Challenges and prospects: graphene oxide-based materials for water remediation including metal ions and organic pollutants

Abstract

The remediation of polluted water via graphene oxide or derived materials has captivated the momentous attention of the scientific community over the past few years. The significant advantage of graphene oxide is its amphiphilic behaviour, making it an excellent candidate to interact chemically or physically with other polymeric matrices. Graphene oxide can be integrated into bio-based polymers such as proteins, chitosan, and lignocellulosic biomass, improving their sorption capacities. The homogeneous incorporation of graphene oxide into a polymeric matrix may substantially enhance its ability to eliminate organics and metal ion pollutants from water or wastewater. Graphene oxide can be used as a functionalized or composite material to enhance the adsorption capacity of the polymers for inorganic and organic contaminants. This review article provides an in-depth analysis of the mechanisms underlying water transport, as well as the antibacterial and oxidative properties of graphene oxide. In addition, the recent advancements in the use of graphene oxide and its derivatives for the remediation of water and wastewater, with a focus on the removal of metals, organic compounds, and microorganisms, have been critically evaluated. The article concludes by discussing the challenges and future prospects of employing graphene oxide-based materials on a larger scale for water remediation.

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Environmental significance

The application of graphene oxide (GO) and its derivatives in water remediation represents a significant advancement in addressing water pollution globally. By combining graphene oxide with bio-based polymers, its amphiphilic properties enhance the adsorption capacity for a wide range of pollutants, including organic compounds, metal ions, and microorganisms. GO's unique structural characteristics and oxygenated functionalities improve water purification by modifying physiochemical properties and increasing dispersibility. Additionally, recent developments in GO-based materials offer sustainable solutions for wastewater treatment and the utilization of unconventional water resources. The widespread adoption of GO technology has the potential to transform water remediation efforts and ensure a safer, more sustainable future.

1. Introduction

Water pollution constitutes a significant risk to the health and welfare of living organisms across the globe. The tremendous rise in industrial processes and agricultural activities became the primary source of spreading toxic chemicals into water bodies. Recent data shows that over 80% of the wastewater is discharged into the environment without any treatment,^1–3 which contains metal ions, organics and biological chemicals that cause serious water pollution issues and ultimately affect the living organisms.^4,5 Heavy metal ions, organic dyes, antibiotics, detergents, insecticides, pesticides and endocrine-disrupting compounds have recently received significant regulatory and research attention.⁶ Enriching these environmental pollutants beyond acceptable ranges poses substantial ecological and health hazards.⁷ Consequently, around 30% of the global population can not access safe drinking water.⁸

Numerous materials are being used for water remediation, including conventional activated carbon, clays, porous materials, surfactants, and polymers.^9,10 However, recent developments related to nanomaterials provide a novel smart material for environmental remediation due to their innovative properties.^11–14 Carbon-based nanomaterials, including carbon nanotubes, fullerenes, and other allotropic forms of carbon, have shown promising futures due to their distinct structure.^15–17 Nanomaterials have been shown to have good potential for environmental remediation due to their more significant specific surface areas and higher reactivities in the form of adsorbents, catalysts and sensors.^18,19

Graphene oxide (GO) is a promising material in water treatment technologies due to its unique structural design, abundance of oxygen-containing functionalities, simple modification, and ability to resist fouling. Additionally, GO has demonstrated potential for removing pollutants from aqueous mediums. These characteristics make it a favorable choice for various water treatment applications.^20,21 Graphene oxide is a monolayer made up of a wrinkled two-dimensional carbon sheet that contains randomly distributed aromatic rings with sp² hybridization and various oxygen-containing functional groups, such as carboxyl, hydroxyl, carbonyl, and epoxy groups, on its basal planes and edges.^22,23 The thickness of the GO is approximately 1 nanometer, while its lateral dimensions range from a few nanometers to several micrometers.²⁴

Oxygenated groups present in graphene oxide (GO) offer a promising advantage in water purification applications. This is due to the polar functional groups that make GO strongly hydrophilic, allowing for excellent dispersibility in various solvents, including water. Additionally, GO's chemical composition allows for the tuning of its physiochemical properties through chemical modification.^25,26 Typically, the nanochannels that exist between neighboring sheets serve as pathways for molecules and ions that are smaller than the interlayer spacing of the GO sheets, while simultaneously blocking the larger ones.

Recent advancements in graphene oxide provide excellent prospects for developing systems for environmental applications.^27–29 The healing process for contaminated water is a great challenge for environmental remediation. Current graphene oxide-derived wastewater treatment approaches and discharge systems could be more effective and sustainable. The multifunctional materials offered by graphene oxide are expected to provide alternate solutions with excellent performance and affordable water and wastewater treatment.^30–32 Graphene oxide itself and its derived materials with other biopolymers such as chitosan, proteins, cellulose-based water and wastewater treatment methods have the potential to overcome significant challenges the existing treatment technologies are facing.^33–35 Graphene oxide-derived materials provide new treatments allowing economically viable consumption of unconventional water resources to increase the water supply.

To the best of our knowledge, there is no existing literature review that critically summarizes and evaluates the challenges and mechanistic insights associated with graphene oxide-derived materials. This article reports recent advances in the use of graphene oxide and its derived materials in combination with polymeric materials for water remediation. This review article offers comprehensive insights into the graphene oxide mechanism of water transport and antibacterial activity, and it briefly discusses the degree of oxidation of graphene oxide. Additionally, the use of graphene oxide-based materials for the remediation of metal ions, microbes and organic pollutants in water is highlighted. Finally, the review addresses the challenges and prospects of utilizing graphene oxide at an industrial scale and provides recommendations for future research.

2. Structure of graphene oxide

The accurate structure of graphene oxide is still dubious. So far, graphene oxide has at least six different structures based on State ¹³C Nuclear Magnetic Resonance (SSNMR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) Spectroscopy,^36–42 as mentioned in Fig. 1. Graphene oxide is a unique oxidized form of carbon form and gigantic polycyclic aromatic hydrocarbons. The precise understanding of graphene oxide structure can make it more attractive to broaden its applications, particularly for water remediation. It is not easy to unravel graphene oxide's physical or chemical characteristics since similar to other organic molecules; it possesses carbon and oxygen atoms. So, its spectroscopic signals match conventional oxygen and carbon atoms signals. In addition, the determination of precise structure becomes more difficult as the structure of the graphene oxide changes with the method of preparation and is strong hygroscopic in nature.⁴² Even, there is no agreement on the conservation of hexagonal lattice structure and co-planarity of carbon layers.

Fig. 1 Possible structures of GO (top five) (a) based on surface species and (b) folded carbon skeleton. Reproduced from ref. 42 with permission from the American Chemical Society, copyright 2006.

The degree of oxidation of GO determines its structural fate to further transform into various material applications, especially for water purification. A study examined the oxidation state and functional group of GO for their impacts on the living organs. Hydrated GO showed maximum carbon radical density which resulted in cell death. However, pristine graphene oxide has less toxicity and reduced graphene oxide exhibited the lowest impacts. This study demonstrated that the GO surface oxidation state has a significant role in generating toxicity in the mammalian living organs.⁴³

Three key issues concerning the structural mystery of graphene oxide must be addressed. Firstly, the formation and conversion pathway of oxygenated groups on the GO surface. Secondly, the stabilization of oxygen-containing functional groups in strong oxidizing conditions. Lastly, the distribution of oxidized and graphitic domains in GO, which occurs randomly. Despite the many researchers who believe that the epoxy group serves as the primary functional group, some propose that the local strain generated by the oxygen-containing functional groups causes the graphene sheets to be cut.^44–46 However, when the graphene oxide is exposed to water, the epoxide is converted to the hydroxyl group by the acid catalysis.^47,48 On the other hand, Chen and coworkers anticipated that the formation of hydroxyl and epoxy functional groups could be formed due to the attack of oxygen and hydroxyl radicals onto the graphite sheets.⁴⁹

The oxidized areas comprised of hydroxyl and epoxy groups are the least stable in a highly oxidized environment. Nevertheless, the chemical composition and structural arrangement of graphene oxide does not undergo significant alteration upon reaching the critical level of oxidation.^50,51 The stability of functional groups in the oxidizing medium is indicative of the functional group chemical stability. The degree of oxidation and the presence of graphitic zones are crucial in determining the properties of the material, as well as its utilization of GO for various applications.^52,53

Dimiev and his group are the first to study the detailed mechanism for GO synthesis from bulk graphite. They reported three individual and independent steps where each intermediate product could be separated, studied and kept under suitable conditions as presented in Fig. 2.

Fig. 2 The initial stage of the process involves the conversion of graphite into a graphite intercalation compound (1 and 2). Subsequently, this compound is transformed into oxidized graphite (3 and 4). Lastly, pristine graphite oxide is converted into conventional graphene oxide (4 and 5). Reproduced from ref. 54 with permission from the American Chemical Society, copyright 2014.

