Graphene Oxide Membranes Research Articles

High antifouling graphene membranes with Fe2O3 nanoparticles in-situ intercalation for selective dye/salt separation

Effective organic dyes selective separation from high salinity textile wastewater consisting of inorganic salts and organic dyes is of great significant for the textile wastewater treatment. Graphene oxide (GO) have been used widely to form ultrathin high-permeance membrane for molecular and ionic sieving. However, swelling and membrane fouling of GO membrane hampered its practical applications. In this work, high stability and antifouling reduced graphene oxide (rGO) membranes were prepared, and Fe2O3 nanoparticles was used as intercalation to turn the membrane interlayer spacing. The rGO/2Fe2O3 nanocomposite blended membrane exhibited high permeance of 24.90 L m−2 h−1 bar−1, excellent organic dyes rejection (98.15 % and 98.69 % for methylene blue and Evans blue, respectively) and low salt retention (6.26 % for NaCl). Meanwhile, this membrane demonstrated a superior selective dye/salt separation factor up to 232 with a high rejection of 99.59 % to Evans blue and a lower salt rejection of 5.03 % to NaCl. Furthermore, nanofiltration experiments towards Evans blue/NaCl mixed solution indicated that the membrane also exhibited excellent antifouling performance with flux recovery rate of >86 % after six fouling/backwash cycles. Therefore, our work may provide a promising idea for the development of two-dimensional nanofiltration membranes for efficient high salinity textile wastewater treatment.

Surface Microstructure Drives Biofilm Formation and Biofouling of Graphene Oxide Membranes in Practical Water Treatment.

Significant progress has been made previously in the research and development of graphene oxide (GO) membranes for water purification, but their biofouling behavior remains poorly understood. In this study, we investigated the biofilm formation and biofouling of GO membranes with different surface microstructures in the context of filtering natural surface water and for an extended operation period (110 days). The results showed that the relatively hydrophilic and smooth Fe(OH)3/GO membrane shaped a thin and spatially heterogeneous biofilm with high stable flux. However, the ability to simultaneously mitigate biofilm formation and reduce biofouling was not observed in the weakly hydrophilic and wrinkled Fe/GO and H-Fe(OH)3/GO membranes. Microbial analyses revealed that the hydrophilicity and roughness distinguished the bacterial communities and metabolic functions. The organic matter-degrading and predatory bacteria were more adapted to hydrophilic and smooth GO surfaces. These functional taxa were involved in the degradation of extracellular polymeric substances (EPS), and improved biofilm heterogeneity. In contrast, the weakly hydrophilic and wrinkled GO surfaces had reduced biodiversity, while unexpectedly boosting the proliferation of EPS-secreting bacteria, resulting in increased biofilm formation and aggravated biofouling. Moreover, all GO membranes achieved sustainable water purification during the entire operating period.

A new suggestion to marine gold extraction: Utilizing reduced graphene oxide membranes within seawater desalination processes

Traditional mining practices not only cause severe environmental issues, but also face the problem of insufficient production capacity of gold to meet its growing demand. The proposed alternative strategies for gold production, such as the extraction of gold from seawater, still keep a formidable challenge due to their strong dependence on adsorbent materials with high capacity, selectivity, and sensitivity, while also needing to meet the demands of being environmentally friendly and cost-effective. In practice, the direct extraction of gold from seawater is limited by its extremely low yield and high energy expenditure. However, if the combination of gold extraction techniques with seawater desalination can substantially reduce the energy consumption, the extraction of gold from seawater will become economical and feasible. In this paper, we evaluate the feasibility of marine gold extraction using reduced graphene oxide membranes (rGOM) during the seawater desalination process. The rGOM can adsorb almost all Au3+ from the solutions with trace concentrations of Au3+ ranging from 10 ppb to 200 ppb. The adsorption quantity is linearly related to the concentration, indicating that the adsorption capacity of rGOM is much higher than the total amount of Au3+ in the solution. Additionally, the rGOM can selectively adsorb 99 % of Au3+ in the mixed solution while hardly adsorbing other common elements in seawater. More importantly, the rGOM exhibits the long-term stability over 30 days when being immersed in the solution, making it directly compatible with the existing seawater desalination processes. These specific properties allow the rGOM to be an ideal candidate for combining the extraction of gold from seawater with seawater desalination processes. Our findings provide a methodology for enhancing the economic efficiency of the extraction of gold from seawater and hold promise for addressing the problem of gold scarcity.

