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Two-dimensional montmorillonite nanolayers (2D Mnt) are excellent adsorbents for methylene blue due to the fully exposed active sites, but the separation of 2D Mnt from water is difficult. The objective of the present study was to assemble 2D Mnt and graphene oxide sheets into a three-dimensional aerogel (3D Mnt-rGO Gel) to achieve easy solid–liquid separation. Structural characterization demonstrated that the Mnt-rGO Gel has a porous 3D structure with Mnt nanolayers distributed uniformly within; the introduction of 2D Mnt could reduce significantly the degree of restacking of graphene sheets. Adsorption tests indicated that 2D Mnt enhances the methylene blue (MB) removal performance of Mnt-rGO Gel with a large adsorption capacity of 207 mg g–1, which may be attributed to the adsorption of MB onto 2D Mnt and the increased adsorption surface of rGO resulting from the reduced restacking of graphene sheets. The MB was removed completely by 300 mg L–1 of Mnt-rGO Gel-3 in 180 min. The adsorption process of MB onto Mnt-rGO Gel followed the pseudo-second order kinetic model and the Langmuir isotherm model. Mnt-rGO Gel also showed good reusability. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results suggested that the adsorption of MB onto Mnt-rGO Gel may be attributed to the π–π interactions between aromatic rings of MB and graphene, hydrogen bonding, and the electrostatic interactions between the nitrogen groups on the MB and oxygen-containing groups on the Mnt-rGO Gel. [ABSTRACT FROM AUTHOR]

The graphene oxides (GOs) with various content of metallic ions impurities were prepared, and the adsorption performance of the GO before and after elution was evaluated. The prepared GOs were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma and atomic force microscopy. The results indicated that the metallic ion impurities hardly affected the interlayer distance, microstructure and thickness of the prepared GOs. The adsorption isotherm and adsorption kinetic results showed that the metallic ions adsorbed on the GO surface had a negative influence on both the adsorption capacity and rate. After eluted by HNO3 or HCl, most of the metallic ions adsorbed on the GO-91 surface were ion-exchanged by the protons of the acid eluents, and the purified GO showed enhanced equilibrium capacities and improved adsorption rate. The elution efficiency of HCl was better than that of HNO3, and the adsorption capacity and rate of the GO eluted by HCl approximately reached to those of the GO prepared from the graphite with high purity. It indicated that HCl could efficiently remove the metallic ions adsorbed on the GO surface. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the adsorption properties of Cd(II) on graphene oxide prepared from amorphous graphite and flaky graphite. The natural graphite was characterized by Scanning electron microscope, X-ray fluorescence spectrometer and X-ray diffraction. The equilibrium data were described well by both Langmuir model and Freundlich model, and the adsorption rate was fitted by Pseudo-second-order precisely. The GOs before and after adsorption were measured by Atomic force microscope, Fourier transform infrared spectrometer and Energy dispersive system. It was found that the larger adsorption capacity of Cd(II) on GO prepared from amorphous graphite was largely attributed to the more oxygenous functional groups appeared on GO-AG. [ABSTRACT FROM AUTHOR]

This study investigated the preparation of graphene oxide from mildly oxidized graphite through ultrasonic exfoliation. Both the original and produced materials were analyzed by ultraviolet-visible spectrophotometer, X-ray diffraction and atomic force microscopy. The results indicated that the exfoliation yield of graphene oxide was proportional to the input ultrasonic energy. In addition, a two-stage exfoliation phenomenon was observed in the exfoliation of mildly oxidized graphite with both ultrasonic homogenizer and cleaner. It also was found that increasing the content of [] in a C-H2SO4-[] reaction system was the most simple and direct method to increase the oxidation degree of graphite oxide. [ABSTRACT FROM AUTHOR]

