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Chitosan (CS) hydrogel beads and hybrid beads made of a blending of CS hydrogels and Multilayer Graphene Oxide (MGO) were synthesized. The hybrid beads were prepared by gelation in NaOH solution of a 1 wt% CS acid solution with addition of MGO at either 1.5 wt% or 3 wt% loading rates. Prepared beads were characterized by infrared spectroscopy, thermogravimetric analysis (TGA), scanning electron cryo-microscopy and Brunauer–Emmett–Teller (BET) specific surface area measurements. $\text{Zn}^{2+}$ and Metoprolol (MTP) adsorption kinetics and isotherms were studied on the pristine and hybrid CS hydrogel beads. The adsorption kinetics of $\text{Zn}^{2+}$ and MTP in hybrid beads is limited by the diffusion to the MGO sites depending on their accessibility. While pure CS is not efficient for the MTP adsorption, the Langmuir-type isotherms of the 3 wt% MGO hydrogel beads (dose: 5 mg/100 mL) show 163 mg$\cdot $g$^{-1}$ maximum adsorption uptake. The MTP adsorption kinetics and isotherm suggest a MTP trapping on the MGO anionic sites (carboxylate groups) by electrostatic interactions. The $\text{Zn}^{2+}$ adsorption capacities are the highest for the 3 wt% MGO hydrogel beads (236 mg$\cdot $g$^{-1}$), and only of 40 mg$\cdot $g$^{-1}$ for the pure CS beads. The presence of $\text{Zn}^{2+}$ adsorption sites in the hybrid bead, such as MGO carboxylate groups giving electrostatic interactions, and CS amine groups leading to complexation, provides synergic adsorption effects. The competitive adsorption of $\text{Zn}^{2+}$ with respect to MTP in equimolar mixture was observed on hybrid beads (dose: 200 mg/100 mL) at 2 mmol$\cdot $L$^{-1}$ initial total concentration. At pollutant initial total concentration lower than 1.5 mmol$\cdot $L$^{-1}$, no competition occurs. The regeneration at pH 4 of the hybrid beads toward MTP or $\text{Zn}^{2+}$ adsorption was found to be 35–40% of the initial adsorption uptake for five adsorption/regeneration cycles.

To improve the dispersion of graphene oxide particles in wood for better thermal conductivity, this paper proposes the feasibility of obtaining graphene oxide with a smaller particle size using ball milling and its application in melamine resin-modified poplar veneer. The median diameter of multilayer graphene oxide was measured to learn the effects of different ball milling conditions on the particle size of graphene oxide, and the optimum ball milling process was chosen. In addition, the microscopic characterization of graphene oxide under the optimum ball milling process was carried out to investigate the microstructural changes in multilayer graphene after ball milling. Furthermore, the thermal conductivity of the graphene oxide/melamine resin-impregnated mixture modified veneer with the optimum ball milling process was also tested. The results show that, under the optimum ball milling process conditions of SDS wet ball milling with a vibration frequency of 30 Hz for 60 min, the particle size of the multilayer graphene was the smallest, and the median diameter could be reduced to 124 nm. Simultaneously, the thermal conductivity of the melamine resin-modified poplar veneer enhanced by the ball-milled graphene reached 0.405 W·m−1·K−1. In addition, it revealed that the number of graphene oxide layers was reduced to four after ball milling. However, the multilayer graphene was partially oxidized, the lamellar structure was destroyed and the crystallinity was reduced. [ABSTRACT FROM AUTHOR]