Development of large-scale laminar-structure nanofiltration membranes for high dye rejection and enhanced robustness: Utilizing potassium ion-crosslinked graphene oxide and polyethyleneimine surface coating

Laminar graphene oxide (GO) membranes are at the forefront of groundbreaking research as a prospective advanced solution for nanofiltration. Both physical and computational experiments have showcased the exceptional efficacy of these GO membranes. However, scalability and robustness issues still remain significant hurdles for the practical implementation of GO membranes. In this study, to address these issues concurrently, we employed tape-casting of GO hydrogel induced by potassium ion crosslinking alongside polyethyleneimine crosslinking between the tape-casted laminar GO layers and the porous support layer. Through this approach, we successfully crafted a scalable laminar GO membrane encompassing an area of 900 cm², characterized by good uniformity. The GO membranes achieved excellent rejection efficiencies of 99.22 %, 99.42 %, and 99.27 % for methylene blue, methyl orange, and rhodamine B, respectively, with 0.77 LMH/bar of pure water permeability. Furthermore, the GO membranes demonstrated enhanced stability, validated by both long-term operation and testing under harsh conditions.

Large-Area Layered Membranes with Precisely Controlled Nano-Confined Channels.

Two-dimensional (2D) nanosheets-based membranes, which have controlled 2D nano-confined channels, are highly desirable for molecular/ionic sieving and confined reactions. However, it is still difficult to develop an efficient method to prepare large-area membranes with high stability, high orientation, and accurately adjustable interlayer spacing. Here, we present a strategy to produce metal ion cross-linked membranes with precisely controlled 2D nano-confined channels and high stability in different solutions using superspreading shear-flow-induced assembly strategy. For example, membranes based on graphene oxide (GO) exhibit interlayer spacing ranging from 8.0±0.1 Å to 10.3±0.2 Å, with a precision of down to 1 Å. At the same time, the value of the orientation order parameter (f) of GO membranes is up to 0.95 and GO membranes exhibit superb stability in different solutions. The strategy we present, which can be generalized to the preparation of 2D nano-confined channels based on a variety of 2D materials, will expand the application scope and provide better performances of membranes.

Large‐Area Layered Membranes with Precisely Controlled Nano‐Confined Channels

Two‐dimensional (2D) nanosheets‐based membranes, which have controlled 2D nano‐confined channels, are highly desirable for molecular/ionic sieving and confined reactions. However, it is still difficult to develop an efficient method to prepare large‐area membranes with high stability, high orientation, and accurately adjustable interlayer spacing. Here, we present a strategy to produce metal ion cross‐linked membranes with precisely controlled 2D nano‐confined channels and high stability in different solutions using superspreading shear‐flow‐induced assembly strategy. For example, membranes based on graphene oxide (GO) exhibit interlayer spacing ranging from 8.0 ± 0.1 Å to 10.3 ± 0.2 Å, with a precision of down to 1 Å. At the same time, the value of the orientation order parameter (f) of GO membranes is up to 0.95 and GO membranes exhibit superb stability in different solutions. The strategy we present, which can be generalized to the preparation of 2D nano‐confined channels based on a variety of 2D materials, will expand the application scope and provide better performances of membranes.

Discrimination of Xylene Isomers by Precisely Tuning the Interlayer Spacing of Reduced Graphene Oxide Membrane.

