Fabricating graphene oxide-based ultrathin hybrid membrane for pervaporation dehydration via layer-by-layer self-assembly driven by multiple interactions

Critical review on emerging photocatalytic membranes for pollutant removal: From preparation to application

Due to synergistically enhanced separation and degradation performances, photocatalytic membranes offer an environmentally friendly and energy-sustainable method for water purification. However, a comprehensive review on preparation and application of photocatalytic membranes is still lacking. Systematically comparing different photocatalytic membrane fabrication methods and revealing the underlying mechanisms of their respective applications are of particular interest. In this review, we first discuss the common preparation methods for photocatalytic membranes in detail, focusing on the main approaches to improve their photocatalytic performance. We elucidate the mechanisms of photocatalytic membrane-based degradation processes, and describe some representative applications of photocatalytic membranes in water treatment. At the same time, the influencing factors that are critical for achieving high removal efficiency are also proposed. In the end, the practical applications and the perspectives for future studies and implementation of photocatalytic membranes are evaluated. This review will serve as a summary to advance researchers' understanding of the advantages of photocatalytic membranes, with the ultimate goal of achieving large-scale relevant applications of photocatalytic membranes in water treatment.

Graphene Membrane for Water-Related Environmental Application: A Comprehensive Review and Perspectives

Graphene-based materials can be potentially utilized for separation membranes due to their unique structural properties such as precise molecular sieving by interlayer spacing or pore structure and excellent stability in harsh environmental conditions. Therefore, graphene-based membranes have been extensively demonstrated for various water treatment applications, including desalination, water extraction, and rare metal ion recovery. While most of the utilization has still been limited to the laboratory scale, emerging studies have dealt with scalable approaches to show commercial feasibility. This review summarizes the recent studies on diverse graphene membrane fabrications and their environmental applications related to water-containing conditions in addition to the molecular separation mechanism and critical factors related to graphene membrane performance. Additionally, we discuss future perspectives and challenges to provide insights into the practical applications of graphene-based membranes on the industrial scale.

Facilitating Water Permeation in Graphene Oxide Membranes via Incorporating Sulfonato Calix[n]arenes

Graphene oxide (GO) with its atomic thickness and abundant functional groups holds great potential in molecular-scale membrane separation. However, constructing high-speed and highly selective water transport channels within GO membranes remains a key challenge. Herein, sulfonato calix[n]arenes (SCn) molecules with a cavity structure, hydrophilic entrance, and hydrophobic wall were incorporated into GO interlayer channels through a layer-by-layer assembly approach to facilitate water permeation in a water/ethanol separation process. The hydrophilic entrance enables preferential access of water molecules to the cavity over ethanol molecules, while the high hydrophobicity of the cavity wall confers low resistance for water diffusion. After incorporating SCn molecules, the membrane shows a remarkable increase in the water/ethanol separation factor from 732 to 1260, while the permeate flux also increases by about 50%. In addition, the strong electrostatic interactions between the building blocks endow the membrane with excellent swelling resistance even under a high water content. This work provides an effective strategy of constructing high-efficiency water transport channels in membrane.

Separation performance of graphene oxide nanofiltration membrane intercalated by MWCNTs and α -Fe2O3 nanoparticles

Nanofiltration (NF) technology is used in the field of water treatment due to its advantages of low energy consumption, high efficiency, and simple process flow. However, the problems of membrane fouling and trade-off (i.e., high flux with low rejection or high rejection with low flux) exist in NF technology, which limit its wide-scale popularization and application. The emphasis of this work is to improve the performance of graphene oxide (GO)-based NF membranes. Multi-walled carbon nanotubes (MWCNTs) and α-Fe2O3 were selected to modify the GO-based membrane by expanding the interlayer spacing and enhancing its antifouling and rejection abilities. Our composite membranes exhibit an increased interlayer spacing of 0.787 nm to 1.1 nm, achieving a high pure water permeation flux of 138.96 Lm-2 h-1, as well as satisfactory rejection rates for salts and dyes (Na2SO4, NaCl, MgCl2, Congo red, and methylene blue). Additionally, the membranes exhibit a relatively good antifouling property. After five cycles of rejection tests, the flux and rejection rate could be recovered to 90 % from 80 % with a 4-h irradiation under visible light. This study provides valuable insights into the development of high-efficiency and advanced NF membranes.

