| 1. |
- Korobov, Mikhail V., et al.
(författare)
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Sorption of polar organic solvents and water by graphite oxide : thermodynamic approach
- 2016
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 102, s. 297-303
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Tidskriftsartikel (refereegranskat)abstract
- Sorption of polar organic solvents CH3OH, C4H8O (THF), CH3CN, C3H7NO (DMF), C2H6OS (DMSO), C5H9NO (NMP) and water was quantitatively evaluated for Hummers (H-GO) and Brodie (B-GO) graphite oxides at T = 298K and at melting temperature (Tm) of the solvents. H-GO showed stronger sorption compared to B-GO for all studied solvents and the increase of sorption upon lowering temperature was observed for both H-GO and B-GO. Thermodynamic equations allowed to explain earlier reported "maximums" of swelling/sorption in the binary systems H-GO – solvent at Tm. The specific relation between the values of enthalpies of sorption and melting leads to the change of sign in enthalpies of sorption at Tm and causes maximal swelling/sorption. The same thermodynamic explanation was given for the "maximum" on the swelling vs. pressure dependence in B-GO and H-GO – H2O systems earlier reported at pressure of phase transition "liquid water-ice VI". Notably higher sorption of H2O was observed for H-GO compared to H-GO membrane (H-GOm) at high relative humidity (RH), RH > 0.75. Experimental sorption isotherm of H-GOm was used to simulate permeation rates of water through H-GOm and to estimate effective diffusion coefficient of water through the membrane.
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| 2. |
- Boulanger, Nicolas, et al.
(författare)
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Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:40, s. 45122-45135
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Tidskriftsartikel (refereegranskat)abstract
- Extremely defect graphene oxide (dGO) is proposed as an advanced sorbent for treatment of radioactive waste and contaminated natural waters. dGO prepared using a modified Hummers oxidation procedure, starting from reduced graphene oxide (rGO) as a precursor, shows significantly higher sorption of U(VI), Am(III), and Eu(III) than standard graphene oxides (GOs). Earlier studies revealed the mechanism of radionuclide sorption related to defects in GO sheets. Therefore, explosive thermal exfoliation of graphite oxide was used to prepare rGO with a large number of defects and holes. Defects and holes are additionally introduced by Hummers oxidation of rGO, thus providing an extremely defect-rich material. Analysis of characterization by XPS, TGA, and FTIR shows that dGO oxygen functionalization is predominantly related to defects, such as flake edges and edge atoms of holes, whereas standard GO exhibits oxygen functional groups mostly on the planar surface. The high abundance of defects in dGO results in a 15-fold increase in sorption capacity of U(VI) compared to that in standard Hummers GO. The improved sorption capacity of dGO is related to abundant carboxylic group attached hole edge atoms of GO flakes as revealed by synchrotron-based extended X-ray absorption fine structure (EXAFS) and high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy.
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| 3. |
- Boulanger, Nicolas, et al.
(författare)
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High Surface Area "3D Graphene Oxide" for Enhanced Sorption of Radionuclides
- 2022
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Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 9:18
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Tidskriftsartikel (refereegranskat)abstract
- Here preparation of high surface area activated reduced graphene oxide (arGO) oxidized into a 3D analogue of defect-rich GO (dGO) is reported. Surface oxidation of arGO results in carbon to oxygen ratio C/O = 3.3, similar to the oxidation state of graphene oxide while preserving high BET surface area of about 880 m2 g−1. Analysis of surface oxidized arGO shows high abundance of oxygen functional groups which converts hydrophobic precursor into hydrophilic material. High surface area carbons provide the whole surface for oxidation without the need of intercalation and lattice expansion. Therefore, surface oxidation methods are sufficient to convert the materials into 3D architectures with chemical properties similar to graphene oxide. The "3D graphene oxide" shows high sorption capacity for U(VI) removal in an extraordinary broad interval of pH. Notably, the surface oxidized carbon material has a rigid 3D structure with micropores accessible for penetration of radionuclide ions. Therefore, the bulk "3D GO" can be used as a sorbent directly without dispersing, the step required for GO to make its surface area accessible for pollutants.
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| 4. |
- Chumakova, Natalia A., et al.
(författare)
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Properties of Graphite Oxide Powders and Membranes as Revealed by Electron Paramagnetic Resonance Spectroscopy
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:39, s. 22750-22759
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Tidskriftsartikel (refereegranskat)abstract
- The spin probe technique was used to study graphite oxide (GO) powders swelled in polar liquids (CH3CN, CH3OH, and H2O) and liquid-free GO membranes (GOM). The nitroxide radicals TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) readily penetrated into the interplane space of GO from the solution. Electron paramagnetic resonance (EPR) spectra of these radical probes were sensitive to molecular mobility and orientation ordering within the internal space of GO. The radicals embedded in swelled GO were in two states with different rotational mobilities. The small fraction of radicals located in the interplane space of GO and detected in the broad range of temperatures was in the state of fast rotation, similar to the same radicals dissolved in bulk liquids, thus providing experimental evidence of formation of a liquid-like media within the interplane space of GO. Such mobile media may be responsible for the unusual permeation properties of GOM, which is reported in the literature. Second, less-mobile fraction of radicals was found to be immobilized at the internal surface of GO and was sensitive to phase transformations in the swelled GO structures. The transformations were detected as anomalies at temperature dependences of rotational mobility of radicals. The detected dependence of EPR spectra of probe radicals on orientation of GOM, relative to the direction of magnetic field in the EPR spectrometer, was used for quantitative characterization of orientation alignment of GO planes within the membranes. Such an approach may serve as an elegant method to estimate the relative quality of membranes and other GO-layered structures.
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| 5. |
- Gurzęda, Bartosz, et al.
(författare)
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Graphite oxide by “chlorate route” oxidation without HNO3 : Does acid matter?
- 2024
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Ingår i: Carbon. - 0008-6223 .- 1873-3891. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Very strong difference in many properties is well documented for graphite oxides (GtO) synthesized by Brodie (BGO) and Hummers (HGO) methods. The difference is typically assigned to the type of oxidant (chlorates or KMnO4, respectively). However, not only oxidants but also acids used in these methods are different. It is still unclear which of the different properties of GtO are dependent on the oxidant or acid used in the synthesis. Here we synthesized a new type of graphite oxide using an oxidation agent typical for the Brodie method (KClO3) in combination with acids so far used only in modified Hummers' method (H2SO4+H3PO4). The GtO synthesized by this method (MGO) demonstrates some properties similar to BGO (higher temperature of exfoliation and less defected structure) but also similarity to some other properties of HGO (absence of sharp swelling transitions). Comparing MGO, BGO, and HGO allows us to distinguish the effects of acids and oxidants on the properties of graphite oxides. The new procedure proposed in this study allows preparation of GtO nearly free from hole/vacancy defects (similarly to BGO) but avoids dangerous HNO3. MGO is suggested as a favorable precursor for the preparation of graphene films by thermal or chemical reduction methods.
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| 6. |
- Kuzenkova, Anastasiia S., et al.
