Oxidation Degree Of Graphene Oxide Research Articles

Regulation of oxidation degree for graphene oxide on hydration process and engineering properties of natural hydraulic lime pastes for grout strengthening of stone cultural relics

The stone cultural relics represented by grottoes carry precious historical and cultural information and are important representations of the mutual learning of civilizations. Fissures are the main threat to stone cultural relics. The development of grout strengthening materials for fissure repair is of great significance to restrain or delay other threats, such as instability, water seepage, and surface weathering. In this work, based on the improved Hummers’ method, graphene oxide (GO) with different oxidation degrees was prepared by adjusting the amount of added KMnO4, which was then added to natural hydraulic lime (NHL2) pastes to explore the effect of the GO oxidation degree on the hydration process and engineering properties of NHL2 pastes. The results indicated that the addition of GO significantly promoted the hydration rate of the NHL2 pastes and resulted in the formation of more regular and ordered flower-like hydration products and aggregates. Compared with the reference sample, the engineering properties of the modified NHL2 pastes, including the mechanical properties and the autogenous shrinkage behavior, were significantly improved. The simulated grouting experiment also indicated that NHL2 pastes had good groutability and interface combination statuses. In the hydration process of NHL2, GO provided nucleation sites. The hydration reactions were preferentially carried out on the GO sheets, and regular aggregates formed to fill the cracks and holes in the NHL2 pastes, which improved the mechanical properties of the strengthened material. This work provides an effective strategy for the grout strengthening of stone cultural relics fissures.

Raman study of directly synthetized graphene oxide films on Si, SiO2/Si and GaAs by remote-catalyzed CVD

Graphene oxide (GO) is an organic material with interesting properties for nanotechnology. Therefore, it is important to understand the processes that lead to its mass production for deposition onto large-size wafers and with high quality; as well as the control of the number of monolayers and the degree of oxidation. In this work, we propose an alternative method for measuring the oxidation degree of GO. We use simulated Raman spectra from different molecular models that, under computational calculations based on density functional theory (DFT), allow us to explain the measured Raman spectra and the approximate molecular structure of the material. In addition, we report on a methodology based on a process of remotely catalyzed chemical vapor deposition (CVD) to synthesize GO in millimeter areas directly onto three different substrates: SiO2/Si, Si, and GaAs. The results can be used to optimize the synthesis processes of GO and improving the performance of this organic material.

Hydrogen bond networks and wrinkles in graphene oxide/nitrile butadiene rubber composites for enhancement of damping capability: Molecular simulation and experimental study

By combining molecular dynamics (MD) simulation and experiments, this work describes a systematic, quantitative study on the nanoscale damping of nitrile butadiene rubber (NBR) by adding graphene oxide (GO) with different oxidation degrees. Using MD simulation, the proposed two-component solubility parameters predict that GO2 (O wt %, 17.05%) and NBR have excellent thermodynamic compatibility. GO2/NBR system shows the largest molar concentration of intermolecular hydrogen bonds and the lowest free volume fraction and mean square displacement. GO2 presents a strong adsorption effect on NBR polymer chains. Meanwhile, the green preparation method of reduced graphene oxide has been developed for improving damping properties of reduced graphene oxide/nitrile butadiene rubber (RGO/NBR) composites. The prepared RGO/NBR composites with tailor-made oxidation degrees are adopted to validate the theoretical prediction by MD simulation. Fourier transform infrared spectroscopy verifies that hydrogen bond networks exist between GO and NBR polymer chains. Two main factors, the number of intermolecular hydrogen bonds and the degree of wrinkles of GO sheets dominate the damping performance of the composites. The results indicate that when the GO oxidation degree is about 17.05%, the damping capability of GO/NBR composites is maximum improved. These results pave the way for the environmentally modifying interface to design high performance GO/rubber composites.