Separating xylene isomers is a challenging task due to their similar physical and chemical properties. In this study, we developed a molecular sieve incorporating a reduced graphene oxide (rGO) membrane for the precise differentiation of xylene isomers. We fabricated GO membranes using a vacuum filtration technique followed by thermal-induced reduction to produce rGO membranes with precisely controllable interlayer spacing. Notably, we could finely tune the interlayer spacing of the rGO membrane from 8.0 to 5.0 Å by simply varying the thermal reduction temperature. We investigated the reverse osmosis separation ability of the rGO membranes for xylene isomers and found that the rGO membrane with an interlayer spacing of 6.1 Å showed a high single component permeance of 0.17 and 0.04 L m-2 h-1 bar-1 for para- and ortho-xylene, respectively, exhibiting clear permselectivity. The separation factor reached 3.4 and 2.8 when 90:10 and 50:50 feed mixtures were used, respectively, with permeance 1 order of magnitude higher than that of current state-of-the-art reverse osmosis membranes. Additionally, the membrane showed negligible permeance and selectivity decay even after continuous operation for more than 5 days, suggesting commendable membrane resistance to solvent swelling and operating pressure.

Janus graphene oxide membrane with rational allocation of functional regions as unidirectional ion valve system

Membrane-based ion sieving is critical to green desalination processes such as sustainable ionic resource extraction. Two-dimensional (2D) graphene oxide (GO) membranes exhibit unique ionic transport properties owning to the supernormal enhancement of channel effects induced by diverse functional regions under nanoconfinement. However, the discrete and random distribution of the hydrophilic/hydrophobic and positively/negatively charged regions restricts the GO membrane to give full play to its potential in selective ions separation. Herein, a novel strategy is proposed to engineer the asymmetric three-tier architecture of a Janus GO membrane with rational allocation of functional regions. The wise series connection of ① surface positively charged hydrophilic layer of PEI, ② intermediate negatively charged hydrophilic layer of GO and ③ bottom hydrophobic porous layer of rGO along the cross-membrane direction established internal gradients of structure, wetting and charge, resulting in reinforced exclusion of retained divalent ions and reduced stagnation of targeted monovalent ions. Based on the continuous anisotropic gradients, the Janus GO membrane was endowed with the unique capability to act as a unidirectional ion valve system, showcasing impressive permeation performance of monovalent ions permeation rate of 0.244 mol m−2 h−1 with monovalent/divalent ions selectivity of 66.1, and remarkable nanofiltration performance of divalent salt rejections of >96.5 % with monovalent/divalent ions separation factor up to 70.9. The implications of this work will revolutionize the regulation and functionalization of 2D nanofluidic channels for selective ions transport, which is highly desirable for a wide range of green desalination applications.

Holey Sheets Enhance the Packing and Osmotic Energy Harvesting of Graphene Oxide Membranes.

Layered membranes assembled from two-dimensional (2D) building blocks such as graphene oxide (GO) are of significant interest in desalination and osmotic power generation because of their ability to selectively transport ions through interconnected 2D nanochannels between stacked layers. However, architectural defects in the final assembled membranes (e.g., wrinkles, voids, and folded layers), which are hard to avoid due to mechanical compliant issues of the sheets during the membrane assembly, disrupt the ionic channel pathways and degrade the stacking geometry of the sheets. This leads to degraded ionic transport performance and the overall structural integrity. In this study, we demonstrate that introducing in-plane nanopores on GO sheets is an effective way to suppress the formation of such architectural imperfections, leading to a more homogeneous membrane. Stacking of porous GO sheets becomes significantly more compact, as the presence of nanopores makes the sheets mechanically softer and more compliant. The resulting membranes exhibit ideal lamellar microstructures with well-aligned and uniform nanochannel pathways. The well-defined nanochannels afford excellent ionic conductivity with an effective transport pathway, resulting in fast, selective ion transport. When applied as a nanofluidic membrane in an osmotic power generation system, the holey GO membrane exhibits higher osmotic power density (13.15 W m-2) and conversion efficiency (46.6%) than the pristine GO membrane under a KCl concentration gradient of 1000-fold.