(författare)
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New insights into the mechanism of graphene oxide and radionuclideinteraction
- 2020
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 158, s. 291-302
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of U(VI), Am(III)/Eu(III) and Cs(I) radionuclides by graphene oxides (GOs) synthesized byHummers’s, Brodie’s and Tour’s methods was studied through a combination of batch experiments withcharacterization by microscopic and spectroscopic techniques such as X-ray photoelectron spectroscopy(XPS), attenuated total reflection fourier-transform infrared spectroscopy (ATR-FTIR), high-energy resolutionfluorescence detected X-Ray absorption spectroscopy (HERFD-XANES), extended X-ray absorptionfine structure (EXAFS) and high resolution transmission electron microscopy (HRTEM). Remarkablydifferent sorption capacity and affinity of radionuclides was found towards GOs synthesized by Hummers’sand Brodie’s methods reflecting different structure and oxidation state of these materials.Mechanism underlying GO e radionuclide interaction is determined using variety of experimentaltechniques. For the first time it is shown here that GO - radionuclides interaction takes place on the smallholes or vacancy defects in the GO sheets. Mechanism of GO’s interaction with radionuclides wasanalyzed and specific functional groups responsible for this interaction were identified. Therefore, a newstrategy to produce improved materials with high capacity for radionuclides suggests the use perforatedand highly defected GO with a larger proportion of carboxylic functional groups.
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| 7. |
- Boulanger, Nicolas, et al.
(författare)
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High surface area activated carbon prepared from wood-based spent mushroom substrate for supercapacitors and water treatment
- 2024
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 680
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Tidskriftsartikel (refereegranskat)abstract
- Edible white-rot fungi are commonly cultivated on wood-based substrates and selectively degrade lignin to a larger extent during their growth. Spent mushroom substrate (SMS) is produced in huge amounts by the mushroom industry and today there is a lack of proven methods to valorize this kind of biomass waste, which in most cases is landfilled or used as fuel. This study demonstrates that birch wood-based SMS from the cultivation of oyster mushrooms can be converted into high-quality activated carbon (AC) with an extremely high surface area of about 3000 m2/g. These activated carbons showed good performance when used in electrodes for supercapacitors, with energy storage parameters nearly identical to AC produced from high-quality virgin birch wood. Moreover, AC produced from SMS showed high potential as an adsorbent for cleaning reactive orange-16 azo dye from aqueous solutions as well as contaminants from synthetic effluents and from real sewage water. The kinetics of adsorption were well represented by the Avrami fractional order model and isotherms of adsorption by the Liu model. The theoretical maximum reactive orange-16 adsorption capacities were approximately 519 mg/g (SMS-based carbon) and 553 mg/g (virgin birch-based carbon). The removal of contaminants from synthetic effluents made of different dyes and inorganic compounds was around 95% and 83% depending on the effluent composition. The removal of contaminants from raw sewage water was around 84%, and from treated sewage water was around 68%. Overall, the results showed that activated carbon prepared from waste generated during cultivation of white-rot fungi is as good as activated carbon prepared from high-quality virgin wood.
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| 8. |
- Boulanger, Nicolas, et al.
(författare)
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Super-oxidized “activated graphene” as 3D analogue of defect graphene oxide : oxidation degree vs U(VI) sorption
- 2023
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Ingår i: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 457
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Tidskriftsartikel (refereegranskat)abstract
- Porous carbons are not favorable for sorption of heavy metals and radionuclides due to absence of suitable binding sites. In this study we explored the limits for surface oxidation of “activated graphene” (AG), porous carbon material with the specific surface area of ∼2700 m2/g produced by activation of reduced graphene oxide (GO). Set of “Super-Oxidized Activated Graphene” (SOAG) materials with high abundance of carboxylic groups on the surface were produced using “soft” oxidation. High degree of oxidation comparable to standard GO (C/O=2.3) was achieved while keeping 3D porous structure with specific surface area of ∼700–800 m2/. The decrease in surface area is related to the oxidation-driven collapse of mesopores while micropores showed higher stability. The increase in the oxidation degree of SOAG is found to result in progressively higher sorption of U(VI), mostly related to the increase in abundance of carboxylic groups. The SOAG demonstrated extraordinarily high sorption of U(VI) with the maximal capacity up to 5400 μmol/g, that is 8.4 – fold increase compared to non-oxidized precursor AG, ∼50 –fold increase compared to standard graphene oxide and twice higher than extremely defect-rich graphene oxide. The trends revealed here show a way to further increase sorption if similar oxidation degree is achieved with smaller sacrifice of surface area.
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| 9. |
- Gurzęda, Bartosz, et al.
(författare)
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Microporous hydrophilic super-oxidized carbons with high surface area for removal of copper ions
- 2024
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 378
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Tidskriftsartikel (refereegranskat)abstract
- Super-oxidized porous carbons produced from reduced graphene oxide have been demonstrated recently to show unique sorption properties. Here we report experiments with identical oxidative treatment applied to four very different types of porous carbon materials with extremely broad range of specific surface area (SSA) ∼350–3400 m2g−1. It is demonstrated that KOH-activated carbons can be oxidized to the same degree as graphene oxide (GO) while preserving a larger part of SSA. Prolonged oxidation with ammonium persulfate resulted in extraordinary high degree of oxidation with C/O ratio reaching 2.1. Precursor carbons with largest share of micropores are found to be more stable against oxidative treatment, while single-walled carbon nanotubes (SWCNT's) are oxidized to much less extent. While mesopores collapse, micropores survive strong oxidation treatment providing materials with rather narrow pore size distribution and high (for given oxidation degree) BET SSA up to ∼1150 m2g−1. Super-oxidized porous carbons (SOPC's) show a high abundance of hydroxyl, epoxide, carbonyl, and carboxyl functional groups (similar to GO). As a result of oxidation, the hydrophobic carbons are converted into hydrophilic materials. Characterization shows that many properties of SOPC (e.g. degree of oxidation, type of functional groups, thermal stability etc.) are rather similar to GO, except for three-dimensional porous structure which can be considered an advantage for sorbent applications. SOPC's demonstrate superior sorption capacity for Cu(II) (up to ∼105 mgg−1), which is 8-fold higher than the value for non-oxidized precursor.
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| 10. |
- Iakunkov, Artem, et al.
(författare)
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Activated graphene as a material for supercapacitor electrodes : effects of surface area, pore size distribution and hydrophilicity
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : RSC Publishing. - 1463-9076 .- 1463-9084. ; 21:32, s. 17901-17912
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Tidskriftsartikel (refereegranskat)abstract
- Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000–3000 m2 g−1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80–90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.
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| 11. |
- Iakunkov, Artem, et al.
(författare)
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Effect of chain length on swelling transitions of Brodie graphite oxide in liquid 1-alcohols
- 2024
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Ingår i: Advanced Materials Interfaces. - : Wiley-VCH Verlagsgesellschaft. - 2196-7350. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Swelling is the most fundamental property of graphite oxides (GO). Here, a structural study of Brodie graphite oxide (BGO) swelling in a set of long chain 1-alcohols (named C11 to C22 according to the number of carbons) performed using synchrotron radiation X-ray diffraction at elevated temperatures is reported. Even the longest of tested alcohols (C22) is found to intercalate BGO with enormous expansion of the interlayer distance from ≈6Å up to ≈63Å, the highest expansion of GO lattice ever reported. Swelling transitions from low temperature α-phase to high temperature β-phase are found for BGO in all alcohols in the C11–C22 set. The transitions correspond to decrease of inter-layer distance correlating with the length of alcohol molecules, and change in their orientation from perpendicular to GO planes to layered parallel to GO (Type II transitions). These transitions are very different compared to BGO swelling transitions (Type I) found in smaller alcohols and related to insertion/de-insertion of additional layer of alcohol parallel to GO. Analysis of general trends in the whole set of 1-alcohols (C1 to C22) shows that the 1-alcohol chain length defines the type of swelling transition with Type I found for alcohols with C<10 and Type II for C>10.
