Browsing by Author "Borghei, Maryam"

Filter results by typing the first few letters
Now showing 1 - 20 of 37
  • Asymmetrical coffee rings from cellulose nanocrystals and prospects in art and design
    (2019-01-15) Klockars, Konrad W.; Yau, Noora E.; Tardy, Blaise L.; Majoinen, Johanna; Kämäräinen, Tero; Miettunen, Kati; Boutonnet, Elisa; Borghei, Maryam; Beidler, Jaana; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The iridescence displayed by films made from cellulose nanocrystals (CNCs) has long been the subject of fundamental research. This has expanded our understanding of colloidal self-assembly towards the development of advanced materials. However, the application of such findings is less reported for visual designs that exploit structural color. Aesthetic outputs are already in reach, but requires input from trend setters in the design and art industries. In this realm, the CNC-based iridescence uniquely offers broadband, multi-colored reflections through the “coffee ring” effect, which arises upon evaporation-induced self-assembly (EISA). Although this effect has been thoroughly studied in the context of axisymmetric patterns, complex geometries remain to be evaluated for large-scale implementation. This is central to the present efforts, where EISA of CNC suspensions occurred onto non-circular surfaces. We used orientation-dependent contact angle measurements, profilometry and fixed-light source photography to unveil the effect of asymmetric drying fluxes at sharp angles, between 30° and 90°, on CNC particle deposition and resulting color patterns. We also demonstrate the causality between increased capillary fluxes and deposition with the help of modelling via energy minimization of the suspension volume onto a given surface and using the diffusion equation to obtain the local concentration of water vapor during EISA. Lastly, we study the effect of background reflections as well as light and temperature resistance of CNC-based reflectors, both important for any deployment. The results from this multidisciplinary effort, involving applied design, art and colloid chemistry, point to the excellent prospects of CNC films for the development of structured and chromatic patterns. Graphical abstract: [Figure not available: see fulltext.].
  • Bicomponent Cellulose Fibrils and Minerals Afford Wicking Channels Stencil-Printed on Paper for Rapid and Reliable Fluidic Platforms
    (2021-11-12) Solin, Katariina; Borghei, Maryam; Imani, Monireh; Kämäräinen, Tero; Kiri, Kaisa; Mäkelä, Tapio; Khakalo, Alexey; Orelma, Hannes; Gane, Patrick A.C.; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Flexible and easy-to-use microfluidic systems are suitable options for point-of-care diagnostics. Here, we investigate liquid transport in fluidic channels produced by stencil printing on flexible substrates as a reproducible and scalable option for diagnostics and paper-based sensing. Optimal printability and flow profiles were obtained by combining minerals with cellulose fibrils of two different characteristic dimensions, in the nano- and microscales, forming channels with ideal wettability. Biomolecular ligands were easily added by inkjet printing on the channels, which were tested for the simultaneous detection of glucose and proteins. Accurate determination of clinically relevant concentrations was possible from linear calibration, confirming the potential of the introduced paper-based diagnostics. The results indicate the promise of simple but reliable fluidic channels for drug and chemical analyses, chromatographic separation, and quality control.
  • Bioactive nanocellulose films with spatial definition
    (2018-07-31) Solin, Katariina
     Kemian tekniikan korkeakoulu | Master's thesis
    In this thesis, fluidic channels were prepared on films made from cellulose nanofibers (CNF) and their potential use in biosensor applications was studied. The main goal was to develop hydrophilic-hydrophobic patterns to controllably produce CNF substrates for microfluidic applications. The work included a detailed investigation, to prevent non-specific adsorption of a type of human serum protein, hIgG, on CNF. A suitable antifouling agent for the CNF films was tested. CNF is a cellulosic material that has at least one dimension in the nanometer range and it is mainly produced mechanically from wood fibers. It can be used to make strong, translucent and smooth films. Two different approaches were tested to prepare 2D-channels on the CNF films: photolithography and inkjet printing of hydrophobic materials. The photolithographic method utilized simultaneously thiol-ene and thiol-yne click chemistries. In the inkjet studies, it was observed that polystyrene dissolved in p-xylene worked successfully. The prepared microfluidic CNF materials were characterized with SEM, AFM, contact angle measurements and liquid flow tests. Additionally, the non-specific protein adsorption was studied by using model CNF films with QCM-D, SPR and AFM techniques. Furthermore, the adsorption of fluorescent hIgG was performed on real CNF films and channels with CLSM method. The molecules used for protein blocking included BSA, fibrinogen and PDMAEMA-block-POEGMA copolymers. The results indicated that the best fluid flow was obtained by inkjet printing channels with polystyrene edges on CNF films. In addition, the PDMAEMA-block-POEGMA copolymer was the best antifouling agent for CNF and it reduced the hIgG adsorption up to 95 %. The successful blocking of the channels point out that these systems could be developed further and possibly be used in future biosensing applications.
