TY - JOUR A1 - Unger, Wolfgang A1 - Khani, M. A1 - Mehdipour, E. A1 - Faghani, A. A1 - Guday, G. A1 - Donskyi, Ievgen A1 - Haag, R. A1 - Adeli, M. T1 - Preparation of graphene oxide by cyanuric chloride as an effective and non-corrosive oxidizing agent N2 - In this work, we report a new method for the synthesis of graphene oxide (GO) using cyanuric chloride as a non-corrosive oxidizing agent. The mild conditions, simple purification, and scalability of this method are significant advantages over common approaches in which harsh oxidizing agents are used. Moreover, a major drawback with the Hummers' method, the production of toxic gases, is not an issue with this process. This method is a safe and large-scale alternative for the production of GO under mild conditions. KW - Graphene oxide KW - Synthesis KW - XPS KW - AFM KW - IR KW - TGA PY - 2016 DO - https://doi.org/10.1039/c6ra23702a SN - 2046-2069 VL - 6 IS - 116 SP - 115055 EP - 115057 PB - The Royal Society of Chemistry AN - OPUS4-39111 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kaur, I. A1 - Ellis, L.-J. A1 - Romer, I. A1 - Tantra, R. A1 - Carriere, M. A1 - Allard, S. A1 - Mayne-L'Hermite, M. A1 - Minelli, C. A1 - Unger, Wolfgang A1 - Potthoff, A. A1 - Rades, Steffi A1 - Valsami-Jones, E. T1 - Dispersion of nanomaterials in aqueous media: Towards protocol optimization N2 - The sonication process is commonly used for de-agglomerating and dispersing nanomaterials in aqueous based media, necessary to improve homogeneity and stability of the suspension. In this study, a systematic step-wise approach is carried out to identify optimal sonication conditions in order to achieve a stable dispersion. This approach has been adopted and shown to be suitable for several nanomaterials (cerium oxide, zinc oxide, and carbon nanotubes) dispersed in deionized (DI) water. However, with any change in either the nanomaterial type or dispersing medium, there needs to be optimization of the basic protocol by adjusting various factors such as sonication time, power, and sonicator type as well as temperature rise during the process. The approach records the dispersion process in detail. This is necessary to identify the time Points as well as other above-mentioned conditions during the sonication process in which there may be undesirable changes, such as damage to the particle surface thus affecting surface properties. Our goal is to offer a harmonized approach that can control the Quality of the final, produced dispersion. Such a guideline is instrumental in ensuring dispersion quality repeatability in the nanoscience community, particularly in the field of nanotoxicology. KW - Dispersion of nanomaterials KW - Aqueous media KW - Protocol development PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-435886 UR - https://www.jove.com/video/56074 DO - https://doi.org/10.3791/56074 SN - 1940-087X IS - 130 SP - e560741, 1 EP - e560741, 23 PB - MyJove Corp. CY - Cambridge, MA, USA AN - OPUS4-43588 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Unger, Wolfgang A1 - Pelster, A. A1 - Tyler, B.J. A1 - Kösgen, M. A1 - Kassenböhmer, R. A1 - Peterson, R.E. A1 - Stöver, M. A1 - Arlinghaus, H. F. T1 - Improved 3D-imaging of a sirolimus/probucol eluting stent coating using laser postionization secondary neutral mass spectrometry and time-of-flight secondary ion mass spectrometry N2 - Implantable drug delivery systems that provide controlled and sustained release of a therapeutic agent are used in a wide variety of applications. Drug eluting stents, which are used to treat coronary artery disease, are among the most widespread of these devices, with an estimated 3x10⁶ implants annually worldwide. Controlling the rate of drug release from these devices relies on precise control of the three dimensional (3D)-distribution of the drug, so methods for measuring this distribution are of great importance. The aims of this work were to determine how 3D-imaging of polymer-free sirolimus/probucol drug eluting stent coatings could be improved through the use of laser postionization secondary neutral mass spectrometry (Laser- SNMS) and Ar cluster sputtering with time-of-flight secondary ion mass spectrometry (ToF-SIMS) and to optimize conditions for this analysis. In this study, 3D-imaging of a sirolimus/probucol dual drug eluting stent has been investigated using Laser-SNMS and ToF-SIMS. Laser-SNMS studies of pure sirolimus and probucol were undertaken