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| 12. |
- Iakunkov, Artem, et al.
(författare)
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Gravimetric tank method to evaluate material-enhanced hydrogen storage by physisorbing materials
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:44, s. 27983-27991
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Tidskriftsartikel (refereegranskat)abstract
- The most common methods to evaluate hydrogen sorption (volumetric and gravimetric) require significant experience and expensive equipment for providing reproducible results. Both methods allow one to measure excess uptake values which are used to calculate the total amount of hydrogen stored inside of a tank as required for applications. Here we propose an easy to use and inexpensive alternative approach which allows one to evaluate directly the weight of hydrogen inside a material-filled test tank. The weight of the same tank filled with compressed hydrogen in the absence of loaded material is used as a reference. We argue that the only parameter which is of importance for hydrogen storage applications is by how much the material improves the total weight of hydrogen inside of the given volume compared to compressed gas. This parameter which we propose to name Gain includes both volumetric and gravimetric characterization of the material; it can be determined directly without knowing the skeletal volume of the material or excess sorption. The feasibility of the Gravimetric Tank (GT) method was tested using several common carbon and Metal Organic Framework (MOF) materials. The best Gain value of ∼12% was found for the Cu-BTC MOF which means that the tank completely filled with this material stores a 12% higher amount of hydrogen compared to H2 gas at the same P–Tconditions. The advantages of the GT method are its inexpensive design, extremely simple procedures and direct results in terms of tank capacity as required for industrial applications. The GT method could be proposed as a standard check for verification of the high hydrogen storage capacity of new materials. The GT method is expected to provide even better accuracy for evaluation of a material's performance for storage of denser gases like e.g. CO2 and CH4.
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| 13. |
- Iakunkov, Artem, 1993-
(författare)
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Materials prepared using graphite oxides : properties and applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Graphite oxides are hydrophilic materials, which have attracted a lot of attention due to unique properties and possible applications. The current thesis includes studies of fundamental properties and applications of graphite oxides as well as materials prepared from graphite oxides such as graphene oxide membranes, defect-rich graphite oxide, reduced graphene oxide and activated reduced graphene oxide. We have studied Hummers and Brodie graphite oxides swelling in a set of normal alcohols from methanol to 1-nonanol using XRD, TGA, DSC, vapour and liquid sorption. Swollen structures with one to five parallel layers of intercalated alcohol molecules were found for Brodie graphite oxide immersed in liquid alcohols. Phase transitions between some of these phases were observed at low temperatures. Brodie graphite oxide was also studied for swelling in molten sugar alcohols. We have demonstrated the formation of an expanded structure of graphite oxide intercalated by molten xylitol and sorbitol. The structure remains stable at ambient conditions after the melt solidification. The swelling of graphite oxide was also investigated in tetrafluoroborate solution in acetonitrile, the solution used as a common electrolyte in energy storage applications. Graphite oxide in these experiments served as a model system due to flexible "pores" provided by temperature-dependent swelling in acetonitrile. Intercalation of electrolyte ions into GO structure resulted in a formation of distinct phase with expanded inter-layer distance. Results of our experiments allow to evaluate minimal “pore size” required to accommodate electrolyte ions in solvate and desolvated states. Swelling pressure is one of the fundamental properties of graphite oxide, which has not been reported previously but important in applications involving swelling under confinement conditions. Significant pressures up to 220bar were measured for bulk graphite oxide due to swelling in water and ethanol. Swelling pressure in the range 3-25 bar was also measured for μm thick membranes. Both powder and membrane samples showed a significant difference in kinetics of building pressure in water and ethanol.Ageing effects were studied using graphene oxide membranes stored on air over prolonged periods starting from weeks and up to five years. The pronounced effects of ageing on chemical composition and swelling of graphene oxide membranes in a set of alcohols (methanol to 1-nonanol) were found. These effects were assigned to chemical modification during air storage rather than to intrinsic metastability of graphene oxide. The structural changes related to the chemical modification of graphene oxide on air are crucial for membrane applications because they significantly affect the size of “permeation channels” provided by swelling. Extremely defective graphene oxide was demonstrated as a promising material for sorbent applications. The defect-rich graphene oxide was prepared using Hummers oxidation of strongly defective reduced graphite oxide instead of well crystalline graphite. The defect-rich graphene oxide showed significant improvement in sorption of radionuclides (U(VI), Am(III), and Eu(III)) compared to standard graphite oxides. High abundance of defects was demonstrated to correlate with the maximal sorption capacity of graphite oxide towards radionuclides and methylene blue. Finally, we have studied activated reduced graphene oxide for application in supercapacitors. This study aimed to reveal correlations between structural parameters of electrode material and supercapacitor performance. We have prepared two sets of materials with a broad range of N2 BET surface area 1000-3000m2g-1 , significant variation of pore size distribution and oxygen content using change of activation temperature and post-synthesis mechanical treatment. Analysis of nitrogen and water sorption isotherms showed that despite negligibly small H2O BET surface area, the total pore volume is very similar for nitrogen and water sorption. The best supercapacitor performance was found to depend on combination of several parameters in a delicate balance of specific surface area, oxygen content, micropore volume and conductivity
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| 14. |
- Iakunkov, Artem, et al.
(författare)
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Swelling of graphene oxide membranes in alcohols : effects of molecule size and air ageing
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7, s. 11331-11337
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Tidskriftsartikel (refereegranskat)abstract
- Swelling of Hummers graphene oxide (HGO) membranes in a set of progressively longer liquid alcohols (methanol to 1-nonanol) was studied using synchrotron radiation XRD after air ageing over prolonged periods of time. Both precursor graphite oxides and freshly prepared HGO membranes were found to swell in the whole set of nine liquid alcohols with an increase of interlayer spacing from ∼7 Å (solvent free) up to ∼26 Å (in 1-nonanol). A pronounced effect of ageing on swelling in alcohols was found for HGO membranes stored in air. The HGO membranes aged for 0.5–1.5 years show progressively slower swelling kinetics, a non-monotonic decrease of saturated swelling in some alcohols and complete disappearance of swelling for alcohol molecules larger than hexanol. Moreover, the HGO membranes stored under ambient conditions for 5 years showed a nearly complete absence of swelling in all alcohols but preserved swelling in water. In contrast, precursor graphite oxide powder showed unmodified swelling in alcohols even after 4 years of ageing. Since the swelling defines the size of permeation channels, the ageing effect is one of the important parameters which could explain the strong variation in reported filtration/separation properties of GO membranes. The time and conditions of air storage require standardization for better reproducibility of results related to performance of GO membranes in various applications. The ageing of GO membranes can be considered not only as a hindrance/degradation for certain applications, but also as a method to tune the swelling properties of HGO membranes for better selectivity in sorption of solvents and for achieving better selective permeability.