In the first step, graphite intercalation occurs, while in the second step, this intercalated compound is converted into an oxidized form of graphite which is called pristine GO. During this step, the oxidizing agent is diffused into the preoccupied galleries of the graphite and is a rate-determining step. The final step is the formation of conventional GO from pristine GO after exposure to a water.⁵⁴ Mouhat et al., proposed realistic chemical models of the GO basal plane surface and their behavior in water. The study exhibited that oxygenated groups, i.e., hydroxyl and epoxides are preferably present on the GO layers.⁵⁵

The catalytic activity of the GO is not very well known and cannot be fabricated due to the limited knowledge of the relationship between its radical contents and chemical/physical structures. A study reported by Komeily-Nia and co-workers indicated that the ratio of C/O is 3.0 with approximately 50 nm thickness is optimum to obtain maximum radical contents, which give graphite oxide with pi bonds around 45% and oxygenated groups about 38%. It is important to mention that sheet thickness of more or less than 50 nm produced low contents of radicals due to more or lacking oxidation. However single sheet of GO with excellent radical contents can only be synthesized via an oxidation–reduction combination.⁵⁶

Chen et al., studied how GO degree of oxidation and yield changes with the change in graphite particle size. The study concluded that graphite with small-size particles produced GO with a higher degree of oxidation and yield than graphite with large-size particles.⁵⁷ However, they did not study how the later size of graphite influenced the GO degree of oxidation. The results revealed that the degree of oxidation was increased with the decrease in the later size of the graphite, and a similar pattern was found for the reduced graphene oxide for both degree of oxidation and specific surface area.⁵⁸

Another study reported by Dimiev et al., envisaged the GO formation mechanism through Hummer's method. They found that the oxidation of graphite does not occur through anhydrous sulfuric acid. In addition, they proposed that water molecules are the species that attack the carbon atoms instead of Mn(VII) oxygen derivatives. However, the withdrawal of electrons by Mn(VII) species from carbon atoms and water attack occur simultaneously, as shown in Scheme 1.⁵⁹

Scheme 1 The addition of water molecules onto the adjacent carbon atoms [1]. The initial addition of a water molecule leads to the formation of the intermediate cation [2], which then converts into the tertiary alcohol [3]. The further oxidation of structure [3] results in the formation of the intermediate cation [4], which eventually transforms into the vicinal diol [5]. Reproduced from ref. 59 with permission from Elsevier, copyright 2020.

The thickness of the graphene oxide layers is one of the important parameters to specify its applications which is directly influenced by the degree of oxidation or oxygen contents.⁶⁰ Park and co-workers answered this question by fabricating GO with a different degree of oxidation. The study shows that the thickness and interlayer spacing of the GO has a direct relationship with the degree of oxidation.

3. Mechanistic insights

3.1. Water transport

Understanding the underlying mechanisms of water transport through graphene oxide membranes is imperative, and the water flow phenomenon needs to be better understood. Various studies have been done to explain the water flow mechanism into graphene oxide membranes. Some researchers suggested that graphene oxide laminate membranes can resemble numerous tiny carbon nanotubes assembled with many oxygenated functional groups.⁶¹ Recently, a study showed that fast water transport occurs through hydrophobic nano-channel regions of GO flakes. This rapid flow of water through nano-channels of GO membranes is considered analogous to carbon nanotube-based membranes in which water moves through the hydrophobic tubes.

However, GO laminates also contain oxidized regions with various oxygen-derived functional groups and defects. However, research has proved that the presence of hydrophobic regions is the main contributor to high-water flux through GO membranes. The pores of pure carbon nanotubes can explain water transport through graphene oxide laminates.

GO membrane comprises GO flakes assembled in a nano-channels network with a distance of around 0.83 nm called d-spacing. This distance between the layers or sheets is increased under a hydrated environment because of the presence of hydrophilic groups on the GO surface.

So far, studies suggested water pathway through the GO membrane in three different ways: across the defect pores (Fig. 3a),^62–65 through inter-edge areas⁶⁶ and through the non-oxidized regions,⁶⁷ which is widely believed to be a result of energetically favourable water transport provided by the hydrophobic regions of the GO flakes.⁶³

Fig. 3 (a): Mechanism of water transport. (b): View of the water molecule distribution in a carbon nanotube. Reproduced from ref. 61 with permission from the Royal Society of Chemistry, copyright 2017.

The transport of water through hydrophobic regions can be explained by three distinct motion mechanisms (Fig. 3b). The first is known as the Fickian mechanism, which occurs when water molecules collide in the direction of movement with disordered molecular motion. The second mechanism, referred to as the single type, is characterized by a limited space that restricts water molecules into a one-chain configuration to prevent collisions with each other.⁶⁸ This type of water motion is observed in the narrow hydrophobic channels of GO membranes, where water molecules possess ordered H-bonds and reduced free energy.⁶⁹ The third mechanism is a ballistic type, in which the motion of condensed water molecules is highly ordered.^64,70

In recent studies, it has been observed that water flow through hydrophobic regions not only confines it into one chain but also transforms it into ice crystallites.⁷¹ The ice exhibits highly mobile behavior due to its high crystallinity and weak interactions with the non-oxidized surface, which contributes to the rapid water flow in both GO membranes and carbon nanotube (CNT) membranes. Chong et al. were the first to investigate the mechanism of water transport in pervaporation, which involves selective permeation and evaporation.⁷² The study concluded that higher pure water flux was found in pervaporation than the pressure-driven permeation as shown in Fig. 4. They proposed a two-step pore flow-evaporation mode to recognize the higher water flux in pervaporation. Furthermore, high-speed water permeation through membranes was ascribed to the high membrane capillary pressure.

Fig. 4 Water transport in graphene oxide membranes. Reproduced from ref. 72 with permission from the Royal Society of Chemistry, copyright 2018.

3.2. Antimicrobial

A significant challenge with the currently available membranes is to control biofouling during water treatment since the adhesion of microorganisms, and subsequent biofilm growth makes it difficult for their optimum operation at an industrial scale. The graphene oxide-based membranes have shown promising antibacterial properties.⁷³ The antibacterial behaviour of graphene oxide depends on the size, number of layers, shape, surface modification and agglomeration/dispersion.⁷⁴ Graphene oxide (GO) is often believed to possess antibacterial properties due to a combination of physical and chemical elements. The former is mechanical in nature and involves the sharp edges of graphene nanosheets cutting through the bacterial cell membrane, causing the intracellular matrix to leak and ultimately resulting in the death of the bacterium (Fig. 5).⁷⁵

Fig. 5 Modes of action of antibacterial effect of graphene oxide.

Liu et al., reported that the antibacterial effect of graphene oxide is independent of superoxide anion reactive oxygen species since they did not detect any superoxide anion production. They also suggested that membrane and oxidation stresses are the primary triggers for antimicrobial actions. They proposed a three-step mechanism for GO antibacterial actions,⁷³ first step involves the initial deposition of cells, which is followed by the application of sharp nanosheets that result in membrane stress in the second phase. The third step involves oxidation that is independent of superoxide anions.

The membrane stress induced by the sharp edges of graphene nanosheets causes physical damage to cell membranes. This leads to the loss of bacterial membrane integrity and the leakage of the RNA.⁷⁶ Alternative suggestions have been proposed that graphene could potentially cause oxidative stress on neural phaeochromocytoma-derived PC12 cells.⁷⁷ The available literature on graphene oxide-based membranes indicates a similarity between graphene oxide and other synthetic carbon nanomaterials. The antimicrobial activity of CNTs is thought to be a result of both “physical” and “chemical” effects.⁷⁸ When bacteria come into direct contact with CNTs, strong physical interactions occur between the two, leading to physical damage to the bacterial cell membranes and the release of intracellular contents.⁷⁹ At the same time, some “small” CNTs may be internalized by the bacterial cells, while larger CNT aggregates may stick to the cell surfaces. A similar process is thought to occur with the graphene oxide membrane.⁸⁰

In graphene oxide membranes, it is observed that mechanical stress on bacterial cells causes the destruction of their cellular structures. This destruction can be attributed to oxidative stress, which can occur via two different pathways. The first pathway involves reactive oxygen species (ROS), which are generated by graphene oxide and induce oxidative stress on neural cells. The second pathway is independent of ROS, and it is hypothesized that the graphene oxide membrane may disrupt the microbial process by directly oxidizing vital cellular structures. Studies have suggested that the ROS-independent mechanism leads to the destruction of bacterial cells.⁸¹ The membrane's cytotoxicity is contingent upon its dispersibility and size. Recently, graphene oxide membrane has been developed and compared with the commercially available membranes.⁸² The graphene membranes show that there are no bacteria attached, while in polymeric derived membranes, bacteria are attached to the surface. The low binding affinity of E. coli to graphene membranes shows potentially less bactericide usage and low chances of membrane failure.

The application of a wrapping mechanism consisting of larger GO sheets was found to inhibit the growth of bacteria. The studies have shown that the sharp-edge influence of GO and rGO through direct contact is ascribed to their antimicrobial activity. The findings of Fan and colleagues were unprecedented, as they were the first to report that graphene oxide and reduced graphene oxide demonstrated exceptional antimicrobial properties.⁷⁶ Each activity was tested against E. coli bacteria and showed very effective inhibition. Another group led by Akhavan also studied the antibacterial activities of GO and rGO nanowalls against Gram-negative and Gram-positive bacteria. The results indicated that rGO nanowalls exhibited better antibacterial activity than GO nanowalls. This was ascribed to more sharp edges of rGO, which offered them more contact with the cell membrane and better charge transfer between bacterial cell membrane and rGO, causing more damage to the bacterial cell membrane.⁷⁷ In a study conducted by the Akhavan group and focused on bacterially reduced graphene oxide sheets, they observed a reduction in the proliferation of bacteria on their surface, even in a favorable environment for microbial growth.⁸³ Tour et al. demonstrated that graphene oxide holds significant promise for bioremediation, due to its capacity to function as a final electron acceptor for both heterotrophs and environmental microorganisms.⁸⁴ In another study, Tu and coworkers have done experimental and theoretical work on the antibacterial activity of graphene oxide. They proposed a new destructive extraction mechanism for the GO cytotoxic and antimicrobial behaviour on a molecular basis using E. coli. The study indicated that nanosheets of GO can go inside the bacteria's cell membrane and extract phospholipids which resulted in the destruction of inner and outer cell membranes.⁸⁵

Li and colleagues recently proposed a captivating and disputed mechanism for the antibacterial activity of graphene oxide. They examined the antibacterial actions of large-area single-layer GO films on conductor Cu, semiconductor Ge, and insulator SiO2, using both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria. The study demonstrated that the antibacterial activity did not originate from reactive oxygen species, but rather it started with the transfer of bacterial membrane electrons to the graphene surface.⁸⁶