  • Biowaste-derived electrode and electrolyte materials for flexible supercapacitors
    (2022-05-01) Al Haj, Yazan; Mousavihashemi, Seyedabolfazl; Robertson, Daria; Borghei, Maryam; Pääkkönen, Timo; Rojas, Orlando J.; Kontturi, Eero; Kallio, Tanja; Vapaavuori, Jaana
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    One of the key challenges in the development of energy storage devices relates to material sourcing in harmony with clean technologies. Herein, cellulose nanocrystals (CNC) extracted from brewery residues are used as transparent hydrogel electrolyte after physical cross-linking with aluminum ions (Al3+). The hydrogel electrolyte (Al-CNC) exhibits an ultrahigh ionic conductivity (∼24.9 mS cm−1), high optical transmittance (∼92.9% at 550 nm wavelength), outstanding compression strength (3.9 MPa at a 70% strain), and tolerates to various deformations (e.g., twisting, folding, rolling). Meanwhile, animal bone biowaste is used to synthesize porous carbon (PC) electrodes (∼879 m2 g−1) that are effective in delivering an outstanding specific capacitance (∼804 F g−1 at 1 A g−1). A fully renewable flexible symmetric supercapacitor is assembled by sandwiching the Al-CNC hydrogel between two bone-derived PC electrodes (PC//Al-CNC//PC). The obtained flexible device displays a high energy density (18.2 Wh kg−1 at 1 425 W kg−1), exceptional power density (20 833 W kg−1 at 7.1 Wh kg−1), and ∼92% capacitance retention after 6 000 cycles at 5 A g−1. We further demonstrated the biowaste-derived high-performance flexible supercapacitors for their mechanical durability and reliable electrochemical performance under bending cycles. All combined, the devices are shown to be ideally suited for renewable energy storage applications.
  • Conductive Carbon Microfibers Derived from Wet-Spun Lignin/Nanocellulose Hydrogels
    (2019-03-18) Wang, Ling; Ago, Mariko; Borghei, Maryam; Ishaq, Amal; Papageorgiou, Anastassios C.; Lundahl, Meri; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We introduce an eco-friendly process to dramatically simplify carbon microfiber fabrication from biobased materials. The microfibers are first produced by wet-spinning in aqueous calcium chloride solution, which provides rapid coagulation of the hydrogel precursors comprising wood-derived lignin and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF). The thermomechanical performance of the obtained lignin/TOCNF filaments is investigated as a function of cellulose nanofibril orientation (wide angle X-ray scattering (WAXS)), morphology (scanning electron microscopy (SEM)), and density. Following direct carbonization of the filaments at 900 °C, carbon microfibers (CMFs) are obtained with remarkably high yield, up to 41%, at lignin loadings of 70 wt % in the precursor microfibers (compared to 23% yield for those produced in the absence of lignin). Without any thermal stabilization or graphitization steps, the morphology, strength, and flexibility of the CMFs are retained to a large degree compared to those of the respective precursors. The electrical conductivity of the CMFs reach values as high as 103 S cm -1 , making them suitable for microelectrodes, fiber-shaped supercapacitors, and wearable electronics. Overall, the cellulose nanofibrils act as structural elements for fast, inexpensive, and environmentally sound wet-spinning while lignin endows CMFs with high carbon yield and electrical conductivity.