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| 15. |
- Iakunkov, Artem, et al.
(författare)
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Swelling of Ti3C2Tx mxene in water and methanol at extreme pressure conditions
- 2024
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Ingår i: Advanced Science. - : John Wiley & Sons. - 2198-3844. ; 11:9
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Tidskriftsartikel (refereegranskat)abstract
- Pressure-induced swelling has been reported earlier for several hydrophilic layered materials. MXene Ti3C2Tx is also a hydrophilic layered material composed by 2D sheets but so far pressure-induced swelling is reported for this material only under conditions of shear stress at MPa pressures. Here, high-pressure experiments are performed with MXenes prepared by two methods known to provide “clay-like” materials. MXene synthesized by etching MAX phase with HCl+LiF demonstrates the effect of pressure-induced swelling at 0.2 GPa with the insertion of additional water layer. The transition is incomplete with two swollen phases (ambient with d(001) = 16.7Å and pressure-induced with d(001) = 19.2Å at 0.2 GPa) co-existing up to the pressure point of water solidification. Therefore, the swelling transition corresponds to change from two-layer water intercalation (2L-phase) to a never previously observed three-layer water intercalation (3L-phase) of MXene. Experiments with MXene prepared by LiCl+HF etching have not revealed pressure-induced swelling in liquid water. Both MXenes also show no anomalous compressibility in liquid methanol. The presence of pressure-induced swelling only in one of the MXenes indicates that the HCl+LiF synthesis method is likely to result in higher abundance of hydrophilic functional groups terminating 2D titanium carbide.
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| 16. |
- Iakunkov, Artem, et al.
(författare)
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Swelling Pressures of Graphite Oxide and Graphene Oxide Membranes in Water and Ethanol
- 2021
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Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 8:14
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Tidskriftsartikel (refereegranskat)abstract
- Swelling of graphene oxide (GO) membranes and bulk graphite oxide under confinement conditions is found to produce pressures up to ≈220 bar. Swelling pressure is important to take into account in many applications of GO membranes, but it has not been previously reported. Swelling pressures are typically measured only for bulk materials. However, it is demonstrated that even µm thick GO membranes develop pressures 3–25 bar due to the volume expansion caused by swelling in water. A rather strong difference in kinetics of pressure increase is found for both graphite oxide and GO membranes in water and ethanol despite similar lattice expansion due to swelling. This effect is attributed to slower penetration of ethanol into GO interlayers. Significantly faster saturation of swelling pressure is found for GO membranes (few hours) as compared to bulk graphite oxides (weeks) due to a higher degree of compaction. Swelling pressure is an important factor in applications, which require confinement, encapsulation of GO membranes or using external pressure to limit the lattice expansion. Finally, the swelling pressure can be used as an estimation for the suction pressure developed in pervaporation or vapor permeation applications, which is suggested as a driving force in rapid water permeation across GO membranes.
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| 17. |
- Iakunkov, Artem, et al.
(författare)
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Swelling properties of graphite oxides and graphene oxide multilayered materials
- 2020
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 12:41, s. 21060-21093
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Forskningsöversikt (refereegranskat)abstract
- Graphite oxide (GtO) and graphene oxide (GO) multilayered laminates are hydrophilic materials easily intercalated by water and other polar solvents. By definition, an increase in the volume of a material connected to the uptake of a liquid or vapour is named swelling. Swelling is a property which defines graphite oxides and graphene oxides. Less oxidized materials not capable of swelling should be named oxidized graphene. The infinite swelling of graphite oxide yields graphene oxide in aqueous dispersions. Graphene oxide sheets dispersed in a polar solvent can be re-assembled into multilayered structures and named depending on applications as films, papers or membranes. The multilayered GO materials exhibit swelling properties which are mostly similar to those of graphite oxides but not identical and in some cases surprisingly different. Swelling is a key property of GO materials in all applications which involve the sorption of water/solvents from vapours, immersion of GO into liquid water/solvents and solution based chemical reactions. These applications include sensors, sorption/removal of pollutants from waste waters, separation of liquid and gas mixtures, nanofiltration, water desalination, water-permeable protective coatings, etc. Swelling defines the distance between graphene oxide sheets in solution-immersed GO materials and the possibility for penetration of ions and molecules inside of interlayers. A high sorption capacity of GO towards many molecules and cations is defined by swelling which makes the very high surface area of GO accessible. GtO and GO swelling is a surprisingly complex phenomenon which is manifested in a variety of different ways. Swelling is strongly different for materials produced using the most common Brodie and Hummers oxidation procedures; it depends on the degree of oxidation, ad temperature and pressure conditions. The value of the GO interlayer distance is especially important in membrane applications. Diffusion of solvent molecules and ions is defined by the size of "permeation channels" provided by the swelled GO structure. According to extensive studies performed over the last decade the exact value of the inter-layer distance in swelled GO depends on the nature of solvent, temperature and pressure conditions, and the pH and concentration of solutions and exhibits pronounced aging effects. This review provides insight into the fundamental swelling properties of multilayered GO and demonstrates links to advanced applications of these materials.
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| 18. |
- Iakunkov, Artem, et al.
(författare)
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Temperature-dependent swelling transitions in MXene Ti3C2Tx
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 14:30, s. 10940-10949
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Tidskriftsartikel (refereegranskat)abstract
- Swelling is a property of hydrophilic layered materials, which enables the penetration of polar solvents into an interlayer space with expansion of the lattice. Here we report an irreversible swelling transition, which occurs in MXenes immersed in excess dimethyl sulfoxide (DMSO) upon heating at 362-370 K with an increase in the interlayer distance by 4.2 Å. The temperature dependence of MXene Ti3C2Tx swelling in several polar solvents was studied using synchrotron radiation X-ray diffraction. MXenes immersed in excess DMSO showed a step-like increase in the interlayer distance from 17.73 Å at 280 K to 22.34 Å above ∼362 K. The phase transformation corresponds to a transition from the MXene structure with one intercalated DMSO layer into a two-layer solvate phase. The transformation is irreversible and the expanded phase remains after cooling back to room temperature. A similar phase transformation was observed also for MXene immersed in a 2 : 1 H2O : DMSO solvent ratio but at a lower temperature. The structure of MXene in the mixed solvent below 328 K was affected by the interstratification of differently hydrated (H2O)/solvated (DMSO) layers. Above the temperature of the transformation, the water was expelled from MXene interlayers and the formation of a pure two-layer DMSO-MXene phase was found. No changes in the swelling state were observed for MXenes immersed in DMSO or methanol at temperatures below ambient down to 173 K. Notably, MXenes do not swell in 1-alcohols larger than ethanol at ambient temperature. Changing the interlayer distance of MXenes by simple temperature cycling can be useful in membrane applications, e.g. when a larger interlayer distance is required for the penetration of ions and molecules into membranes. Swelling is also very important in electrode materials since it allows penetration of the electrolyte ions into the interlayers of the MXene structure.
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| 19. |
- Khaliha, Sara, et al.
