| 1. |
- Co, Michelle, 1975-, et al.
(författare)
-
Degradation effects in the extraction of antioxidants from birch bark using water at elevated temperature and pressure
- 2012
-
Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 716, s. 40-48
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments with birch bark samples have been carried to enable a distinction between extraction and degradation effects during pressurised hot water extraction. Two samples, E80 and El 80, contained birch bark extracts obtained after extraction at 80 and 180 degrees C for up to 45 min, respectively. Two other samples, P80 and P180, were only extracted for 5 min at the two temperatures and were thereafter filtered and hydrothermally treated at 80 and 180 degrees C, respectively. During the latter treatment, samples were collected at different times to assess the stability of the extracted compounds. An offline DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, as well as a high performance liquid chromatographic separation coupled to an electrochemical detector, were used to determine the antioxidant capacity of the processed samples. The results obtained with the different techniques were compared to assess the yield of the extraction and degradation processes. In addition, an online hyphenated system comprising high performance liquid chromatography coupled to diode-array; electrochemical; and tandem mass spectrometric detection (HPLC-DAD-ECD-MS/MS) was used to study the compositions of the extracts in more detail. The results for the samples processed at 80 degrees C showed that the extraction reached a steady-state already after 5 min, and that the extracted compounds were stable throughout the entire extraction process. Processing at 180 degrees C, on the other hand, gave rise to partly degraded extracts with a multitude of peaks in both the diode array and electrochemical detectors, and a higher antioxidant capacity compared to for the extracts obtained at 80 degrees C. It is concluded that HPLC-DAD-ECD is a more appropriate technique for the determination of antioxidants than the DPPH assay. The mass spectrometric results indicate that one of the extracted antioxidants, catechin, was isomerised to its diastereoisomers; (+)-catechin, (-)-catechin, (+)-epicatechin, and (-)-epicatechin.
|
|
| 2. |
- Nyström, Gustav, et al.
(författare)
-
A Nanocellulose Polypyrrole Composite Based on Microfibrillated Cellulose from Wood
- 2010
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 114:12, s. 4178-4182
-
Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that it is possible to coat the individual fibers of wood-based nanocellulose with polypyrrole using in situ chemical polymerization to obtain an electrically conducting continuous high-surface-area composite. The experimental results indicate that the high surface area of the water dispersed material, to a large extent, is maintained upon normal drying without the use of any solvent exchange. Thus, the employed chemical polymerization of polypyrrole on the microfibrillated cellulose (MFC) nanofibers in the hydrogel gives rise to a composite, the structure of which—unlike that of uncoated MFC paper—does not collapse upon drying. The dry composite has a surface area of 90 m2/g and a conductivity of 1.5 S/cm, is electrochemically active, and exhibits an ion-exchange capacity for chloride ions of 289 C/g corresponding to a specific capacity of 80 mAh/g. The straightforwardness of the fabrication of the present nanocellulose composites should significantly facilitate industrial manufacturing of highly porous, electroactive conductive paper materials for applications including ion-exchange and paper-based energy storage devices.
|
|
| 3. |
- Razaq, Aamir, et al.
(författare)
-
High-capacity Conductive Nanocellulose Paper Sheets for Electrochemically Controlled Extraction of DNA Oligomers
- 2011
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:12, s. e29243-
-
Tidskriftsartikel (refereegranskat)abstract
- Highly porous polypyrrole (PPy)-nanocellulose paper sheets have been evaluated as inexpensive and disposable electrochemically controlled three-dimensional solid phase extraction materials. The composites, which had a total anion exchange capacity of about 1.1 mol kg(-1), were used for extraction and subsequent release of negatively charged fluorophore tagged DNA oligomers via galvanostatic oxidation and reduction of a 30-50 nm conformal PPy layer on the cellulose substrate. The ion exchange capacity, which was, at least, two orders of magnitude higher than those previously reached in electrochemically controlled extraction, originated from the high surface area (i.e. 80 m(2) g(-1)) of the porous composites and the thin PPy layer which ensured excellent access to the ion exchange material. This enabled the extractions to be carried out faster and with better control of the PPy charge than with previously employed approaches. Experiments in equimolar mixtures of (dT)(6), (dT)(20), and (dT)(40) DNA oligomers showed that all oligomers could be extracted, and that the smallest oligomer was preferentially released with an efficiency of up to 40% during the reduction of the PPy layer. These results indicate that the present material is very promising for the development of inexpensive and efficient electrochemically controlled ion-exchange membranes for batch-wise extraction of biomolecules.