  • Coupling Nanofibril Lateral Size and Residual Lignin to Tailor the Properties of Lignocellulose Films
    (2019-10-09) Imani, Monireh; Ghasemian, Ali; Dehghani-Firouzabadi, Mohammad Reza; Afra, Elyas; Borghei, Maryam; Johansson, Leena S.; Gane, Patrick A.C.; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Lignocellulosic nanofibrils (LCNF) are produced from a single source of unbleached, oxidized wood fibers by serial disintegration, high-pressure microfluidization, and homogenization. Sequential centrifugation enables fractionation by fibril width (≈5, ≈9, and ≈18 nm). LCNF residual lignin of high molecular mass reports together with the finest fraction (LCNF-fine), whereas the more strongly cellulose-bound lignin, of relatively lower molecular mass, associates with the coarsest fraction (LCNF-coarse). Hot pressing softens the amorphous lignin, which fills the interstices between fibrils and acts as an in-built interfacial cross-linker. Thus, going from the LCNF-fine to the LCNF-course films, it is possible to obtain a range of values for the structural consolidation (density from 0.9 to 1.2 g cm−3 and porosity from 19% to 40%), surface roughness (RMS from ≈6 to 13 nm), and strength (elastic modulus from 8 to ≈12 GPa). The concentration of free hydroxyl groups controls effectively the direct surface interactions with liquids. The apparent surface energy dispersive component tracks with the total surface free energy and appears to be strongly influenced by the higher porosity as the fibril lateral size increases. The results demonstrate the possibility to tailor nanofibril cross-linking and associated optical and thermo-mechanical performance of LCNF films.
  • Cross-linked and surface-modified cellulose acetate as a cover layer for paper-based electrochromic devices
    (2021-05-14) Kaschuk, Joice Jaqueline; Borghei, Maryam; Solin, Katariina; Tripathi, Anurodh; Khakalo, Alexey; Leite, Fábio A. S.; Branco, Aida; Amores de Sousa, Miriam C.; Frollini, Elisabete; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We studied the surface and microstructure of cellulose acetate (CA) films to tailor their barrier and mechanical properties for application in electrochromic devices (ECDs). Cross-linking of CA was carried out with pyromellitic dianhydride to enhance the properties relative to unmodified CA: solvent resistance (by 43% in acetone and 37% in DMSO), strength (by 91% for tensile at break), and barrier (by 65% to oxygen and 92% to water vapor). Surface modification via tetraethyl orthosilicate and octyltrichlorosilane endowed the films with hydrophobicity, stiffness, and further enhanced solvent resistance. A detailed comparison of structural, chemical, surface, and thermal properties was performed by using X-ray diffraction, dynamic mechanical analyses, Fourier-transform infrared spectroscopy, and atomic force microscopy. Coplanar ECDs were synthesized by incorporating a hydrogel electrolyte comprising TEMPO-oxidized cellulose nanofibrils and an ionic liquid. When applied as the top layer in the ECDs, cross-linked and hydrophobized CA films extended the functionality of the assembled displays. The results indicate excellent prospects for CA films in achieving environmental-friendly ECDs that can replace poly(ethylene terephthalate)-based counterparts.
  • Dataset for natural organic matter treatment by tailored biochars
    (2019-08-01) Yazdani, Maryam Roza; Duimovich, Nicola; Tiraferri, Alberto; Laurell, Panu; Borghei, Maryam; Zimmerman, Julie B.; Vahala, Riku
     Data Article
    The dataset presented here are collected for tailoring biochars from pinecone biomass through chemical modification for the adsorption of natural organic matter (NOM) from lake water. The data includes schematics, figures and tables. The characterization of biomass and tailored biochars by Brunauer, Emmett and Teller surface area measurement (BET), thermogravimetric analysis (TGA), energy dispersive X-ray (EDX) along with the adsorption of NOM from lake water by the tailored bichars and the desorption using alkaline solution are provided. This is complimentary dataset for the experimental set-up and data gathered related to the article [1] on biochar fabrication and lake water treatment. See this article [1] for further information and discussion.
  • Effect of Anisotropy of Cellulose Nanocrystal Suspensions on Stratification, Domain Structure Formation, and Structural Colors
    (2018-05-12) Klockars, Konrad; Tardy, Blaise; Borghei, Maryam; Tripathi, Anurodh; Garcia Greca, Luiz; Rojas Gaona, Orlando
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Outstanding optical and mechanical properties can be obtained from hierarchical assemblies of nanoparticles. Herein, the formation of helically ordered, chiral nematic films obtained from aqueous suspensions of cellulose nanocrystals (CNCs) were studied as a function of the initial suspension state. Specifically, nanoparticle organization and the structural colors displayed by the resultant dry films were investigated as a function of the anisotropic volume fraction (AVF), which depended on the initial CNC concentration and equilibration time. The development of structural color and the extent of macroscopic stratification were studied by optical and scanning electron microscopy as well as UV–vis spectroscopy. Overall, suspensions above the critical threshold required for formation of liquid crystals resulted in CNC films assembled with longer ranged order, more homogeneous pitches along the cross sections, and narrower specific absorption bands. This effect was more pronounced for the suspensions that were closer to equilibrium prior to drying. Thus, we show that high AVF and more extensive phase separation in CNC suspensions resulted in large, long-range ordered chiral nematic domains in dried films. Additionally, the average CNC aspect ratio and size distribution in the two separated phases were measured and correlated to the formation of structured domains in the dried assemblies.