Ultrasmall graphene oxide for combination of enhanced chemotherapy and photothermal therapy of breast cancer

Combination of chemotherapy and photothermal therapy (PTT) is an effective way for the treatment of cancer. Graphene oxide (GO) with a large specific surface area and strong near-infrared (NIR) absorbance have been widely used as both the chemotherapeutic carriers and photothermal agents. The smaller lateral size and higher oxidation degree of GO corresponding to better dispersion in water and lower cytotoxicity. Therefore, the preparation of ultrafine GO nanosheets (UGO) with the controlled size and high oxidation degree is of significant importance to meet the demands of biological applications. Herein, we developed a versatile drug delivery nanoplatform based on poly(dopamine) (PDA) modified ultrasmall graphene oxide (UGO) with small size (average size of 30 nm) and high oxidation content (45 wt. %). The fabricated PDA-modified UGO (UGP) exhibits well biocompatibility, excellent photothermal performance and high drug loading capacity of doxorubicin (DOX). Under NIR laser irradiation, the photothermal-induced release of DOX could achieve the combination of chemotherapy and PTT for efficient therapy of breast cancer. This work established UGO as a novel drug delivery with excellent photothermal performance for the combination of chemotherapy and PTT of tumors.

Simultaneously tuning interfacial and interlaminar properties of glass fiber fabric/epoxy laminated composites via modifying fibers with graphene oxide

A series of graphene oxide (GO) with various oxidation degrees were synthesized in this work and then grafted onto the surface of glass fiber fabric (GFf), and subsequently a resin infusion process was engaged in the fabrication of GFf/epoxy laminated composites. Interlaminar and interfacial properties as well as interlaminar microstructure of laminated composites were investigated in detail. Results showed that various oxygen-containing functional groups on the GO surface due to oxidation degrees endowed GO with different dispersion states in composites and strengthening/toughening efficiency, thus greatly influenced composites’ interlaminar and interfacial adhesion. Also, the desorption and diffusion of GO from the fiber surface into matrix-enriched interlaminar region during the resin infusion process were evidenced. Making use of a moderate weight ratio of oxidation agent (KMnO4)/graphite (2:1), the optimal oxidation degree of GO was achieved for reinforcing fiber/matrix interface and matrix-enriched interlaminar regions. Under this case, the interlaminar shear strength and work of fracture of resultant composites were raised by 28.2% and 138.3%, respectively; storage moduli in glass regions and at the beginning of rubbery regions were enhanced by 22.3% and 104.5%, respectively; the significantly fiber/matrix interfacial adhesion and glass-transition temperature were obtained, compared with those of the control sample. This work provides a guiding strategy for optimizing strength and toughness of fiber-reinforced composites by regulating GO oxidation degrees.

A non-heat-source process for preparing graphene oxide with low energy consumption.

As the most widely used method for preparing graphene oxide (GO), Hummers' method always involves a key step, that is adding water to concentrated sulfuric acid. We found that if this process is cancelled, the oxidation degree of GO will be significantly reduced. This means that the heat released during concentrated sulfuric acid dilution will promote further oxidation of GO. In this paper, we fully utilize the heat released during concentrated sulfuric acid dilution to develop a new non-heat-source process without any low-/high-temperature auxiliar, exponentially reducing the energy consumption and largely avoiding the frequent temperature control. The result shows that GO prepared by Hummers' method and that prepared by the proposed process show a similar structure, composition, morphology, and defect degree. Meanwhile, the corresponding reduced GO (rGO) obtained after reduction shows similar capacitive behavior. Their specific capacitances are 243.6 F g-1 and 240.3 F g-1 at 1 A g-1, respectively, and they both have a long-term cycling performance (with a 100% capacitance retention after 10 000 cycles at 30 A g-1). This study provides a new strategy for the preparation of GO with low energy consumption.

Tailoring the graphene oxide chemical structure and morphology as a key to polypropylene nanocomposite performance

AbstractIn this work, we designed and studied two synthetic routes, based on modified Hummers method, to obtain graphene oxide (GO), and investigated their influence on the performance of polypropylene (PP)/GO nanocomposites. The two synthetic routes differed in the application condition of the oxidizing agent, potassium permanganate (KMnO4), which was added either as a powder (GO‐P) or as a water solution (GO‐S). This apparently subtle synthetic change yielded GOs with different degrees of oxidation and particle sizes, where GO‐P presented a higher oxidation degree and smaller particles. The different GOs were then melt‐blended with PP and the correlation between their different chemical/morphological structures and the nanocomposites' thermomechanical/rheological properties were evaluated. The milder oxidation process suffered by GO‐S, and consequent less hydrophilic character, yielded a PP/GO‐S nanocomposite with improved performance as the consequence of a better matrix/filler chemical affinity, mainly in compositions with lower GO‐S contents. The thermal stability was increased by more than 10°C when 0.1 wt% GO‐S was inserted into PP. When compared to the composition with 0.1 wt% GO‐P, the increase was 13°C. Reinforcing effects were also observed in that sample (with 0.1 wt% GO‐S), which exhibited the highest storage modulus and complex viscosity. These results suggest that tailoring the GO's oxidation degree and morphology is a key point to obtain an ideal interfacial interaction between phases.