Energy Application of Graphene Based Membrane: Hydrogen Separation

Hydrogen gas (H2 ) is a viable energy carrier that has the potential to replace the traditional fossil fuels and contribute to achieving zero net emissions, making it an attractive option for a hydrogen-based society. However, current H2 purification technologies are often limited by high energy consumption, and as a result, there is a growing demand for alternative techniques that offer higher H2 purity and energy efficiency. Membrane separation has emerged as a promising approach for obtaining high-purity H2 gas with low energy consumption. Nevertheless, despite years of development, commercial polymeric membranes have limited performance, prompting researchers to explore alternative materials. In this context, carbon-based membranes, specifically graphene-based nanomaterials, have gained significant attention as potential membrane materials due to their unique properties. In this review, we provide a comprehensive overview of carbon-based membranes for H2 gas separation, fabrication of the membrane, and its characterization, including their advantages and limitations. We also explore the current technological challenges and suggest insights into future research directions, highlighting potential ways to improve graphene-based membranes performance for H2 separations.

Separation Mechanisms and Anti-Fouling Properties of a Microporous Polyvinylidene Fluoride-Polyacrylic Acid-Graphene Oxide (PVDF-PAA-GO) Composite Membrane with Salt and Protein Solutions

This research demonstrates the preparation of composite membranes containing graphene oxide (GO) and investigates the separation mechanisms of various salts and bovine serum albumin (BSA) solutions. A microporous polyvinylidene fluoride-polyacrylic acid-GO (PVDF-PAA-GO) separation layer was fabricated on non-woven support. The GO-incorporating composite resulted in enlarged pore size (0.16 μm) compared with the control membrane (0.12 μm). The zeta potential of the GO composite was reduced to -31 from -19 mV. The resulting membranes with and without GO were examined for water permeability and rejection efficiency with single salt and BSA solutions. Using the non-woven/PVDF-PAA composite, the permeance values were 88-190 kg/m²hMPa, and the salt rejection coefficients were 9-28% for Na₂SO₄, MgCl₂, MgSO₄, and NaCl solutions. These salt removals were based on the Donnan exclusion mechanism considering the ion radii and membrane pore size. Incorporating GO into the separation layer exhibited limited impacts on the filtration of salt solutions, but significantly reduced BSA membrane adhesion and increased permeance. The negatively charged protein reached almost complete removal (98.4%) from the highly negatively charged GO-containing membrane. The GO additive improved the anti-fouling property of the composite membrane and enhanced BSA separation from the salt solution.

Recent Progress of Adsorptive Ultrafiltration Membranes in Water Treatment—A Mini Review

Adsorptive ultrafiltration mixed matrix membranes (MMMs) are a new strategy, developed in recent years, to remove harmful cations and small-molecule organics from wastewater and drinking water, which achieve ultrafiltration and adsorption functions in one unit and are considered to be among the promising technologies that have exhibited efficiency and competence in water reuse. This mini review concerns the research progress of adsorptive ultrafiltration MMMs for removing heavy metal ions and small-molecule organics. We firstly introduce the types and classifications of adsorptive ultrafiltration MMMs (their classifications can be established based on the type of the adsorbent used). Furthermore, we discuss the removal mechanism of adsorptive ultrafiltration MMMs, as well as summarizing the main fabrication techniques for adsorptive ultrafiltration membranes. In addition, we identified some of the issues and challenges of the practical application for adsorptive ultrafiltration.

Investigating the potential of ammonium retention by graphene oxide ceramic nanofiltration membranes for the treatment of semiconductor wastewater

Ceramic membranes with high chemical and fouling resistance can play a critical role in treating industrial wastewater. In the present study, we demonstrate the fabrication of graphene oxide (GO) assembled ceramic nanofiltration (NF) membranes that provide effective ammonium retention and excellent fouling resistance for treating semiconductor wastewater. The GO-ceramic NF membranes were prepared via a layer-by-layer (LbL) assembly of GO and polyethyleneimine (PEI) on a ceramic ultrafiltration (UF) substrate. The successful fabrication of the GO-ceramic NF membranes was verified through surface characterization and pore size evaluation. We also investigated the performance of GO-ceramic NF membranes assembled with different numbers of bilayers for the rejection of ammonium ions. GO-ceramic NF membranes with three GO-PEI bilayers exhibited 8.4- and 3.2-times higher ammonium removal with simulated and real semiconductor wastewater, respectively, compared to the pristine ceramic UF substrate. We also assessed flux recovery after filtration using real semiconductor wastewater samples to validate the lower fouling potential of the GO-ceramic NF membranes. Results indicate that flux recovery increases from 39.1 % in the pristine UF substrate to 71.0 % and 90.8 % for the three- and ten-bilayers GO-ceramic NF membranes, respectively. The low-fouling GO-ceramic NF membranes developed in this study are effective and promising options for the removal of ammonium ions from semiconductor wastewater.