  • The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell
    (2012-12) Kanninen, Petri; Borghei, Maryam; Ruiz, Virginia; Kauppinen, Esko I.; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion® contents (30, 50 and 70 wt% or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in a DMFC and characterization with various techniques before and after this measurement. Of the pristine MEAs, MEA50 reached the highest power and current densities. During the 9-day measurement at a constant current, the performance of MEA30 decreased the most (−124 μV h−1), while the MEA50 was almost stable (−11 μV h−1) and performance of MEA70 improved (+115 μV h−1). After the measurement, the MEA50 remained the best MEA in terms of performance. The optimum anode Nafion content for commercial Vulcan carbon black supported PtRu catalysts is between 20 and 40 wt%, so the GNF-supported catalyst requires more Nafion to reach its peak power. This difference is explained by the tubular geometry of the catalyst support, which requires more Nafion to form a penetrating proton conductive network than the spherical Vulcan. Mass transfer limitations are mitigated by the porous 3D structure of the GNF catalyst layer and possible changes in the compact Nafion filled catalyst layers during constant current production.
  • Effects of non-solvents and electrolytes on the formation and properties of cellulose I filaments
    (2019-12-01) Wang, Ling; Lundahl, Meri J.; Greca, Luiz G.; Papageorgiou, Anastassios C.; Borghei, Maryam; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; however, so far, the role of the coagulation solvent has not been systematically elucidated in this context. This work considers organic non-solvents (ethanol, acetone) and aqueous electrolyte solutions (NaCl(aq), HCl(aq), CaCl2(aq)) for the coagulation of negatively charged cellulose nanofibrils via wet spinning. The associated mechanisms of coagulation with such non-solvents resulted in different spinnability, coagulation and drying time. The properties of the achieved filaments varied depending strongly on the coagulant used: filaments obtained from electrolytes (using Ca2+ and H+ as counterions) demonstrated better water/moisture stability and thermomechanical properties. In contrast, the filaments formed from organic non-solvents (with Na+ as counterions) showed high moisture sorption and low hornification when subjected to cycles of high and low humidity (dynamic vapor sorption experiments) and swelled extensively upon immersion in water. Our observations highlight the critical role of counter-ions and non-solvents in filament formation and performance. Some of the fundamental aspects are further revealed by using quartz crystal microgravimetry with model films of nanocelluloses subjected to the respective solvent exchange.
  • Electrically Conductive Thin Films Based on Nanofibrillated Cellulose : Interactions with Water and Applications in Humidity Sensing
    (2020-08-12) Solin, Katariina; Borghei, Maryam; Sel, Ozlem; Orelma, Hannes; Johansson, Leena Sisko; Perrot, Hubert; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    TEMPO-oxidized cellulose nanofibrils (TOCNF) and oxidized carbon nanotubes (CNT) were used as humidity-responsive films and evaluated using electroacoustic admittance (quartz crystal microbalance with impedance monitoring, QCM-I) and electrical resistivity. Water uptake and swelling phenomena were investigated in a range of relative humidity (% RH) between 30 and 60% and temperatures between 25 and 50 °C. The presence of CNT endowed fibril networks with high water accessibility, enabling fast and sensitive response to changes in humidity, with mass gains of up to 20%. The TOCNF-based sensors became viscoelastic upon water uptake, as quantified by the Martin-Granstaff model. Sensing elements were supported on glass and paper substrates and confirmed a wide window of operation in terms of cyclic % RH, bending, adhesion, and durability. The electrical resistance of the supported films increased by ∼15% with changes in % RH from 20 to 60%. The proposed system offers a great potential to monitor changes in smart packaging.
