| 1. |
- Abbaszad Rafi, Abdolrahim, et al.
(författare)
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A facile route for concurrent fabrication and surface selective functionalization of cellulose nanofibers by lactic acid mediated catalysis
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322 .- 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Celulose nanofibers are lightweight, recycable, biodegradable, and renewable. Hence, there is a great interest of using them instead of fossil-based components in new materials and biocomposites. In this study, we disclose an environmentally benign (green) one-step reaction approach to fabricate lactic acid ester functionalized cellulose nanofibrils from wood-derived pulp fibers in high yields. This was accomplished by converting wood-derived pulp fibers to nanofibrillated “cellulose lactate” under mild conditions using lactic acid as both the reaction media and catalyst. Thus, in parallel to the cellulose nanofibril production, concurrent lactic acid-catalyzed esterification of lactic acid to the cellulose nanofibers surface occured. The direct lactic acid esterification, which is a surface selective functionalization and reversible (de-attaching the ester groups by cleavage of the ester bonds), of the cellulose nanofibrils was confirmed by low numbers of degree of substitution, and FT-IR analyses. Thus, autocatalytic esterification and cellulose hydrolysis occurred without the need of metal based or a harsh mineral acid catalysts, which has disadvantages such as acid corrosiveness and high recovery cost of acid. Moreover, adding a mineral acid as a co-catalyst significantly decreased the yield of the nanocellulose. The lactic acid media is successfully recycled in multiple reaction cycles producing the corresponding nanocellulose fibers in high yields. The disclosed green cellulose nanofibril production route is industrial relevant and gives direct access to nanocellulose for use in variety of applications such as sustainable filaments, composites, packaging and strengthening of recycled fibers.
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| 2. |
- Afewerki, Samson, et al.
(författare)
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Combined Catalysis for Engineering Bioinspired, Lignin-Based, Long-Lasting, Adhesive, Self-Mending, Antimicrobial Hydrogels
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:12, s. 17004-17017
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Tidskriftsartikel (refereegranskat)abstract
- The engineering of multifunctional biomaterials using a facile sustainable methodology that follows the principles of green chemistry is still largely unexplored but would be very beneficial to the world. Here, the employment of catalytic reactions in combination with biomass-derived starting materials in the design of biomaterials would promote the development of eco-friendly technologies and sustainable materials. Herein, we disclose the combination of two catalytic cycles (combined catalysis) comprising oxidative decarboxylation and quinone-catechol redox catalysis for engineering lignin-based multifunctional antimicrobial hydrogels. The bioinspired design mimics the catechol chemistry employed by marine mussels in nature. The resultant multifunctional sustainable hydrogels (1) are robust and elastic, (2) have strong antimicrobial activity, (3) are adhesive to skin tissue and various other surfaces, and (4) are able to self-mend. A systematic characterization was carried out to fully elucidate and understand the facile and efficient catalytic strategy and the subsequent multifunctional materials. Electron paramagnetic resonance analysis confirmed the long-lasting quinone-catechol redox environment within the hydrogel system. Initial in vitro biocompatibility studies demonstrated the low toxicity of the hydrogels. This proof-of-concept strategy could be developed into an important technological platform for the eco-friendly, bioinspired design of other multifunctional hydrogels and their use in various biomedical and flexible electronic applications.
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| 3. |
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| 4. |
- Afewerki, Samson, 1985-, et al.
(författare)
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Sustainable and recyclable heterogenous palladium catalysts from rice husk-derived biosilicates for Suzuki-Miyaura cross-couplings, aerobic oxidations and stereoselective cascade carbocyclizations
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- A new eco-friendly approach for the preparation of sustainable heterogeneous palladium catalysts from rice husk-derived biogenic silica (RHP-Si and RHU-Si). The designed heterogeneously supported palladium species (RHP-Si-NH2-Pd and RHU-Si-NH2-Pd) were fully characterized and successfully employed as catalysts for various chemical transformations (C–C bond-forming reactions, aerobic oxidations and carbocyclizations). Suzuki-Miyaura transformations were highly efficient in a green solvent system (H2O:EtOH (1:1) with excellent recyclability, providing the cross-coupling products with a wide range of functionalities in high isolated yields (up to 99%). Palladium species (Pd(0)-nanoparticles or Pd(II)) were also efficient catalysts in the green aerobic oxidation of an allylic alcohol and a co-catalytic stereoselective cascade carbocyclization transformation. In the latter case, a quaternary stereocenter was formed with excellent stereoselectivity (up to 27:1 dr).
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| 5. |
- Afewerki, Samson, 1985-, et al.
(författare)
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Sustainable Design for the Direct Fabrication and Highly Versatile Functionalization of Nanocelluloses
- 2017
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Ingår i: Global Challenges. - Weinheim : Wiley. - 2056-6646. ; 1:7
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Tidskriftsartikel (refereegranskat)abstract
- This study describes a novel sustainable concept for the scalable direct fabrication and functionalization of nanocellulose from wood pulp with reduced energy consumption. A central concept is the use of metal-free small organic molecules as mediators and catalysts for the production and subsequent versatile surface engineering of the cellulosic nanomaterials via organocatalysis and click chemistry. Here, organoclick chemistry enables the selective functionalization of nanocelluloses with different organic molecules as well as the binding of palladium ions or nanoparticles. The nanocellulosic material is also shown to function as a sustainable support for heterogeneous catalysis in modern organic synthesis (e.g., Suzuki cross-coupling transformations in water). The reported strategy not only addresses obstacles and challenges for the future utilization of nanocellulose (e.g., low moisture resistance, the need for green chemistry, and energy-intensive production) but also enables new applications for nanocellulosic materials in different areas.
