| 1. |
- Anusuyadevi, Prasaanth Ravi, et al.
(författare)
-
Floating Photocatalysts for Effluent Refinement Based on Stable Pickering Cellulose Foams and Graphitic Carbon Nitride (g-C3N4)
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:35, s. 22411-22419
-
Tidskriftsartikel (refereegranskat)abstract
- The transfer of heterogeneous photocatalysis applications from the laboratory to real-life aqueous systems is challenging due to the higher density of photocatalysts compared to water, light attenuation effects in water, complicated recovery protocols, and metal pollution from metal-based photocatalysts. In this work, we overcome these obstacles by developing a buoyant Pickering photocatalyst carrier based on green cellulose nanofibers (CNFs) derived from wood. The air bubbles in the carrier were stable because the particle surfactants provided thermodynamic stability and the derived photocatalytic foams floated on water throughout the test period (4 weeks). A metal-free semiconductor photocatalyst, g-C3N4, was facilely embedded inside the foam by mixing the photocatalyst with the air-bubble suspension followed by casting and drying to produce solid foams. When tested under mild irradiation conditions (visible light, low energy LEDs) and no agitation, almost three times more dye was removed after 6 h for the floating g-C3N4-CNF nanocomposite foam, compared to the pure g-C3N4 powder residing on the bottom of a ca. 2 cm-high water pillar. The buoyancy and physicochemical properties of the carrier material were imperative to render escalated oxygenation, high photon utilization, and faster dye degradation. The reported assembly protocol is facile, general, and provides a new strategy for assembling green floating foams that can potentially carry a number of different photocatalysts.
|
|
| 2. |
- Anusuyadevi, Prasaanth Ravi, et al.
(författare)
-
Photoresponsive and Polarization-Sensitive Structural Colors from Cellulose/Liquid Crystal Nanophotonic Structures
- 2021
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 33:36, s. 2101519-
-
Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanocrystals (CNCs) possess the ability to form helical periodic structures that generate structural colors. Due to the helicity, such self-assembled cellulose structures preferentially reflect left-handed circularly polarized light of certain colors, while they remain transparent to right-handed circularly polarized light. This study shows that combination with a liquid crystal enables modulation of the optical response to obtain light reflection of both handedness but with reversed spectral profiles. As a result, the nanophotonic systems provide vibrant structural colors that are tunable via the incident light polarization. The results are attributed to the liquid crystal aligning on the CNC/glucose film, to form a birefringent layer that twists the incident light polarization before interaction with the chiral cellulose nanocomposite. Using a photoresponsive liquid crystal, this effect can further be turned off by exposure to UV light, which switches the nematic liquid crystal into a nonbirefringent isotropic phase. The study highlights the potential of hybrid cellulose systems to create self-assembled yet advanced photoresponsive and polarization-tunable nanophotonics.
|
|
| 3. |
- Budnyak, Tetyana, et al.
(författare)
-
Peculiarities of synthesis and properties of lignin-silica nanocomposites prepared by sol-gel method
- 2018
-
Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 8:11, s. 1-18
-
Tidskriftsartikel (refereegranskat)abstract
- The development of advanced hybrid materials based on polymers from biorenewable sources and mineral nanoparticles is currently of high importance. In this paper, we applied softwood kraft lignins for the synthesis of lignin/SiO2 nanostructured composites. We described the peculiarities of composites formation in the sol-gel process through the incorporation of the lignin into a silica network during the hydrolysis of tetraethoxysilane (TEOS). The initial activation of lignins was achieved by means of a Mannich reaction with 3-aminopropyltriethoxysilane (APTES). In the study, we present a detailed investigation of the physicochemical characteristics of initial kraft lignins and modified lignins on each step of the synthesis. Thus, 2D-NMR, P-31-NMR, size-exclusion chromatography (SEC) and dynamic light scattering (DLS) were applied to analyze the characteristics of pristine lignins and lignins in dioxan:water solutions. X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) were used to confirm the formation of the lignin-silica network and characterize the surface and bulk structures of the obtained hybrids. Termogravimetric analysis (TGA) in nitrogen and air atmosphere were applied to a detailed investigation of the thermal properties of pristine lignins and lignins on each step of modification. SEM confirmed the nanostructure of the obtained composites. As was demonstrated, the activation of lignin is crucial for the sol-gel formation of a silica network in order to create novel hybrid materials from lignins and alkoxysilanes (e.g., TEOS). It was concluded that the structure of the lignin had an impact on its reactivity during the activation reaction, and consequently affected the properties of the final hybrid materials.
|
|
| 4. |
- Ciftci, Göksu Cinar, et al.