Studies suggested that contact of bacteria with GO resulted in an electron donor–acceptor reaction from the bacterial cell membrane to the GO and created oxidative stress independent of reactive oxygen species. So, the surface of graphene oxide is mainly responsible for its antimicrobial action instead of the edges. There are studies available where the antibacterial activity of graphene oxide was determined by the composition of the media.⁸⁷ Hui et al. unveiled the underlying mechanism related to its bactericidal nature in saline media and nutrient broth. The study mentioned that GO sheets have bactericidal ability in saline media. However, provided with Luria-Bertani (LB) broth, its bactericidal activity was gradually deactivated. The study suggested that basal planes govern the antibacterial activity of graphene oxide sheets. The antibacterial activity of the graphene oxide sheets in LB broth was reduced as the sheet's basal planes were masked due to noncovalent adsorption, which in turn decreased the GO antibacterial action.⁸⁸

However, it has not yet been confirmed that the antibacterial behavior of graphene oxide is only imparted by the basal planes. There are two possibilities; first, masking may be thick, making the edges challenging to penetrate the bacterial membrane. Second, nanosheets cannot wrap around the bacteria due to rigidity contributed by thick masking. A. áde Leon coworkers used the Langmuir–Blodgett deposition method, which immobilized the edges on the substrate and prevented it from puncturing or wrapping the bacteria.⁷⁵ They found that the greater the number of layers better the antibacterial activity against E. coli. In another study, a graphene oxide (GO) sheet with silver (Ag) nanoparticles (GO–Ag) was prepared in the presence of silver nitrate (AgNO₃) and sodium citrate. The antibacterial activity of GO and GO–Ag was examined using the standard counting plate method. The findings revealed that the adhered cells were completely inhibited after exposure to the GO–Ag nanocomposite.⁸⁹

Another interesting mode of antibacterial effect was observed, referred to as the self-killing effect. A study showed the interaction of bacteria with graphene oxide that was converted into a reduced form by glycolysis. This reduced form of graphene oxide further inhibited bacterial growth than the graphene oxide that was not bacterially reduced.⁸³

The antibacterial effectiveness of graphene oxide (GO) in water is enhanced by combining it with calcium ions (Ca²⁺), which mitigate GO's aggregation tendency. Ca²⁺ reduces the negative charge on GO's surface, promoting bacterial adhesion and facilitating the co-settlement of GO and bacteria.⁹⁰ A study conducted by Lei led to the development of biomimetic mineralization of zirconium dioxide nanoparticles on seaweed residue grafted with oxidized graphene for effective antibacterial action against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). This study presents new technologies for water purification, a straightforward approach for creating biomass composite membranes, and valuable insights into the use of seaweed waste and pathogen destruction in wastewater treatment.⁹¹ Green-rGO, synthesized using Tinospora cordifolia extract, demonstrates antibacterial properties against Staphylococcus aureus and Escherichia coli, with 10–17 mm inhibition zones, showcasing its potential in water purification and biomedical applications.⁹² Shati and coworkers prepared a unique substrate comprising zinc copper ferrite (ZnCuFe₂O₄), polyethyleneimine (PEI), and graphene oxide (GO) sheets attached to mesoporous MCM-48. This substrate effectively prevents the growth of bacterial strains Staphylococcus aureus and Escherichia coli.⁹³ A study was reported to create the Fe₃O₄/GO/Zn–Fe LDH (FGZ) nanocomposite, with a special emphasis on its antibacterial characteristics. The FGZ nanocomposite demonstrates remarkable antibacterial activity against both Gram-positive S. aureus (75.09%) and Gram-negative E. coli (80.53%) bacteria, indicating its potential for use in antimicrobial and water treatment products. These results emphasize the positive antibacterial effects of the FGZ nanocomposite.⁹⁴

A study highlighting the development of an eco-friendly and budget-friendly method for producing reduced graphene oxide by utilizing green extracts derived from curry leaves and tulsi seeds as reducing agents, while focusing on its antibacterial properties. The study revealed notable antibacterial activity against E. coli bacteria and fungal strains. These results showcase the versatile applications of these materials, suggesting their potential use in antimicrobial materials and water treatment.⁹⁵

A novel approach to combating antibiotic resistance involves developing a zirconium-doped zinc–aluminum layered double hydroxide/graphene oxide (Zn–Al–Zr LDHs/GO) nanocomposite for efficient removal of antibiotic-resistant genes (ARGs) and bacteria (ARBs). This nanocomposite inactivates kanamycin-resistant E. coli under full-wavelength light irradiation in under 50 minutes, demonstrating exceptional photocatalytic sterilization. The Zn–Al–Zr LDHs/GO disrupts the bacteria's respiratory chain by generating singlet oxygen (¹O₂), reducing adenosine triphosphate (ATP) production, and inhibiting DNA repair, ligase, and polymerase proteins. This study offers a promising method for effectively eliminating ARB and ARGs, addressing crucial antibiotic resistance issues in microbial populations.⁹⁶ The dissipation dynamics and transformation of the herbicide atrazine (ATZ) in the presence of graphene oxide (GO) in river water provide insight into their coexistence and effects on microbial communities. The results showed a great impact on the microbes on the number of microbial and bacterial diversity. Crucially, the presence of GO increases the relative abundance of bacteria that degrade ATZ and Chitinophagales, indicating a possible role of GO in promoting ATZ transformation by elevating the abundance of specific microbial groups.⁹⁷

Recently, a study examines the antibacterial properties of a nanocomposite made up of graphene oxide and SiO₂ against both Gram-negative and Gram-positive bacteria.⁹⁸ Combining silver nanoparticles (Ag NPs) and antibacterial natural rosin with chitosan (CS) and polyvinyl alcohol (PVA) blend, decorated graphene oxide (GO) can be employed to develop bio-adsorbent nanomembranes that effectively pathogens from contaminated water resources. Data indicate that the CS/PVA-3% nanomembrane is a potential option for removing biological species from water resources, particularly for irrigation and agricultural applications.⁹⁹

3.3. Antifouling properties

Fouling has a significant impact on the performance, lifespan, and separation capacity of membranes used for filtration. When the pores or a layer of cake forms on the surface of the membrane, it can block the flow, which in turn reduces the membrane's flux.¹⁰⁰ A filtration membrane that has high permeability, rejection rate, and resistance to fouling for an extended period is typically considered ideal. Graphene oxide (GO) is a promising material for creating antimicrobial surfaces due to its potent antimicrobial properties.¹⁰¹ The major problem associated with current polyimide-derived membranes is fouling, which is a significant issue. However, this issue can be resolved by using graphene oxide-based membranes. Graphene-based materials have demonstrated strong antibacterial properties.¹⁰²

To the best of our knowledge, the first detailed study on graphene-based material related to their antibacterial property and mechanism of action was reported by Shaobin Liu et al.⁷³ They compared the antibacterial activity of four different forms of graphene-based materials, i.e., graphite, graphite oxide, graphene oxide and reduced graphene oxide toward Escherichia coli (E. coli). The study revealed that graphene oxide dispersion showed maximum antibacterial activity against E. coli as compared to graphite, and graphite oxide and reduced graphene oxide with the same concentration, and under similar incubation conditions. Direct contact with graphene nanosheets disrupts the cell membrane of the microorganism. Scanning electron microscope (SEM) images of the graphene materials displayed that direct contact caused the microorganism's cell membrane disruption and led to cell death, as depicted in Fig. 6. They described the bacterial cytotoxicity of graphene-based materials due to the combined effect of oxidative and membrane stress. They proposed a three-step mechanism to explain the antibacterial property of graphene-based materials. They also concluded that graphene materials possessing higher density of functional groups and are smaller in size, have more chances to interact with bacterial cells. The same phenomenon was observed in GO aggregates, as they have the smallest average size among the four types of materials and showed the highest antibacterial activity.

Fig. 6 The SEM images illustrate the visual appearance of E. coli bacteria after a 2-hour incubation with saline solution in (a and b), the bacteria following a 2-hour incubation with GO dispersion at a concentration of 40 μg mL⁻¹ (c and d), and after a 2-hour incubation with rGO dispersion at a concentration of 40 μg mL⁻¹ in (e and f). Reproduced from ref. 73 with permission from the American Chemical Society, copyright 2011.

The study reported by F. Perreault et al. investigated the relationship between the size of GO antimicrobial activity and Gram-negative bacteria Escherichia coli.¹⁰¹ The findings revealed that the antimicrobial activity of GO surface coatings increased fourfold when the GO sheet area was reduced from 0.65 to 0.01 μm². The increased antimicrobial activity of smaller GO sheets is attributed to oxidative mechanisms, which are associated with the higher defect density of smaller sheets. This research offers valuable insights that will contribute to the advancement of graphene-based antimicrobial surface coatings in the future. In another study, researchers attached active groups of biguanide to the surface of graphene oxide sheets through covalent functionalization. They then combined the modified GO sheets with magnetic nanoparticles to produce a magnetic graphene-based composite called MMGO, which was incorporated into a polyethersulfone (PES) polymer matrix. The resulting nanofiltration membrane (0.5 wt% MMGO) demonstrated exceptional copper removal, achieving 92%, while exhibiting dye rejection of nearly 99%.¹⁰³

Understanding the basic reasons behind the antifouling properties is difficult since it is a complex phenomenon. Generally, the surface hydrophobicity of the membrane increased their fouling property.¹⁰⁴ Various ways such as material modification, blending with other polymers or surface modification have increased the membrane hydrophilicity. The addition of hydrophilic nanoparticles was a promising approach to improve the membranes' antifouling properties, which also increases the water flux through the membrane.¹⁰⁵

