| 1. |
- Brülls, Steffen, 1991, et al.
(author)
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Bonding between π-Conjugated Polycations and Monolayer Graphene: Decisive Role of Anions
- 2023
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:4, s. 1917-28
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Journal article (peer-reviewed)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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| 2. |
- Franco Tabares, Sebastian, et al.
(author)
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Chemical bonding to novel translucent zirconias: A mechanical and molecular investigation
- 2019
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In: Journal of Adhesive Dentistry. - 1757-9988 .- 1461-5185. ; 21:2, s. 107-116
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Journal article (peer-reviewed)abstract
- Purpose: To investigate direct bonding of a 10-MDP-based cement to two novel translucent yttria-stabilized tetragonal zirconia polycrystal ceramics (4Y-TZP, 5Y-TZP) and observe the influence of thermocycling on this bonding. Materials and Methods: Powders of presintered and isostatically pressed 5Y-TZP, 4Y-TZP and 3Y-TZP were mixed with a 10-MDP-based cement (Panavia F 2.0), then stored in deionized water for 48 h at 37°C or thermocycled 10,000 times. Raman spectroscopy and Fourier-transform infrared spectroscopy were used to assess the presence of a functional group (PO32-) that could indicate bonding before and after thermocycling. X-ray photoelectron spectroscopy was used to identify the presence of the suspected Zr-O-P bond in the same specimens. A shearbond strength (SBS) test was conducted based on ISO 29022:2013. Results: Marked peaks assigned to the asymmetric vibrations of the PO32- functional group were observed in both zirconias before and after thermocycling. The binding energy corresponding to Zr-O-P interactions (531.5 eV) was masked by the aluminosilicate in the filler of the cement. Shear bond strengths were approximately 20 MPa after water storage and approximately 6 MPa after thermocycling. No differences were found between the control group and the translucent zirconias. Conclusion: Direct bonding of the 10-MDP-based cement to both 4Y-TZP and 5Y-TZP was highly plausible. Both 4YTZP and 5Y-TZP may be promising alternatives to glass-ceramic restorations.
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| 3. |
- Guo, Zengwei, et al.
(author)
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Nanostructured micro particles as a low-cost and sustainable catalyst in the recycling of PET fiber waste by the glycolysis method
- 2021
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In: Waste Management. - : Elsevier Ltd. - 0956-053X .- 1879-2456. ; 126, s. 559-566
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Journal article (peer-reviewed)abstract
- Magnetic Mg-Al-O@Fe3O4 micro particles were synthesized by coating nanosized Mg-Al double oxides onto Fe3O4 micro particles. The formed hierarchical structure gave Mg-Al-O@Fe3O4 micro particles a high active surface area, which enabled these micro particles to work efficiently as a catalyst in the glycolysis of poly(ethylene terephthalate) (PET). The bis(hydroxyethyl) terephthalate (BHET) yield reached above 80 mol% in the presence of 0.5 wt% of Mg-Al-O@Fe3O4 micro catalyst in the reaction system within 90 min at 240 °C. After the reaction, Mg-Al-O@Fe3O4 micro catalyst was easily retrieved by a magnetic decantation and can be repetitively used for two times with a high catalytic efficiency. After that, the deactivated Mg-Al-O@Fe3O4 micro catalyst can be regenerated by heat treatment. The regenerated Mg-Al-O@Fe3O4 micro catalyst displays a comparable catalytic performance as that of the virgin catalyst. In addition, the Mg-Al double oxides and Fe3O4 micro particles are low-cost and environmentally benign. Therefore, the Mg-Al-O@Fe3O4 micro catalyst may contribute to an economically and environmentally improved large-scale circular recycling of PET fiber waste. © 2021 The Author(s)
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| 4. |
- Knutsson, Pavleta, 1980, et al.
(author)
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Role of potassium in the enhancement of the catalytic activity of calcium oxide towards tar reduction
- 2018
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 229, s. 88-95
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Journal article (peer-reviewed)abstract
- Gasification in fluidized bed systems is considered to be a highly promising alternative for the thermal conversion of biomass. A major challenge for this process is the formed tars, which represent a loss of energy from the product gas and entail additional costs for their removal. Olivine is considered to be the most effective catalytic bed material in terms of its impact on tar levels in the product gas. Additions and modifications to olivine have revealed the potential to enhance its catalytic activity. In the present study, the effect of the addition of K 2 CO 3 to the gasification process on the tar decomposition capability of olivine were evaluated. The effect of the added K 2 CO 3 on the product gas was assessed in the 30-MWth pilot gasification plant GoBiGas. Once dec reases in the tar level were detected, samples of the bed material were extracted from the system and evaluated for morphological and chemical changes related to the observed catalytic effect. SEM-EDX and XPS analyses of the surfaces of the olivine particles indicate that the additive is involved in the formation of mixed oxides of Ca and K within the outermost layer of the olivine particles. DFT modeling showed that the formation of mixed Ca and K oxides changes the oxidation potential of the surface, which may explain the increased activity of ash-coated olivine towards tar reduction.
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| 5. |
- Reddy, Vijeth Venkataram, 1990-, et al.