Chitosan (CS) hydrogel beads and hybrid beads made of a blending of CS hydrogels and Multilayer Graphene Oxide (MGO) were synthesized. The hybrid beads were prepared by gelation in NaOH solution of a 1 wt% CS acid solution with addition of MGO at either 1.5 wt% or 3 wt% loading rates. Prepared beads were characterized by infrared spectroscopy, thermogravimetric analysis (TGA), scanning electron cryo-microscopy and Brunauer--Emmett--Teller (BET) specific surface area measurements. Zn2+ and Metoprolol (MTP) adsorption kinetics and isotherms were studied on the pristine and hybrid CS hydrogel beads. The adsorption kinetics of Zn2+ and MTP in hybrid beads is limited by the diffusion to the MGO sites depending on their accessibility. While pure CS is not efficient for the MTP adsorption, the Langmuir-type isotherms of the 3wt% MGO hydrogel beads (dose: 5 mg/100 mL) show 163 mg⋅g-1 maximum adsorption uptake. The MTP adsorption kinetics and isotherm suggest a MTP trapping on the MGO anionic sites (carboxylate groups) by electrostatic interactions. The Zn2+ adsorption capacities are the highest for the 3 wt% MGO hydrogel beads (236 mg⋅g-1), and only of 40 mg⋅g-1 for the pure CS beads. The presence of Zn2+ adsorption sites in the hybrid bead, such as MGO carboxylate groups giving electrostatic interactions, and CS amine groups leading to complexation, provides synergic adsorption effects. The competitive adsorption of Zn2+ with respect to MTP in equimolar mixture was observed on hybrid beads (dose: 200 mg/100 mL) at 2 mmol⋅L-1 initial total concentration. At pollutant initial total concentration lower than 1.5 mmol⋅L-1, no competition occurs. The regeneration at pH 4 of the hybrid beads toward MTP or Zn2+ adsorption was found to be 35-40% of the initial adsorption uptake for five adsorption/regeneration cycles. [ABSTRACT FROM AUTHOR]

To address the performance deterioration of ZIF-8 for the adsorption of copper ions caused by powder volume pressure and particle aggregation, we employed multilayer graphene oxide (MGO) as a support to prepare composite adsorbents (MGO@ZIF-8) by using the in situ growth of ZIF-8 on MGO. Due to a good interfacial compatibility and affinity between ZIF-8 and graphene nanosheets, the MGO@ZIF-8 was successfully prepared. The optimal Cu2+ adsorption conditions of MGO@ZIF-8 were obtained through single factor experiments and orthogonal experiments. Surprisingly, the Cu2+ adsorption capacity was significantly improved by the integration of MGO and ZIF-8, and the maximum Cu2+ adsorption capacity of MGO@ZIF-8 reached 431.63 mg/g under the optimal adsorption conditions. Furthermore, the kinetic fitting and isotherm curve fitting confirmed that the adsorption law of Cu2+ by MGO@ZIF-8 was the pseudo-second-order kinetic model and the Langmuir isotherm model, which indicated that the process of Cu2+ adsorption was monolayer chemisorption. This work provides a new approach for designing and constructing ZIF-8 composites, and also offers an efficient means for the removal of heavy metals.

To improve the dispersion of graphene oxide particles in wood for better thermal conductivity, this paper proposes the feasibility of obtaining graphene oxide with a smaller particle size using ball milling and its application in melamine resin-modified poplar veneer. The median diameter of multilayer graphene oxide was measured to learn the effects of different ball milling conditions on the particle size of graphene oxide, and the optimum ball milling process was chosen. In addition, the microscopic characterization of graphene oxide under the optimum ball milling process was carried out to investigate the microstructural changes in multilayer graphene after ball milling. Furthermore, the thermal conductivity of the graphene oxide/melamine resin-impregnated mixture modified veneer with the optimum ball milling process was also tested. The results show that, under the optimum ball milling process conditions of SDS wet ball milling with a vibration frequency of 30 Hz for 60 min, the particle size of the multilayer graphene was the smallest, and the median diameter could be reduced to 124 nm. Simultaneously, the thermal conductivity of the melamine resin-modified poplar veneer enhanced by the ball-milled graphene reached 0.405 W·m−1·K−1. In addition, it revealed that the number of graphene oxide layers was reduced to four after ball milling. However, the multilayer graphene was partially oxidized, the lamellar structure was destroyed and the crystallinity was reduced.