using 30 keV Bi₃⁺ primary Ions and a 157 nm excimer postionization laser. Under optimal conditions, a greater than 100-fold increase in detected ion yield was observed for Laser-SNMS when compared to ToF-SIMS, although ToF-SIMS provided equal or greater yields for higher mass characteristic ions. Although the optimal laser power density for detecting probucol (5x10⁶W/cm²) was significantly lower than the optimum for sirolimus(7x10⁷W/cm²), an intermediate laser power density of 1x10⁷W/cm² was sufficient to allow imaging of both drugs. Using individual selected ion signals, ToF-SIMS and Laser-SNMS produced similar images of the two drug species. When using, however, a multivariate approach (Maximum autocorrelation factors), Laser-SNMS provided significant improvements in image contrast and small area detection when compared to ToF-SIMS. Following optimization of the technique, 3D-images of the dual drug eluting stent coating were obtained using 10 keV Ar₂₀₀₀⁺ cluster ions for sputtering and 30 keV Bi₃⁺ cluster ions for Analysis for both ToF-SIMS and Laser-SNMS. This work demonstrates the advantages of Laser-SNMS for 3D-imaging of pharmaceutical devices, which has not been previously published. Both ToF-SIMS and Laser-SNMS revealed that the outermost surface of the drug eluting coating contained pure sirolimus to a depth of a few tens of nanometers, with a few channels of sirolimus extending to a depth of around 1 lm. Below about 1 lm, the two drugs were uniformly mixed. Using the 10 keV Ar₂₀₀₀⁺ sputter beam, the authors were able to sputter through the complete drug coating (~6 μm) without observing any accumulated damage in the organic layer. The two techniques showed complementary strengths: ToF-SIMS offers faster data collection and better detected ion yield for larger characteristic ions than Laser-SNMS, and Laser-SNMS offers significantly enhanced detected ion yield for smaller fragment ions, allowing for improved Image contrast and Resolution of smaller features. KW - Imaging ToF SIMS KW - Eluting stent PY - 2016 DO - https://doi.org/10.1116/1.4964687 SN - 1934-8630 SN - 1559-4106 VL - 11 IS - 4 SP - 041001-1 EP - 041001-10 PB - AVS: Science & Technology of Materials, Interfaces, and Processing AN - OPUS4-38272 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kovacevic, E. A1 - Strunskus, T. A1 - Santhosh, N. M. A1 - Zavasnik, Z. A1 - Unger, Wolfgang A1 - Sauvage, T. A1 - Ammar, M.-R. A1 - Cvelbar, U. A1 - Berndt, J. T1 - Thermal stability studies of plasma deposited hydrogenated carbon nitride nanostructures N2 - Thermally stable carbon nitride nanostructures have potential applications in surface coatings and automotive fields. In this work, hydrogenated nitrogen-rich carbon nitride nanoparticles have been synthesised via low-pressure low-power plasma vapour deposition technique from methane/Nitrogen gas mixture in a dry process. Thermal stability of the initially prepared hydrogenated carbon Nitride structures has been analysed by near-edge X-ray absorption fine-structure spectroscopy (NEXAFS, insitu), Raman spectroscopy, scanning and transmission electron microscopy and nuclear reaction Analysis (NRA). Thermal studies reveal the excellent stability of the material and nitrogen-rich characteristics (N/C ratio 0.5e0.2 ± 0.01). The obtained results suggest transformation of sp3-rich as-deposited carbon Nitride into sp2-carbon phase with more graphitic features upon thermal annealing. Such in-situ thermal studies of plasma deposited carbon nitrides confirm the conversion of sp3-rich phase to sp2-rich carbon phase at the critical temperature (about 450 K), without a huge loss in nitrogen content. The analysis revealed that the material is a stable plasma deposit after this critical temperature up to >1100 K. Additionally, super hydrophilic carbon nitride nanostructure transforms into a hydrophobic surface after thermal annealing. These thermally stable hydrophobic carbon nitride nanoparticles could be used as a promising material for the hydrophobic coatings for various applications, especially for harsh conditions. KW - Carbon nanoparticles KW - Hydrogenated nanostructures KW - Plasma deposition KW - NEXAFS KW - Thermal annealing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-536163 DO - https://doi.org/10.1016/j.carbon.2021.08.008 SN - 0008-6223 VL - 184 SP - 82 EP - 90 PB - Elsevier Ltd. AN - OPUS4-53616 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -