| 1. |
- Beladi-Mousavi, S. M., et al.
(författare)
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Poly(vinylferrocene)-Reduced Graphene Oxide as a High Power/High Capacity Cathodic Battery Material
- 2016
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 6:12
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Tidskriftsartikel (refereegranskat)abstract
- The preparation and performance of a new cathodic battery material consisting of a composite of poly(vinylferrocene) (PVFc) and reduced graphene oxide (rGO) is described. It shows the highest charge/discharge efficiency (at a rate of 100 A g(-1)) ever reported for ferrocene-polymer materials. The composite allows for specific capacities up to 0.21 mAh cm(-2) (770 mC cm(-2), 29 mu m film thickness) at a specific capacity density of 114 mAh g(-1) and less than 5% performance decay over 300 cycles. The composite material is binder free and the charge storing PVFc accounts for 88% of the total weight of the cathodic material. The superb performance is based on (i) perfect self-assembling of oxidized PVFc on graphene oxide (GO) leading to PVFc@GO, (ii) its stepwise (n steps) transfer onto a current collector (CC) (PVFc@GO)(n) @CC (n = drop casting steps), and (iii) the efficient electrochemical transformation of GO into rGO in the composite using viologen as homogeneous electrocatalyst. The self-assembling step is analyzed by zeta potential and atomic force microscopy (AFM) studies, demonstrating heavy ferrocene loading on GO and a mesoporous composite structure, respectively. Complete GO/rGO transition and quantitative ClO4- on breathing of the composite are found by electrochemical quartz crystal microbalance and by electrochemical AFM.
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| 2. |
- Brülls, Steffen, 1991, et al.
(författare)
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Bonding between π-Conjugated Polycations and Monolayer Graphene: Decisive Role of Anions
- 2023
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:4, s. 1917-28
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Tidskriftsartikel (refereegranskat)abstract
- Functionalization and precise modulation of the electronic properties of graphene are key processes in the development of new applications of this promising material. This study examines the potential of using organic polycations as p-dopants and/or anchoring motifs for non-covalent functionalization. A library of hybrid materials was prepared through wet-chemical non-covalent functionalization. Both chemical vapor deposition graphene and reduced graphene oxide were functionalized with a series of neutral and polycationic benzimidazole-based systems. We report on how both the number of anions and the size, shape, and magnitude of the positive charge of the benzimidazole-based systems cooperatively affect the redox properties as well as the affinity for and the nature of bonding to graphene. The redox properties of the benzimidazole-based systems were studied by cyclic voltammetry. The functionalized graphene materials were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Density functional theory calculations were performed to make contact between the experimental results obtained for molecular samples and hybrid materials. No universal dependence of the binding affinity on a single parameter, such as the amount of positive charge or the size of the system, was found. Instead, the cooperative effect of the three-dimensional structure of the benzimidazole-based systems and the number of anions was found to play a pivotal role. Together, these parameters determine the degree of partial electron sharing and magnitude of dispersion forces involved in the binding of members of this family of benzimidazole-based systems to graphene.
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| 3. |
- Butz, B., et al.
(författare)
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Highly Intact and Pure Oxo-Functionalized Graphene: Synthesis and Electron-Beam-Induced Reduction
- 2016
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Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:51, s. 15771-15774
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Tidskriftsartikel (refereegranskat)abstract
- Controlling the chemistry of graphene is necessary to enable applications in materials and life sciences. Research beyond graphene oxide is targeted to avoid the highly defective character of the carbon framework. Herein, we show how to optimize the synthesis of oxo-functionalized graphene (oxo-G) to prepare high-quality monolayer flakes that even allow for direct transmission electron microscopy investigation at atomic resolution (HRTEM). The role of undesired residuals is addressed and sources are eliminated. HRTEM provides clear evidence for the exceptional integrity of the carbon framework of such oxo-G sheets. The patchy distribution of oxo-functionality on the nm-scale, observed on our highly clean oxo-G sheets, corroborates theoretical predictions. Moreover, defined electron-beam irradiation facilitates gentle de-functionalization of oxo-G sheets, a new route towards clean graphene, which is a breakthrough for localized graphene chemistry.
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| 4. |
- Cantatore, Valentina, 1986, et al.