Multilayer graphene oxide was synthesized by anodic oxidation of dispersed graphite, and the efficiency of its use as an electrode material for a supercapacitor was shown. In an alcohol suspension, the thickness of multilayer graphene oxide particles is less than 0.1 μm with an area of more than 100 μm2. The multilayer graphene oxide electrode has a high specific capacity of 107 F g–1 and a high charge retention rate of 97% after 5000 cycles at a current of 2 A g–1. The multilayer graphene oxide electrode demonstrated a maximum specific energy of 8.7 W h kg–1 at a current density of 0.1 A g–1 and a maximum power of 2291.1 W kg–1 at a current density of 4 A g–1. The impedance data at various DC voltages showed that after 5000 cycles, the charge transfer resistance increases by 26%. It was found that multilayer graphene oxide synthesized by the electrochemical method is a promising electrode material for producing a symmetric supercapacitor. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) materials have been extensively employed in mesenchymal stem cell (MSCs) research due to its unique nanotopography. Herein, various concentrations of GO flakes were used to fabricate different thickness of multilayer graphene oxide (m-GO) films using a simple drop-casting method and characterized by FTIR and AFM. The biocompatibility of m-GO films in culturing WJ-MSCs was investigated based on cell morphology, cell viability and osteogenic differentiation ability. Importantly, WJ-MSCs adhered and proliferated successfully on the m-GO films (6.25 µg, 12.5 µg and 25 µg) and showed no difference in cell morphology and viability after 5 days culture. Moreover, the WJ-MSCs growth on GO films (6.25 µg, 12.5 µg and 25 µg) enhanced the osteogenic differentiation as compared to the control (glass coverslip). Hence, the simple and inexpensive drop-casted fabrication strategy could provide biocompatible m-GO films to unlock the wider potential of WJ-MCSs in tissue engineering application. [ABSTRACT FROM AUTHOR]

Amino-functionalized multilayer graphene oxide (Am-nGO) has been synthesized and applied to remove the reactive drimaren red (DR) from aqueous solutions. Infrared spectroscopy evidenced amine and amide presence by peaks at 1579 cm−1 and a band between 3300 and 3500 cm−1. Raman spectroscopy showed an increment in ID/IG ratio after amino-Fe3O4-functionalization of nGO from 1.05 to 1.20, referent to an increase in sp3 domain disorder. The isoelectric point of Am-nGO was pH 8.1. From kinetic study, the equilibrium was achieved within 90 min; moreover, pseudo-n-order model satisfactorily fitted to the experimental data. Kinetic constant (kn) was 0.71 mg1−n g1−n min−1 and modeled equilibrium sorption capacity (qe) 219.17 mg g−1. Equilibrium experiments showed monolayer adsorption capacity (qm) of 219.75 mg g−1, and BET model best fitted to the equilibrium data, indicating that the adsorption process happened with multiple layers formation. From sorption thermodynamics, the standard free energy of Gibbs and enthalpy were respectively − 31.91 kJ mol−1 (at 298 K) and 66.43 kJ mol−1. Such data evidence the spontaneous and chemical behavior of DR adsorption as a consequence of strong electron donor-receptor interactions between the dye and the nanosorbent. By phytotoxicity assessment, Am-nGO showed inexpressive inhibitory potential to American lettuce seeds in comparison with its precursor nGO and graphite nanoplatelets. [ABSTRACT FROM AUTHOR]

