| 1. |
- Al-Maqdasi, Zainab, 1986-, et al.
(författare)
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Conductive Regenerated Cellulose Fibers for Multi-Functional Composites : Mechanical and Structural Investigation
- 2021
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Ingår i: Materials. - Basel, Switzerland : MDPI. - 1996-1944. ; 14:7
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Tidskriftsartikel (refereegranskat)abstract
- Regenerated cellulose fibers coated with copper via electroless plating process are investigated for their mechanical properties, molecular structure changes, and suitability for use in sensing applications. Mechanical properties are evaluated in terms of tensile stiffness and strength of fiber tows before, during and after the plating process. The effect of the treatment on the molecular structure of fibers is investigated by measuring their thermal stability with differential scanning calorimetry and obtaining Raman spectra of fibers at different stages of the treatment. Results show that the last stage in the electroless process (the plating step) is the most detrimental, causing changes in fibers’ properties. Fibers seem to lose their structural integrity and develop surface defects that result in a substantial loss in their mechanical strength. However, repeating the process more than once or elongating the residence time in the plating bath does not show a further negative effect on the strength but contributes to the increase in the copper coating thickness, and, subsequently, the final stiffness of the tows. Monitoring the changes in resistance values with applied strain on a model composite made of these conductive tows show an excellent correlation between the increase in strain and increase in electrical resistance. These results indicate that these fibers show potential when combined with conventional composites of glass or carbon fibers as structure monitoring devices without largely affecting their mechanical performance.
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| 2. |
- Di Mauro, Alessandro, et al.
(författare)
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Surface Modification by Vanadium Pentoxide Turns Oxide Nanocrystals into Powerful Adsorbents of Methylene Blue
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 533, s. 369-374
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: If nanocrystals of such semiconductor as SnO2 and TiO2, which are not known as powerful adsorbents, have their surface modified by layer of V2O5, how will the adsorption properties be affected? Answering this question would provide a new set of surface properties to be designed by surface engineering of oxide nanocrystals.Experiments: SnO2 and TiO2 colloidal nanocrystals were prepared by coupling sol-gel and solvothermal synthesis. By co-processing with V chloroalkoxide and subsequent heat-treatment at 400-500 °C, surface deposition of V2O5 layers was obtained. The methylene blue adsorption onto the prepared materials was tested and compared with the pure oxide supports. Cycling of the materials and analysis of the adsorption process was also investigated.Findings: The V-modified nanocrystals extracted ∼ 80% methylene blue from 1.5 x 10-5 M aqueous solution after 15 min only, contrarily to pure materials, which took up only 30% of the dye even after 120 min. Comparison with pure commercial V2O5 showed that the peculiar adsorption properties were imparted by the surface deposition of the V2O5-like layers. This report demonstrates that new classes of adsorbing materials can be conceived by suitably coupling different metal oxides.
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| 3. |
- Di Mauro, Alessandro, et al.
(författare)
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Visible Light Photodegradation of Dyes and Paracetamol by Direct Sensitization Mechanism onto Metallic MoO2 Nanocrystals
- 2021
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Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier. - 1010-6030 .- 1873-2666. ; 413
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Tidskriftsartikel (refereegranskat)abstract
- MoO2 nanocrystals were prepared by solvothermal treatment of a Mo chloromethoxide at 250 °C in oleic acid. The monoclinic MoO2 phase, with a mean crystallite size of 29 nm, formed through reduction of molybdenum bronzes. The as-prepared MoO2 nanocrystals were free from organics, allowing their use in photodegradation tests of organic pollutants (methylene blue, rhodamine B, paracetamol), without any preliminary purification treatment of the nanocrystals. It was found that MoO2 was an efficient adsorbent of methylene blue (43 mg g-1 for 1.5 × 10−4 M concentration) in the dark and an efficient photodegradation catalyst under visible light (all methylene blue removed from the solution after 240 min). From the analysis of the combined photodegradation tests of rhodamine B and paracetamol, it was clarified that direct sensitization was responsible for photodegradation. This finding was related to the work function value of metallic MoO2, placed at more negative values if compared with other metallic materials.
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| 4. |
- Epifani, Mauro, et al.