Polyethersulfone (PES) derived membranes (ultra- and nano-filtration) are widely used for commercial and laboratory purposes. However, fouling is the main issue with this polymer to expand its applications in filtration processes. Fouling effects, the membrane performance caused in low water permeability. Numerous ways have been introduced to overcome fouling using hydrophilic moieties, such as blending with graphene oxide, grafting co-monomers or short-chain molecules, inserting nanoparticles, etc.^106–110

Rahimi et al. incorporated inorganic nanoparticle into the polyethersulfone-derived membrane to deal with fouling. For this purpose, they embedded graphene oxide nanoplates with varying concentration of 0.1, 0.5, 1 wt%, into a polyethersulfone (PES) membrane to improve its antibacterial properties. The effectiveness of the membranes in resisting fouling was assessed using powdered milk solution, and the results revealed that incorporating GO at a concentration of 0.5% led to a significant enhancement in the fouling resistance of the PES membrane when compared to the membrane without GO.¹⁰⁵ One of the good ways to overcome biofouling is introducing inorganic nanoparticles ascribed to greater hydrophilicity or morphological changes in the membrane.¹¹¹ Musico and colleagues developed cellulose nitrate filters with graphene oxide (GO) and poly(N-vinyl carbazole)–graphene oxide (PVK–GO) coatings to enhance their surface properties. The integration of graphene and graphene oxide-based nanomaterials on the surfaces of filters and their interaction with the bacteria have been demonstrated with SEM imaging of the surface morphologies of unmodified and modified membrane filters before and after filtration, as shown in Fig. 7. SEM images of the filters exhibited that coating the membrane with graphene and graphene oxide-based nanomaterials decreased the membrane's pore size. As a result, an increase in bacteria retention was observed as compared to unmodified and PVK-modified membrane filters.¹¹²

Fig. 7 Scanning electron microscopy images of (a and b) cellulose nitrate filters, (c and d) poly(N-vinylcarbazole) coated membranes, (e and f) graphene-coated membranes, (g and h) poly(N-vinylcarbazole)-graphene nanocomposite coated membranes, (i and j) graphene oxide coated membranes and (k and l) poly(N-vinylcarbazole)-graphene oxide nanocomposite coated membranes. Reproduced from ref. 112 with permission from the American Chemical Society, copyright 2014.

Another study has been reported by Safarpour and coworkers on polyethersulfone (PES) based nanofiltration membrane blended with reduced graphene (rGO) and titanium dioxide (TiO₂) in the phase inversion method. Fouling of the membranes was studied using bovine serum albumin (BSA) solution filtration and found that 0.1 wt% rGO/TiO₂ membrane exhibited the best antifouling property as to TiO₂/PES and GO/PES membranes. An interesting result was obtained since hydrophilicity is believed to increase the membrane's antifouling ability, which is not the case here, as reduced graphene oxide has less electrophilicity than graphene oxide. The addition of TiO₂ might play an important role as a hydrophilic additive, increasing its hydrophilicity and enhancing its antifouling resistance.¹¹³

The fouling of the membrane limits its performance and fouling resistance can be measured by reflux recovered after simple flushing. The functionalization of the graphene oxide is another good way to improve its antifouling properties. Zambare et al. reported polysulfone mixed matrix membranes comprising amine functionalized graphene oxide i.e., polyamines, ethylenediamine, diethylenetriamine and triethylenetetramine. The incorporation of the polyethylene amines enhanced the interlayer spacing between the nanosheets of graphene oxide, which improved their dispersion in polysulfone–N-methyl-2-pyrrolidone (NMP) solution. The amine group's presence on the functionalized graphene oxide nanosheets produces phase separation areas, giving membranes with higher porosity and finer pores. The membranes performance results indicated that their water flux was enhanced to 170.5 LMH bar⁻¹ with 90.5% bovine serum albumin (BSA) rejection.¹¹⁴

A technique known as surface-initiated ring-opening metathesis polymerization (SI-ROMP) was utilized to modify the surfaces of graphene oxide (GO) with hydrophobic and antifouling monomers in order to control biofouling. The results showed that optimal copolymerization activity could be attained at specific molar ratios, which preserved the GO intercalated layer structure but with a decrease in layer spacing due to the formation of polymers. It was observed that the modified GO displayed enhanced resistance to protein adsorption, particularly towards large molecular weight proteins, indicating its potential for reducing biofouling. This study presents a practical approach for creating antifouling surfaces through controlled surface modification, providing valuable information for improving materials used in the management of biofouling in various applications.¹¹⁵ Banerjee and coworkers developed a versatile mixed matrix membrane (MMM) by incorporating mesoporous Mg–Al–Ti ternary composite oxide nanoparticles (NPs) within a polysulfone membrane, with a focus on biofouling prevention. The membrane exhibited anti-fouling capabilities, recovering 92.5% of flow after filtering a bovine serum albumin solution. These membranes have great potential for practical water treatment applications, particularly in minimizing biofouling-related issues in water purification processes.¹¹⁶

The GO sheet disintegrates due to hydration in the aqueous media. The poor structure stability of the graphene oxide derived membrane is one of the significant drawbacks of expanding their water treatment applications. Lim et al. prepared graphene oxide derived membrane by covalently cross-linked to bio-based tannic acid (TA) using hyper-branched polyethyleneimine (PEI). This cross-linking gave a stable layered structure and improved the dimensional stability as well as ion separation. The graphene oxide cross-linked membrane showed better water flux and a higher rejection rate for NaCl and MgSO₄ than commercial nanofiltration membranes_. It exhibited higher bactericidal activity against E. coli than the alone graphene oxide membrane.¹¹⁷

The utilization of GO laminates has limitations due to their instability in aqueous solution and poor monovalent ion rejection rate. As GO is hydrophilic and its nanosheets can easily be hydrated, its laminates' structure is lost.¹¹⁸ In addition, they have a low rejection of smaller ions.^119,120 Lastly, the data available related to the antibacterial activity of graphene oxide membranes are inconsistent. The GO membranes can reject the monovalent ions; theoretically, its nanochannels should be less than 7 Å as the sodium ions radius is 3.6 Å.¹²¹ However, the distance between nanochannels increases by ∼9 Å due to hydration. As a result, small ions can infiltrate through the GO membrane nanochannels.⁶² Overall, GO's antibacterial performance depends on factors such as structure planarity, lateral size, presence of functional groups on the surface, degree of oxidation, and oxidation state during interaction with the bacterial membrane.

An effective solution was devised through the utilization of GO-coated membranes containing zwitterionic materials, which demonstrated exceptional resistance to fouling and sustained long-term stability. This development represents a substantial advancement in environmental technology.¹²² Fe(III) and tannic acid-treated graphene oxide (GO) laminar membranes exhibit enhanced selectivity and antifouling properties for nanofiltration. The treatment partially reduces the upper GO structure and forms a metal–polyphenol network, mitigating flaws caused by uneven stacking and natural swelling of GO nanosheets. This approach conceals horizontal flaws, enhances steric hindrance, reduces irreversible pore blockage, shields flaws, and decreases adhesion forces, offering promise for developing GO-based membranes with improved nanofiltration performance.¹²³ Electroconductive membranes (ECMs) were developed to solve fouling issues, from polyether sulfone (PES) and laser-induced graphene (LIG), combining reduction, precipitation, and filtration. The membranes are optimized for PES concentration and thickness, showing high permeability and rejection rates. In biofouling tests, ECMs significantly reduce organism attachment compared to traditional membranes, showcasing their anti-biofouling properties. This study demonstrates that next-generation ECMs offer promising solutions for biofouling and pollutant removal, advancing water purification technologies.¹²⁴ A recent study has shown that graphene oxide-based membranes incorporating perfluoroalkyl chains exhibit exceptional antifouling properties. These membranes maintain high flux recovery ratios and low flux decrease ratios, even at high permeance, making them suitable for oil–water separation applications. This research provides a promising method for producing antifouling membranes by enhancing both fouling resistance and release properties through careful control of surface chemistry. This breakthrough offers significant advantages in the fight against biofouling in membrane technologies.¹²⁵

4. Utilization in water remediation

4.1. Metal ions removal

Nowadays, metal ions water pollution is one of the biggest issues worldwide. It is very challenging to decontaminate the metal ions in polluted water due to their higher solubility and mobility within the water.¹²⁶ In addition, they have the ability to interact with surrounding elements through redox reactions and form complexes, which makes their separation difficult.^127–129 Many emerging techniques are being investigated for metal ions water remediation.^130–132 Among these, graphene oxide and derived materials showed promising results, as shown in Table 1.