  • Electrolyte membranes based on ultrafine fibers of acetylated cellulose for improved and long-lasting dye-sensitized solar cells
    (2019-07) Kaschuk, Joice Jaqueline; Miettunen, Kati; Borghei, Maryam; Frollini, Elisabete; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Electrospun nanofibers obtained from cellulose acetate before (CA) and after (DCA) deacetylation were used as electrolyte membranes in dye-sensitized solar cells. As holders of the active components of the device and compared to the reference system, the CA and DCA membranes increased the average device efficiency by as much as 14%. The membranes enhanced the charge transfer at the counter electrode (assessed by the Ohmic and charge transfer resistance and corresponding Helmholtz capacitance). Simultaneously, the photoelectrode did not interfere with the performance as measured by the short-circuit current density, open circuit voltage, fill factor and conversion efficiency. Long-term stability tests (light soaking) showed that the CA- and DCA-based solar cells sustain operation for at least 500 h. For long term use and/or to serve as a scaffold for other purposes, DCA performs better than CA. The proposed active electrolyte membranes are expected to open the way toward rapid and continuous assembly of dye sensitize solar cells using cellulose esters. Graphical abstract: [Figure not available: see fulltext.].
  • Enhanced performance of a silicon microfabricated direct methanol fuel cell with PtRu catalysts supported on few-walled carbon nanotubes
    (2014-02-01) Borghei, Maryam; Scotti, Gianmario; Kanninen, Petri; Weckman, Timo; Anoshkin, Ilya V.; Nasibulin, Albert G.; Franssila, Sami; Kauppinen, Esko I.; Kallio, Tanja; Ruiz, Virginia
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Silicon micro fuel cells (Si-MFCs) are promising power supplies for microelectronic applications, however their development is still at early stages compared to the conventional proton exchange membrane fuel cells (PEMFCs). There are not many published reports on the durability of Si-MFCs and those available only projected the life-time of standard Vulcan based catalysts. However, the limited durability resulting from carbon corrosion is one of the crucial issues in fuel cells. In this study, Si-MFC with an integrated silicon nanograss diffusion layer is used for the direct methanol fuel cell investigations. The long-term (3-day) performance of PtRu catalysts supported on different carbon supports, namely Vulcan, Graphitized carbon nanofibers (GNFs) and Few-walled carbon nanotubes (FWCNTs), was studied. PtRu-FWCNTs and PtRu-GNFs exhibited respectively 471% (20.0 mW cm-2) and 274% (13.1 mW cm-2) power density enhancements compared to PtRu-Vulcan (3.5 mW cm-2). After 3-day durability measurements, power density stayed at 72, 68 and 91% of the initial value, respectively for PtRu-FWCNTs, PtRu-GNFs and PtRu-Vulcan. To evaluate the influence of carbon supports as well as the distribution and the size of the nanoparticles on the overall performance of Si-MFCs, further characterizations with Raman, BET, XRD, SEM and TEM were performed.
  • Evaporation-induced self-assembly of cellulose nanocrystals from aqueous suspensions into chiral nematic solid structures
    (2018-06-05) Klockars, Konrad
     Kemian tekniikan korkeakoulu | Master's thesis
    Biobased and renewable cellulose nanocrystals (CNC) can form hierarchically structured assemblies with impressive optical and mechanical properties. These rod-shaped nanoparticles, produced through acid hydrolysis of biomass, self-assemble in aqueous suspensions and form a liquid crystalline anisotropic volume fraction (AVF), the extent of which depends on the concentration. The anisotropic chiral nematic liquid crystalline phase can be preserved in the dry state through evaporation-induced self-assembly (EISA). This transition is not fully understood and requires more thorough inspection, in order to create large-scale defect-free structures for demanding applications, such as impact resistant materials. This work addresses this by studying the conditions during EISA for producing highly ordered CNC films. Solid CNC films display structural colour, whose intensity and uniformity reveal how well the chiral nematic order is preserved and defined within the film. UV-Vis spectroscopy, optical microscopy and scanning electron microscopy (SEM) provide information on the formation and distribution of the structural colour. In the first part of this work, the EISA drying temperature was varied (23, 28, 36, 41, 51 and 61°C). The results showed deteriorated helical order within solid films produced at higher drying temperatures. This conclusion was deduced from UV-Vis spectroscopy data that implied a larger distribution of structural colours in the films dried at elevated temperatures. In the second part, five different concentrations of the suspensions (3-7% w/w), and thereby AVFs, were used, while keeping the drying conditions the same. One set of samples was dried immediately after casting, while another set was equilibrated prior to drying. The characterization of the dry films by microscopy, UV-Vis and SEM showed that suspensions dried from a high AVF and an equilibrated state produced films with more homogeneous, long-range order, having larger chiral nematic domains. In contrast, films dried from AVF=0 lacked long-range order and did not benefit from equilibration.