(författare)
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Rhodium as efficient additive for boosting acetone sensing by TiO2 nanocrystals : Beyond the classical view of noble metal additives
- 2020
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 319
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Tidskriftsartikel (refereegranskat)abstract
- Anatase TiO2 nanocrystals were prepared by solvothermal synthesis and modified by in- situ generated Rh nanoparticles, with a starting nominal Rh:Ti atomic concentration of 0.01 and 0.05. After heat-treatment at 400 °C the TiO2 host was still in the anatase crystallographic phase, embedding Rh nanoparticles homogeneously distributed and whose surface had been oxidized to Rh2O3, as established by X-ray diffraction, Transmission Electron Microscopy and X-ray Photoelectron spectroscopy. Moreover, Rh seemed also homogeneously distributed in elemental form or as Rh2O3 nanoclusters. The acetone sensing properties of the resulting materials were enhanced by Rh addition, featuring a response increase of one order of magnitude at the best operating temperature of 300 °C. Moreover, Rh addition enlarged the detection range down to 10 ppm whereas pure TiO2 was not able of giving an appreciable response already at a concentration as high as 50 ppm. From the sensing data, the enhancement of the sensor response was attributed to the finely dispersed Rh species and not to the oxidized Rh nanocrystals.
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| 5. |
- Landström, Anton, et al.
(författare)
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Chemisorption of 3-hydroxyflavone Onto TiO2 Nanoparticles: Optical and Charge Transfer Properties
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 3-hydroxyflavone (3HF) is chemisorbed on TiO2 nanoparticle films with an Al2O3 interlayer through a facile dip coating process. The films are characterized with UV-Vis and IR absorption spectroscopy, fluorescence spectroscopy, energy-dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The 3HF adduct is shown to bond to the substrate through the carbonyl group, resulting in a bathochromic shift in its absorption spectra similar to that observed in 3HF-metal chelates. The emission spectrum is quenched in the case of adsorption on TiO2, but strongly enhanced in the case of Al2O3, with a quantum yield (9.3%) exceeding that of uncoordinated 3HF in acetonitrile.
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| 6. |
- Landström, Anton, et al.
(författare)
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Electron spectroscopies of 3-hydroxyflavone and 7-hydroxyflavone in MCM-41 silica nanoparticles and in acetonitrile solutions. Experimental data and DFT/TD-DFT calculations
- 2021
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Ingår i: Data in Brief. - : Elsevier. - 2352-3409. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- The data presented here concern the photophysical characterization of luminescent MCM-41 nanoparticles doped with 3-hydroxyflavone and 7-hydroxyflavone, two fluorescent flavonoids. UV-Vis and fluorescence spectra obtained on freshly-prepared samples and aged (2 months exposed to air) samples are shown. The effect of light exposure is also studied. In parallel, experiments have been carried out in acetonitrile solutions of the two flavonoids as a term of comparison. Time-dependent density functional theory calculations have also been used to simulate UV-Vis and emission spectra of different species for both flavonoids (neutral molecule, tautomers, cationic and anionic forms), taking into account the effect of the surrounding medium (solvent). Density functional theory calculations of vibrational spectra (IR, Raman) of neutral and tautomeric species of 3HF and 7HF are also provided.
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| 7. |
- Landström, Anton, et al.
(författare)
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Fluorescent silica MCM-41 nanoparticles based on flavonoids: Direct post-doping encapsulation and spectral characterization
- 2021
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Ingår i: Dyes and pigments. - : Elsevier. - 0143-7208 .- 1873-3743. ; 185, Part A
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Tidskriftsartikel (refereegranskat)abstract
- Flavones and flavonols are naturally-occurring organic molecules with interesting biological, chemical and photophysical properties. In recent years their interaction with silica surfaces has received increasing attention. In this work, the flavonol 3-hydroxyflavone (3HF) and the flavone 7-hydroxyflavone (7HF) have been encapsulated in MCM-41 mesoporous silica nanoparticles (NP) via a post-doping procedure, and their photophysics characterized by both steady state and time-resolved spectroscopic techniques. Both flavonoid-doped NPs resulted to be highly fluorescent, even after two months of exposure to air at room temperature. UV light irradiation results in a moderate decrease of the fluorescence quantum yield. Complementary UV-Vis and fluorescence experiments of 3HF and 7HF in solutions and TD-DFT calculations to simulate absorption and emission spectra have been carried out in order to better rationalize the exact nature of the emitting species. Whereas for 3HF-doped NPs the tautomer emission in the green predominates, the fluorescence of 7HF-doped NPs is likely to arise from the cationic or the phototautomeric form of the flavonoid. The results show that organic fluorophore-based fluorescent silica NPs can be easily obtained by a post-doping procedure and represent a first step towards the development of a simple strategy for the encapsulation in MCM-41 NPs of flavonoids and other organic molecules.