Table 1 Graphene oxide derived materials for removal of inorganics

GO and GO derived materials	Type of contaminant	Adsorption capacity (mg g^−1)	Ref.
ZrO2/GO	U(VI)	128	133
3D-rGO aerogel decorated with (Fe3O4@SiO2)	Pb(II), Cd(II) and Cu(II)	∼455 Pb(II), 448 Cd(II) and 232 Cu(II) mg g^−1 of adsorbent	134
GO-g-P4VP@PAA hydrogel	Pb(II), Cd(II)	257.28 for Pb(II) and 175.79 for Cd(II)	135
2,6-Diamino pyridine–RGO	Cr(VI)	393.7	136
PPY–GO	Cr(VI)	497.1	137
Graphene oxide/magnetic lignin-based nanoparticle	Pb(II) and Ni(II)	Pb(II) and Ni(II) ions to 147.88 and 110.25	138
PANI–GO	Cr(VI)	1149.4	139
M–GO	Co(II)	12.9	140
PVC/PPD/GO paper-like material	Pb(II)	44.80	141
GO	Cu(II)	46.6	142
GO aerogel	Cu(II)	19.1	143
Ionic liquid-assisted mesoporous GO–SiO2 nanocomposite	Pb(II) and As(III)	Pb(II) and As(III) were found to be 527 and 30	144
GO	Pb(II)	842	145
EDTA–GO	Pb(II)	4797 ± 46	146
Graphene oxide modified with sodium alginate	Pb(II), Zn(II), and Cd(II)	887.21, 161.25, and 139.62 for Pb(II), Zn(II), and Cd(II)	147
MC–GO	Pb(II)	76.9	148
PPy–RGO	Hg(II)	980	149
GO/paper	Pb(II), Ni(II) and Cd(II)	75.41 mg g^−1, 29.04 mg g^−1 and 31.35 Pb(II), Ni(II) and Cd(II)	150
CGGO	Cu(II)	∼120	151
	Pb(II)	99
GO	Au(III)	108.3	152
	Pd(II)	80.8
	Pt(IV)	71.4
Graphene oxide embedded calcium alginate (GOCA) beads	Pb(II), Hg(II) and Cd(II) ions	602, 374, 181 for Pb(II), Hg(II) and Cd(II) ions	153
GO	Cd(II)	106.3	154
	Co(II)	68.2
Aero gel derived from sodium alginate (SA), graphene oxide (GO), and β-cyclodextrin (βCD)	Cu(II) and Cd(II)	Cu^2+ and Cd^2+ for 48.49 and 174.85 mg g^−1	155
Chitosan–GO	Au(III)	1076.6	156
	Pd(II)	216.9
Polyethyleneimine-grafted graphene oxide (PEI/GO)	Pb(II)	64.94	157

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Feng Li et al. reported a cheap, green, and recyclable lignosulfonate-modified graphene hydrogel (LS-GHs). They used a one-step eco-friendly method for the graphene oxide to remove Pb(II) from wastewater on a large scale. The results showed that synthesized hydrogel could adsorb a high concentration of Pb(II) with a capacity of 1210 mg g⁻¹, which is the highest among all the Pb(II) adsorbents reported so far.¹⁵⁸ Zhu et al. utilized vacuum filtration to produce biohybrid membranes composed of graphene oxide/cellulose nanofibers for water purification. These biohybrids demonstrated a noteworthy adsorption capacity for Cu(II) due to the presence of oxidized cellulose nanofibers, which allowed for the formation of a unique “arrested state” within the water. This “arrested state” was the result of ionic cross-linking between the adsorbed Cu(II) and the negatively charged oxidized cellulose nanofibers and GO phase.¹⁵⁹ Increasing the duration of hydroiodic acid vapor exposure is a simple method for adjusting the size of graphene oxide (GO) nanochannels on a sub-nanometer scale. These nanochannels, which are created by the non-oxidized hydrophobic portion of the GO surface, facilitate rapid water transport.

The surface modification of graphene oxide is one of the most common methods to enhance its adsorption capacity. The graphene oxide surface is easily modified with amine using organic transformation due to the presence of hydroxyl, carboxyl, and epoxy groups on its surface. Sahoo et al., modified the surface of graphene oxide using ethylene diamine and decorated ZnO–ZnFe₂O₄ on this amine-functionalized graphene oxide. This resulted in more surface activity for Cr(VI) adsorption. Most importantly, chromium's adsorption capacity was not affected due to the presence of other ions such as Ni²⁺, Cu²⁺, NO₃⁻, SO₄²⁻, and Cl⁻ in the aqueous media. Cr(VI) adsorption was carried out through electrostatic force and chelation formation with amine groups on the graphene oxide surface.¹⁶⁰ Trimercapto-s-triazine-trisodium (TMT-15), salt has excellent chelation ability for metals and is used as an adsorbent for wastewater treatment.^161,162 Its regeneration and recycling are very difficult as it is used in the solution form. Graphene oxide with a mesoporous layered “sandwich” like structure (GO/Fe₃O₄/TMT-15) showed good adsorption capacities for Pb²⁺ and Cd²⁺ from contaminated water. The adsorbent was recyclable due to the presence of Fe₃O₄, making it easier to separate from the wastewater.¹⁶³

Chen and coworkers fabricated the GO membrane on a polyethersulfone (PES) membrane to separate Hg²⁺ from desulfurization wastewater. The presence of Na⁺ ions showed an inhibitory effect on the separation of mercury. Since Sodium ion is highly ionizable that makes it difficult to bind with film and excess of Na⁺ damage the GO membrane structure.¹⁶⁴ A graphene oxide membrane from ethylenediaminetetraacetic acid (EDTA)-functionalized magnetic chitosan (CS) was reported using a reduction precipitation method. The membrane can remove heavy metals i.e., Pb²⁺, Cu²⁺, and As³⁺ from water/wastewater. A maximum adsorption capacity of 206.52, 207.26, and 42.75 mg g ⁻¹ for Pb²⁺, Cu²⁺, and As³⁺ respectively was reported. Langmuir and Freundlich's isotherm was used to evaluate the equilibrium data, while Lagergren pseudo-first-order and pseudo-second-order kinetic models were used to analyze the heavy metal adsorption reaction kinetics.¹⁶⁵

The one-pot method developed by Pirveysian et al. was utilized for the synthesis of sulfur-functionalized graphene oxide (GO-SOxR) through the combination of sodium sulfide and water. The resulting synthesized composites were investigated for their ability to remove Pb(II), Cd(II), Ni(II), and Zn(II) as heavy metal ions from aqueous solutions. Furthermore, kinetics studies were carried out to evaluate the adsorption of the heavy metal ions, and equilibrium adsorption isotherms were employed to analyze the data. The experimental data obtained from the kinetic studies was found to fit the pseudo-second order model.¹⁶⁶

Graphene oxide-derived membranes were modified with covalently linked bovine serum albumin (BSA) to remove the Co(II), Cu(II), AuCl₄⁻ and Fe(II) ions. The membranes showed selective AuCl₄ absorption from HAuCl₄ solution ascribed to BSA's metal binding ability and the graphene oxide's large surface area. In addition, membranes exhibited better selectivity for Co(II) as compared to Cu(II) and Fe(II).¹⁶⁷ In another study, carboxylated graphene oxide was modified with chitosan to improve its adsorption capacity for chromium (Cr), cadmium (Cd), lead (Pb) and uranium (U). The study has shown that GO adsorption capacity increased up to 92.4 (64.93 mg g⁻¹), 94.6 (384.61 mg g⁻¹), 90.2 (68.49 mg g⁻¹), and 90.6% (49.50 mg g⁻¹) for the U, Pb, Cr, and Cd, respectively. The adsorption of heavy metals followed the Langmuir adsorption isotherm behaviour. The thermodynamics results confirmed that the nature of the adsorption of metals through the GO composite was endothermic and spontaneous.¹⁶⁸ Magnetic graphene oxide was polymerized using chitosan solution and glutaraldehyde solution to obtain the beads for Pb(II) from the aqueous solution. The lead adsorption improved to 187 mg g⁻¹ and followed Langmuir isothermal model. The study concluded that beads can be re-used after treatment with acid for upto four adsorption–desorption cycles.¹⁶⁹ In another study, graphene oxide–chitosan nanocomposite was functionalized with ethylenediaminetetraacetic acid (EDTA) for the removal of Hg(II) and Cu(II) from the wastewater. The adsorption of metals followed the Langmuir isothermal model and exhibited maximum adsorption of 324 ± 3.30, and 130 ± 2.80 mg g⁻¹ for Hg(II) and Cu(II), respectively.¹⁷⁰ Choi and co-workers modified the chitosan–graphene oxide with gadolinium oxide for arsenic(V) adsorption from water. The composites exhibited maximum efficacy (252.12 mg g⁻¹) for arsenic removal from pH 3–7, ascribed to the presence of oxygenated groups of the chitosan–graphene oxide and π–π bond electrons of the gadolinium oxide.¹⁷¹

Graphene oxide was functionalized with hyperbranched polyamide amine and cellulose to enhance its adsorption of Pb, Cd, and Cu divalent metal ions. The amide linkage between the GO carboxyl group and the amino group of the hyperbranched polyamide amine increased the active groups on the GO surface and improved adsorption. Dialdehyde cellulose was also grafted onto the GO/HPAMAM through Schiff base formation, increasing the number of hydroxyl groups and contact area for heavy metal ions. The maximum adsorption capacities of graphene oxide reached 680.3, 418.4, and 280.1 mg g⁻¹ at 25 °C for Pb(II), Cd(II), and Cu(II), respectively. The adsorption followed the pseudo-second-order kinetic model and the Langmuir isotherm model.¹⁷² In another study, graphene oxide was modified with cellulose acetate in the presence of calcium carbonate to synthesize composites to remove Ni(II) from wastewater. The modification resulted in an increase of Ni(II) adsorption due to the large surface area. The adsorption of Ni(II) ions was assessed with a concentration from 10–40 mg L⁻¹ with a removal efficiency of 96.77%.¹⁷³ In a recent study, graphene oxide was cross-linked with chicken feathers keratin to improve its adsorption capacity for the simultaneous removal of oxyanions (As, Se, Cr) and cations (Ni, Co, Pb, Cd and Zn) up to 99%, from laboratory synthetic wastewater containing metals concentration upto 600 μg L⁻¹. This improved adsorption of keratin was ascribed to the chemical linkage through esterification with the graphene oxide, which exposed more active sites on the surface. Moreover, the study revealed that the adsorption of metal cations and anions occurs through complexation, electrostatic interaction and chelation for the simultaneous removal of metal ions in a single treatment.¹⁷⁴

A study by Rathod et al. prepared a component of the graphene oxide/orange peel/chitosan composite (GO–OP–CS) for the adsorption of Cd(II) ions in aqueous solutions. This hybrid product was found to have enhanced physicochemical characteristics and metal ion adsorption capabilities, which were analyzed using various analytical techniques. The composite demonstrated a high adsorption capacity (q_max) of 537.63 mg g⁻¹.¹⁷⁵