(författare)
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Design strategy of a graphene based bio-sensor for glucose
- 2018
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 137, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- A novel graphene-based glucose sensor-design is formulated and explored in silico. An ad hoc host molecule is tailored to bind to glucose by multiple hydrogen bonds. A pyridinic core is chosen for this receptor in order to allow for “socket-plug” dative bonding to boron sites of boron doped graphene. The modeling employs DFT (Density Functional Theory) together with an effective aqueous environment to take into account the solvation effect. High selectivity is demonstrated for the suggested host molecule towards glucose as compared to other possible competitors in blood such as fructose, biotin and ascorbic acid. A route to achieve improved sensitivity, exploiting the hydrophilic/hydrophobic properties of the host + glucose system for enhanced selective binding to the hydrophobic boron doped graphene support is discussed.
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| 5. |
- Chen, Haiwei, et al.
(författare)
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Extending the environmental lifetime of unpackaged perovskite solar cells through interfacial design
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:30, s. 11604-11610
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Tidskriftsartikel (refereegranskat)abstract
- Solution-processed oxo-functionalized graphene (oxo-G1) is employed to substitute hydrophilic PEDOT:PSS as an anode interfacial layer for perovskite solar cells. The resulting devices exhibit a reasonably high power conversion efficiency (PCE) of 15.2% in the planar inverted architecture with oxo-G1 as a hole transporting material (HTM), and most importantly, deploy the full open-circuit voltage (Voc) of up to 1.1 V. Moreover, oxo-G1 effectively slows down the ingress of water vapor into the device stack resulting in significantly enhanced environmental stability of unpackaged cells under illumination with 80% of the initial PCE being reached after 500 h. Without encapsulation, ∼60% of the initial PCE is retained after ∼1000 h of light soaking under 0.5 sun and ambient conditions maintaining the temperature beneath 30 °C. Moreover, the unsealed perovskite device retains 92% of its initial PCE after about 1900 h under ambient conditions and in the dark. Our results underpin that controlling water diffusion into perovskite cells through advanced interface engineering is a crucial step towards prolonged environmental stability.
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| 6. |
- Dimiev, Ayrat M., et al.
(författare)
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Graphene Oxide: Fundamentals and Applications
- 2016
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Due to its unique properties, graphene oxide has become one of the most studied materials of the last decade and a great variety of applications have been reported in areas such as sensors, catalysis and biomedical applications. This comprehensive volume systematically describes the fundamental aspects and applications of graphene oxide. The book is designed as an introduction to the topic, so each chapter begins with a discussion on fundamental concepts, then proceeds to review and summarize recent advances in the field. Divided into two parts, the first part covers fundamental aspects of graphene oxide and includes chapters on formation and chemical structure, characterization methods, reduction methods, rheology and optical properties of graphene oxide solutions. Part Two covers numerous graphene oxide applications including field effect transistors, transparent conductive films, sensors, energy harvesting and storage, membranes, composite materials, catalysis and biomedical applications. In each case the differences and advantages of graphene oxide over its non-oxidised counterpart are discussed. The book concludes with a chapter on the challenges of industrial-scale graphene oxide production. Graphene Oxide: Fundamentals and Applications is a valuable reference for academic researchers, and industry scientists interested in graphene oxide, graphene and other carbon materials. © 2017 John Wiley & Sons, Ltd. All rights reserved.
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| 7. |
- Eigler, Siegfried, 1978, et al.
(författare)
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Characterization Techniques
- 2016
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Ingår i: Graphene Oxide: Fundamentals and Applications. - Chichester, UK : John Wiley & Sons, Ltd. - 9781119069447 ; , s. 85-120
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Solid-state nuclear magnetic resonance spectroscopy (SSNMR) not only is a reliable tool to determine the structure of organic molecular compounds, but also has developed into a suitable technique to characterize graphene oxide (GO) and has the potential to make structural analysis of GO derivatives possible. Common spectroscopic techniques are introduced, and the advances of SSNMR for analyzing the structure of GO are summarized. Finally, the prospects of SSNMR are discussed. Fourier-transform infrared (FTIR) spectroscopy is a simple and robust method to analyze GO. It is not very representative, since absorption bands from the fingerprint region are almost impossible to reveal due to the overlapping of numerous signals. Also, FTIR is the most commonly misinterpreted method among all those used for GO characterization. Nevertheless, FTIR has played an important role in revealing some specific functional groups. Several real examples are discussed. X-ray photoelectron spectroscopy (XPS) is a very powerful tool in characterizing GO and its composites. The ability to detect heteroatoms makes XPS superior even when compared to SSNMR. XPS also provides the chemical or electronic state for each element. With respect to GO, XPS provides not only the elemental content, but also the nature and the relative content of the functional groups. Raman spectroscopy is a reliable tool to determine and visualize the heterogeneity of graphene-family materials, including single-layer graphene and some specific types of reduced graphene oxide (RGO). It is a highly sensitive method to determine and quantify the amount of defects in graphene. Here, the basic principles of Raman spectroscopy and the basic interpretation of spectra are given. In addition, using an example, we show how to perform statistical analysis and how to use these data as a basis for statistical Raman microscopy. Being a very powerful tool for characterizing graphene-family materials in general, Raman spectroscopy is not very informative when used on typical GO samples. The density of defects in GO is very high, and Raman spectroscopy cannot resolve different defect densities after some threshold defect density has been reached. The density of defects in typical GO samples is beyond this threshold. However, Raman spectroscopy is a very powerful tool for characterizing some specially prepared low-defect-density RGO samples. Microscopy is broadly used to characterize GO in terms of the flakes' size, thickness, number of layers, etc. High-resolution transmission electron microscopy (HRTEM) has been exploited to reveal the fine chemical structure of GO. For the first time HRTEM has confirmed the two-type-domain structure of GO. In this chapter, as well as HRTEM, the following microscopy methods are reviewed: scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Several examples of how these methods have been used to characterize GO are reviewed.