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| 6. |
- Akansel, Serkan, et al.
(författare)
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Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
- 2018
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:30
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Tidskriftsartikel (refereegranskat)abstract
- Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.
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| 7. |
- Ali, Hasan, 1985-, et al.
(författare)
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Noise-dependent bias in quantitative STEM-EMCD experiments revealed by bootstrapping
- 2024
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Ingår i: Ultramicroscopy. - : Elsevier. - 0304-3991 .- 1879-2723. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic circular dichroism (EMCD) is a powerful technique for estimating element-specific magnetic moments of materials on nanoscale with the potential to reach atomic resolution in transmission electron microscopes. However, the fundamentally weak EMCD signal strength complicates quantification of magnetic moments, as this requires very high precision, especially in the denominator of the sum rules. Here, we employ a statistical resampling technique known as bootstrapping to an experimental EMCD dataset to produce an empirical estimate of the noise-dependent error distribution resulting from application of EMCD sum rules to bcc iron in a 3-beam orientation. We observe clear experimental evidence that noisy EMCD signals preferentially bias the estimation of magnetic moments, further supporting this with error distributions produced by Monte-Carlo simulations. Finally, we propose guidelines for the recognition and minimization of this bias in the estimation of magnetic moments.
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| 8. |
- Ali, Hasan, 1985-, et al.
(författare)
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Single scan STEM-EMCD in 3-beam orientation using a quadruple aperture
- 2023
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- The need to acquire multiple angle-resolved electron energy loss spectra (EELS) is one of the several critical challenges associated with electron magnetic circular dichroism (EMCD) experiments. If the experiments are performed by scanning a nanometer to atomic-sized electron probe on a specific region of a sample, the precision of the local magnetic information extracted from such data highly depends on the accuracy of the spatial registration between multiple scans. For an EMCD experiment in a 3-beam orientation, this means that the same specimen area must be scanned four times while keeping all the experimental conditions same. This is a non-trivial task as there is a high chance of morphological and chemical modification as well as non-systematic local orientation variations of the crystal between the different scans due to beam damage, contamination and spatial drift. In this work, we employ a custom-made quadruple aperture to acquire the four EELS spectra needed for the EMCD analysis in a single electron beam scan, thus removing the above-mentioned complexities. We demonstrate a quantitative EMCD result for a beam convergence angle corresponding to sub-nm probe size and compare the EMCD results for different detector geometries.
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| 9. |
- Alimohammadzadeh, Rana, et al.
(författare)
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Direct Organocatalytic Thioglycolic Acid Esterification of Cellulose Nanocrystals : A simple entry to click chemistry on the surface of nanocellulose
- 2022
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Ingår i: Carbohydrate Polymer Technologies and Applications. - : Elsevier BV. - 2666-8939. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The mild and simple direct organocatalytic esterification of cellulose nanocrystals (CNC) and nanocellulose-based materials (e.g. foams and films) with thioglycolic acid (TGA) is disclosed. The transformation gives the corresponding thiol group (-SH) functionalized crystalline nanocellulose (CNC-SH) using simple, naturally occurring, and non-toxic organic acids (e.g. tartaric acid) as catalysts. We also discovered that the direct esterification of cellulose with TGA is autocatalytic (i.e. the TGA is catalyzing its own esterification). The introduction of the -SH functionality at the nanocellulose surface opens up for further selective applications. This was demonstrated by attaching organic catalysts and fluorescent molecules, which are useful as sensors, to the CNC-SH surface by thiol-ene click chemistry. Another application is to use the CNC-SH-based foam as a heterogeneous biomimetic reducing agent, which is stable during multiple recycles, for the copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (“click” reaction).
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| 10. |
- Asfaw, Habtom D., Dr. 1986-, et al.
(författare)
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Bio-derived hard carbon nanosheets with high rate sodium-ion storage characteristics
- 2022
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Ingår i: Sustainable Materials and Technologies. - : Elsevier. - 2214-9937. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Biomass is a sustainable precursor of hard carbons destined for use in sodium-ion batteries. This study explores the synthesis of hard carbon nanosheets (HCNS) from oxidized cork and impact of synthesis temperature on the hard carbon characteristics. An increase in the carbonization temperature from 1000 to 1500 °C generally leads to lower BET specific surface areas (~55 to 20 m2 g−1) and d002 interlayer spacing (~ 4.0 to 3.7 Å). The effect of synthesis temperature is reflected in the initial coulombic efficiency (iCE) which increases from 72% at 1000 °C to 88% at 1500 °C, as a result of the decrease in surface area, and structural defects in the hard carbon as verified using Raman scattering. The impact of cycling temperature (~25, 30 and 55 °C) on the rate capability and long-term cycling is investigated using high precision coulometry cycler. For a galvanostatic test at 20 mA g−1 and ~ 25 °C, a reversible capacity of 276 mAh g−1 is observed with an iCE of ~88%. Increasing cycling temperature enhances the rate performance, but slightly lowers the iCE (~86% at 30 °C and ~ 81% at 55 °C). At 20 mA g−1, the reversible capacities obtained at 30 °C and 55 °C are on average ~ 260 and ~ 270 mAh g−1, respectively. For constant-current constant-voltage (CCCV) tests conducted at 30 °C, reversible capacities ranging from 252 to 268, 247–252, and 237–242 mAh g−1 can be obtained at 10, 100, and 1000 mA g−1, respectively. The respective capacities obtained at 55 °C are about 272–290, 260–279, and 234–265 mAh g−1 at 10, 100 and 1000 mA g−1. The applicability of the HCNS electrodes is eventually evaluated in full-cells with Prussian white cathodes, for which a discharge capacity of 152 mAh g−1 is obtained with an iCE of ~90%.
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