Li et al. utilized a combination of solvothermal synthesis and pyrolysis techniques to synthesize magnetic Fe₃O₄/graphene oxide (GO) nanocomposites from the MIL-100(Fe)/GO precursor. These nanocomposites were successfully synthesized and can be used for the adsorption of As(V) over a broad pH range of 2–9. The isotherm model indicates that As(V) has an adsorption capacity of up to approximately 20.00 mg g⁻¹. Additionally, functional Fe-MOFs based on adsorption derivatives can be used to treat wastewater contaminated with arsenic.¹⁷⁶

Mai et al., used the co-precipitation technique was used to synthesize a novel nanocomposite known as magnetic graphene oxide on activated carbon (MGO/AC). This nanocomposite was designed for the efficient extraction of As(V) from aqueous solutions. The MGO/AC material achieved an equilibrium adsorption capacity of 14.25 mg g⁻¹ at ambient temperature, with As(V) reaching a maximum adsorption effectiveness of almost 98% after 60 minutes. The specific surface area of the material was 708.25 m² g⁻¹.¹⁷⁷

According to Yan et al., they developed and utilized a novel sulfonated group and triethylenetetramine modified GO/chitosan (T-SGO-CS) adsorbent for the removal of heavy metal ions from single-metal, binary-metal, and ternary-metal solutions. The adsorption capacities for Pb²⁺, Cd²⁺, and Ni²⁺ were 312.28 mg g⁻¹, 260.52 mg g⁻¹, and 84.61 mg g⁻¹, respectively. Additionally, T-SGO-CS demonstrated a high adsorption capacity and was recyclable for Pb²⁺, Cd²⁺, and Ni²⁺.¹⁷⁸ The GO–ZrATMP composite was synthesized by Lanakapati et al. through the integration of GO, zirconium, and amino trimethylene phosphonic acid (ATMP). This combination resulted in the efficient adsorption of Pb²⁺, Cd²⁺, and Hg²⁺ from aqueous solutions. Specifically, the adsorption capacities for these heavy metals were found to be 373, 320, and 281 mg g⁻¹, respectively. The current study unequivocally demonstrates the exceptional effectiveness of the GO–ZrATMP composite in removing heavy metals from both wastewater and groundwater.¹⁷⁹

Al-Wahaibi et al. introduced a novel technique for immobilizing EDTA onto graphene oxide (GO) using ethylene diamine as a crosslinker to eliminate heavy metals. The successful covalent immobilization of EDTA was confirmed by FTIR and TGA analysis. The sorption capacity of Pb(II), Cu(II), and Zn(II) from aqueous solutions onto GO–EDTA (Na-form) at 25 °C and 35 °C was investigated, with capacity values of 72.4, 46.5, and 28.0 mg g⁻¹, respectively, and 86.2, 56.8, and 31.95 mg g⁻¹ at the same temperatures for the respective metals.¹⁸⁰ Farrukh et al., utilized ZnO nanoparticles that were grafted onto graphene oxide (GO) after its surface was altered using biopolymer chitosan (CS). The study investigated GO/ZnO/CS as an adsorbent to eliminate Pb(II) and Cr(VI) ions from aqueous solutions. The optimal conditions for Pb(II) ions were pH 5, 60 mg L⁻¹, and 120 minutes of contact time, with an adsorption capacity of 110.88 mg g⁻¹ and a removal efficiency of 92.4%. For Cr(VI) ions, the optimal conditions were pH 2, 60 mg L⁻¹, and 112 minutes of contact time, with an adsorption capacity of 84.5 mg g⁻¹ and a removal efficiency of 70.5%.¹⁸¹

4.2. Organics removal

Various industries such as textile, paper, pesticides, food, printing, dyeing, pharmaceuticals and cosmetics use organics extensively to develop their products. The processed water heavily consists of organics, i.e., dyes or antibiotics, which are released into the water bodies after partial or without treatment. The dyes are highly soluble organic compounds in water and are difficult to remove before discharging them into the water streams.¹⁸² Dyes can give a colour because of the chromophore presence in their molecular structures.^183–185 On the other hand, antibiotics in groundwater change the microbial population and biotransformation processes, which are carried out through microbes-facilitated nitrogen.^186,187 The dyes are removed from wastewater using various techniques such as coagulation, distillation, absorption, chemical oxidation and membrane. However, a combination of chemical and biological processes and anaerobic–aerobic biological methods are also being used.^188,189

Recently, graphene oxide and its derived materials have gained much attention in removing the organics from industrial wastewater due to its unique properties, as shown in Tables 2 and 3. The graphene oxide can be either modified with other agents or can act as a modifying agent to increase their removal capacity for the organics. Vo et al. reported the synthesis of a biopolymer sponge from the crosslinked gelatin–chitosan–poly(vinyl alcohol) mixture by dipping it into the graphene oxide solution. The results indicated that adsorption for the Congo red and Rhodamine B was increased due to the graphene oxide.¹⁹⁰ In a investigation, researchers utilized a graphene oxide/cellulose nanowhisker nanocomposite hydrogel to efficiently eliminate cationic dyes, including methylene blue and Rhodamine B, from wastewater. The hydrogel demonstrated a remarkable absorption capacity.¹⁹¹ The preparation of nanocomposites was achieved through a simple method, which involved the covalent functionalization of cellulose nanowhiskers with graphene oxide. The outcomes indicated that these materials exhibited exceptional performance in the removal of dyes, achieving 100% removal of MB and 90% removal of RhB at equilibrium. The high adsorption capacity and rapid recovery of these nanocomposites make them ideal candidates for the treatment of wastewater.

Table 2 Graphene oxide derived materials for removal of organics

GO or GO derived materials	Pollutants	Conditions	Adsorption capacity	Ref.
Agar-graphene oxide (A-GO) hydrogel	Chloroquine diphosphate, and the cationic dye safranin-O	20 mg L	63 mg g^−1 and 100 mg g^−1 for chloroquine and safranin-O	192
		24 °C with initial pH of around 7
GO nanofiltration membrane	BF	298.15 K	98.88%	193
	Methylene blue	Initial concentration is 10 mg L^−1. 2 h	98.97%
	Methyl orange		100%
	Ethylene blue		99.99%
Carboxymethyl cellulose and genipin crosslinked carboxyalkyl–chitosan combined with sulfonated GO	Sulphamethoxazole, sulphapyridine	Initial concentration 5–40 mg L^−1	Sulphamethoxazole (312.28), sulphapyridine (161.89)	194
		pH = (6 and 8)
		30 min
PEN/GO–PDA nanofibrous composite membrane	Direct blue 14	25 °C, pH 3	High rejection (99.8%) with the concentration of 100 mg L^−1	195
Polyethersulfone nanofiltration membrane modified by magnetic graphene oxide/metformin hybrid	Direct red 16 as an azo dye	pH 6.0 ± 0.1	30 mg L^−1 overall concentration rejection about 99%	103
		Initial concentration 30 mg L^−1
		60 min
Polylactic acid@graphene oxide/chitosan sponge	Crystal violet	pH of 8 and 35 °C	50 mg L^−1 total conc. of solution	196
			Excellent removal efficiency 97.8 ± 0.5%
	1-Naphthylamine		28.4 (243.1)
	Orange G	—	20.8
Graphene oxide–cellulose nanowhiskers nanocomposite hydrogel	Methylene blue	—	100%	191
			122.5 mg L^−1
			Contact time 20 min, 25 °C and pH of 7
	Rhodamine	—	62 mg L^−1
			90%
			Contact time 40 min, 25 °C and pH of 7
Magnetic iron oxide (IO) incorporated chitosan–graphene oxide (CSGO) hydrogel nanocomposites	MB removal	10 mL of MB solution (0.005–0.05 mM), pH 3–11, 298 K	74.93 mg g^−1	197
3D barium alginate–bentonite–graphene oxide derived hydrogel	Methylene blue	20 mL solution	710.3 mg g^−1	198
PVA/PCMC/GO/bentonite	MB removal	—	172.41 mg g^−1	199
Ammonia-functionalized graphene oxide (NH3GO) sheets	Basic blue 41 (BB41), anionic dye methyl orange (MO), and ionic 4-nitrophenol (4-NP)	10 mg of NH3GO was selected for BB41, whereas 30 mg was selected for MO and 4-NP	199.5, 64.0, and 54.1 mg g^−1	200

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Table 3 Reduced graphene oxide derived materials for removal of organics

rGO or rGO derived materials	Pollutants	Conditions	Adsorption capacity	Ref.
rGO–Eu composite aerogel	Aqueous solution containing different dyes	2 mL	Eriochrome black T and malachite green 1572.5 and 1367.6 mg g^−1	201
RGO	Methylene blue	10–20 mg L^−1, 283 K	158 mg g^−1	202
RGO	Orange G	—	5.98
Fe3O4–RGO	Rhodamine B	10 mg predissolved in 0.2 mL DI water, pH values (3.45, 7.55, and 11.45)	∼50 mg g^−1	203
	Rhodamine 6G		∼30
	Acid blue 92		∼90
	Orange (II)		∼90
	Malachite green		∼50
	New coccine		∼45
Fe3O4–RGO	Methylene blue	—	167.2 mg g^−1	204
	Neutral red	—	171.3
	Trypan blue	—	50.0
Magnetic Fe2O4–RGO	Rhodamine B	—	22.5 mg g^−1	205
	Methylene blue	—	34.7
Poly(acrylamide)–RGO	Methylene blue	—	1530	206
Reduced graphene oxide@cellulose nanocrystals aerogel (rGCA)/ethylene-propylene-diene monomer (EPDM) composites (rGCA/EPDM)	Organic solvents (N-hexane, xylene, ethanol, paraffin oil, dichloromethane)	—	92%	207
			15–24 g g^−1
IO–RGO	TBBPA	—	∼35 mg g^−1	208

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An efficient and durable graphene oxide nanofibrous membrane was reported for dye removal by Zhan et al.¹⁹⁵ The membrane consisted of electrospun poly(arylene ether nitrile) (PEN) nanofibrous as a substrate, and bioinspired polydopamine (PDA) coated graphene oxide. The material was prepared using an electrospinning technique and hot-pressing treatment. The membrane showed permeate flux of 99.7 L m⁻² h⁻¹ (0.1 MPa, pH = 3.0) and a high rejection (99.8%) for the blue 14 dye (100 mg L⁻¹, 25 °C). Besides, the nanofibrous membrane had good reusability and antifouling properties. The adsorption of the anionic dye removal was explained with electrostatic repulsion.