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| 8. |
- Eigler, Siegfried, 1978
(författare)
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Controlled Chemistry Approach to the Oxo-Functionalization of Graphene
- 2016
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 22:21, s. 7012-7027
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Forskningsöversikt (refereegranskat)abstract
- Graphene is the best-studied 2D material available. However, its production is still challenging and the quality depends on the preparation procedure. Now, more than a decade after the outstanding experiments conducted on graphene, the most successful wet-chemical approach to graphene and functionalized graphene is based on the oxidation of graphite. Graphene oxide has been known for more than a century; however, the structure bears variable large amounts of lattice defects that render the development of a controlled chemistry impossible. The controlled oxo-functionalization of graphene avoids the formation of defects within the ?-framework of carbon atoms, making the synthesis of specific molecular architectures possible. The scope of this review is to introduce the field of oxo-functionalizing graphene. In particular, the differences between GO and oxo-functionalized graphene are described in detail. Moreover analytical methods that allow determining lattice defects and functional groups are introduced followed by summarizing the current state of controlled oxo-functionalization of graphene.
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| 9. |
- Eigler, Siegfried, 1978, et al.
(författare)
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Functionalization and Reduction of Graphene Oxide
- 2016
-
Ingår i: Graphene Oxide: Fundamentals and Applications. - Chichester, UK : John Wiley & Sons, Ltd. - 9781119069447 ; , s. 175-229
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The chemistry of graphene oxide (GO) is a growing field of research. The modification of the surface properties of GO is the main goal in application-driven research. Successful functionalization protocols must be interpreted in accordance with the chemical structure of the original GO, and therefore, in this chapter, crucial aspects of the chemical structure of GO are introduced first. Next, the thermal and chemical stability of GO is reviewed, followed by introducing wet-chemical non-covalent and covalent reaction principles. The covalent functionalization of GO requires special attention. When chemical reaction principles, well known from organic chemistry, are applied to GO, it remains challenging to prove the successful accomplishment of reactions by analyzing the as-modified GO product. We pay special attention to the reactivity of the edges of defects and provide alternative explanations for interpreting experimental results, where necessary. Next, chemical reduction methods are summarized; special accent is placed on differentiating true chemical reduction from so-called "thermal reduction". Several examples for the functionalization of reduced graphene oxide (RGO) are considered next. While discussing GO chemical properties, in parallel with typical GO, we discuss these properties for the oxo-functionalized graphene (oxo-G1), a type of GO with very low density of structural defects. This sheds additional light on the role of defects in GO chemistry. Finally, additional properties of oxo-G1 are introduced. Oxo-G1 can act as a compound that enables the controlled chemistry for the design and synthesis of functional materials and devices.
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| 10. |
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| 11. |
- Eigler, Siegfried, 1978
(författare)
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Graphene Synthesis
- 2016
-
Ingår i: Graphene Technology: From Laboratory to Fabrication. - Weinheim, Germany : Wiley-VCH Verlag GmbH & Co. KGaA. - 9783527687541 ; , s. 19-61
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Methods for the synthesis of graphene are highlighted in this chapter. Either graphite or small molecules can be used as the source of graphene. Wet-chemical methods for the direct delamination of graphene starting from graphite will be highlighted, as well as methods that involve chemical functionalization of graphene layers of graphite. Especially, the chemical functionalization can provide solution processable precursors to graphene that allow the integration of graphene in matrices or devices. However, synthesis of graphene from macromolecules remains a challenge, although there is promising progress. Further, the confusion in the literature about the term graphene, few-layer graphene, and graphite is clarified. Therefore, information will be given that makes it possible to distinguish between these. Furthermore, emphasis is laid on the polydispersity of graphene in many terms, such as the size of flakes or the density of defects.