Unraveling the Atomistic Mechanisms Underlying Effective Reverse Osmosis Filtration by Graphene Oxide Membranes

Unraveling the Atomistic Mechanisms Underlying Effective Reverse Osmosis Filtration by Graphene Oxide Membranes

Constructing novel GO microcomposite membranes with β-CD based microporous nanosheets for efficient dye/salt separation

Graphene oxide (GO) membrane is considered as one of the preferred choice for textile wastewater treatment thanks to its unique 2D interlayer channel features. However, GO laminar stacking is inclined to water-induced structure instability, and the narrow interlayer spacing limit mass transport efficiency, hampering its effectiveness in water treatment applications. Herein, a layer-by-layer stacked microcomposite membrane based on GO and highly microporous β-cyclodextrin based nanosheets (β-CDNS) served as intercalator was developed. The distinctive layered structure was further stabilized by covalent cross-linking with glutaraldehyde (GA). The microporous β-CDNS offered additional nanochannels that facilitated the rapid penetration of water molecules, while the abundant -OH groups provided sites for chemical cross-linking, enhancing membrane stability. The optimal GO/β-CDNS1 membrane exhibited a superior water permeance of up to 83.5 LMH/bar, with >99 % rejection for dyes such as Congo red (CR), methyl blue (MB), and chrome black T (CBT), 95.5 % for acid fuchsin (AF). Meanwhile, the GO/β-CDNS1 membrane demonstrated ultra-low (<5 %) retention for inorganic salts (MgSO4, MgCl2 and NaCl), with a separation factor as high as 194 for MB/NaCl mixtures. Therefore, employing functional interlayer nano-additives to well regulate the GO interlayer structure offers a promising guideline for developing high-performance GO-based membranes.

Thin polyamide layer cross-linked graphene-oxide based ceramic membranes for efficient separation of the surfactant stabilized oil-in-water emulsions

Two-dimensional (2D) graphene oxide (GO) membranes (GOM) have great potential in separation applications. However, GOMs face two distinct challenges: low flux arising from their tight stacking and instability arising from re-exfoliation of GO sheets in solution. To address these challenges, herein, we report the functionalization of basal planes of GO layers with 2-[2-(3-Trimethoxysilylpropylamino)ethylamino]ethylamine (TSE), followed by transforming them into membranes through a two-step process. In the first step, the functionalized GO sheets were assembled onto the porous ceramic support. At this stage, the interlayer distance between GO sheets was modulated via TSE’s long hydrocarbon chain. Afterward, the free amines of TSE on functionalized GO membranes (fGOM) surface were cross-linked with trimesoyl chloride (TMC) to prepare a hydrophilic thin-layer on top of fGOM (TL-fGOM), further enhancing their stability. Further, TL-fGOMs were tested for oil-in-water-emulsion separation. The increased interlayer distance and the increased surface hydrophilic nature of TL-fGOM offered ultra-high water permeance, 4860 % higher compared to the non-functionalized GOM. Moreover, the separation efficiency of TL-fGOM improved from 37 % of that of ceramic membranes to 99.5 %. Additionally, they showed excellent anti-fouling properties. After exposing the membranes to 500 ppm emulsion for 10 hours in batches, the flux recovery ratio exceeded 90 %. The TL-fGOM in our work demonstrated outstanding performance in purifying oily emulsions containing diesel/toluene/heptane-in-water. All these results revealed that the appropriate functionalization of graphene oxide could assist in forming a thin layer of graphene oxide on the support membranes, offering high separation efficiency and fouling resistance. This approach can be extended further to utilize the graphene oxide membranes for practical applications.