The graphene oxide-based membranes show excellent removal capabilities, ion selectivity and antifouling properties. These membranes have ideal prospects for wastewater treatment. Although, there is a need to improve the synthetic methods for developing graphene oxide membranes and align them with the present industry setup.

Singh et al., reported in situ formation of chitosan–graphene oxide hydrogel by incorporating iron oxide and used it to remove methylene blue.¹⁹⁷ The results exhibited that iron oxide was successfully grafted on the chitosan–graphene oxide composite. The structural analysis confirmed an amide bond formation between the hydroxyl of GO and the amino group of the chitosan. Additionally, the number of hydroxyl groups was increased due to the formation of nucleophilic attack of chitosan amino groups on the graphene oxide's epoxy. These structural changes in the hydrogel provided more adsorption sites for the organics and showed good recyclability and rapid adsorption of methylene blue even after four successive cycles.

In another study, MnO₂ nanorods were used on the graphene oxide grafted chitosan surface. The resulting material was tested for methylene blue (MB) and amido black 10B (AB) adsorption. The study indicated that MB showed better removal than AB within 24 min and 97% removal, which is much better than the material without MnO₂ nanorods. This increase in adsorption was ascribed due to the enhanced number of oxygen-containing functionalities and great electrostatic interactions between the MnO₂ nanorods and graphene oxide grafted chitosan. Most importantly, the material stability was increased tremendously and maintained after 10 successive adsorption experiments.²⁰⁹ Tran et al. also reported the chitosan-derived composites using different content of graphene oxide to improve their adsorption performance. They optimized the contents of graphene oxide on a lower percentage to make it practical and promising for the adsorption of dyes. The study concluded that composites were tested for methylene blue, and electrostatic interactions and pore space occupation present in the composites dominated the adsorption process. Furthermore, after the 4th adsorption–regeneration cycle, removal of MB can be achieved by more than 75%.²¹⁰

Graphene oxide itself can be modified with different agents to increase its adsorption capacity to remove the dyes. Abd-Elhamid and co-workers used low-cost tri-sodium citrate to functionalize graphene oxide in the presence of tetraethylorthosilicate. Trisodium citrate functionalized was further tested for the adsorption of cationic organic dyes, i.e., methylene blue and crystal violet (CV). The synthesized adsorbent had better adsorption capacity for CV than MB.²¹¹ Reduced graphene oxide sponges were prepared using vitamin C and cellulose nanocrystals for the adsorption of methylene blue. The adsorption performance was assessed over a pH range and recognized the sponge field changes in the surface and pore chemistry.²¹² Magnetic chitosan–graphene oxide composites were prepared with copper ferrite (MCSGO) nanoparticles. The composite was used to assess the removal of safranin O (SAF), and indigo carmine (IC) dyes from the wastewater. The study indicated that the nanocomposite showed excellent stability and recycling and has excellent adsorption performance for both dyes, and no major loss in the removal efficiency was observed after 5 cycles of the adsorption–desorption process.²¹³ Calcium oxide nanoparticles were prepared from fishbone and eggshell and, incorporated into graphene oxide using durian shell-activated carbon as a cross-linker. These graphene oxide-derived nanocomposites were assessed for methylene blue adsorption from the aqueous environment. The removal of MB dye was carried out by hydrogen bonding, electrostatic and π–π interactions. Notably, adsorption performance remained stable even after the 10 successive cycles.²¹⁴ In another study conducted by Almarri et al., prepared graphene oxide-derived composites with cupric oxide and lanthanum oxide to remove the MB. The findings revealed that composites showed more than 80% removal of methylene blue.²¹⁵ de Farias and coworkers prepared the polystyrene films, which were coated with GO and used to remove methylene blue. The PS/GO-derived composite films had nearly 2.3 times greater removal capacity than pure polystyrene membranes.²¹⁶

The study reported by Yilmaz et al., used graphene oxide-derived composites for the selective adsorption of methylene blue from the mixture of methyl orange and methylene blue. Graphene oxide was modified with hexadecyltrimethylammonium bromide and tetraethylorthosilicate to obtain graphene oxide/hollow mesoporous silica composites. The prepared composite showed maximum adsorption at a pH of 9 for methylene blue removal. This study also corroborated the previous studies where electrostatic attraction and π–π stacking interaction were considered the main adsorption forces for methylene blue adsorption.²¹⁷

Joshi et al., prepared the graphene oxide composites aerogel by gelatinizing GO with the cellulose derived from the fruit waste. The results indicated that the composite exhibited better adsorption for methylene blue and Rhodamine 6G (cation dyes) than the methyl orange and rose Bengal (anionic dyes) due to the electrostatic interactions, which were confirmed by the negative zeta potential.²¹⁸ De Figueiredo Neves and coworkers reported a novel graphene oxide derivative containing quaternary ammonium salt. The composite was used for the adsorption of basic brown 4 (BB4) dye removal and showed removal up to 95%. Graphene oxide-derived composite also showed dye uptake upto 64% after three successive cycles. The authors claimed that the composite's basic brown 4 dye removal capacity exceeds carbon nanotubes and active carbons. Furthermore, results suggested the involvement of hydrophobic and π–π electron interactions in removing the dye.²¹⁹ In another study, extra carboxylic groups were produced on the surface of graphene oxide and incorporated into the carboxymethyl cellulose (CMC) microbeads. The results demonstrated that the fabrication of the adsorbent showed better reusability for nine continuous cycles with high adsorption for the MB dye removal.²²⁰

In another study, graphene oxide–chitosan composite hydrogel was prepared and used to remove methylene blue, rhodamine B (RhB), methylene orange and Congo red (CR). The results revealed that the MB and RhB had better adsorption performance than the MO and CR. Furthermore, composite removal capacity remained unchanged for four continuous adsorption-washing cycles.²²¹ A multifunctional graphene oxide composite material was reported in removing methylene blue (MB), methylene green (MG5) (cationic) and acid red 1 (AR1) (anionic) dye. The graphene oxide composite was synthesized using a titanate nanotube and layered double hydroxides. The study demonstrated that cationic dye adsorption was increased with the increase in pH, while anionic dye adsorption was increased with the decrease in pH. In addition, ion exchange was ascribed to the main adsorption mechanism for dye removal with a minor contribution from hydrogen bonding and van der Waals forces.²²²

Graphene oxide-based materials have also demonstrated great potential in the adsorption of organic acids and aromatics as evidenced by various studies. Yasmin and her colleagues prepared a graphene oxide-based nickel–iron superparamagnetic nano adsorbent (GO/Ni–Fe) using electronic waste to effectively eliminate doxycycline (DXC) in water. The study determined that the maximum adsorption capacity was achieved with 90% removal in just 20 minutes, using a low adsorbent dose of 0.1 g L⁻¹ at pH 5, and a maximum adsorption capacity of 13.02 mg g⁻¹ at 25 °C.²²³

Masoudinia et al. fabricated a magnetic chitosan/zinc oxide nanocomposite (CS/ZnO–Fe₃O₄) for the effective adsorptive removal of hazardous aromatic micropollutants from wastewater samples, including the antibiotic cephalexin (CFX) and the dye eosin B (EB). The maximum adsorption capacity (Q_max) for CFX and EB was 81.38 and 144.4 mg g⁻¹, respectively, according to their corresponding Langmuir isotherm models.²²⁴ This adsorption behavior is ascribed to the oxygen-functional groups through mechanisms i.e., Yoshida H-bonding, electrostatic interactions, n–π stacking interactions, and dipole–dipole H-bonding as shown in Fig. 8. The study also revealed that the adsorption was monolayer which occurred more likely by chemisorption.

Fig. 8 Possible adsorption mechanisms of eosin B (EB) and cefalexin (CFX). Reproduced from ref. 224 with permission from Elsevier copyright 2024.

Diclofenac is an aromatic amine compound that was studied using graphene oxide materials. For this purpose, Jo et al., reported a nanocomposite of magnetite and reduced graphene oxide (Fe₃O₄/RGO) which was synthesized through a microwave-assisted solvothermal method. This process involved a coupled adsorption–catalysis mechanism and was applied in the treatment of wastewater. The maximum adsorption capacity for DCF, as determined by the Langmuir model, was 80.33 mg g⁻¹. It was observed that the DCF removal efficiency was higher under acidic conditions.²²⁵ Guo et al., developed a three-dimensional Mg–Al layered double hydroxide decorated reduced graphene oxide nanocomposite (3D (Mg–Al) LDH/rGO) to study the adsorption of ciprofloxacin (CIP). The nanocomposite's rich mesoporous structure and elevated specific surface area showed high adsorption of CIP. The maximal adsorption capacities of CIP, as predicted by the Langmuir model, was 775.2 mg g⁻¹ at 288 K.²²⁶

Ma and coworkers reported a composite material that combined transition metal iron and graphene, immobilized onto a nickel foam substrate. This composite material was designed to accelerate electron transfer and catalyze the production of hydroxyl radicals (·OH) production. The material was used to degrade sulfadiazine, 2,2′,4,4′-tetrehydroxybenzophenone, and rhodamine B. The rGO/Fe–nickel foam (NF) cathode system demonstrated excellent removal effects, removing these compounds almost completely in 120 minutes. Furthermore, this system showed remarkable efficiency in removing three aromatic organic contaminants at a 100% rate in only two hours.²²⁷