(författare)
-
Defective graphene nanosheets for drinking water purification : Adsorption mechanism, performance, and recovery
- 2021
-
Ingår i: FlatChem. - : Elsevier. - 2452-2627. ; 29
-
Tidskriftsartikel (refereegranskat)abstract
- Defect-rich graphene oxide (dGO) was used as sorbent for organic contaminants of emerging concern in tap water, including drugs and dyes, and the performance compared to those of lower-defects graphene types. The role of holes and carbonyl- carboxylic groups on graphene nanosheets surface on the adsorption mechanism and efficiency was investigated. dGO showed enhanced adsorption capacity toward two fluoroquinolone antibiotics (ofloxacin, OFLOX, and ciprofloxacin, CIPRO) in tap water with a maximum capacity of 650 mg/g, compared to 204 mg/g for Hummers derived commercial GO (hGO) and 125 mg/g for less defected Brodie derived GO (bGO) for OFLOX. The role of defects on the selective adsorption of OFLOX was also modelled by MD simulations, highlighting a mechanism mainly driven by the shape complementarity between the graphene holes and the molecules. Adsorption isotherms revealed different adsorption model for dGO, with a Langmuir fitting for dGO and BET fitting for all the other investigated samples. The maximum adsorption capacity of dGO for OFLOX was about six times higher than that of Granular Activated Carbon (95 mg/g), the industrial adsorption standard technology. Finally, it was also demonstrated that dGO can be recovered from treated water by ultrafiltration, this preventing secondary contamination risks and enabling safe use of graphene nanosheets for water purification.
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| 20. |
- Kim, Y, et al.
(författare)
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Nanomagnetic shielding : High-resolution NMR in carbon allotropes
- 2010
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606 .- 1089-7690. ; 132, s. 021102-
-
Tidskriftsartikel (refereegranskat)abstract
- Theunderstanding and control of the magnetic properties of carbon-based materialsis of fundamental relevance in applications in nano- and biosciences.Ring currents do play a basic role in those systems.In particular the inner cavities of nanotubes offer an idealenvironment to investigate the magnetism of synthetic materials at thenanoscale. Here, by means of 13C high resolution NMR ofencapsulated molecules in peapod hybrid materials, we report the largestdiamagnetic shifts (down to −68.3 ppm) ever observed in carbonallotropes, which is connected to the enhancement of the aromaticityof the nanotube envelope upon doping. This diamagnetic shift canbe externally controlled by in situ modifications such as dopingor electrostatic charging. Moreover, defects such as C-vacancies, pentagons, andchemical functionalization of the outer nanotube quench this diamagnetic effectand restore NMR signatures to slightly paramagnetic shifts compared tononencapsulated molecules. The magnetic interactions reported here are robust phenomenaindependent of temperature and proportional to the applied magnetic field.The magnitude, tunability, and stability of the magnetic effects makethe peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronicsand nanobiomedical engineering
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| 21. |
- Klechikov, Alexey, et al.
(författare)
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Graphite oxide swelling in molten sugar alcohols and their aqueous solutions
- 2018
-
Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 140, s. 157-163
-
Tidskriftsartikel (refereegranskat)abstract
- Graphite oxides (GO) are intercalated rapidly by one to several layers of solvent when immersed in liquid but the GO solvates are typically unstable on air due to solvent evaporation. Here we study swelling of GO in solvents (sugar alcohols) with melting temperature point above ambient. Using in situ synchrotron radiation XRD experiments we demonstrated GO swelling in molten xylitol and sorbitol. The expanded GO structure intercalated with one layer of xylitol or sorbitol is preserved upon solidification of melt and cooling back to ambient conditions. The structure of solid solvates of GO with xylitol and sorbitol is based on non-covalent interaction and pristine GO can be recovered by washing in water. Intercalation of xylitol and sorbitol into GO structure in aqueous solutions yields similar but less ordered structure of GO/sugar alcohol solid solvates. Very similar inter-layer distance was observed for GO intercalated by sugar alcohols in melt and for GO immersed in sugar solutions. This result shows that sugar alcohols penetrate into GO inter-layer space without hydration shell forming 2D layers with orientation parallel to graphene oxide sheets. Therefore, hydration diameter of molecules should not be considered as decisive factor for permeation through graphene oxide inter-layers in multilayered membranes.
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| 22. |
- Klechikov, Alexey, et al.
(författare)
-
Swelling of Thin Graphene Oxide Films Studied by in Situ Neutron Reflectivity
- 2018
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:24, s. 13106-13116
-
Tidskriftsartikel (refereegranskat)abstract
- Permeation of multilayered graphene oxide (GO) membranes by polar solvents is known to correlate with their swelling properties and amount of sorbed solvent. However, quantitative estimation of sorption using standard (e.g., gravimetric) methods is technically challenging for few nanometers thick GO membranes/films exposed to solvent vapors. Neutron reflectivity (NR) was used here to evaluate the amount of solvents intercalated into the film which consists of only ∼31.5 layers of GO. Analysis of NR data recorded from the GO film exposed to vapors of polar solvents provides information about change of film thickness due to swelling, amount of intercalated solvent, and selectivity in sorption of solvents from binary mixtures. A quantitative study of GO film sorption was performed for D2O, d-methanol, ethanol, dimethyl sulfoxide (DMSO), acetonitrile, dimethylformamide (DMF), and acetone. Using isotopic contrast, we estimated selectivity in sorption of ethanol/d-methanol mixtures by the GO film. Estimation of sorption selectivity was also performed for D2O/DMF, D2O/DMSO, and D2O/acetonitrile binary mixtures. Sorption of polar solvents was compared for the thin GO film, micrometer thick free standing GO membranes, and graphite oxide powders.
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| 23. |
- Li, Gui, et al.
(författare)
-
Activated carbons with extremely high surface area produced from cones, bark and wood using the same procedure
- 2023
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 13:21, s. 14543-14553
-
Tidskriftsartikel (refereegranskat)abstract
- Activated carbons have been previously produced from a huge variety of biomaterials often reporting advantages of using certain precursors. Here we used pine cones, spruce cones, larch cones and a pine bark/wood chip mixture to produce activated carbons in order to verify the influence of the precursor on properties of the final materials. The biochars were converted into activated carbons with extremely high BET surface area up to ∼3500 m2 g−1 (among the highest reported) using identical carbonization and KOH activation procedures. The activated carbons produced from all precursors demonstrated similar specific surface area (SSA), pore size distribution and performance to electrodes in supercapacitors. Activated carbons produced from wood waste appeared to be also very similar to “activated graphene” prepared by the same KOH procedure. Hydrogen sorption of AC follows expected uptake vs. SSA trends and energy storage parameters of supercapacitor electrodes prepared from AC are very similar for all tested precursors. It can be concluded that the type of precursor (biomaterial or reduced graphene oxide) has smaller importance for producing high surface area activated carbons compared to details of carbonization and activation. Nearly all kinds of wood waste provided by the forest industry can possibly be converted into high quality AC suitable for preparation of electrode materials.
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| 24. |
- Li, Gui, et al.
(författare)
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In operando study of microsupercapacitors with gel electrolytes using nano-beam synchrotron x-ray diffraction
- 2024
-
Ingår i: Batteries & Supercaps. - : Wiley-VCH Verlagsgesellschaft. - 2566-6223.