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The electrochemical method for synthesizing multilayer graphene oxide by the anodic oxidation of disperse graphite in sulfuric acid is proposed. The possibility of sequential dispersion of graphite in the course of its electrochemical oxidation, hydrolysis, and thermolysis is demonstrated. It is shown that the resulting nanostructured materials tend to form agglomerates in aqueous dispersions. When treated with supersonic, the size of oxidized graphite particles decreases noticeably and they form multilayer graphene oxide. Thermolysis (250°С) leads to a considerable expansion of oxidized graphite particles (the inflation coefficient 1490 cm3 g–1) and reduction of oxygen-containing functional groups. The structure of thus obtained material includes polygraphene sheets with the thickness of 0.01–0.1 µm and contains pores of 1–10 µm. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is extensively studied as a template material for mesenchymal stem cell application due to its two-dimensional nature and unique functionalization chemistries. Herein, a new type of peptide-conjugated multilayer graphene oxide (peptide/m-GO film) was fabricated and used as biomaterial for culturing human Wharton’s jelly-derived mesenchymal stem cells (WJ-MSCs). The characterization of the peptide/m-GO films was performed, and the biocompatibility of the WJ-MSCs on the peptide/m-GO films was investigated. The results demonstrated that the peptide conjugate on the m-GO film did not hamper the normal growth of WJ-MSCs but supported the growth of WJ-MSCs after the 6-day culture period. In addition, the osteogenic differentiation of WJ-MSCs on the peptide/m-GO films was enhanced as compared with the parent m-GO film. Therefore, such peptide-conjugated m-GO films could provide a highly biocompatible and multifunctional 2D material to tailor the potential application of WJ-MSCs in bone tissue regeneration.

Water and concentrated solutions of acids (HCl, HPO, and HPO) or HO are clustered at the interfaces of nanosilicas and multi-layer graphene oxide (MLGO) as shown by low-temperature H NMR spectroscopy. The acid solutions in contact with silica or MLGO powders placed in nonpolar (CCl) or weakly polar (CDCl) media form nanodomains and clusters of several types and sizes with different contents of water and solutes. This differentiation of the solutions is stronger at a surface of more compacted nanosilicas because of enhanced confinement effects in narrower pores (voids) between adjacent nanoparticles. For MLGO, the confined space effects are relatively weak but the formation of ice crystallites during freezing of the suspension changes the material texture. Obtained results are of importance for deeper insight into the mechanism of the interfacial behavior of complex solutions under different confined space effects and due to the influence of organic co-solvents. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is extensively studied as a template material for mesenchymal stem cell application due to its two-dimensional nature and unique functionalization chemistries. Herein, a new type of peptide-conjugated multilayer graphene oxide (peptide/m-GO film) was fabricated and used as biomaterial for culturing human Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs). The characterization of the peptide/m-GO films was performed, and the biocompatibility of the WJ-MSCs on the peptide/m-GO films was investigated. The results demonstrated that the peptide conjugate on the m-GO film did not hamper the normal growth of WJ-MSCs but supported the growth of WJ-MSCs after the 6-day culture period. In addition, the osteogenic differentiation of WJ-MSCs on the peptide/m-GO films was enhanced as compared with the parent m-GO film. Therefore, such peptide-conjugated m-GO films could provide a highly biocompatible and multifunctional 2D material to tailor the potential application of WJ-MSCs in bone tissue regeneration. [ABSTRACT FROM AUTHOR]

• Factors affecting interlayer spacing of multilayer GO sheets were revealed by MDs. • Interlayer spacing was positively correlated with ' R ' and temperature. • The distance between inner layers changed little with the stacking layer number. • Spacing decreased first and then recovered at a critical strain depended on ' R '. Multilayer graphene oxide (GO) has shown promising applications in ion sieving, gas separation and water purification. However, accurate control of interlayer spacing is still the bottleneck of practical application. In this paper, molecular dynamic simulations have been conducted to reveal the effects of oxygen-containing group density, thickness, temperature and applied strain on the interlayer spacing of multilayer GO sheets systematically. It is found that the interlayer spacing of multilayer GO is positively correlated with oxygen-containing group density and temperature. The interlayer spacing between the outer layer and the secondary outer layer are smaller than these between the inner layers. The distance between inner layers change little with the thickness. When the oxygen-containing group density is below 20%, the interlayer spacing decreases slightly with the increasing strains, while it reaches 30%, the interlayer space decreases first and then recovers at a turning point with an applied strain of 6% owing to the breakage of C–C bond in epoxy groups. Our results would provide a guidance for interlayer spacing controlling and separation membrane designing. [ABSTRACT FROM AUTHOR]