The adsorption of Zn(II) in aqueous solutions on graphene oxide (GO) prepared from low-purity of natural amorphous graphite has been studied in this work. The study was performed through the measurements of Zeta potential, atomic force microscope, Fourier transform infrared spectrum and X-ray photoelectron spectroscopy. The results indicated that the adsorption followed the Langmuir model with the maximum Zn(II) adsorption capacity of 73 mg/g at pH 7.0. In addition, the adsorption was well described by the pseudo-second-order kinetics model. The mechanism of the Zn(II) adsorption on GO was mainly attributed to chemical adsorption through complexation reaction between Zn(II) and hydroxyl or carboxyl groups on the GO sheets, while the electrostatic interaction also contribute to the whole interaction. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The adsorption of gold cyanide complex ion (Au(CN) 2 − ) on graphene oxide-polyethylenimine hydrogel (GO/PEI hydrogel) from gold cyanidation has been studied to explore the possibility of the application of GO/PEI hydrogel in gold cyanidation process for extracting gold from ores. The adsorption was carried out in artificial Au(CN) 2 − aqueous solution with GO/PEI hydrogel as adsorbent. The experimental results, as well as IR, XPS and SEM−EDS, have shown that GO/PEI hydrogel exhibited a high adsorption capacity and a fast adsorption rate of Au(CN) 2 − , suggesting that GO/PEI hydrogel might be a good adsorbent for the recovery of Au(CN) 2 − . The adsorption of Au(CN) 2 − on GO/PEI hydrogel obeyed the Langmuir isotherm model and fitted well with the pseudo second order model. The good recovery of Au(CN) 2 − was largely related to the porous structure, large specific surface area, as well as the oxygenous functional groups on the surface of GO/PEI hydrogel. [ABSTRACT FROM AUTHOR]

Cationic surfactants in water are difficult to be degraded, leading to serious water pollution. In this work, graphene oxide (GO) was used as an adsorbent for removing Dodecylamine Hydrochloride (DACl), a representative cationic surfactant. X-ray diffraction (XRD), FT-IR spectroscopy and atomic force microscope (AFM) were used to characterize the prepared GO. The adsorption of DACl on GO have been investigated through measurements of adsorption capacity, zeta potential, FTIR, and X-ray photoelectron spectroscopy (XPS). The experimental results have shown that the adsorption kinetics could be described as a rate-limiting pseudo second-order process, and the adsorption isotherm agreed well with the Freundlich model. GO was a good adsorbent for DACl removal, compared with coal fly ash and powdered activated carbon. The adsorption process was endothermic, and could be attributed to electrostatic interaction and hydrogen bonding between DACl and GO. [ABSTRACT FROM AUTHOR]

The relationship between the defects of reduced graphene oxide (RGO) and the oxidation degree of graphite in the preparation of graphene with chemical conversion method has been studied in this work. This study was performed on an artificial graphite through the measurements of X ray diffraction, Raman spectroscopy and particle size analysis. The experimental results have shown that there indeed was a close relationship between the defects and the oxidation degree, which appeared in the form of S-type curve. Also, it was found that a low KMnO 4 addition would lead to a partial oxidation of graphite, leaving defects mainly on the edges of RGO; with a high KMnO 4 addition, the defects on RGO mostly appeared on the surfaces. [ABSTRACT FROM AUTHOR]

The recovery of gold cyanide complex Au(CN) 2 − from gold cyanidation with graphene oxide (GO) and GO hydrogel have been studied to explore the possibility of the application of GO or GO hydrogel in gold cyanidation process for extracting gold. The study was performed on the adsorption of artificial Au(CN) 2 − aqueous solution on GO and GO hydrogel. The adsorption results, as well as the SEM-EDS, AFM and XPS, demonstrated that GO was a better adsorbent for the recovery of Au(CN) 2 − from aqueous solution than conventional activated carbon because of its higher adsorption capacity and adsorption rate. It has been also found that the adsorption of Au(CN) 2 − on GO followed the Langmuir isotherm and fitted well with both the pseudo-first-order and pseudo-second-order kinetics models. The recovery of Au(CN) 2 − with GO might be attributed to the interaction between Au(CN) 2 − and oxygenous function groups on GO surface. GO hydrogel exhibited excellent Au(CN) 2 − adsorption property and easy separation, which enabled it a potential adsorbent in gold cyanidation. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The removal of Pb(II) from wastewater by graphene oxide (GO) using foam flotation was first investigated. Effects of initial solution pH, and the dosage of GO, emulsified kerosene and terpenic oil on the Pb(II) removal and turbidity of the residual solution were systematically examined. The experimental results showed that the initial solution pH and dosage of GO significantly affected the removal of Pb(II), and more than 99% of Pb(II) could be removed under the optimum conditions. The turbidity of the residual solution could decrease to 1.4 NTU at the optimal dosage of emulsified kerosene and terpenic oil. Moreover, the flotation-desorption cycles were carried out to evaluate the practical reusability of GO, and the Pb(II) removal maintained as high as 84.9% in the sixth regeneration. It indicated that GO could be efficiently reused in the process of foam flotation. This study provides an effective strategy for the selection of an optimized method to remove the spent GO from solution compared with the conventional methods including sedimentation, centrifugation and filtration, etc. [ABSTRACT FROM AUTHOR]