-
Tidskriftsartikel (refereegranskat)abstract
- Synchrotron radiation X-ray diffraction (XRD) with nanoscale beam size was used here for in situ and in operando study of micro-supercapacitors (MSC) with gel electrolyte and MXene Ti3C2Tx electrodes. The electrode structure was characterized as a function of applied voltage and distance from the gap separating electrodes using microscopic cells with cylindrical shape designed for transmission mode XRD. The devices with gel electrolytes based on H2SO4 (with H2O/PVA and DMSO/PVA) showed stable performance with no changes in MXene structure under voltage swaps between positive and negative values. Experiments with KI-based electrolytes demonstrated changes of MXene structure correlated with decrease of energy storage parameters under conditions of increased operation voltage starting from 0.8 V. The optimal performance of the MSCs was observed when the MXene structure remained unchanged upon switching the applied voltage polarity. The changes of inter-layer distance of MXene upon swap of applied voltage correlate with decrease of device performance and are undesirable for stable operation of MSC's. We also tested feasibility of X-ray fluorescence (XRF) for characterization of electrolyte ion migration in MSCs using 2D element mapping. Irreversible sorption of iodine by MXene was found using XRF mapping of charged electrodes using standard in-plane MSC device and KI electrolyte.
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| 25. |
- Lin, Hu, et al.
(författare)
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Rapid aging of bilayer graphene oxide
- 2022
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:48, s. 20658-20667
-
Tidskriftsartikel (refereegranskat)abstract
- Atomic force microscopy (AFM) imaging was used to study swelling of individual bilayer graphene oxide (GO) flakes in water and ethanol vapors. We found that within 5 days after sample deposition the swelling of bilayered Hummers GO (HGO) in ethanol vapors disappears nearly completely, whereas the swelling in water remains not affected. Swelling can therefore be used as a sensitive indicator of rapid aging of bilayered HGO, which occurs both in air and under inert gas. The surprising ability of 5-days-aged bilayered HGO to swell in water but not in ethanol fits to the effects observed in μm-thick GO membranes after several years of aging. Remarkably, bilayered Brodie GO (BGO) maintains swelling in ethanol after storing it under the same conditions as HGO. Moreover, we demonstrate that AFM can be used to detect hole defects in individual GO sheets. The BGO bilayer swelling in ethanol vapors starts either on the flake edges or in very few points, forming ∼2 Å height fronts, which propagate slowly within interlayer spaces in all directions. The increase of the average distance between HGO sheets occurs simultaneously all over the flake, demonstrating a high abundance of hole defects. Our results imply that the permeation path length in HGO membranes must be significantly shorter compared to BGO, which is important to take into account in the modeling of membrane permeation.
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| 26. |
- Mishukova, Viktoriia, et al.
(författare)
-
Facile fabrication of graphene-based high-performance microsupercapacitors operating at a high temperature of 150 °C
- 2021
-
Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 3:16, s. 4674-4679
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Tidskriftsartikel (refereegranskat)abstract
- Many industry applications require electronic circuits and systems to operate at high temperatures over 150 °C. Although planar microsupercapacitors (MSCs) have great potential for miniaturized on-chip integrated energy storage components, most of the present devices can only operate at low temperatures (<100 °C). In this work, we have demonstrated a facile process to fabricate activated graphene-based MSCs that can work at temperatures as high as 150 °C with high areal capacitance over 10 mF cm−2and good cycling performance. Remarkably, the devices exhibit no capacitance degradation during temperature cycling between 25 °C and 150 °C, thanks to the thermal stability of the active components.
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| 27. |
- Mishukova, Viktoriia, et al.
(författare)
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Microsupercapacitors Working at 250 °C
- 2023
-
Ingår i: Batteries & Supercaps. - : Wiley-VCH Verlagsgesellschaft. - 2566-6223.
-
Tidskriftsartikel (refereegranskat)abstract
- The raised demand for portable electronics in high-temperature environments (>150 °C) stimulates the search for solutions to release the temperature constraints of power supply. All-solid-state microsupercapacitors (MSCs) are envisioned as promising on-chip power supply components, but at present, nearly none of them can work at temperature over 200 °C, mainly restricted by the electrolytes which possess either low thermal stability or incompatible fabrication process with on-chip integration. In this work, we have developed a novel process to fabricate highly thermally stable ionic liquid/ceramic composite electrolytes for on-chip integrated MSCs. Remarkably, the electrolytes enable MSCs with graphene-based electrodes to operate at temperatures as high as 250 °C with a high areal capacitance (~72 mF cm−2 at 5 mV s−1) and good cycling stability (70 % capacitance retention after 1000 cycles at 1.4 mA cm−2).
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| 28. |
- Moreno-Fernández, Gelines, et al.
(författare)
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Ball-milling-enhanced capacitive charge storage of activated graphene in aqueous, organic and ionic liquid electrolytes
- 2021
-
Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 370
-
Tidskriftsartikel (refereegranskat)abstract
- Ball-milling under either air or argon is explored as a facile way to adjust the textural properties, surface chemistry and morphology of activated reduced graphene oxide to the requirements for optimum electrode materials in electrical double layer capacitors operating in aqueous (KOH), organic (tetraethylammonium tetrafluoroborate in acetonitrile) and ionic liquid (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) electrolytes. Ball-milling is evidenced to specifically remove excessively large pores through the collapse of mesoporosity with no negative effect on in-pore resistance in any electrolyte, a concomitant improvement in volume-based storage and no loss of gravimetric performance. Ball-milling under air results in high oxygen content in the materials, which brings about performance deterioration in tetraethylammonium tetrafluoroborate in acetonitrile, but not significantly in aqueous and ionic liquid electrolytes. The best performance is achieved using activated graphene ball-milling under argon, with a volumetric capacitance of 90, 60, 70 F.cm−3 and a characteristic cell response time of 0.28, 1.3 and 8 s for aqueous, organic and ionic liquid electrolyte. While the highest energy density of 25 Wh.L−1 is reached in ionic liquid electrolyte at a cell potential of 3 V, the highest practical power density of 15 kW.L−1 is measured in tetraethylammonium tetrafluoroborate in acetonitrile at the energy density of 10 Wh.L−1. Our study underscores that simple ball-milling can provide the best trade-off among multiple performance parameters, resulting in sufficiently high volumetric capacitance with no detriment in high-rate response and cycle stability.
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| 29. |
- Nordenström, Andreas, et al.
(författare)
-
Acetylation of graphite oxide
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 22:37, s. 21059-21067
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Tidskriftsartikel (refereegranskat)abstract
- Unlike many methods of chemical modification of Graphite Oxide (GO) reported during 1930-1960 and re-studied in much detail over the last decade, acetylation somehow escaped attention and remained almost completely unexplored. Acetylated Graphite Oxide (AcGO) was prepared using a reaction with acetic anhydride. Successful acetylation is evidenced by an increase in the average interlayer distance fromd(001) = 7.8 angstrom in the precursor GO to 10 angstrom in AcGO. The amount of oxygen in AcGO significantly decreased compared to the precursor GO (C/O = 2.2), reflecting partial reduction of GO in the process of acetylation and resulting in a scarcely functionalized material with C/O = 6.2. A theoretical model of the complete acetylation of GO results in a non-porous close packed molecular structure with an interlayer distance of similar to 10 angstrom, in good agreement with experiment. Remarkably, AcGO shows significant swelling despite the oxidation degree being comparable to that of reduced GO, which does not swell in polar solvents. Moreover, AcGO shows swelling in acetonitrile similar to that of the precursor GO but not in water, thus providing an example of selectivity in the sorption of common polar solvents. The low oxidation degree combined with selective swelling properties makes AcGO a promising material for membrane applications.