A novel approach to prepare highly oxidized graphene oxide: structural and electrochemical investigations

This research presents two new modified Hummers' methods which include the pre-oxidation of graphite powder by mixtures of H3BO3/H2SO4 and H3BO3/H2SO4/CrO3. Compared to the traditional Hummers’ method, these significant improvements substantially enhanced the number of oxygen functionalities onto graphene oxide (GO) layers. The GO samples were characterized by X-ray photoelectron spectroscopy (XPS), Boehm titration, Raman spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), and zeta potential analysis. Boehm titration results showed that GO layers contain oxygen functionalities such as phenolic, ketone, lactone, carboxyl, and epoxy. Quantitative XPS analysis reveals that GO obtained using a pre-oxidation step with H2SO4/H3BO3/CrO3 mixture has a higher oxidation degree (C/O = 1.03). Moreover, this sample possessed a greater number of electronegative functional groups, resulting in the decrease of the zeta potential (-43.3 mV). Raman analysis revealed a slightly higher structural disorder in GO layers during the increase in oxidation levels. Further, reduced GO (rGO) obtained from new synthesized GO were tested as label-free H2O2 sensors electrodes. The electrochemical investigations showed that the samples were prospective on H2O2 sensing. Our results suggest that the properties of rGO can be tuned by varying the oxidation degree of GO, which may stimulate new developments in rGO-based sensors.

The role of oxidation level in mass-transport properties and dehumidification performance of graphene oxide membranes

Here we report on gas and vapor transport properties of ultra-thin graphene oxide (GO) membranes, with various C:O ratios. Graphene oxide nanosheets with an average lateral size of 800 nm and C:O ratio ranging from 2.11 to 1.81 have been obtained using improved Hummers’ method by variation of graphite:KMnO4 ratio. Thin-film selective layers based on the obtained graphene oxide have been spin-coated onto porous substrates. To extend the C:O range to 2.60, thermal reduction of GO membranes was applied. A decrease in C:O ratio leads to significant water vapor permeance growth to over 60 m3(STP)·m−2·bar−1·h−1 while the permeance towards permanent gases reduces slightly. According to the permeation and sorption measurements, a decisive role of H2O diffusivity has been established, while the water sorption capacity of the graphene oxide stays nearly independent of C:O ratio in GO. The result is supported by semi-empirical modeling which reveals diminution of H2O jump activation barriers with both increasing GO interlayer spacing and its oxidation degree. The height of the activation barriers was found to vary up to an order of magnitude within the entire range of relative humidity (0–100% RH), lowering significantly for strongly oxidized GO. Our results evidence the necessity of attaining maximum GO oxidation degree for improving water transport in GO, especially at low partial pressures.

Graphene Oxide Membranes for Tunable Ion Sieving in Acidic Radioactive Waste.

Graphene oxide (GO) membranes with unique nanolayer structure have demonstrated excellent separation capability based on their size‐selective effect, but there are few reports on achieving ion–ion separation, because it is difficult to inhibit the swelling effect of GO nano sheets as well as to precisely control the interlayer spacing d to a specific value between the sizes of different metal ions. Here, selective separation of uranium from acidic radioactive waste containing multication is achieved through a precise dual‐adjustment strategy on d. It is found that GO swelling is greatly restricted in highly acidic solution due to protonation effect. Then the interlayer spacing is further precisely reduced to below the diameter of uranyl ion by increasing the oxidation degree of GO. Sieving uranyl ions from other nuclide ions is successfully realized in pH =3–3 mol L−1 nitric acid solutions.