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| 12. |
- Feicht, Patrick, et al.
(författare)
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Systematic evaluation of different types of graphene oxide in respect to variations in their in-plane modulus
- 2017
-
Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 114, s. 700-705
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Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide samples prepared in various laboratories following a diversity of synthesis protocols based on Brodie's (BGO) and Hummers/Offeman's (HGO) methods were compared in respect of their in plane moduli. A simple wrinkling method allowed for a spatial resolution <1.5 pm by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600 GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200 GPa for HGO types. This would suggest that there are no two equal GO samples and GO should not be regarded a compound but rather a class of materials with very variable physical properties. While large differences between Brodie's and Hummers/Offeman's types might have been expected, even within the group of Hummers/Offeman's types pronounced differences are observed that, based on C-13 solid-state NMR, were related to over-functionalization versus over-oxidation.
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| 13. |
- Feierabend, Maja, 1990, et al.
(författare)
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Molecule signatures in photoluminescence spectra of transition metal dichalcogenides
- 2018
-
Ingår i: Physical Review Materials. - 2475-9953. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Monolayer transition metal dichalcogenides (TMDs) show an optimal surface-to-volume ratio and are thus promising candidates for novel molecule sensor devices. It was recently predicted that a certain class of molecules exhibiting a large dipole moment can be detected through the activation of optically inaccessible (dark) excitonic states in absorption spectra of tungsten-based TMDs. In this paper, we investigate the molecule signatures in photoluminescence spectra in dependence of a number of different experimentally accessible quantities, such as excitation density, temperature, as well as molecular characteristics including the dipole moment and its orientation, molecule-TMD distance, molecular coverage, and distribution. We show that under certain optimal conditions even room-temperature detection of molecules can be achieved.
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| 14. |
- Flyunt, R., et al.
(författare)
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High quality reduced graphene oxide flakes by fast kinetically controlled and clean indirect UV-induced radical reduction
- 2016
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 8:14, s. 7572-7579
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Tidskriftsartikel (refereegranskat)abstract
- This work highlights a surprisingly simple and kinetically controlled highly efficient indirect method for the production of high quality reduced graphene oxide (rGO) flakes via UV irradiation of aqueous dispersions of graphene oxide (GO), in which the GO is not excited directly. While the direct photoexcitation of aqueous GO (when GO is the only light-absorbing component) takes several hours of reaction time at ambient temperature (4 h) leading only to a partial GO reduction, the addition of small amounts of isopropanol and acetone (2% and 1%) leads to a dramatically shortened reaction time by more than two orders of magnitude (2 min) and a very efficient and soft reduction of graphene oxide. This method avoids the formation of non-volatile species and in turn contamination of the produced rGO and it is based on the highly efficient generation of reducing carbon centered isopropanol radicals via the reaction of triplet acetone with isopropanol. While the direct photolysis of GO dispersions easily leads to degradation of the carbon lattice of GO and thus to a relatively low electric conductivity of the films of flakes, our indirect photoreduction of GO instead largely avoids the formation of defects, keeping the carbon lattice intact. Mechanisms of the direct and indirect photoreduction of GO have been elucidated and compared. Raman spectroscopy, XPS and conductivity measurements prove the efficiency of the indirect photoreduction in comparison with the state-of-the-art reduction method for GO (hydriodic acid/trifluoroacetic acid). The rapid reduction times and water solvent containing only small amounts of isopropanol and acetone may allow easy process up-scaling for technical applications and low-energy consumption.
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| 15. |
- Kahnt, Axel, 1980, et al.
(författare)
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Shedding light on the soft and efficient free radical induced reduction of graphene oxide: Hidden mechanisms and energetics
- 2016
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:73, s. 68835-68845
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Tidskriftsartikel (refereegranskat)abstract
- Reduction of graphene oxide (GO) in aqueous dispersions by strongly reducing free radicals has recently been identified to be a very powerful approach, because functional groups are removed softly but efficiently, and non-volatile impurities as well as defects are largely avoided. However, the reaction mechanisms remained somewhat speculative. Recently we showed that GO can be efficiently reduced in water by indirect photoreduction mediated by (CH3)2C(OH) radicals generated via the reaction of triplet acetone with isopropanol. Those radicals efficiently defunctionalize oxo-groups of GO forming the carbon lattice without generating additional defects. In this comprehensive study we shed more light on the reaction mechanism of reduction of GO by H, CO2 -, (CH3)2C(OH) and CH3CH(OH) by combining pulsed radiolysis and determine its overall energetics via quantum-chemical calculations. In time-dependent experiments mechanistic insights have been obtained and unknown intermediates have been discovered. Moreover, different reduction mechanisms, such as radical addition, electron-transfer, concerted water elimination and HCO3 - elimination are identified. Here we show that all mechanisms lead to sp2-carbon formation and therefore high quality graphene by reductive defunctionalization.