Sustainable removal of Cr(VI) using graphene oxide-zinc oxide nanohybrid: Adsorption kinetics, isotherms and thermodynamics

Metal-based adsorbents are limited for hexavalent chromium [Cr(VI)] adsorption from aqueous solutions because of their low adsorption capacities and slow adsorption kinetics. In the present study, decorated zinc oxide (ZnO) nanoparticles (NPs) on graphene oxide (GO) nanoparticles were synthesized via the solvothermal process. The deposition of ZnO NPs on graphene oxide for the nanohybrid (ZnO-GO) improves Cr(VI) mobility in the nanocomposite or nanohybrid, thereby improving the Cr(VI) adsorption kinetics and removal capacity. Surface deposition of ZnO on graphene oxide was characterized through Fourie Transform Infra-red (FTIR), UV-Visible, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) techniques. These characterizations suggest the formation of ZnO-GO nanocomposite with a specific area of 32.95 m²/g and pore volume of 0.058 cm²/g. Batch adsorption analysis was carried to evaluate the influence of operational parameters, equilibrium isotherm, adsorption kinetics and thermodynamics. The removal efficiency of Cr(VI) increases with increasing time and adsorbent dosage. FTIR, FESEM and BET analysis before and after the adsorption studies suggest the obvious changes in the surface functionalization and morphology of the ZnO-GO nanocomposites. The removal efficiency increases from high-acidic to neutral pH and continues to decrease under alkaline conditions as well. Mathematical modeling validates that the adsorption follows Langmuir isotherm and fits well with the pseudo 2nd order kinetics (Type 5) model, indicating a homogeneous adsorption process. The thermodynamics study reveals that Cr(VI) adsorption on ZnO-GO is spontaneous, endothermic, and entropy-driven. A negative value of Gibb's Free Energy represents the thermodynamic spontaneity and feasibility of the sorption process. To the best of our knowledge, this is the first study of Cr(VI) removal from aqueous solution using this hybrid nanocomposite at near-neutral pH. The synthesized nanocomposites prove to be excellent candidates for Cr(VI) removal from water bodies and natural wastewater systems.

Mixed-dimensional membranes: chemistry and structure-property relationships

Tremendous progress in two-dimensional (2D) nanomaterial chemistry affords abundant opportunities for the sustainable development of membranes and membrane processes. In this review, we propose the concept of mixed dimensional membranes (MDMs), which are fabricated through the integration of 2D materials with nanomaterials of different dimensionality and chemistry. Complementing mixed matrix membranes or hybrid membranes, MDMs stimulate different conceptual thinking about designing advanced membranes from the angle of the dimensions of the building blocks as well as the final structures, including the nanochannels and the bulk structures. In this review, we survey MDMs (denoted nD/2D, where n is 0, 1 or 3) in terms of the dimensions of membrane-forming nanomaterials, as well as their fabrication methods. Subsequently, we highlight three kinds of nanochannels, which are 1D nanochannels within 1D/2D membranes, 2D nanochannels within 0D/2D membranes, and 3D nanochannels within 3D/2D membranes. Strategies to tune the physical and chemical microenvironments of the nanochannels as well as the bulk structures based on the size, type, structure and chemical character of nanomaterials are discussed. Some representative applications of MDMs are illustrated for gas molecular separations, liquid molecular separations, ionic separations and oil/water separation. Finally, current challenges and a future perspective on MDMs are presented.

Thin film nanocomposite membrane with triple-layer structure for enhanced water flux and antibacterial capacity

Triple-layered thin film composite (TFC) forward osmosis (FO) membranes prepared on interlayer-based supports have overcome the limitations of conventional porous substrates due to the formation of ultrathin and highly selective polyamide (PA) layers. However, mitigating the internal concentration polarization (ICP) and biofouling of TFC membranes remain a great challenge. Herein, we designed a novel triple-layered thin film nanocomposite (TFN) FO membrane with incorporation of silver (Ag) decorated graphene oxide quantum dots (GOQD) into PA layer via interfacial polymerization on a carbon nanotube (CNT) interlayer-based polyether sulfone substrate. By contrast with the TFC membranes, the newly developed GOQD/Ag incorporated triple-layered TFN membrane (TFN-GOQD/Ag) exhibited a great alleviation for ICP accompanied with a prominently enhanced water flux of 65.8 L·m^-2·h^-1 and decreased specific reverse salt flux of 1.4 g·m^-2·h^-1 by employing 1 M NaCl solution as draw solution. Moreover, the TFN-GOQD/Ag membrane possessed prominent antibacterial activity against both E. coli (99.8%) and S. aureus (97.3%). Noteworthy, the obtained TFN membrane demonstrated a controlled release of Ag⁺ along with long-term antibacterial potential and outstanding fouling resistance during the FO process. This work provides a new avenue to fabricate newly FO membranes with superior performance for water cleaning treatment.