Tuning the hierarchical pore structure of graphene oxide through dual thermal activation for high-performance supercapacitor

Herein, we introduce a simple method to prepare hierarchical graphene with a tunable pore structure by activating graphene oxide (GO) with a two-step thermal annealing process. First, GO was treated at 600 °C by rapid thermal annealing in air, followed by subsequent thermal annealing in N2. The prepared graphene powder comprised abundant slit nanopores and micropores, showing a large specific surface area of 653.2 m2/g with a microporous surface area of 367.2 m2/g under optimized conditions. The pore structure was easily tunable by controlling the oxidation degree of GO and by the second annealing process. When the graphene powder was used as the supercapacitor electrode, a specific capacitance of 372.1 F/g was achieved at 0.5 A/g in 1 M H2SO4 electrolyte, which is a significantly enhanced value compared to that obtained using activated carbon and commercial reduced GO. The performance of the supercapacitor was highly stable, showing 103.8% retention of specific capacitance after 10,000 cycles at 10 A/g. The influence of pore structure on the supercapacitor performance was systematically investigated by varying the ratio of micro- and external surface areas of graphene.

Cryogenic mechanical properties of graphene oxide/epoxy nanocomposites: Influence of graphene oxide with different oxidation degrees

In this contribution, the impact of graphene oxide (GO) with different oxidation degrees on the cryogenic mechanical properties of GO/epoxy nanocomposites is investigated. GO samples with varied oxidation degrees were prepared using a modified Hummers’ method. It was found that GO exhibited better dispersion in the matrix and improved interfacial interactions with epoxy resin as its oxidation degree increased. Resultantly, GO/epoxy nanocomposites showed increased tensile properties at room temperature (RT) and liquid nitrogen temperature (LNT) as GO oxidation degree increased and reached the idealist performance with appropriate GO oxidation degree. Under low GO loading of 0.10 wt% GO/epoxy nanocomposites exhibited the highest tensile strength of 78.0 MPa at RT and 123.2 MPa at LNT, 31% and 14% higher than that of neat epoxy, respectively. Based on the fractured surface investigation, toughening mechanisms of GO for epoxy nanocomposites at RT and LNT were analyzed, between which there existed significant differences.

Study on the fabrication and tribological behavior of self-assembled functionalized graphene oxide in water

A new lubricating coating with functionalized graphene oxide (fGO) consisting of graphene oxide (GO) with different oxidation degrees, n-octylamine basal plane functionalized GO (bGO), and edge functionalized GO (eGO) was developed with or without 3-aminopropyltrimethoxysilane (APTMS) to reduce friction in macroscale contact with water. The optimal preparation condition of the coating was obtained by the single factor evaluation of a series of factors (20 % APTMS aqueous solution, 12 h immersion time, 0.05 mg/mL GO aqueous solution, and 100 °C curing temperature). The effect of the oxidation degree and functionalization of GO on the friction-reducing and anti-wear behavior of the coating was explored. The coatings with a higher GO oxidation degree exhibited better friction-reduction and anti-wear performance. In addition, the friction-reducing capability of the APTMS-bGO coating was greater than that of APTMS-eGO.

Interaction between Biocompatible Graphene Oxide and Live Shewanella in the Self-Assembled Hydrogel: The Role of Physicochemical Properties.

Understanding the interaction of graphene materials with bacterial cells is crucial for exploiting their environmental applications. Meanwhile, knowledge on the mechanism of graphene oxide (GO) action to bacteria is still incomplete. This study focused on the inter-relationship of biocompatible GO and the well-known dissimilatory metal-reducing bacteria Shewanella, in view of the biographene hydrogel (BGH), a self-assembly of GO and live bacteria. The results showed that, among various inter-related physicochemical properties of GO, the sheet area determined the bacterial survival and the gelation potential with the same Shewanella strain. For the biocompatible GO sheet above 0.30 μm2, the larger the GO, the higher the speed of BGH assembling. Only 22 h was needed to obtain BGH using GO with an average area of 1.83 μm2 (maximum in this study). The GO oxidation degree was found to be another critical factor affecting whether BGH formed or not, with a referential threshold of C/O > 1.75. Finally, surface force of GO was detected and correlated with the bacterial adhesion behavior for the first time, confirming that the large GO in the low oxidation state has high resultant force to attract bacteria. All these findings pave a promising way to develop a GO-bacteria complex like BGH to treat industrial wastewater in the future.