Stacked graphene-oxide (GO) membranes have been reported to have promising potential for desalination. One key issue in the development of such membranes is understanding the atomistic water-permeation mechanism determined by the highly variable nature of GO (including membrane morphology, surface chemistry, osmotic pressure, and surface area). To clearly understand this variability, not only individual but also synergistic effects, i.e., the nonlinear cumulative effects of membrane properties, should be investigated. Hence, this paper explores how lateral and vertical permeation mechanisms differ with changes in the morphology and surface chemistry, either discretely or simultaneously, using both experiments and simulations. Experiments reveal that the GO water-permeation performance is dominated by the heterogeneous structural and chemical nature of GO. To investigate individual and synergistic effects on water dynamics, we performed molecular-dynamics simulations. The synergistic effects were more marked on the lateral permeation mechanisms than on the vertical mechanism in GO membranes. When the membrane nanochannels had a narrow intersheet distance or no gap overlap, the lateral permeation mechanism was found to be completely different owing to the interplay between these properties. Unlabelled Image • Structural and chemical nature dominates GO membrane water-permeation performance. • Effects of structure and chemical composition are explored singly and collectively. • Synergistic effects were more marked on lateral permeation mechanisms. [ABSTRACT FROM AUTHOR]

Amino-functionalized multilayer graphene oxide (Am-nGO) has been synthesized and applied to remove the reactive drimaren red (DR) from aqueous solutions. Infrared spectroscopy evidenced amine and amide presence by peaks at 1579 cm -1 and a band between 3300 and 3500 cm -1 . Raman spectroscopy showed an increment in I D /I G ratio after amino-Fe 3 O 4 -functionalization of nGO from 1.05 to 1.20, referent to an increase in sp 3 domain disorder. The isoelectric point of Am-nGO was pH 8.1. From kinetic study, the equilibrium was achieved within 90 min; moreover, pseudo-n-order model satisfactorily fitted to the experimental data. Kinetic constant (k n ) was 0.71 mg 1-n  g 1-n  min -1 and modeled equilibrium sorption capacity (q e ) 219.17 mg g -1 . Equilibrium experiments showed monolayer adsorption capacity (q m ) of 219.75 mg g -1 , and BET model best fitted to the equilibrium data, indicating that the adsorption process happened with multiple layers formation. From sorption thermodynamics, the standard free energy of Gibbs and enthalpy were respectively - 31.91 kJ mol -1 (at 298 K) and 66.43 kJ mol -1 . Such data evidence the spontaneous and chemical behavior of DR adsorption as a consequence of strong electron donor-receptor interactions between the dye and the nanosorbent. By phytotoxicity assessment, Am-nGO showed inexpressive inhibitory potential to American lettuce seeds in comparison with its precursor nGO and graphite nanoplatelets.

Transport of ionic solutions through graphene oxide (GO) membranes is a complicated issue because the complex and tortuous structure inside makes it very hard to clarify. Using molecular dynamics (MD) simulations, we investigated the mechanism of water transport and ion movement across multilayer GO. The significant flow rate is considerably influenced by the structural parameters of GO membranes. Because of the size effect on a shrunken real flow area, there is disagreement between the classical continuum model and nanoscaled flow. To eliminate the variance, we obtained modified geometrical parameters from density analysis and used them in the developed hydrodynamic model to give a precise depiction of water flow. Four kinds of solutions (i.e., NaCl, KCl, MgCl 2 , and CaCl 2 ) and different configurational GO sheets were considered to clarify the influence on salt permeation. It is found that the abilities of permeation to ions are not totally up to the hydration radius. Even though the ionic hydration shell is greater than the opening space, the ions can also pass through the split because of the special double-deck hydration structure. In the structure of GO, a smaller layer separation with greater offsetting gaps could substantially enhance the membrane's ability to reject salt. This work establishes molecular insight into the effects of configurational structures and salt species on desalination performance, providing useful guidelines for the design of multilayer GO membranes.