High performance lamellar structured graphene oxide nanocomposite membranes via Fe3O4-coordinated phytic acid control of interlayer spacing for organic solvent nanofiltration (OSN)

Graphene oxide (GO), a 2D nanomaterial known for its precise molecular sieving, holds potential for Organic Solvent Nanofiltration (OSN) and wastewater treatment. However, challenges such as thin interlayer spacing, extended diffusion pathways, and susceptibility to dehydration and negative charge-induced swelling limit its separation performance. To overcome these limitations, Herein, we have fabricated novel Fe3O4 coordinated PhA intercalated GO nanocomposite membranes. Impressively, these nanocomposite membranes exhibited remarkable separation efficiency for dyes, pesticides, and pharmaceutical ingredients, addressing the drawbacks associated with pristine GO membranes and enhancing their overall performance. The optimum G10(1)/P1.5-F100µL nanocomposite membrane displayed impressive solvent permeance of 40.43, 33.45, 20.70, 16.24, and 5.6 L/m2 h bar for acetone, methanol, water, ethanol, and IPA, respectively, while maintaining a rejection rate of ≥98.97 % for the MO dye (MW = 327.33 g/mol). Furthermore, the membrane exhibited outstanding efficiency in separating tetracycline (TC) in ethanol (≥97.97 %) and Pendimethalin (PM) in water (≥99.88 %). Additionally, it demonstrated high rejection capabilities for MB (≥98 %) and CR (≥98.78 %) in harsh DMF solvent. Importantly, the nanocomposite membrane displayed outstanding durability throughout continuous separation of Pendimethalin (PM) in a water solution over a period of 168 h. The PM separation remained nearly unchanged for the entire 168-h duration, demonstrating high mechanical strength and chemical stability. Additionally, the single nanocomposite membrane showcased high efficiency in feed change separation, successfully separating CR in ethanol and PM in water. These results, compared to the other GO-based nanocomposite membranes, demonstrate the exceptional stability and immense potential for real OSN applications.

Exploring the potential of graphene oxide membranes for vapor permeation

This review explores the applicability of graphene oxide (GO) membranes in vapor permeation, emphasizing their unique properties and promising capabilities. In the context of eco-friendly separation processes, such as pervaporation (PV) and vapor permeation (VP), GO membranes can selectively permeate water vapor to separate vapor mixtures. Their distinct structure, featuring slip flow and precise water molecule alignment in angstrom-scale interlayer spaces, facilitates fast water transport. This review proposes the selective adsorption–pore flow–evaporation model as a plausible mechanism for vapor permeation through GO membranes. Despite extensive research on GO membranes for PV in separating mixtures, their application in VP remains underexplored. Nevertheless, their selectivity for water vapor and effectiveness in gas dehumidification processes emphasize their applicability for chemical dehydration (purification). Future research in this field can advance membrane technologies, offering more sustainable and efficient separation processes across various industries for purifying and recycling chemicals and separating azeotropic mixtures.

Non-covalent and covalent-synergistical-interaction assembled GO self-supporting membrane with excellent alignment for ultrahigh H2 barrier applications

The emerging graphene oxide membranes (GOm) showcase superiority in molecule barrier applications, yet their hydrogen (H2) barrier performance is still less than ideal due to the insufficient control of GOm assembly architecture. Here, molecular patch engineering, in which amino rich polyethyleneimine (PEI) is controllably introduced into the GO system, is proposed to construct a highly aligned self-supporting PGO membrane (PGOm) for exceptional H2 barrier performance. Based on the non-covalent and covalent interactions between GO nanosheets and PEI, the assembly behavior of GO nanosheets from the liquid phase to the solid phase is efficiently optimized in both extension and alignment synergistically, resulting in the superior alignments of PGOm with a Herman's orientation factor as high as 0.86. Owing to the excellent alignments, the hydrogen permeability (PH2) of PGOm is substantially reduced to a mere 2.28 cm3 cm/(cm2·s·Pa)·10−15 even at a high temperature of 80 °C, representing a remarkable three-order-of-magnitude decrease compared to GOm. Additionally, at 25 °C, the PH2 of PGOm-enhanced epoxy sandwich composites is minimized to 1.2 cm3 cm/(cm2·s·Pa)·10−15, approximately 50 times lower than that of pure EP. This highlights the significant potential of PGOm in enhancing the gas tightness of composite pressure vessels.