The interphase and thermal conductivity of graphene oxide/butadiene-styrene-vinyl pyridine rubber composites: A combined molecular simulation and experimental study

In this study, how the oxidation degree of graphene oxide (GO) affects the dispersion of GO and the interfacial adhesion in butadiene–styrene–vinyl pyridine rubber (VPR)/GO composites, as well as the interfacial thermal transport were investigated by molecular dynamics simulation. Subsequently, the composites containing different oxidation degrees of GO were prepared by the chemical reduction GO in situ to verify the theoretical predictions and explore the relationship between the microstructures and macroscopic performance. The results showed that with the increase of oxidation degree of GO, the compatibility between GO and VPR improved first and then reduced, while the interface interaction enhanced gradually. The best oxidation degree of GO was acquired at about 15%, for which case the optimal dispersion of GO, the best mechanical properties and highest thermal conductivity of the composites are achieved. Although increasing the oxidation degree of GO can reduce the interfacial thermal resistance, the decreased intrinsic thermal conductivity and re-aggregation of GO with high oxidation degree would limit the increase in thermal conductivity of the composites. This study may provide a valuable guidance for chemical modifying graphene surface to optimize the GO/rubber composite properties.

Graphene oxide-drove transformation of NiS/Ni3S4 microbars towards Ni3S4 polyhedrons for supercapacitor

Ni3S4 is regarded as one of the promising electrode materials for energy storage, but the difficulty in obtaining its pure phase hinders its wide applications. In this work, we introduced a novel method to in-situ synthesize Ni3S4@reduced graphene oxide (rGO) composite, where graphene oxide (GO) was found to induce the oxidation of Ni2+ to Ni3+ and the morphology transformation from microbar to polyhedron during the hydrothermal process. The influence of the content and oxidation degree of GO on the phase composition and morphology of nickel sulfide is investigated. It is found that the oxygen-containing functional group of GO is responsible for the change of valence state, which thus drives the transformation of NiS/Ni3S4 towards Ni3S4. The obtained Ni3S4@rGO composite shows a high energy storage capacity (1830 F g−1 at 2 A g−1), remarkably higher than the unpurified phase NiS/Ni3S4 (830 F g−1). Correspondingly, the assembled asymmetry supercapacitor indicates a high energy density of 37.3 Wh kg−1 at a power density of 398 W kg−1. More importantly, the capacitance retention reaches 91.4 % after 10,000 cycles at a current density of 2 A g−1. Thus, this research overcomes the difficulty of synthesizing the pure Ni3S4 phase, which provides a new available pathway for constructing high-performance electrode materials.

High-quality preparation of graphene oxide via the Hummers' method: Understanding the roles of the intercalator, oxidant, and graphite particle size

The Hummers' method, in which concentrated sulfuric acid (H2SO4) acts as the intercalator and potassium permanganate serves as the oxidant, is a commonly used method to prepare graphene oxide (GO). The amounts of intercalator and oxidant along with the particle size of graphite are important factors that affect the structure and properties of GO. In this study, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, ultraviolet–visible spectroscopy, scanning electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, thermogravimetric analysis, and atomic force microscopy were used to characterize the effects of these factors on the structure and properties of GO. The results show that the amount of intercalator and oxidant clearly affect the types of oxygen-containing functional groups in the GO structure along with the oxidation degree of GO. Increasing the dosages of intercalator and oxidant can improve the oxidation degree of GO, facilitating the preparation of typical GO. Sodium nitrate (NaNO3) has a synergistic effect with H2SO4 during the process of graphite oxidation, which is helpful for the intercalation and oxidation of graphite. Increasing the oxidation degree of graphite can increase the interlayer spacing, which is conducive to the exfoliation of GO. However, the use of excessive NaNO3 is not conducive to improving GO oxidation. The effect of graphite particle size on GO interlayer spacing is greater than that of NaNO3. The obtained results provide a reference for the preparation of GO with controllable structure.

