| 1. |
- Karpov, Sergei, V, et al.
(författare)
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One-Pot Synthesis of Hyperbranched Polyurethane-Triazoles with Controlled Structural, Molecular Weight and Hydrodynamic Characteristics
- 2022
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 14:21
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Tidskriftsartikel (refereegranskat)abstract
- We report a simple and convenient approach to the one-pot synthesis of hyperbranched polyurethane-triazoles with desirable properties. This method is based on in situ generation of an AB(2) + A(2) + B-4 azide-acetylene monomer mixture of known composition, due to quantitative reactions of urethane formation between isophorone diisocyanate (IPDI), 1,3-diazidopropanol-2 (DAPOL) (in the first stage) and propargyl alcohol (in the second stage). The obtained monomer mixture can be involved in step-growth polymerization by azide-alkyne cycloaddition without additional purification (in the third stage). The properties of the resulting polymers should depend on the composition of the monomer mixture. Therefore, first the model revealing the correlation between the monomer composition and the ratio and reactivity of the IPDI and DAPOL active groups is developed and proven. In addition, the newly developed structural kinetic model considering the substitution effect at polyaddition of the complex mixture of monomers allows the prediction of the degree of branching of the target polymer. Based on our calculations, the hyperbranched polyurethane-triazoles were synthesized under found conditions. All products were characterized by H-1 NMR, FTIR, SEC, DLS, DSC, TGA and viscometry methods. It was shown that the degree of branching, molecular weight, intrinsic viscosity, and hydrodynamic radius of the final hyperbranched polymers can be specified at the first stage of one-pot synthesis. The obtained hyperbranched polyurethane-triazoles showed a degree of branching from 0.21 to 0.44 (calculated DB-0.25 and 0.45, respectively).
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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. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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 SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:18, 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 approximate to 7 angstrom (solvent free) up to approximate to 26 angstrom (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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| 10. |
- 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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