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| 30. |
- Nordenström, Andreas, et al.
(författare)
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High-surface-area activated carbon from pine cones for semi-industrial spray deposition of supercapacitor electrodes
- 2022
-
Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 4:21, s. 4689-4700
-
Tidskriftsartikel (refereegranskat)abstract
- High surface area carbons are so far the best materials for industrial manufacturing of supercapacitor electrodes. Here we demonstrate that pine cones, an abundant bio-precursor currently considered as a waste in the wood industry, can be used to prepare activated carbons with a BET surface area exceeding 3000 m2 g−1. It is found that the same KOH activation procedure applied to reduced graphene oxide (rGO) and pine cone derived biochars results in carbon materials with a similar surface area, pore size distribution and performance in supercapacitor (SC) electrodes. It can be argued that “activated graphene” and activated carbon are essentially the same kind of material with a porous 3D structure. It is demonstrated that the pine cone derived activated carbon (PC-AC) can be used as a main part of aqueous dispersions stabilized by graphene oxide for spray deposition of electrodes. The PC-AC based electrodes prepared using a semi-industrial spray gun machine and laboratory scale blade deposition of these dispersions were compared to pellet electrodes.
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| 31. |
- Nordenström, Andreas, 1991-, et al.
(författare)
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Neutron reflectivity for testing graphene oxide films sorption of EuCl3 in ethanol solution
- 2024
-
Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 261:6
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectivity (NR) was used to study the sorption of Eu(III) by graphene oxide (GO) films exposed to ethanol solution of EuCl3. Most of the earlier sorption studies have been performed using GO dispersed in solution. In contrast, layered structure of GO films imposes limitations for penetration of ions between individual sheets. The analysis of NR data recorded before and after sorption under vacuum demonstrates an increase of GO film thickness due to sorption by 35–40%. The characterization of chemical state of Eu(III) sorbed by GO films by X-ray absorption near-edge structure (XANES) in high-energy resolution fluorescence detection (HERFD) method at the Eu L3 edge reveals that it remains the same as in anhydrous EuCl3. Analysis of all collected data including reference experiments with bulk GO samples allows to conclude that EuCl3 penetrates into GO interlayers with ethanol solution and remains trapped in interlayers after evaporation of ethanol. Sorption of EuCl3 results in nearly complete amorphization of film and likely formation of voids, thus making NR models based on specific volume of unit cell not valid for quantitative evaluation of Eu sorption. Limitations of NR method must be taken into account in future studies of sorption by thin films.
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| 32. |
- Nordenström, Andreas, 1991-
(författare)
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Properties and applications of materials based on graphite oxide
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Graphite oxide (GO) is a hydrophilic, layered material prepared by oxidation of graphite. In the first part of this thesis, we studied materials produced from GO by intercalation and functionalization. The second part of the thesis was focused on supercapacitor applications of high surface area carbons prepared from GO using chemical activation. A detailed study of acetylated GO (AcGO) was performed to verify structure and properties of this material. Reports from 1960’s suggested that AcGO has “pillared” structure. Our analysis showed that the AcGO demonstrates expanded structure due to acetylation but exhibits negligible specific surface area and should not be considered as a pillared material. Pillared reduced GO (prGO) was prepared by applying mild annealing to GO material pillared with tetrapod-shaped amine molecules. PrGO showed relatively high surface area due to remaining pillaring molecules in the structure. The prGO is hydrophobic and exhibits 100x improved conductivity compared to precursor. PrGO is one of few true pillared structures reported in literature so far, and the first ever prepared starting from pillared GO.We also investigated the sorption of common dyes, methylene blue (MB), rose bengal (RB) and crystal violet (CV), by multilayered graphene oxide materials. We found that MB dissolved in ethanol intercalates the GO structure, as evidenced by significant expansion of inter-layer distance, and increase in weight due to sorption. In contrast to MB, GO is not easily intercalated by CV and RB dyes. We believe that the flat MB molecule shape allows easier insertion between GO layers compared to twisted and non-flat CV and RB molecules. Our results suggest that penetration into GO inter-layers depends not only on the size of molecules, but also on the shape.Temperature dependent study of structures formed by Brodie GO (BGO) in liquid alkyl alcohols was performed for a set starting from undecyl alcohol (no. of C=11) and up to behenyl alcohol (no. of C=22). We found that BGO exhibits strong swelling in all molten alcohols in this set. Heating just above the melting point of alcohol results in expansion of inter-layer distance of GO due to intercalation of two layers of alcohol molecules in orientation perpendicular to graphene oxide planes (α-phase). Further heating of α-phase results in incongruent melting and formation of new phase with significantly smaller inter-layer distance and amount of intercalated alcohol (β-phase). The transition from α-to β-phase is distinctly different compared to swelling transitions previously observed for BGO in smaller alcohols (no. of C<10). A more detailed study of the BGO-C16 system revealed that β-phase has structure with alcohol molecules forming layers mostly in parallel to graphene oxide orientation.In the second part of this thesis we studied activated reduced GO (a-rGO) as electrode material in supercapacitors. A-rGO is a high surface material (~3000 m2g-1) obtained by KOH activation of rGO. We developed formulations for stable aqueous dispersions of a-rGO optimized for preparation of electrodes by semi-industrial spray-gun deposition. The electrodes prepared by spray deposition showed energy storage parameters only slightly lower compared to lab scale blade-deposited electrodes. Spray-gun deposition might provide significant advantage for industry over conventional methods to prepare electrodes from a-rGO. We also applied KOH activation procedure, optimized for producing high surface area a-rGO, to biochar prepared from pine cones. Using this cost free “waste” picked up in Umeå region forest we produced high quality activated carbon very similar to a-rGO in terms of structure, pore size and surface area. Overall, the energy storage parameters of electrodes prepared using the activated carbon from pine cones were on the same level as a-rGO electrodes, which are produced by a lot more complex and expensive chemical treatments.
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| 33. |
- Nordenström, Andreas, et al.
(författare)
-
Thermally reduced pillared GO with precisely defined slit pore size
- 2020
-
Ingår i: RSC Advances. - 2046-2069. ; 10:12, s. 6831-6839
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide (GO) pillared with tetrakis(4-aminophenyl)methane (TKAM) molecules shows a narrow distribution of pore size, relatively high specific surface area, but it is hydrophilic and electrically not conductive. Analysis of XRD, N2 sorption, XPS, TGA and FTIR data proved that the pillared structure and relatively high surface area (∼350 m2 g−1) are preserved even after thermal reduction of GO pillared with TKAM molecules. Unlike many other organic pillaring molecules, TKAM is stable at temperatures above the point of GO thermal reduction, as demonstrated by TGA. Therefore, gentle annealing results in the formation of reduced graphene oxide (rGO) pillared with TKAM molecules. The TKAM pillared reduced graphene oxide (PrGO/TKAM) is less hydrophilic as found using dynamic vapor sorption (DVS) and more electrically conductive compared to pillared GO, but preserves an increased interlayer-distance of about 12 Å (compared to ∼7.5 Å in pristine GO). Thus we provide one of the first examples of porous rGO pillared with organic molecules and well-defined size of hydrophobic slit pores. Analysis of pore size distribution using nitrogen sorption isotherms demonstrates a single peak for pore size of ∼7 Å, which makes PrGO/TKAM rather promising for membrane and molecular sieve applications.