(författare)
-
Tailoring of rheological properties and structural polydispersity effects in microfibrillated cellulose suspensions
- 2020
-
Ingår i: Cellulose. - : Springer Science+Business Media B.V.. - 0969-0239 .- 1572-882X. ; 27:16, s. 9227-9241
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: Industrial production of low-charge microfibrillated cellulose (MFC) typically results in wide fibril size distributions. This polydispersity influences viscosity, overall colloidal stability, and rheological properties of MFC suspensions and gels in aqueous systems. In this work, a systematic rheological analysis is performed for industrially prepared MFC and fractions of different size distributions. Gel formation and flow characteristics (e.g., shear-thinning) of each fraction are examined under neutral and acidic conditions and compared with the unfractionated MFC suspension. The effects of size, aspect ratio, and surface charge on the rheology of semi-dilute MFC suspensions are discussed. The results demonstrate that particle size and aspect ratio distribution control the viscoelasticity and shear-thinning properties of MFC suspensions. An increased fraction of small diameter nanofibrils, by ex situ addition of the fine particles with high aspect ratio or removal of the coarsest particles (with lower aspect ratio) by fractionation, significantly enhances the storage modulus and the yield stress of the complex mixture, compared to the properties of the coarser fractions. New insights are also reported on the tailoring of the rheology of highly polydisperse fibrillar mixtures, where the rheological contributions of each fraction are discussed. Graphic abstract: [Figure not available: see fulltext.].
|
|
| 5. |
- Fang, Mei, et al.
(författare)
-
Tuning room temperature ferromagnetism of 'in-situ' inkjet printed Fe-doped ZnO films
- 2019
-
Ingår i: Semiconductor Science and Technology. - : IOP PUBLISHING LTD. - 0268-1242 .- 1361-6641. ; 34:5
-
Tidskriftsartikel (refereegranskat)abstract
- ZnO is a wide-band gap semiconductor widely used in optical and electric devices, associating with ferromagnetism at low dimension endowing its possibility for functional applications with magneto-optical and magneto-electric properties. We prepared ZnO and Fe-doped ZnO thin films 'in-situ' on substrate by inkjet printing, and tuned the room temperature ferromagnetism (RTFM) of the film by Fe-doping concentration, film thickness and post annealing temperature. It was found that by Fe doping the saturation magnetization (M-s) of the film can be enhanced by more than 4 folds comparing with the un-doped film, i.e. from 0.9 emu g(-1) for the ZnO film to 3.8 emu g(-1) for the Fe-doped ZnO film with comparable thickness. The enhancement was attributed to the introduction of un-paired 3d electrons which formed long range ferromagnetic ordering, as well as the consequent structure changes with smaller grains which increased the interface induced magnetism. By changing the annealing temperature and the film thickness, the defect-induced ferromagnetism was investigated. The RTFM shows thickness dependence with peak saturation magnetization value of 4.44 emu g(-1) for the 45 nm thick film. The work provides an effective way of tuning magnetism in ZnO based films for functional device applications.
|
|
| 6. |
- Halysh, Vita, et al.
(författare)
-
Effect of oxidative treatment on composition and properties of sorbents prepared from sugarcane residues
- 2019
-
Ingår i: Industrial crops and products (Print). - : ELSEVIER. - 0926-6690 .- 1872-633X. ; 139
-
Tidskriftsartikel (refereegranskat)abstract
- Efficient sorbents for the removal of cationic dye were prepared from sugarcane bagasse (stalk) and straw (leaves) by oxidative pre-treatment with hydrogen peroxide (H2O2) in acetic acid. The effects of variables, such as concentration of H2O2, temperature and time on the properties of the fiber sorbents obtained were studied according to a 2(3) full-factorial design. For comparison, an oxidative treatment of sugarcane biomass with glacial acetic acid was also used. The yields of the materials obtained and their chemical composition were characterized and compared. Fourier transform infrared spectroscopy, field-emission scanning electron microscopy and benzene vapor adsorption were used to investigate the structural properties and morphology of the initial materials and sorbents. The sorption of methylene blue dye was used to assess the efficiency of dye removal by the sorbents. The pre-treatment conditions significantly affected the sorbent yield, their chemical composition (contents of cellulose, lignin and ash) as well as their sorption properties. The cellulosic sorbent (C-sorbent) from sugarcane bagasse obtained by pre-treatment with H2O2 in acetic acid and the lignocellulosic sorbent (LC-sorbent) from sugarcane straw obtained by pre-treatment with glacial acetic acid, had the highest sorption capacity for the methylene blue dye. For both types of sorbents, the sorption capacity increased with chemical pretreatment as a result of an increase in pore volume.
|
|
| 7. |
- Larsson, Per A., 1980-, et al.
(författare)
-
Towards optimised size distribution in commercial microfibrillated cellulose : a fractionation approach
- 2019
-
Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 26:3, s. 1565-1575
-
Tidskriftsartikel (refereegranskat)abstract
- For the successful commercialisation of microfibrillated cellulose (MFC) it is of utmost importance to carefully characterise the constituent cellulose particles. This could for instance lead to the development of MFC grades with size distributions tailored for specific applications. Characterization of MFC is challenging due to the heterogeneous chemical and structural nature of MFC. This study describes a fractionation approach that combines two steps of physical sieving of larger particles and a final centrifugation step to separate out the smallest, colloidally stable particles, resulting in four distinctly different size fractions. The properties, such as size and charge, of each fraction were studied, as well as MFC filtration time, film formation, and film properties (mechanical and optical). It was found that virtually all surface charges, determined by polyelectrolyte adsorption, are located in the colloidally stable fraction of the MFC. In addition, the amount of available surface charges can be used as an estimate of the degree of fibrillation of the MFC. The partly fibrillated particles frequently displayed a branching, fringed morphology. Mechanical testing of films from the different fractions revealed that the removal of large particles may be more important for strength than achieving full fibrillation. Overall, this study demonstrates that by controlling the size distribution in MFC grades, property profiles including dewatering time to make films by filtration, rheology, film strength and optical transmittance could be optimised. [GRAPHICS] .
|
|
| 8. |
- Masood, Ansar, et al.