Sub-nano porous graphene-based membranes enabled by in-situ-grown ZIF-8 for enhanced CO2 capture

Graphene oxide (GO) membranes hold promise for selective CO2 adsorption over N2 due to their carboxyl groups, making them attractive for flue gas CO2 capture. However, challenges such as limited carboxyl content, flexible nanosheets, and dense layer stacking hinder their N2/CO2 gas selectivity, pressure resistance, and permeability. In this study, we introduce a specific sub-nanometer framework structure within GO membranes by in-situ growing ZIF-8 nanocrystals. This novel approach, achieved through simultaneous infiltration of zinc nitrate and 2-methylimidazole precursors on both sides of the membrane, enhances CO2 capture and pressure resistance capabilities of resulting ZIF-8@GO composite membranes. Additionally, the incorporation of carboxylated wrinkled graphene (WG) and ethylenediamine (EDA) cross-linking agent molecules improves CO2 capture capability and introduces reinforced porous structures to enhance permeability. Experimental results demonstrate remarkable permeability, selectivity, and pressure resistance of the prepared ZIF-8@EDA-GO/WG composite membranes. Under a gas pressure of 0.2 MPa, permeability reaches 1850 GPU, with theoretical selectivity for N2/CO2 single gas and separation factors for mixed gases of 18.3 and 32.3, respectively, surpassing conventional GO membranes (3 GPU, 1.1, and 1.2). Even under elevated air pressure conditions (1.2 MPa), the composite membranes maintain a theoretical selectivity of 13.4. Our CO2 capture membrane design strategy not only advances the development of functional membranes but also contributes to mitigating CO2 emissions from flue gas, thereby combating global warming.

Polyoxometalate Clusters Confined in Reduced Graphene Oxide Membranes for Effective Ion Sieving and Desalination.

Efficient 2D membranes play a critical role in water purification and desalination. However, most 2D membranes, such as graphene oxide (GO) membranes, tend to swell or disintegrate in liquid, making precise ionic sieving a tough challenge. Herein, the fabrication of the polyoxometalate clusters (PW12) intercalated reduced graphene oxide (rGO) membrane (rGO-PW12) is reported through a polyoxometalate-assisted in situ photoreduction strategy. The intercalated PW12 result in the interlayer spacing in the sub-nanometer scale and induce a nanoconfinement effect to repel the ions in various salt solutions. The permeation rate of rGO-PW12 membranes are about two orders of magnitude lower than those through the GO membrane. The confinement of nanochannels also generate the excellent non-swelling stability of rGO-PW12 membranes in aqueous solutions up to 400 h. Moreover, when applied in forward osmosis, the rGO-PW12 membranes with a thickness of 90nm not only exhibit a high-water permeance of up to 0.11790 L m-2 h-1 bar-1 and high NaCl rejection (98.3%), but also reveal an ultrahigh water/salt selectivity of 4740. Such significantly improved ion-exclusion ability and high-water flux benefit from the multi-interactions and nanoconfinement effect between PW12 and rGO nanosheets, which afford a well-interlinked lamellar structure via hydrogen bonding and van der Waals interactions.

GO-based membranes with enhanced stability and permeability by implanting etched-MXene nanosheets: The role of binding energy in stabilizing 2D membranes