Modification Approaches to Enhance Dehydration Properties of Sodium Alginate-Based Pervaporation Membranes

Transport characteristics of sodium alginate (SA) membranes cross-linked with CaCl₂ and modified with fullerenol and fullerene derivative with L-arginine for pervaporation dehydration were improved applying various approaches, including the selection of a porous substrate for the creation of a thin selective SA-based layer, and the deposition of nano-sized polyelectrolyte (PEL) layers through the use of a layer-by-layer (Lbl) method. The impacts of commercial porous substrates made of polyacrylonitrile (PAN), regenerated cellulose, and aromatic polysulfone amide were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), standard porosimetry method, and water filtration. The effects of PEL combinations (such as poly(sodium 4-styrene sulfonate) (PSS)/SA, PSS/chitosan, PSS/polyacrylic acid, PSS/poly(allylamine hydrochloride)) and the number of PEL bilayers deposited with the Lbl technique on the properties of the SA and SA/fullerene derivative membranes were studied by SEM, AFM, and contact angle measurements. The best characteristics were exhibited by a cross-linked PAN-supported SA/fullerenol (5%) membrane with five PSS/SA bilayers: permeation flux of 0.68–1.38 kg/(m²h), 0.18–1.55 kg/(m²h), and 0.50–1.15 kg/(m²h), and over 99.7, 99.0, and 89.0 wt.% water in the permeate for the pervaporation dehydration of isopropanol (12–70 wt.% water), ethanol (4–70 wt.% water), and tetrahydrofuran (5.7–70 wt.% water), respectively. It was demonstrated that the mutual application of bulk and surface modifications essentially improved the membrane’s characteristics in pervaporation dehydration.

Engineered two-dimensional nanomaterials: an emerging paradigm for water purification and monitoring

Water scarcity has become an increasingly complex challenge with the growth of the global population, economic expansion, and climate change, highlighting the demand for advanced water treatment technologies that can provide clean water in a scalable, reliable, affordable, and sustainable manner. Recent advancements on 2D nanomaterials (2DM) open a new pathway for addressing the grand challenge of water treatment owing to their unique structures and superior properties. Emerging 2D nanostructures such as graphene, MoS₂, MXene, h-BN, g-C₃N₄, and black phosphorus have demonstrated an unprecedented surface-to-volume ratio, which promises ultralow material use, ultrafast processing time, and ultrahigh treatment efficiency for water cleaning/monitoring. In this review, we provide a state-of-the-art account on engineered 2D nanomaterials and their applications in emerging water technologies, involving separation, adsorption, photocatalysis, and pollutant detection. The fundamental design strategies of 2DM are discussed with emphasis on their physicochemical properties, underlying mechanism and targeted applications in different scenarios. This review concludes with a perspective on the pressing challenges and emerging opportunities in 2DM-enabled wastewater treatment and water-quality monitoring. This review can help to elaborate the structure-processing-property relationship of 2DM, and aims to guide the design of next-generation 2DM systems for the development of selective, multifunctional, programmable, and even intelligent water technologies. The global significance of clean water for future generations sheds new light and much inspiration in this rising field to enhance the efficiency and affordability of water treatment and secure a global water supply in a growing portion of the world.

Layer-by-layer assembly of bio-inspired borate/graphene oxide membranes for dye removal