In this work, floc-flotation has been introduced into the elimination of graphene oxide (GO) from water for the first time, so as to reduce its potential risk and biotoxicity. Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM) were used to characterize the prepared GO, and the floc-flotation of GO have been studied both experimentally and theoretically. Extended DLVO theory has been applied to predict the hydrophobic agglomeration of GO, while the effects of dodecylamine hydrochloride (DAH) concentration, pH and stirring strength on the floc-flotation have been discussed. It has been found that the addition of DAH could induce GO surfaces hydrophobic, while appropriate stirring strength provided the kinetic energy for overcoming the energy barrier between the approaching particles. As a result, the hydrophobic agglomeration of GO could be greatly promoted and then the flotation separation of flocs from water could be efficiently realized. This processing could remove up to 98% of the GO nanoparticles form water, resulting in a much less environmental concern for GO in natural water bodies. [ABSTRACT FROM AUTHOR]

Magnetic reduced graphene oxide hydrogel as an adsorbent could be easily separated from water or solid suspensions. In this work, reduced graphene oxide/magnetite/ascorbic acid hydrogel (rGO/Fe 3 O 4 /AAH) was fabricated through one-step hydrothermal method as the adsorbent for gold-cyanide complex ions (Au(CN) 2 − ) in aqueous solution. The study was performed through the measurement of adsorption capacity and characterization via XRD, FT-IR, Raman, SEM, TEM and XPS. The results indicated that nano-scale magnetite particles were successfully anchored on rGO sheets and three-dimensional rGO/Fe 3 O 4 /AAH was generated during the hydrothermal process. The adsorption results suggested that rGO/Fe 3 O 4 /AAH was an effective adsorbent for recovering Au(CN) 2 − from aqueous solution with the maximum adsorption capacity of 309 mg/g, while the spent rGO/Fe 3 O 4 /AAH could be easily collected using a magnetic separator. The adsorption of Au(CN) 2 − on rGO/Fe 3 O 4 /AAH was found to be spontaneous, endothermic process. These results could be of great significant guidance for efficiently recovering Au(CN) 2 − from ore slurry in the future. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) and its composites have attracted widespread attentions as novel adsorbents for the adsorption of various heavy metal contaminants. Because of the unique physicochemical characteristics, they might become an excellent and most potential adsorbent. This review summarizes the application of GO and its composites as a superior adsorbent for the removal of heavy metal ions from water. The adsorption affinity and mechanisms, affecting factors and regeneration are highlighted. Moreover, the challenges for the commercial uses are discussed. [ABSTRACT FROM AUTHOR]

• Graphene oxide was modified by polyaluminium chloride; • HAO@GO exhibited an excellent adsorption capacity towards fluoride; • Chemical adsorption and ligand exchange are responsible for the adsorption of fluoride onto HAO@GO. Adsorption methods have garnered significant attention for fluoride removal from water bodies owing to their superior selectivity, simple operations, and wider applicability. However, the development of adsorbents with higher adsorption performances requires significant attention. Here, graphene oxide is endowed with excellent affinity towards fluoride by doping polyhydroxy complexes onto its surface structure and regulating the potential charge. Multiple detection measurements involving scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were employed to demonstrate the textural properties of graphene oxide (GO) modified by polyaluminium chloride (HAO@GO). Conversely, the effects of parameters including the preparation conditions, co-existing competitive ions, recyclability, contact time, and initial concentration on the adsorption behaviors were systematically determined. The adsorption experimental data were fitted well by the Langmuir isotherm model and pseudo-first-order model. The calculated maximum adsorption capacity was 129.23 mg/g at room temperature (25 °C) and a pH of 7.00, which is greater than that of most reported adsorbents. The existence of competitive anions, such as NO 3 - , SO 4 2 - , and PO 4 3 - , unavoidably interferes with fluoride adsorption. TEM, zero point of charge test, adsorption isotherm, and X-ray photoelectron spectroscopy (XPS) tests indicated that chemical adsorption and ligand exchange are responsible for the adsorption of fluoride onto HAO@GO. [ABSTRACT FROM AUTHOR]