Mohamed and colleagues synthesized an electrochemically exfoliated graphene oxide-based photocatalyst using triple-chain (sodium 1,4-bis(neopentyloxy)-3-(neopentylcarbonyl)-1,4-dioxobutane-2-sulfonate; TC14) and single-chain (sodium dodecyl sulphate; SDS) anionic surfactants and used to remove methylene blue (MB) dye. Among all the surfactants used, TC14 achieved the highest MB removal rate of 98.53%, which was significantly higher than the SDS system (50.94%) and ZnO alone (42.33%).²²⁸

Wang et al. have successfully deposited nanoflakes onto a 3D-reduced graphene oxide (3D-rGO) supporting γ-AlOOH. This material was created using a hydrothermal method and boasts a high specific surface area, 3D macrostructure, and an abundance of mesopores. These characteristics enable it to efficiently remove ciprofloxacin (CIP) and methylene blue (MB). The Langmuir model was found to accurately represent MB and CIP adsorption, as determined by isotherm fitting results. Additionally, γ-AlOOH/3D-rGO demonstrated exceptional adsorption capacity for both MB and CIP, with maximum values of 930.08 mg g⁻¹ at 288 K and 353.91 mg g⁻¹ at 318 K, respectively.²²⁹

To efficiently eliminate phenolic compounds from water and wastewater, a polyacrylonitrile (PAN) nanofiber was impregnated with graphene oxide (GO) using electrospinning. The optimal pH for phenol removal with all nanofiber mats was determined to be 7, and the maximum removal rates for pure PAN, PAN/2.5 GO, and PAN/5 GO at a dose of 2 mg were found to be 61.39, 77.21 and 92.76%, respectively. PAN, PAN/2.5 GO and PAN/5 GO were found to have maximal monolayer adsorption capacities of 57.4, 66.1, and 69.7 mg g⁻¹, respectively.²³⁰

4.3. Graphene oxide for membranes modification

Graphene oxide has gained significant interest as a promising material for enhancing the efficiency of membranes. Specifically, it possesses the potential to increase water permeability while simultaneously providing effective purification. In a study led by Sibt-e-Hassan et al., a method was introduced for effectively removing lead from freshwater using zwitterionic graphene oxide-coated membranes that meet the WHO effluent standards. These membranes demonstrated resistance to bacterial adhesion and fouling, maintaining performance under various conditions. The results highlighted the significance of employing novel environmental technologies to mitigate the detrimental effects of heavy metal contamination on ecosystems and human health.¹²² A recent study has reported a critical innovation in the development of electrically conductive ceramic membranes for water treatment, which addresses the issue of membrane fouling and enhances the effectiveness of contaminant removal.²³¹ The study showcases improved membrane properties, such as increased flux, porosity, hydrophilicity, zeta potential, and roughness, by incorporating highly conductive polypyrrole (PPy) covered with graphene oxide (GO) or reduced graphene oxide (rGO). The reduced electrical resistivity resulting from GO/rGO's facilitates the synthesis of a full conductive network between PPy and the ceramic membrane, leading to improved filtering performance. Notably, the membranes' specific flow under an electric field is higher than that of traditional ceramic membranes, indicating significant promise for water remediation applications.

Conventional wastewater treatment methods struggle to eliminate antibiotics, which have detrimental effects on ecosystems and public health. To address this issue, the research focuses on the development and evaluation of a novel two-dimensional (2D) lamellar graphene oxide (GO)/Ti₃C₂Tx membrane for the removal of antibiotics. Compared to pristine membranes, the 50% GO/Ti₃C₂Tx version demonstrates notable improvements in water flux and tetracycline rejection. Furthermore, the composite membrane exhibits improved antifouling characteristics, suggesting more effective and long-lasting wastewater treatment options.²³²

The cleaning up of dye/salt wastewater, which has become increasingly important in recent times, by creating highly efficient nanofiltration membranes. A recent study employs a synergistic polyelectrolytes-Zr-MOF hydrated construction (UiO@S-GO) to intercalate GO nanosheets, resulting in the development of a new graphene oxide-based nanofiltration membrane (GO/UiO@S-GO-8). By integrating cationic amino groups (–NH₂) with hydrophilic, high-density anionic sulfonic groups (SO₃⁻), the innovative approach yields a membrane with remarkable structural stability, anti-pollution capabilities, and separation abilities.²³³

A DA/PEI and GO cross-linked network was employed to improve the performance of the graphene oxide-based membrane. The modified membrane exhibited an impressive water flux of 326.7 L m⁻² h⁻¹ and high rejection rates for Cu²⁺, Pb²⁺, and Zn²⁺ ions. The study suggested that the cross-linking reaction between the oxygen-containing functional groups on the GO flakes and the DA/PEI was the primary mechanism responsible for the high flux. The GO@DA/PEI membrane demonstrated exceptional long-term stability and anti-fouling capabilities even under humic acid presence.²³⁴

5. Challenges and future outlooks

The graphene oxide fabrication process is very complex and time-consuming. Most importantly, maintaining the derived products' quality is challenging. It is easy to be assured of quality on a laboratory scale; however, the chances of contamination in the resulting materials are very high in mass production. The cost of the fabrication process is very high, which ultimately affects its utilization for water remediation at an industrial scale.

Although great progress has been made in developing graphene oxide materials for water remediation, many factors limit the use of GO at a larger scale, such as mass graphene oxide production on a larger scale with greater quantity and cost-effective methods. Another market obstacle is the availability of other cheap substitutes, which impedes its utilization for various applications, including water treatment. The third major factor considered is the safe storage and transportation of the material, which is still in question whether it should be stored and transported in dry or wet form, ultimately causing the distribution problem, and increasing the cost. This issue can be overcome by storing GO in suspended form but in a dilute dispersive form, again efficiency and cost of transporting the water-containing product is a big challenge.^235,236 Besides, technical downsides may negatively impact the commercialization potential of graphene oxide-based materials for water remediation.

The other main problem with graphene oxide and reduced utilization is the process parameters, such as the nature and concentration of the oxidizing agent, the graphite's size and shape and the reaction time. These factors affect the properties of the resulting graphene oxide and reduced graphene oxide, ultimately determining their fate for a particular application. Though, the toxicity of GO on the human skin depends on its size, shape and other physicochemical properties. Numerous studies have reported that exposure to graphene oxide and its derivatives in high concentrations for a longer period causes membrane damage, indicating low toxicity to skin cells.

The toxicity of graphene oxide is still in its infancy, and many questions need to be addressed. A study reported by Gies and Zou (2018) used three different commercially available graphene oxide to assess its toxicity with six different cell lines. The study concluded that the toxicity of graphene oxide affected different cell lines differently as adherent cells exhibited lesser responses than the suspended cells.²³⁷ It is essential for both academia and industry to address the following questions, as this will expand the potential applications of graphene oxide and its derivatives in water remediation.

• A thorough understanding of the process for oxidizing graphene to attain a specific level of oxidation is essential.

• Undertake comprehensive assessment of water purification process employing graphene oxide and its derivatives.

• The enhancement of techniques for reducing graphene oxide to attain a material with a controlled oxidation level.

• In-depth investigation of the antibacterial behavior of graphene oxide and its derived materials under various conditions, such as its size and shape, as well as other experimental factors.

• A comprehensive grasp of the antimicrobial properties demonstrated by graphene oxides and their derivatives.

• Refinement of the reaction conditions to obtain consistent oxidation levels in graphene oxide and graphene oxide.

• Development of cost-effective and eco-friendly methods to expand graphene oxide applications.

• Thorough assessment of graphene oxide's toxicity, degradation and biodegradation processes of graphene oxide and its derivatives.

The use of graphene oxide and its derivatives with biopolymers and synthetic polymers in water remediation applications has shown great potential and has made significant progress. Nevertheless, research in this area is still in its early stages and requires a more comprehensive perspective to become market-oriented and competitive with other commercial water treatment techniques. The challenge of recycling or recovering adsorbed pollutants from graphene oxide-based materials is of utmost importance, as it would be beneficial for both the environment and industries. This could potentially revolutionize the way we prevent secondary pollutants and bring about economic advantages in production. However, the mechanism behind graphene oxide-based materials and pollutants is still not fully understood. Further analysis and exploration of the application of these materials in real water and wastewater systems is needed, as most previous research has been conducted on a lab scale. Comprehensive thermodynamic, kinetic, and equilibrium studies must be carried out to confirm the feasibility of using graphene-based materials at an industrial scale.

6. Summary

The development of graphene oxide-based materials for water and wastewater treatment has made significant progress since the beginning of the 21st century. Graphene oxide is a unique material with exceptional properties that make it suitable for a wide range of applications for contaminant removal, from thin atomic membranes to composite materials with other natural polymers that have exceptionally high surface areas. To further advance this field, future research should focus on finding new and cost-effective methods for large-scale production of graphene-based materials, as well as a deeper understanding of the properties of graphene oxide and its derivatives, the mechanisms of contaminant removal, and the potential toxicity of these materials for water treatment. If these synthetic, technological, and commercialization challenges are addressed in the years to come, graphene oxide-based materials have the potential to revolutionize water remediation. Therefore, it is crucial that ongoing research efforts are dedicated to expanding and improving graphene oxide-based materials for water detoxification.

Data availability

This review article is based on previously reported studies. Therefore, there are no new data to disclose. All referenced studies have been appropriately cited, respecting the intellectual property of the original authors.

Author contributions

The conception, drafting, and preparation of the original manuscript were undertaken by M. Z. The reviewing, editing, and supervision of the manuscript were performed by RMS and A. U. All authors have carefully read and agreed to the final version of the manuscript that was published.

Conflicts of interest

The authors hereby attest that they possess no financial or personal interests that could be perceived as competing or have influenced the work presented in this review article.

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