(författare)
-
Fabrication and tuning soft magnetic and magneto-optical properties of BMGs based Fe-B-Nb-Ni transparent thin films, obtained by Pulsed Laser Deposition
- 2014
-
Ingår i: International Journal of Astrobiology. - : Springer Nature. - 1473-5504 .- 1475-3006. ; 1649:4
-
Tidskriftsartikel (refereegranskat)abstract
- We have fabricated by pulse laser deposition very thin (∼5-7 nm) and thick (∼27-408 nm) films of composition Fe66B24Nb4Ni6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exploit soft magnetic characteristics with low HC, and high MS values. The magnetic hysteretic loops of the as-deposited thicker films on silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness and 2) the onset of a two stage process during the approach to magnetic saturation. The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft-magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (≤200°C); the thicker films can be tailored to exhibit a simple soft-magnetic square loop with low HC. The ∼5-7 nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation (FR) measurement technique. Very high values of FR in the range 4-20 deg/μm almost linearly dependent on the wavelength of light in the range 405-611 nm are observed. The observed high values of Faraday rotation over a wide range of wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.
|
|
| 9. |
- Podkościelna, B., et al.
(författare)
-
Novel Porous Materials Obtained from Technical Lignins and Their Methacrylate Derivatives Copolymerized with Styrene and Divinylbenzene
- 2017
-
Ingår i: ChemistrySelect. - : Wiley-Blackwell. - 2365-6549. ; 2:7, s. 2257-2264
-
Tidskriftsartikel (refereegranskat)abstract
- The increasing availability of various types of technical lignins as result of the emergence of new biorefinery technologies has boosted the interest in the commercialization of lignin-based materials. Here we suggest a novel method for the preparation of uniform porous microspheres through emulsion-suspension polymerization of various technical lignins and related methacrylates with styrene (St) and divinylbenzene (DVB). Obtained microspheres have diameters in the range of 5–50 μm, with a more uniform shape for copolymers that contains lignin derivatives. Nitrogen sorption with DFT theory indicates that the microspheres are mesoporous materials with specific surface areas in the range of 230–270 m2g−1 but with significant differences in pore volume, especially in the mesopores size range (0–0.65 cm3g−1). Theoretical modeling of lignin alone and in St-DVB composites shows changes in polarity of the structures, which have become mosaics with hydrophilic and hydrophobic functionalities. This structure affects the properties of the interfacial water and, therefore, can affect the adsorption of both polar and nonpolar adsorbates in solid-phase extraction.
|
|
| 10. |
- Pylypchuk, Ievgen, V, et al.
(författare)
-
Structural and molecular-weight-dependency in the formation of lignin nanoparticles from fractionated soft- And hardwood lignins
- 2021
-
Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 23:8, s. 3061-3072
-
Tidskriftsartikel (refereegranskat)abstract
- The use of lignin from forests as a renewable resource is a greener alternative to the petrochemical industry and accelerates the progress towards the development of more environmentally friendly industrial processes. A better understanding of the complexity of lignin as a raw material is necessary for creating new sustainable value chains, and a deeper understanding of the forces and interactions driving the self-assembly of lignin nanoparticles (LNPs) is required to create new, more advanced lignin nanomaterials. In the current study, “a library” of LNPs made from both softwood (spruce) and hardwood (eucalyptus) lignins was prepared utilizing green solvents-fractionated kraft lignins with narrow structural and molecular weight dispersity, and the LNPs were thoroughly characterized with respect to their size, shape, and surface properties. For both spruce and eucalyptus lignin fractions, the size of the LNPs decreased with increasingMwwith a decreasing number of phenolic hydroxyls and an increasing number of aliphatic hydroxyl units in the lignin fraction. The diameter of the LNP's could be varied between 80 and 500 nm, depending on theMwof the initial lignin and its concentration. The number of methoxy and phenolic groups in the aromatic ring, the aliphatic hydroxyls and β-O-4 bonds in side chains in lignin fractions affect the morphology and surface structure of the LNPs to a significant degree. The LNP's with shapes ranging from doughnut-like structures to filled interconnected spheres were prepared, depending on the type of lignin phenylpropanoid units (botanical origin), concentration, and other properties of the lignin fractions. The identified strong dependence of the properties of the LNPs on the inherent properties of the lignin from which they were derived reveals that it is of crucial importance to select the appropriate starting lignin materials for the controlled design and synthesis of LNPs. This reduces costs for the subsequent purification and further processing of the LNPs, and prevents environmental pollution by minimizing the usage of resources. The obtained knowledge provides a clear guideline for the design of new biomass-based materials.
|
|