Dye wastewater is harmful to the ecological environment because of its potential biological toxicity, teratogenicity, carcinogenicity, and mutagenicity. We fabricated a layered graphene oxide (GO) membrane through layer-by-layer (LBL) self-assembly. We used borate to crosslink with GO on a polyethyleneimine (PEI)-coated hydrolyzed polyacrylonitrile (hPAN) support. Fourier transform infrared (FTIR) spectrometry, Raman spectra, and x-ray photoelectron spectroscopy (XPS) confirmed the presence of a crosslinking reaction. The dynamic thermomechanical analysis (DMA) results indicated that the introduction of borate can significantly improve the mechanical properties of the membrane. The Young's modulus, ultimate tensile strength, and proportional limit of borate that was assembled twice as the outermost layer were increased by 110.81%, 62.37%, and 53.72%, respectively, as compared to those of a single-layered GO membrane. Moreover, the pure water fluxes of the layered GO membrane did not obviously decrease with an increase in the number of layers. The flux of the membrane with an outermost layer of borate was greater than that of the previous GO layer. The salt and dye rejection of the membranes was augmented with an increase in the number of layers. For the GO membrane assembled three times, rejection to methyl orange (MO), methylene blue (MB), NaCl, MgCl_2, and MgSO₄ reached 74.02%, 88.56%, 14.55%, 27.50%, and 41.95%, respectively. The use of borate as an inorganic crosslinker can avoid the environmental pollution caused by organic agents, and improve the mechanical properties as well as the filter capability of the layered GO membrane. Therefore, this study presents a novel method of membrane preparation for dye removal.

A highly hydrophilic benzenesulfonic-grafted graphene oxide-based hybrid membrane for ethanol dehydration

A new type of hybrid membrane was prepared by blending sodium alginate (SA) with benzenesulfonic-grafted graphene oxide (BS@GO), which showed higher hydrophilicity and more defects or edges than GO to create channels for the transfer of water molecules. BS@GO was synthesized by reacting aryl diazonium salts with graphene oxide (GO). The BS@GO sheets were aligned parallelly to the membrane surface and affected the interactions between the SA chains. BS@GO could improve the hydrophilicity and pervaporation properties of SA-based hybrid membranes. Also, compared to GO fillers, BS@GO fillers could supply higher water permeance to improve the pervaporation flux and separation factor. For the pervaporation of 90 wt% aqueous ethanol at 343 K, the optimum hybrid membrane with 1.5 wt% BS@GO in the SA matrix showed the maximum permeate flux of 703 ± 89 g m^-2 h^-1 (1.4 times higher than that of an SA membrane), and the highest separation factor was 5480 ± 94 (5.6 times higher than that of the SA membrane). Moreover, the hybrid membrane exhibited good stability and separation ability during long-term testing.

Computational methods towards increased efficiency design of graphene membranes for gas separation and water desalination

The potential impact of climate change is widely known as having serious consequences. The themes of water desalination and gas separation are closely related to the environment and energy industry. Graphene-based membranes are promising filtration devices for the two tasks. This review aims to supply a comprehensive overview of the recent computational studies investigating the performance of graphene-based membranes used in water desalination or gas separation. With the use of computational methods, the literature covered finds evidence for key factors, such as pore shape and density, affecting the performance of the investigated membranes. The reviewed studies are expected to act as an impulse towards more computational studies and eventually actual design of graphene-based membranes for water desalination and gas separation.

Development of Graphene Oxide Framework Membranes via the "from" and "to" Cross-Linking Approach for Ion-Selective Separations

Graphene oxide (GO) membranes with well-defined nanochannels formed between the stacked GO nanosheets find great interest in molecular separations. However, GO membranes are unstable in aqueous solution environments because of weak interactions between the stacked nanosheets. Herein, we developed a preparation method by diminishing the self-contained oxidized functional groups in GO and subsequent cross-linking to form GO framework (GOF) membranes with excellent aqueous solution stability. GOF membranes were fabricated by alternate deposition of branched polyethylenimine (BPEI) and a mixed solution of GO and thiourea (TU). Structural elucidation illustrated that the TU partially reduced the GO molecules and acted as a "to" cross-linker by bridging adjacent GO nanosheets through in-plane and out-of-plane of interactions. During the GO deposition, BPEI performed the role as a "from" cross-linker by binding the TU-linked GO laminates to form stable GOF membranes with well-defined nanochannels. Morphological studies confirmed the formation of the tightly packed structure for BPEI/GO_TU membranes due to the high Π-Π interactions between the GO nanosheets and bridging effect of TU. The GOF membranes exhibited a rejection of 99.5% for anionic dye methyl orange and cationic dye rhodamine B. The BPEI/GO_TU membranes fabricated from 12 bilayers using 0.25 mg/mL of GO solution have a pure water flux of 24 L m^-2 h^-1 and a Na₂SO₄ rejection of 94%; this permeability is 2.5 times higher than that of commercial nanofiltration membranes. Moreover, (BPEI/GO_TU)₁₂ GOF membranes exhibited excellent aqueous solution stability in acidic and basic conditions. The excellent separation performance and aqueous solution stability of the BPEI/GO_TU membranes are intricately linked to the partial reduction and cross-linking of GO nanosheets in GOF membranes. Thus, the "from" and "to" cross-linking approach developed in this work can be extended for the fabrication of structurally stable membranes from other 2D materials.

