| 1. |
- 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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| 2. |
- 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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| 3. |
- 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
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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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| 4. |
- 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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| 5. |
- 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
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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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| 6. |
- Naumov, A., et al.
(författare)
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Graphene Oxide: A One- versus Two-Component Material
- 2016
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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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| 7. |
- 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
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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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