Optimization design on simultaneously strengthening and toughening graphene-based nacre-like materials through noncovalent interaction

Nacre exhibits outstanding mechanical properties due to its hierarchically microstructural features and associated multiscale deformation behaviors, enlightening human to design high-performance graphene-based nacre-like materials (GNMs) in the past decade. However, those GNMs mimicking brick-and-mortar microstructure always cannot give consideration to both strength and toughness because the pullout process of graphene oxide (GO) sheets that amplifies toughness in GNMs is extremely limited compared to natural nacre. Toward this end, a combination of modified shear-lag model and atomic simulations is proposed to investigate the optimal strategy of simultaneously strengthening and toughening for GNMs reinforced by strong noncovalent interfacial interactions. The modified shear-lag model can well couple the interlayer sliding and structural stability to characterize the toughening effect during the pullout process. We demonstrate that the interfacial toughness and shear strength tuned by interlayer noncovalent interactions significantly impact the effective tensile strength of GNMs, while toughness is mainly dominated by the interlayer sliding before strain localization during the pullout process of GO sheets. Melamine molecule is chosen as the representative interlayer crosslink agent owing to the ultrastrong noncovalent interaction between melamine and GO. Our atomic simulations indicate that melamine bound to GO by anomalous hydrogen bonding can greatly improve the interfacial shear stress and maintain the interlayer energy-dissipation efficiency resulting from the breaking and reforming of hydrogen bonds. An optimal range of melamine content and GO oxidation degree is then explored for synchronously superior strength and toughness by balancing the competitions among the reduction of intralayer tensile limit of GO sheets, the improvement of the interlayer shear strength, and the reduction of interfacial toughness. In particular, a scaling law is proposed as the evaluation criterion to correlate the inner inelastic deformation of GNMs and their mechanical properties, revealing why interlayer noncovalent interaction can optimize strength and toughness simultaneously while most other crosslinks usually cannot.

Graphene Oxide Oxygen Content Affects Physical and Biological Properties of Scaffolds Based on Chitosan/Graphene Oxide Conjugates.

Tissue engineering is a highly interdisciplinary field of medicine aiming at regenerating damaged tissues by combining cells with porous scaffolds materials. Scaffolds are templates for tissue regeneration and should ensure suitable cell adhesion and mechanical stability throughout the application period. Chitosan (CS) is a biocompatible polymer highly investigated for scaffold preparation but suffers from poor mechanical strength. In this study, graphene oxide (GO) was conjugated to chitosan at two weight ratios 0.3% and 1%, and the resulting conjugates were used to prepare composite scaffolds with improved mechanical strength. To study the effect of GO oxidation degree on scaffold mechanical and biological properties, GO samples at two different oxygen contents were employed. The obtained GO/CS scaffolds were highly porous and showed good swelling in water, though to a lesser extent than pure CS scaffold. In contrast, GO increased scaffold thermal stability and mechanical strength with respect to pure CS, especially when the GO at low oxygen content was used. The scaffold in vitro cytocompatibility using human primary dermal fibroblasts was also affected by the type of used GO. Specifically, the GO with less content of oxygen provided the scaffold with the best biocompatibility.

Effects of oxidation degree on photo-transformation and the resulting toxicity of graphene oxide in aqueous environment

Graphene oxide (GO) has been demonstrated to be key component for diverse applications. However, their potential environmental reactivity, fate and risk have not been fully evaluated to date. In this study, we investigated the photochemical reactivity of four types of GO with different oxidation degrees in aqueous environment, and their related toxicity to two bacterial models Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was further compared. After UV-irradiation, a large amount of oxygen functional groups on GO were reduced and the electronic conjugations within GO were restored as indicated by UV–visible absorption spectra, X-ray photoelectron spectroscopy and Raman spectroscopy analysis. Moreover, the higher the oxidation degree of the pristine GO was, the more obvious of the photo-transformation changes were. In order to further reveal the photochemical reactivity mechanisms, the reactive oxygen species (ROS) generation of GO was monitored. The quantity of ROS including singlet oxygen (1O2), superoxide anions (O2·-), and hydroxyl radicals (·OH) increased with increasing oxidation degree of GO, which was in accordance with the previous characterization results. Scanning electron microscopy and cell growth analyses of E. coli and S. aureus showed that the photochemical transformation enhanced the toxicity of GO, which might be due to an increase in functional group density. The higher conductivity of the reduced graphene oxide (RGO) was responsible for its stronger toxicity than GO through membrane damage and oxidative stress to bacteria. This study revealed that the oxidation degrees play important roles in photochemical transformation and the resulting toxicity of GO, which is helpful for understanding the environmental behaviors and risks of GO in aquatic environments.