(author)
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Characterization of subsurface deformation of turned brasses: Lead brass (CuZn39Pb3) and lead free brass (CuZn21Si3P)
- 2019
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In: Journal of Physics: Conference Series. - Bristol, UK : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1183:1
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Conference paper (peer-reviewed)abstract
- © Published under licence by IOP Publishing Ltd. The adverse effects of lead on human health and the recycling problems of copper alloys with lead content has led to the increase in concern for reducing/eliminating the use of lead in brass and other copper alloys. The real challenge prevails in sustainable manufacturing of lead free brass and to maintain as well as control the surface integrity when lead is substituted in the brass with silicon. This article is part of the study that focuses on characterizing the surface integrity of machined lead brass and lead free brass. This paper deals with the study of surface layer characteristics of brass samples, investigating the subsurface deformation influenced by the turning operation. It is important to study the plastic deformation under the machined surface which directly affects the performance of the material on further machining or application. In this study, metallographic investigations are performed on turned samples of lead brass and lead free brass and include comparisons between the study samples based on the plastic deformations quantified by grain orientations and microhardness measurements. The study performed successfully characterizes the subsurface deformation and the results suggest slightly higher subsurface deformation in turned lead brass as compared to lead free brass.
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| 6. |
- Schultheiss, Fredrik, et al.
(author)
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Machinability of CuZn21Si3P brass
- 2016
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In: Materials Science and Technology. - : Informa UK Limited. - 1743-2847 .- 0267-0836. ; 32:17, s. 1744-1750
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Journal article (peer-reviewed)abstract
- New brass alloys containing less or even no lead are being developed, decreasing the environmental impact of the material. One example of an alternative brass is CuZn21Si3P, which contains less than 0.09 wt-% Pb. The research presented in this article evaluates the machinability of CuZn21Si3P as compared to more common, lead-containing free-machining brasses. The results show a marked decrease in the machinability of CuZn21Si3P. When longitudinally turning CuZn21Si3P the cutting tool failed after 142 min of machining. This tool wear was to a large extent remedied through the use of a coating on the cutting tool. CuZn21Si3P appears as a viable substitute for lead-containing brasses, thus implying the possibility for improving the sustainability of modern production.
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| 7. |
- Tam, Eric, 1980, et al.
(author)
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Residual stress analysis of machined lead-free and lead-containing brasses
- 2016
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In: Materials Science and Technology. - : Informa UK Limited. - 1743-2847 .- 0267-0836. ; 32:17, s. 1789-1793
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Journal article (peer-reviewed)abstract
- Legislations demand low lead content in drinking water and low lead leaching from the water supply facilities. Lead-free brass (LFB) can fit in. The benefits of such alloy are acknowledged in both functional and environmental points of view. The relatively high strength of LFB means that the process condition and residual stress generation can be different as compared to the conventional brass. In this study, residual stress generation for a LFB (CuZn21Si3P) and a lead-containing brass (CuZn39Pb3) in a face-turning experiment is studied. Besides stress analysis, structural characterisation is also conducted. Stress generation in the feed and cutting directions of two brasses is depicted. Machined topography is measured to evaluate the surface integrity in connection with the machining conditions.
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| 8. |
- Brülls, Steffen, 1991, et al.
(author)
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Evidence for Electron Transfer between Graphene and Non-Covalently Bound pi-Systems
- 2020
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In: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 26:29, s. 6694-6702
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Journal article (peer-reviewed)abstract
- Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet-chemical non-covalent functionalization of graphene with cationic pi-systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF-SIMS. The charged pi-systems show a p-doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p-doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping.
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| 9. |
- Click, Natalie, et al.
(author)
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Innovative recycling of high purity silver from silicon solar cells by acid leaching and ultrasonication
- 2024
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In: Solar Energy Materials and Solar Cells. - 0927-0248. ; 270
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Journal article (peer-reviewed)abstract
- Precious and scarce silver (Ag) is used as a front electrical contact in silicon solar panels. With massive amounts of solar panel waste coming to end-of-life, it is imperative to recover all the Ag from these modules. In this paper, we propose a novel method to easily reclaim Ag from end-of-life silicon solar cells using low concentration sulfuric acid (H2SO4) leaching followed by ultrasonication. Our process simplifies the Ag recycling procedure by directly recovering the Ag contacts from solar cells, eliminating the need for secondary precipitation/electrodeposition. First, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) was used to study the leaching and ultrasonication process on rejected solar wafers. Next, a solar panel from landfill was heated in a furnace to burn off the polymer encapsulant. The silicon wafers were then collected from the burning process and leached in 2 M H2SO4 at two different shaking speeds for 48 h at room temperature. Finally, the end-of-life silicon wafer pieces were collected, sonicated in water, and then the sonication water was centrifuged to show a proof-of-concept to recover the Ag contacts. Inductively coupled plasma optical emission spectroscopy (ICPOES) is used to monitor dissolved elements in the leachate as a function of time and shaking speed. XPS is used to evaluate the composition of the silicon cell wafer surface before and after H2SO4 leaching. SEM is used to image the recovered Ag contacts morphology and EDX confirms the recovered particles contain high amounts of Ag. A proposed schematic illustrates the authors’ hypothesis for the peeling mechanism.
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| 10. |
- Hammersberg, Peter, 1961, et al.
(author)
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Study of Barkhausen Emission from the Surface Martensite Layer on Induction-hardened Carbon Steel
- 2018
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In: 12th European Conference on Non-Destructive Testing (ECNDT 2018), Gothenburg 2018, June 11-15 (ECNDT 2018). ; 2018:08
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Conference paper (peer-reviewed)abstract
- Induction hardening is one of the finishing processes to improve hardness and wear resistance on steel products by developing a hard martensite-rich surface layer. Non-destructive Barkhausen noise (BN) evaluation is used for quality assurance. While the routine production is set to develop a desirable hardening depth of this specific structure, the variations of microstructure and grain size overlay the outbound results in the assessment and make the interpretation unambiguous. This work correlates the different parameters in BN-signal with the deviations from the targeted martensite by predictive, physical and numerical modelling means.
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