverse osmosis and electrodialysis. In this review, we specifically proposed the factors that affect chloride removal process and the corresponding strategies for improving removal efficiency. In the last section, the remaining challenges of method explorations and material developments were stated to provide guidelines for future development of chloride removal technologies.

Functional GO-based membranes for water treatment and desalination: Fabrication methods, performance and advantages. A review

Graphene oxide (GO) and GO-based materials have gained a significant interest in the membrane synthesis and functionalization sector in the recent years. Inspired by their unique and tuneable properties, several GO-based nanomaterials have been investigated and utilized as effective nanofillers for various membranes in the water treatment, purification and desalination sectors. This paper comprehensively reviews the recent advances of GO utilization in pressure, concentration and thermal-driven membrane processes. A brief overview on GO particles, properties, synthesis and functionalization methods was provided. The conventional and the state-of-art fabrication methods of GO-based membranes were summarized and discussed, and consequently the GO-based membranes were classified into different categories. The applications, types, and the performance in terms of flux and rejection were summarized and reviewed. The advantages of GO-based membranes in terms of antifouling properties, bactericidal effects, mechanical strength and stability have been reviewed, too. The review gives insights on the future perspectives of GO functional materials and their potential use in the various membrane processes discussed herein.

Ongoing progress on novel nanocomposite membranes for the separation of heavy metals from contaminated water

Membranes, as the primary separation element of membrane-based processes, have greatly attracted the attention of researchers in several water treatment applications, including wastewater treatment, water purification, water disinfection, toxic and non-toxic chemical molecules, heavy metals, among others. Today, the removal of heavy metals from water has become challenging, in which chemical engineers are approaching new materials in membrane technologies. Therefore, the current review elucidates the progress of using different concepts of membranes and potential novel materials for such separations, identifying that polymeric membranes can exhibit a removal efficiency from 77 up to 99%; while novel nanocomposite membranes are able to offer complete removal of heavy metals (up to 100%), together with unprecedented permeation rates (from 80 up to 1, 300 L m^-2 h^-1). Thereby, the review also addresses the highlighted literature survey of using polymeric and nanocomposite membranes for heavy metal removal, highlighting the relevant insights and denoted metal uptake mechanisms. Moreover, it gives up-to-date information related to those novel nanocomposite materials and their contribution to heavy metals separation. Finally, the concluding remarks, future perspectives, and strategies for new researchers in the field are given according to the recent findings of this comprehensive review.

Chitosan-Based Nanocomposite Polymeric Membranes for Water Purification-A Review

During the past few years, researchers have focused their attention on developing innovative nanocomposite polymeric membranes with applications in water purification. Natural and synthetic polymers were considered, and it was proven that chitosan-based materials presented important features. This review presents an overview regarding diverse materials used in developing innovative chitosan-based nanocomposite polymeric membranes for water purification. The first part of the review presents a detailed introduction about chitosan, highlighting the fact that is a biocompatible, biodegradable, low-cost, nontoxic biopolymer, having unique structure and interesting properties, and also antibacterial and antioxidant activities, reasons for using it in water treatment applications. To use chitosan-based materials for developing nanocomposite polymeric membranes for wastewater purification applications must enhance their performance by using different materials. In the second part of the review, the performance's features will be presented as a consequence of adding different nanoparticles, also showing the effect that those nanoparticles could bring on other polymeric membranes. Among these features, pollutant's retention and enhancing thermo-mechanical properties will be mentioned. The focus of the third section of the review will illustrate chitosan-based nanocomposite as polymeric membranes for water purification. Over the last few years, researchers have demonstrated that adsorbent nanocomposite polymeric membranes are powerful, important, and potential instruments in separation or removal of pollutants, such as heavy metals, dyes, and other toxic compounds presented in water systems. Lastly, we conclude this review with a summary of the most important applications of chitosan-based nanocomposite polymeric membranes and their perspectives in water purification.

Ultra-low pressure cellulose-based nanofiltration membrane fabricated on layer-by-layer assembly for efficient sodium chloride removal

Cellulose is a renewable, biodegradable, biocompatible, and sustainable material. A bamboo cellulose-based nanofiltration membrane (LBL-NF-CS/BCM) was prepared with a combination of layer-by-layer assembly and spraying methods. The chemical structure, morphology, and surface charge of the resultant LBL-NF-CS/BCM composite membranes were characterized based on Thermo Gravimetric Analysis (TGA), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy Scanning (XPS). The nanofiltration performance of the LBL-NF-CS/BCM composite membranes was evaluated using 500 ppm NaCl solutions under 0.3 MPa pressure. It was found that the LBL-NF-CS/BCM composite membranes had a rejection rate of about 36.11 % against a 500 ppm NaCl solution under the conditions tested, and membrane flux of about 12.08 L/(m² h) was reached. The combined layer-by-layer assembly and spraying provides a scalable and convenient process concept for nanofiltration membrane fabrication.

Design of ultrathin hybrid membranes with improved retention efficiency of molecular dyes

Nanocellulose–graphene oxide ultrathin coatings for water purification membranes with excellent swelling resistance, permeability and dyes retention are presented.

A Novel Thin-Film Nanocomposite Nanofiltration Membrane by Incorporating 3D Hyperbranched Polymer Functionalized 2D Graphene Oxide

In order to develop a high-performance thin-film nanocomposite (TFN) nanofiltration (NF) membrane, the functionalized graphene-based nanomaterial (GO-HBE-COOH) was synthesized by combining two-dimensional graphene oxide (GO) with a three-dimensional hyperbranched polymer, which was used as the novel nanofiller and successfully embedded into the polypiperazine-amide (PPA) active layers on polysulfone (PSU) substrates via interfacial polymerization (IP) process. The resultant NF membranes were characterized using ATR-FTIR, SEM, and AFM, while their performance was evaluated in terms of water flux, salt rejection, antifouling ability, and chlorine resistance. The influence of GO-HBE-COOH concentration on the morphologies, properties, and performance of TFN NF membranes was investigated. With the addition of 60 ppm GO-HBE-COOH, the TFN-GHC-60 NF membrane exhibited the optimal water flux without a sacrifice of the salt rejection. It was found that the introduction of GO-HBE-COOH nanosheets favored the formation of a thinner and smoother nanocomposite active layer with an enhanced hydrophilicity and negative charge. As a result, TFN NF membranes demonstrated a superior permeaselectivity, antifouling ability, and chlorine resistance over the conventional PPA thin-film composite (TFC) membranes.

Thin-Film Nanocomposite Forward-Osmosis Membranes on Hydrophilic Microfiltration Support with an Intermediate Layer of Graphene Oxide and Multiwall Carbon Nanotube

A novel thin-film nanocomposite forward-osmosis (FO) membrane was fabricated on hydrophilic nylon microfiltration (MF) support by interfacial polymerization with the assistance of an intermediate layer of graphene oxide and multiwall carbon nanotube (GO/MWCNT). The chemical composition, structure, and surface properties of the synthesized FO membranes were studied using various characterization methods. It was found that the GO/MWCNT composite layer not only provided ultrafast nanochannels for water transport but also reduced the thickness of the polyamide layer by up to 60%. As a result, the novel FO membrane exhibited a higher water flux and lower reverse salt flux compared with the membrane synthesized without the GO/MWCNT intermediate layer. This method offers promising opportunities to fabricate thin-film composite membranes on microfiltration substrates for FO application with inhibited concentration polarization phenomenon and expected separation performance.

Progress of Nanocomposite Membranes for Water Treatment

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes have provided great advances, e.g., enhancing on hydrophilicity, suppressing the accumulation of pollutants and foulants, enhancing rejection efficiencies and improving mechanical properties and thermal stabilities. Thereby, the aim of this work is to provide up-to-date information related to those novel nanocomposite membranes and their contribution for water treatment applications.

Graphene Oxide Quantum Dots Incorporated into a Thin Film Nanocomposite Membrane with High Flux and Antifouling Properties for Low-Pressure Nanofiltration

Graphene oxide quantum dots (GOQDs), novel carbon-based nanomaterials, have attracted tremendous research interest due to their unique properties associated with both graphene and quantum dots. In the present study, thin film nanocomposite (TFN) membranes comprising GOQDs dispersed within a tannic acid (TA) film were fabricated by an interfacial polymerization reaction for low-pressure nanofiltration (NF). The resultant TA/GOQDs TFN membranes had measurably smoother and more hydrophilic, negatively charged surfaces compared to the similarly formed TA thin film composite (TFC) membrane. Owing to the loose active layer structure and the combination of Donnan exclusion and steric hindrance, the TA/GOQDs TFN membrane showed a pure water flux up to 23.33 L/m²·h (0.2 MPa), which was 1.5 times more than that of pristine TA TFC membrane, while high dye rejection to Congo red (99.8%) and methylene blue (97.6%) was kept. In addition, the TA/GOQDs TFN membrane presented better antifouling properties, which was ascribed to the favorable changes in membrane hydrophilicity, ζ-potential, and surface roughness. These results indicated the great potential of such membranes in wastewater treatment, separation, and purification in many industrial fields.

Enhancing the performance of thin-film nanocomposite nanofiltration membranes using MAH-modified GO nanosheets

In this work, novel thin-film nanocompostie NF membranes were developed through modification with maleic anhydride functionalized graphene oxideviainterfacial polymerization, which showed the enhanced water flux with retaining high salt rejection.