Membranes for dehydration of alcohols via pervaporation

Alcohols are the essential chemicals used in a variety of pharmaceutical and chemical industries. The extreme purity of alcohols in many of such industrial applications is essential. Though distillation is one of the methods used conventionally to purify alcohols, the method consumes more energy and requires carcinogenic entertainers, making the process environmentally toxic. Alternatively, efforts have been made to focus research efforts on alcohol dehydration by the pervaporation (PV) separation technique using polymeric membranes. The present review is focused on alcohol dehydration using PV separation technique, which is the most efficient and benign method of purifying alcohols that are required in fine chemicals synthesis and developing pharmaceutical formulations. This review will discuss about the latest developments in the area of PV technique used in alcohol dehydration using a variety of novel membranes.

Fabrication of Stacked Graphene Oxide Nanosheet Membranes Using Triethanolamine as a Crosslinker and Mild Reducing Agent for Water Treatment

Two-dimensional (2D) nanosheets show promise for the development of water treatment membranes with extraordinary separation properties and the advantages of atomic thickness with micrometer-sized lateral dimensions. Stacked graphene oxide (GO)-based membranes can demonstrate unique molecular sieving properties with fast water permeation. However, improvements to the structural stability of the membranes in water to avoid problems such as swelling, disruption of the ordered GO layer and decreased rejection are crucial issues. This study reports the fabrication of stacked GO nanosheet membranes by simple vacuum filtration using triethanolamine (TEOA) as a crosslinker and mild reducing agent for improved structural stability and membrane performance. Results show that GO membranes modified with TEOA (GO-TEOA membranes) have a higher structural stability in water than unmodified GO membranes, resulting in improved salt rejection performance. Furthermore, GO-TEOA membranes show stable water permeance at applied pressures up to 9 bar with Na₂SO₄ rejection of 85%, suggesting the potential benefits for water treatment applications.

New type of alginate/chitosan microparticle membranes for highly efficient pervaporative dehydration of ethanol

A new type of composite alginate membranes filled with chitosan (CS) and three different modified chitosan submicron particles, i.e. phosphorylated (CS-P), glycidol (CS-G) or glutaraldehyde (CS-GA) crosslinked ones, were prepared, and the pervaporation of water/ethanol mixture was investigated. The influence of various chitosan particles and their content on the transport properties of membranes was discussed. It was found that the addition of chitosan particles into the alginate matrix has a prominent effect on the ethanol/water separation efficiency. All tested membranes are characterized simultaneously by a high flux and selectivity, exhibiting advantageous properties, and outperforming numerous conventional materials. The best results were achieved for alginate membranes filled with phosphorylated chitosan particles at 10 wt%, for which separation factor, flux and PSI were equal to 136.2, 1.90 kg m-2 h-1 and 256.9 kg m-2 h-1, respectively.

Ultrathin reduced graphene oxide/MOF nanofiltration membrane with improved purification performance at low pressure

Here we demonstrated an alternative partial reduction graphene oxide/metal-organic frameworks nano-scale laminated membrane for dyes and heavy metal ions removal at low pressure. Compared with pure prGO membranes, the novel UiO-66-(COOH)₂/prGO membranes with loose structure and excellent selective permeability demonstrated significant enhancements of permeation for low-pressure nanofiltration. The UiO-66-(COOH)₂/prGO membranes possess more nanochannels structure, high surface charge and stability, which were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The experiment result indicated that the flux of composite membranes for pure water was 20.0 ± 2.5 Lm^-2h^-1bar^-1, about 2.9 times higher than that (6.5 ± 1.2 Lm^-2h^-1bar^-1) of the pristine prGO membranes at the same prGO loading. The high rejection of UiO-66-(COOH)₂/prGO membranes for organic dyes (98.2 ± 1.7% for negatively charged congo red and 92.55 ± 2.5% for positively charged methylene blue) were exhibited. Moreover, the rejection for heavy metal ions also can be efficiently improved up to 96.5-83.1% for Cu²⁺ and 92.6-80.4% for Cd²⁺, indicating the positive effect of the electrostatic interaction on the nanochannels for ions. Therefore, it is reasonable to believe that novel UiO-66-(COOH)₂/prGO membranes have great potential application in water treatment.