Graphene oxide (GO) stands out as a promising choice for the construction of next generation nanofiltration membranes in wastewater purification. Nevertheless, achieving the requisite stability and optimal permeability for effective separation of aqueous molecules and ions poses a formidable challenge for graphene oxide membranes. In this study, a series of GO/etched-MXene membranes with markedly enhanced stability and permeability was fabricated to provide high-level performance. Due to seemly etching process, the optimal GO/etched-MXene membrane featured additional nanochannels for faster mass transfer, consequently evincing a high water permeance of 88.2 ± 3.8 L m−2 h−1 bar−1 with an excellent dye/salt separation efficiency (CR/NaCl selectivity = 22.6, CR/Na2SO4 selectivity = 42.0). Noticeably, the introduction of etched-MXene nanosheets demonstrated a pronounced enhancement in stabilizing the GO membrane within aqueous environment. The density functional theory (DFT) calculations showed that the binding energy of MXene nanosheets (−7.68 eV) was significantly larger than GO nanosheets (−1.11 eV). According to charge difference density results, compared with GO nanosheets, the electrons transfer in MXene nanosheets was more concentrated. As a result, the specially-designed GO/etched-MXene membranes could maintain a stable separation performance during crossflow filtration, while the pristine GO membrane rapidly cracked. This approach is anticipated to establish a theoretical framework for comprehending the contribution of nanosheet binding energy in stabilizing two-dimensional membranes, fostering synergistic advantages in the advancement of GO membranes characterized by both elevated water permeance and requisite stability in water treatment.

In situ oxidation of reduced graphene oxide membranes by peracetic acid for dye desalination

Graphene oxide (GO) membranes with tunable interlayer spacings are of interest for dye removal from salty textile wastewater, and the membranes are often reduced to improve their stability, which inevitably lowers water permeance. Herein, we demonstrate that reduced GO (rGO) membranes can be facilely modified using peracetic acid (PAA) in situ to dramatically enhance water permeance while retaining dye rejection. Specifically, PAA-modified membranes (PrGO) are synthesized by vacuum-filtering hydrazine-reduced rGO nanosheets onto Nylon substrate and then exposing them to PAA solutions. The effects of the rGO layer thickness, PAA content, and PAA exposure time on the membrane chemistry, nanostructures, and salt/dye separation properties are thoroughly examined. For example, the PAA oxidation of a 100 nm-thick rGO membrane for 10 min increases water permeance by 180 %, from 35 to 93 Liter m−2 h−1 bar−1, and decreases Na2SO4 rejection from 10 % to 3.3 % while retaining the rejection of Congo red at ≈99.7 %. The PrGO membranes exhibit stable water permeance and >99 % dye rejection in multi-cycle tests in a crossflow system, surpassing state-of-the-art GO membranes and showcasing their potential for practical applications.

Enhancing stability and performance of graphene oxide membrane grafted on low-cost rich-silica support: A comparative study of two activation approaches

Although graphene oxide has shown encouraging results in membrane field, it has a major stability issue when coated on ceramic supports, particularly those formed of geomaterials. This work aims to prepare stable graphene oxide layer deposited on a low-cost rich-silica support. The graphene oxide membrane was prepared using grafting method, which included surface activation and modification followed by the graphene oxide layer coating. Siloxane functional groups were activated using either hydrochloric acid or piranha solution to determine which of them provided the highest membrane stability. The support surface was chemically modified using 3-glycidoxypropyltrimethoxysilan followed by the deposition of graphene oxide nanosheets using evaporation-assisted assembly. According to Fourier-transform infrared spectroscopy, the support activated with piranha solution has more silanol functional groups than the support activated with hydrochloric acid while the appearance of 3-glycidoxypropyltrimethoxysilan band on the modified support, proves the accomplishment of grafting. The stability test of the membrane demonstrated a highly stable deposited layer for the graphene oxide membrane activated with piranha solution in different pH contrary to the non-grafted graphene oxide membrane and the graphene oxide membrane activated with hydrochloric acid that peeled off from the support. On the support activated with piranha solution, 3-glycidoxypropyltrimethoxysilan concentration was investigated and an optimal value of 0.1 mol L−1 was determined. The filtration performance of the membrane was assessed by the removal of anionic and cationic dyes. For anionic dyes, the membrane rejection reached a value of 90 % for direct red 80 and 87 % for methyl orange. For the rhodamine B considered as cationic dye, the membrane rejection reached a value of 81 %. The membrane may be considered sustainable since it is inexpensive and emits at least 9.76 kg CO2eq m−2 less than other ceramic membranes during its preparation.