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| 34. |
- Rebrikova, Anastasiya T., et al.
(författare)
-
Swollen Structures of Brodie Graphite Oxide as Solid Solvates
- 2020
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:42, s. 23410-23418
-
Tidskriftsartikel (refereegranskat)abstract
- Swelling of Brodie graphite oxide (B-GO) was studied for a series of normal alcohols from methanol to 1-nonanol. Isopiestic, X-ray diffraction (XRD), thermogravimetric, and differential scanning calorimetry data demonstrated that sorption of polar liquids into GO lamellas formed the set of regular swollen structures, simple binary "solid solvates", characterized by the distance between the GO planes and the value of sorption. Temperature-composition behavior of the swollen structures was adequately described by conventional binary phase diagrams. Phase transformation of the low-temperature swollen structure of B-GO with 1-nonanol gave a clear example of incongruent melting transition typical for the binary solvates. A discreet set of the interplane distances observed by XRD and the stepwise equilibrium desorption pointed to the layered arrangement of solvent molecules in the swollen structures. The swollen structures with one to five parallel layers were observed for a series of normal alcohols with B-GO. The average volume of one layer, 0.36 +/- 0.06 cm(3) g(-1) B-GO, was almost the same for rather different organic liquids and was possibly restricted by the internal geometry of B-GO. This internal volume available for the sorption of the first layer was reasonably estimated from geometrical parameters of B-GO.
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| 35. |
- Sandström, Robin, et al.
(författare)
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Evaluation of Fluorine and Sulfonic Acid Co-functionalized Graphene Oxide Membranes in Hydrogen Proton Exchange Membrane Fuel Cell Conditions
- 2019
-
Ingår i: Sustainable Energy & Fuels. - : Royal Society of Medicine Press. - 2398-4902. ; 3:7, s. 1790-1798
-
Tidskriftsartikel (refereegranskat)abstract
- The use of graphene oxide (GO) based membranes consisting of self-assembled flakes with a lamellar structure represents an intriguing strategy to spatially separate reactants while facilitating proton transport in proton exchange membranes (PEM). Here we chemically modify GO to evaluate the role of fluorine and sulfonic acid groups on the performance of H2/O2 based PEM fuel cells. Mild fluorination is achieved by the presence of hydrogen fluoride during oxidation and subsequent sulfonation resulted in fluorine and SO3- co-functionalized GO. Membrane electrode assembly performance in low temperature and moderate humidity conditions suggested that both functional groups contribute to reduced H2 crossover compared to appropriate reference membranes. Moreover, fluorine groups promoted an enhanced hydrolytic stability while contributing to prevent structural degradation after constant potential experiments whereas sulfonic acid demonstrated a stabilizing effect by preserving proton conductivity.
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| 36. |
- Shayimova, Julia, et al.
(författare)
-
Carboxyl groups do not play the major role in binding metal cations by graphene oxide
- 2021
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:32, s. 17430-17439
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the chemical interactions of Mn2+ ions with graphene oxides, prepared by Hummers' (HGO) and Brodie's (BGO) methods in aqueous solutions by means of NMR relaxation. Carboxyl groups, which are always present in HGO in significant quantities, are often considered as the main binding sites for metal ions. Here we demonstrate that metal ions are bound efficiently by BGO, containing a negligibly small quantity of carboxyl groups. The difference in the shape of the relaxation curves is due mostly to the difference in the solubility and exfoliation degree of the two GO samples in aqueous media. HGO binds Mn2+ in the broad pH range, including highly acidic solutions, while BGO binds only at pH > 6, since it is not dispersible in water at lower pH values. The ability of BGO to chemically bind Mn2+ despite lacking sulfate and carboxyl groups, coupled with our earlier published findings, strongly suggests that carboxyl groups do not play the main role in binding metal ions by GO, as is commonly believed. We propose that metal ions initiate a significant transformation in the GO structure to attain the most efficient coordination of metal ions. This reorganization might involve the metal cation induced C-C bond cleavage with the formation of enols at the newly formed edges.
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| 37. |
- Sun, Jinhua, 1987, et al.
(författare)
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Covalent Organic Framework (COF-1) under High Pressure
- 2020
-
Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 59:3, s. 1087-1092
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Tidskriftsartikel (refereegranskat)abstract
- COF-1 has a structure with rigid 2D layers composed of benzene and B3O3 rings and weak van der Waals bonding between the layers. The as-synthesized COF-1 structure contains pores occupied by solvent molecules. A high surface area empty-pore structure is obtained after vacuum annealing. High-pressure XRD and Raman experiments with mesitylene-filled (COF-1-M) and empty-pore COF-1 demonstrate partial amorphization and collapse of the framework structure above 12–15 GPa. The ambient pressure structure of COF-1-M can be reversibly recovered after compression up to 10–15 GPa. Remarkable stability of highly porous COF-1 structure at pressures at least up to 10 GPa is found even for the empty-pore structure. The bulk modulus of the COF-1 structure (11.2(5) GPa) and linear incompressibilities (k[100]=111(5) GPa, k[001]=15.0(5) GPa) were evaluated from the analysis of XRD data and cross-checked against first-principles calculations. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 38. |
- Sun, Jinhua, 1987, et al.
(författare)
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Critical Role of Functional Groups Containing N, S, and O on Graphene Surface for Stable and Fast Charging Li-S Batteries
- 2021
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 17:17
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Tidskriftsartikel (refereegranskat)abstract
- Lithium‐sulfur (Li‐S) batteries are considered one of the most promising energy storage technologies, possibly replacing the state‐of‐the‐art lithium‐ion (Li‐ion) batteries owing to their high energy density, low cost, and eco‐compatibility. However, the migration of high‐order lithium polysulfides (LiPs) to the lithium surface and the sluggish electrochemical kinetics pose challenges to their commercialization. The interactions between the cathode and LiPs can be enhanced by the doping of the carbon host with heteroatoms, however with relatively low doping content (<10%) in the bulk of the carbon, which can hardly interact with LiPs at the host surface. In this study, the grafting of versatile functional groups with designable properties (e.g., catalytic effects) directly on the surface of the carbon host is proposed to enhance interactions with LiPs. As model systems, benzene groups containing N/O and S/O atoms are vertically grafted and uniformly distributed on the surface of expanded reduced graphene oxide, fostering a stable interface between the cathode and LiPs. The combination of experiments and density functional theory calculations demonstrate improvements in chemical interactions between graphene and LiPs, with an enhancement in the electrochemical kinetics, power, and energy densities.
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| 39. |
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