The adsorption of methylene blue (MB) on graphene oxide (GO) prepared from an economical and resourceful amorphous graphite (AG) was studied. The effects of pH, foreign ions and concentrations of KClO 4 on MB removal were also evaluated. XRD, FT-IR, XPS, AFM and an Analyzer were employed to characterize the prepared GO. The results indicated that the C/O mass ratio of GO reached 1.84 and that thin layers (thickness of which less than 2 nm) accounted for 83.76%. The results of batch experiments showed that the adsorption of MB in the presence of cations decreased in the sequence Li + ≈ Na + > K + , while it was reduced in the order ClO 4 − > NO 3 − > Cl − in the presence of anions. MB removal in ClO 4 − was independent of solution pH, which may be ascribed to the synergistic effect between GO and ClO 4 − . The adsorption process was well described by a pseudo-second-order kinetics model, and the adsorption isotherm agreed well with the Langmuir model. [ABSTRACT FROM AUTHOR]

The characterisation of reduced graphene oxides (rGOs) prepared from natural flaky, lumpy, and amorphous graphites using Hummers method was investigated. The prepared graphite oxides (GrOs) and rGOs were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy, atomic force microscopy and electrochemical performance. The results showed that amorphous graphite was much easier to oxidise than lumpy and flaky graphites and was preferable for preparing single or double layer graphene because low graphitisation degree, high defect degree, high specific surface area and small crystal size were beneficial for (1) the oxidants to attack the exposed carbon atoms, (2) the intercalation of oxidants, and (3) the diffusion of oxidants between graphitic layers. In addition, rGO synthesised from amorphous graphite had the most defects and the smallest size of the in-plane sp 2 domains compared to those obtained from the other two nature graphites. [ABSTRACT FROM AUTHOR]

Comparative study has been performed on the adsorption of Pb(II) on graphene oxides (GOs) prepared from flaky, lump and amorphous graphites with the Hummers method in this work. The GOs were characterized by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Chemical analysis, Raman spectroscopy and Atomic force microscope. The results indicated that GO prepared from amorphous graphite had lower C/O ratio and more thin layers (less than 2 nm in thickness) than those prepared from the other two natural graphites. The adsorption process was well described by the pseudo-second-order kinetics model, and the equilibrium data agreed precisely with the Langmuir model. The hydroxyl and carboxyl located at the edges of GO sheets mainly participated in the complexation of Pb(II), and different GO sheets were bridged by Pb(II) through simultaneously bonding the marginal oxygenous groups. [ABSTRACT FROM AUTHOR]

Three-dimensional reduced graphene oxide/montmorillonite nanosheet aerogels (RGMTAs) have been successfully fabricated through hydrothermal method. X-ray diffraction and field-emission scanning electron microscope were used to characterize the structures of RGMTAs, and the electrochemical performance was investigated by electrochemical measurements. The restacking of reduced graphene oxide aerogel can be effectively inhibited without obvious structure change by using a small amount of montmorillonite nanosheets (Mts). The reduced graphene oxide/Mts aerogel shows enhanced electrochemical performance with a high specific capacitance of 275 F g−1 at a current density of 1 A g−1, and excellent rate capability. Moreover, though it is not conductive, excessive Mts only slightly increase the equivalent series resistance and charge transfer resistance. This work demonstrates that 2D Mts can reduce the restacking degree of graphene sheets, and the 3D reduced graphene oxide/Mt. nanosheet aerogel is a potential electrode material for supercapacitor applications. • 2D montmorillonite nanosheets can inhibit the restacking of reduced graphene oxide sheets. • Excessive montmorillonite nanosheets only slightly increase the equivalent series resistance and charge transfer resistance. • The reduced graphene oxide/montmorillonite nanosheet aerogel shows enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide aerogels (RGOAs) were obtained through steam reduction of freeze-dried graphene oxide hydrogels with different suspension pH. X-ray diffraction and field-emission scanning electron microscope were used to characterize the structures of graphene oxide aerogels (GOAs), and electrochemical measurements were used to study the electrochemical performance of RGOAs. The results show that the structure of GOA is greatly affected by the suspension pH, and the GOA prepared at pH 3 has low restacking degree. The RGOAs obtained by steam reduction can retain the 3D structure well. The RGOAs reduced at 180 ℃ exhibits a high specific capacitance of 265 F g−1 at a current density of 1 A g−1, and excellent rate capability. This work suggests that steam reduction of freeze-dried GO hydrogels with a low degree of stacking is a feasible approach to prepare RGOAs as electrode material for supercapacitor application. [ABSTRACT FROM AUTHOR]