|
|
| 4. |
- Asfaw, Habtom Desta
(författare)
-
Multifunctional Carbon Foams by Emulsion Templating : Synthesis, Microstructure, and 3D Li-ion Microbatteries
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon foams are among the existing electrode designs proposed for use in 3D Li-ion microbatteries. For such electrodes to find applications in practical microbatteries, however, their void sizes, specific surface areas and pore volumes need be optimized. This thesis concerns the synthesis of highly porous carbon foams and their multifunctional applications in 3D microbatteries. The carbon foams are derived from polymers that are obtained by polymerizing high internal phase water-in-oil emulsions (HIPEs).In general, the carbonization of the sulfonated polymers yielded hierarchically porous structures with void sizes ranging from 2 to 35 µm and a BET specific surface area as high as 630 m2 g-1. Thermogravimetric and spectroscopic evidence indicated that the sulfonic acid groups, introduced during sulfonation, transformed above 250 oC to thioether (-C-S-) crosslinks which were responsible for the thermal stability and charring tendency of the polymer precursors. Depending on the preparation of the HIPEs, the specific surface areas and void-size distributions were observed to vary considerably. In addition, the pyrolysis temperature could also affect the microstructures, the degree of graphitization, and the surface chemistry of the carbon foams.Various potential applications were explored for the bespoke carbon foams. First, their use as freestanding active materials in 3D microbatteries was studied. The carbon foams obtained at 700 to 1500 oC suffered from significant irreversible capacity loss during the initial discharge. In an effort to alleviate this drawback, the pyrolysis temperature was raised to 2200 oC. The resulting carbon foams were observed to deliver high, stable areal capacities over several cycles. Secondly, the possibility of using these structures as 3D current collectors for various active materials was investigated in-depth. As a proof-of-concept demonstration, positive active materials like polyaniline and LiFePO4 were deposited on the 3D architectures by means of electrodeposition and sol-gel approach, respectively. In both cases, the composite electrodes exhibited reasonably high cyclability and rate performance at different current densities. The syntheses of niobium and molybdenum oxides and their potential application as electrodes in microbatteries were also studied. In such applications, the carbon foams served dual purposes as 3D scaffolds and as reducing reactants in the carbothermal reduction process. Finally, a facile method of coating carbon substrates with oxide nanosheets was developed. The approach involved the exfoliation of crystalline VO2 to prepare dispersions of hydrated V2O5, which were subsequently cast onto CNT paper to form oxide films of different thicknesses.
|
|
| 5. |
- Andersson, Claes-Henrik, 1980-, et al.
(författare)
-
Synthesis and characterization of a ferrocene-linked bis-fullerene[60] dumbbell
- 2012
-
Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; 41:8, s. 2374-2381
-
Tidskriftsartikel (refereegranskat)abstract
- A new [60]fullerene dumbbell consisting of two fulleropyrrolidines connected to a central ferrocene unit by amide linkages has been prepared and fully characterized by elemental analysis, 1H NMR, UV/Vis, fluorescence and mass spectrometry. The electrochemical properties as determined by cyclic voltammetry show ground state electronic communication between the ferrocene and the fullerene units. In addition, the preparaton of a ferrocene building block for an alternative linking approach is presented.
|
|
| 6. |
|
|
| 7. |
- Asfaw, Habtom Desta, 1986-, et al.
(författare)
-
Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
-
Ingår i: Nanoscale. - Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sol–gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm−2 at 0.1 mA cm−2 (lowest rate) and 1.1 mA h cm−2 at 6 mA cm−2(highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.
|
|
| 8. |
- Zettersten, Camilla, 1978-, et al.
(författare)
-
Identification and Characterization of Polyphenolic Antioxidants Using On-Line Liquid Chromatography, Electrochemistry, and Electrospray Ionization Tandem Mass Spectrometry
- 2009
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 81:21, s. 8968-8977
-
Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that electrochemistry (EC) coupled to liquid chromatography (LC) and electrospray ionization tandem mass spectrometry (LC/EC/ESI-MS/MS) can be used to rapidly obtain information about the antioxidant activity (i.e., oxidation potential) and capacity (i.e., amount) of polyphenolic compounds, including catechin, kaempferol, resveratrol, quercetin, and quercetin glucosides. The described on-line LC/EC/ESI-MS/MS method facilitates the detection and characterization of individual antioxidants based on a combination of the obtained m/z values for the antioxidants and their oxidation products, the potential dependences for the ion intensities, and correlations between the retention times in the LC, EC, and MS chromatograms. As these results provide patterns that can be used in rapid screening for antioxidants in complex samples, the method should be a valuable complement to chemical assays commonly used to determine the total antioxidant capacity of samples. It is shown that the antioxidant capacity for a mixture of polyphenolic compounds depends on the redox potential employed in the evaluation, and this should consequently be taken into account when comparing results from different total antioxidant capacity assays. It is also demonstrated that the inherent antioxidant capacities of phenolic compounds increase with an increasing number of hydroxyl groups and that the potential needed to oxidize the remaining hydroxyl groups increases successively upon oxidation of the compound. Unlike chemical assays, which generally do not provide any information about the identities of the compounds on the molecular level, the present screening method can be used to identify individual antioxidants, rank compounds with respect to their ease of oxidation, and to study the antioxidant capacity at any redox potential of interest.
|
|
| 9. |
|
|
| 10. |
- Cheah, Seng Kian, et al.
(författare)
-
Self-Supported Three-Dimensional Nanoelectrodes for Microbattery Applications
- 2009
-
Ingår i: Nano letters (Print). - : American Chemical Society. - 1530-6984 .- 1530-6992. ; 9:9, s. 3230-3233
-
Tidskriftsartikel (refereegranskat)abstract
- A nanostructured three-dimensional (3D) microbattery has been produced and cycled in a Li-ion battery. It consists of a current collector of aluminum nanorods, a uniform layer of 17 nm TiO2 covering the nanorods made using ALD, an electrolyte and metallic lithium counter electrode. The battery is electrochemically cycled more than 50 times. The increase in total capacity is 10 times when using a 3D architechture compared to a 2D system for the same footprint area.
|
|