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| 16. |
- Naumov, A., et al.
(författare)
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Graphene Oxide: A One- versus Two-Component Material
- 2016
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 138:36, s. 11445-11448
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Tidskriftsartikel (refereegranskat)abstract
- The structure of graphene oxide (GO) is a matter of discussion. While established GO models are based on functional groups attached to the carbon framework, another frequently used model claims that GO consists of two components, a slightly oxidized graphene core and highly oxidized molecular species, oxidative debris (OD), adsorbed on it. Those adsorbents are claimed to be the origin for optical properties of GO. Here, we examine this model by preparing GO with a low degree of functionalization, combining it with OD and studying the optical properties of both components and their combination in an artificial two-component system. The analyses of absorption and emission spectra as well as lifetime measurements reveal that properties of the combined system are,distinctly different from those of GO. That confirms structural models of GO as a separate oxygenated hexagonal carbon framework with optical properties governed by its internal structure rather than the presence of OD: Understanding the structure of GO allows further reliable interpretation of its optical and electronic properties and enables controlled processing of GO.
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| 17. |
- Pieper, H., et al.
(författare)
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Oxo-Functionalized Graphene as a Cell Membrane Carrier of Nucleic Acid Probes Controlled by Aging
- 2016
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 22:43, s. 15389-15395
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Tidskriftsartikel (refereegranskat)abstract
- We applied a fluorescein-containing oligonucleotide ( ON) to probe surface properties of oxidized graphene ( oxo-G) and observed that graphene-like patches are formed upon aging of oxo-G, indicated by enhanced probe binding and by FTIR spectroscopic analysis. By using a recently developed fluorogenic endoperoxide ( EP) probe, we confirmed that during the aging process the amount of EPs on the oxo-G surface is reduced. Furthermore, aging was found to strongly affect cell membrane carrier properties of this material. In particular, freshly prepared oxo-G does not act as a carrier, whereas oxo-G aged for 28 days at 4 degrees C is an excellent carrier. Based on these data we prepared an optimized oxo-G, which has a low-defect density, binds ONs, is not toxic, and acts as cell membrane carrier. We successfully applied this material to design fluorogenic probes of representative intracellular nucleic acids 28S rRNA and beta-actin-mRNA. The results will help to standardize oxidized graphene derivatives for biomedical and bioanalytical applications.
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| 18. |
- Rietsch, Philipp, et al.
(författare)
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Fluorescence of a chiral pentaphene derivative derived from the hexabenzocoronene Motif
- 2019
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 55:71, s. 10515-10518
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Tidskriftsartikel (refereegranskat)abstract
- A new fluorescent pentaphene derivative is presented that differs from hexabenzocoronene (HBC) by one carbon atom in the basal plane skeleton. A 500% increased fluorescence quantum yield is measured compared to the HBC derivative. The pentaphene compound, obtained by a modified Scholl oxidation, is also emissive in the solid-state, due to the packing motif in the crystal.
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| 19. |
- Schindler, Severin, 1987, et al.
(författare)
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Focused electron beam based direct-write fabrication of graphene and amorphous carbon from oxo-functionalized graphene on silicon dioxide
- 2017
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 19:4, s. 2683-2686
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Tidskriftsartikel (refereegranskat)abstract
- Controlled patterning of graphene is an important task towards device fabrication and thus is the focus of current research activities. Graphene oxide (GO) is a solution-processible precursor of graphene. It can be patterned by thermal processing. However, thermal processing of GO leads to decomposition and CO2 formation. Alternatively, focused electron beam induced processing (FEBIP) techniques can be used to pattern graphene with high spatial resolution. Based on this approach, we explore FEBIP of GO deposited on SiO2. Using oxo-functionalized graphene (oxo-G) with an in-plane lattice defect density of 1% we are able to image the electron beam-induced effects by scanning Raman microscopy for the first time. Depending on electron energy (2-30 keV) and doses (50-800 mC m(-2)) either reduction of GO or formation of permanent lattice defects occurs. This result reflects a step towards controlled FEBIP processing of oxo-G.
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