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| 8. |
- Landström, Anton
(författare)
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Nanostructured Metal Oxide Semiconductors for Functional Applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about nanostructured metal oxides, their properties, and some of their applications. Semiconducting metal oxides like TiO2, ZnO,and SnO2 have a wide band gap, which means they absorb UV light andgenerate electron-hole pairs. These charge carriers can be harnessed andused for a variety of purposes, such as electricity generation in solar cells,hydrogen production by means of photolysis and electrolysis, andenvironmental remediation by mineralizing pollutants in photocatalyticreactions. However, they are typically not very efficient when comparedwith e.g. noble metals in catalysis or silicon in solar cells , and so a widevariety of strategies have been employed to remedy their weaknesses.Such strategies include structuring the materials at the nanoscale, and thefabrication of composite materials and heterostructures.In this work, some advanced hybrid materials have been studied,composed of metal oxide and various additives, such as reduced grapheneoxide (rGO), other metal oxides, and flavonoids. The materials have beenextensively characterized in order to determine how these additives affectthe processes going on in some of the mentioned applications. Thestudied systems include rGO-ZnO, SnO2-ZnO, Rh-TiO2, MoO2, SiO2coupled to 3-hydroxyflavone and 7-hydroxyflavone, and 3-hydroxyflavone-TiO2.Particles of ZnO-encapsulated rGO exhibited a good photocatalyticactivity towards the degradation of rhodamine B and phenol, but it wasfound that the main determinant of the performance was the quality ofthe semiconductor component as opposed to any favorable interactionsbetween ZnO and rGO. However, the incorporation of rGO could stillalmost double the observed performance, which was attributed to apassivation of the defects in the metal oxide host, as well as a beneficialimpact of electrochemical properties such as charge transfer resistance anddouble-layer capacitance of the resulting material.Core-shell nanoparticles consisting of a SnO2 core and a ZnO shell weresuccessfully synthesized and employed as photocatalyst and as photoanodein dye-sensitized solar cells (DSSCs). The ZnO shell improved theperformance in both photocatalysis and DSSCs by nearly a factor of two,due to a combination of the favorable properties of the two metal oxides ,and the formation of a heterojunction in the interface between them.Rhodium as an additive to TiO2 nanocrystals proved to effectivelyimprove the response in gas sensing experiments. The rhodium exhibitedcomplex speciation, however, being distributed as a homogeneouscoating of Rh(III) as well as nanocrystals of elemental rhodium,highlighting the need for deep characterization in this class of materials.Metallic MoO2 nanocrystals were synthesized and tested in photocatalysis.Due to their electronic nature, they cannot support photocatalysisaccording to the traditional reaction scheme, because metals cannotgenerate electron-hole pairs. However, they still exhibited significantphotocatalytic activity towards methylene blue, rhodamine B, andparacetamol. This was attributed to a direct sensitization mechanismwhere the dye is photoexcited and undergoes electron transfer, madepossible due to the comparatively low work function in MoO2. This alsoenables it to assist in the degradation of non-absorbing molecules in thesolution. 3-hydroxyflavone (3HF) and 7-hydroxyflavone (7HF) were combinedwith MCM-41 silica nanoparticles via a post-doping procedure, and theirphotophysics characterized by steady-state and time-resolvedspectroscopic techniques. Both flavonoid-coated nanoparticles turned outto be highly fluorescent and stable when exposed to air at roomtemperature, showing that organic fluorophore-based solid-state emitterscan be obtained by simple methods. Furthermore, 3HF was coupled toTiO2 nanoparticles with a similarly simple adsorption procedure. In thiscase the result was a chemisorption of the flavonoid, which appears to bevery similar to a chelation of the metal ions in the metal oxide substrate.The fluorescence in the resulting materials is nearly completely quenched,but when a nanometer-thin layer of Al2O3 is applied on the TiO2, it isinstead strongly enhanced. This work therefore represents a rather noveland facile way to produce flavonoid-metal complexes.
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| 9. |
- Landström, Anton, et al.
(författare)
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Reduced graphene oxide-ZnO hybrid composites as photocatalysts : The role of nature of the molecular target in catalytic performance
- 2021
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Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 47:14, s. 19346-19355
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Tidskriftsartikel (refereegranskat)abstract
- Spurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water.Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach.
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| 10. |
- Landström, Anton, et al.
(författare)
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Thermal Defect Modulation and Functional Performance : A Case Study on ZnO–rGO Nanocomposites
- 2019
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Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 256:12
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Tidskriftsartikel (refereegranskat)abstract
- Herein, a reduced graphene oxide–zinc oxide (rGO–ZnO) hybrid nanocomposite (1 wt% rGO) is synthesized and heat treated at different temperatures, aimed at modulating the intrinsic bulk/surface defects naturally present in nano‐ZnO. The correlation of both the dispersion of rGO within the metal oxide scaffold and the defects present on the semiconductor crystalline lattice with the photocatalytic performance toward the degradation of a molecular dye in water is investigated and discussed. It is shown that several processes compete to determine the catalytic skill of the nanocomposite, which can be enhanced by a simple thermal treatment at moderate temperatures.
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