  • Experimental and Computational Investigation of Hydrogen Evolution Reaction Mechanism on Nitrogen Functionalized Carbon Nanotubes
    (2018-09-07) Tuomi, Sami; Pakkanen, Olli J.; Borghei, Maryam; Kronberg, Rasmus; Sainio, Jani; Kauppinen, Esko I.; Nasibulin, Albert G.; Laasonen, Kari; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Designing earth-abundant element based efficient and durable electrocatalysts for hydrogen evolution reaction (HER) is attracting growing attention as the renewable electricity supply sector urgently needs sustainable methods for storing energy. Nitrogen functionalized carbon nanomaterials are an interesting electrocatalysts option because of their attractive electrical properties, excellent chemical stability and catalytic activity. Hence, this study reports the HER mechanism on nitrogen functionalized few-walled carbon nanotubes (N-FWCNT). With this earth-abundant element based catalyst 250mV overpotential is required to reach 10mAcm-2 current density and so its HER activity is comparable to other non-noble metal catalysts, and clearly among the highest previously reported for N-FWCNTs. To gain fundament insight on their functioning, computational analysis has been carried out to verify the effect of nitrogen and to analyze the reaction mechanism. The reaction mechanism has also been analyzed experimentally with a pH series, and both the methods suggest that the HER proceeds via the Volmer-Heyrovský mechanism. Overall hydrogen surface coverage on N-FWCNT is also suggested to affect the HER rate. Interestingly, in the studied structure, carbons in vicinity of nitrogen atoms, but not directly bound to nitrogen, appear to promote the HER most actively. Furthermore, durability of N-FWCNTs has been demonstrated by operating a full electrolyzer cell for five weeks.
  • Films based on crosslinked TEMPO-oxidized cellulose and predictive analysis via machine learning
    (2018-12-01) Özkan, Merve; Borghei, Maryam; Karakoç, Alp; Rojas, Orlando J.; Paltakari, Jouni
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We systematically investigated the effect of film-forming polyvinyl alcohol and crosslinkers, glyoxal and ammonium zirconium carbonate, on the optical and surface properties of films produced from TEMPO-oxidized cellulose nanofibers (TOCNFs). In this regard, UV-light transmittance, surface roughness and wetting behavior of the films were assessed. Optimization was carried out as a function of film composition following the "random forest" machine learning algorithm for regression analysis. As a result, the design of tailor-made TOCNF-based films can be achieved with reduced experimental expenditure. We envision this approach to be useful in facilitating adoption of TOCNF for the design of emerging flexible electronics, and related platforms.
  • High Axial Ratio Nanochitins for Ultrastrong and Shape-Recoverable Hydrogels and Cryogels via Ice Templating
    (2019-03-26) Liu, Liang; Bai, Long; Tripathi, Anurodh; Yu, Juan; Wang, Zhiguo; Borghei, Maryam; Fan, Yimin; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    High yield (>85%) and low-energy deconstruction of never-dried residual marine biomass is proposed following partial deacetylation and microfluidization. This process results in chitin nanofibrils (nanochitin, NCh) of ultrahigh axial size (aspect ratios of up to 500), one of the largest for bioderived nanomaterials. The nanochitins are colloidally stable in water (ζ-potential = +95 mV) and produce highly entangled networks upon pH shift. Viscoelastic and strong hydrogels are formed by ice templating upon freezing and thawing with simultaneous cross-linking. Slow supercooling and ice nucleation at -20 °C make ice crystals grow slowly and exclude nanochitin and cross-linkers, becoming spatially confined at the interface. At a nanochitin concentration as low as 0.4 wt %, highly viscoelastic hydrogels are formed, with a storage modulus of ∼16 kPa, at least an order of magnitude larger compared to those measured for the strongest chitin-derived hydrogels reported so far. Moreover, the water absorption capacity of the hydrogels reaches a value of 466 g g -1 . Lyophilization is effective in producing cryogels with a density that can be tailored in a wide range of values, from 0.89 to 10.83 mg·cm -3 , and corresponding porosity, between 99.24 and 99.94%. Nitrogen adsorption results indicate reversible adsorption and desorption cycles of macroporous structures. A fast shape recovery is registered from compressive stress-strain hysteresis loops. After 80% compressive strain, the cryogels recovered fast and completely upon load release. The extreme values in these and other physical properties have not been achieved before for neither chitin nor nanocellulosic cryogels. They are explained to be the result of (a) the ultrahigh axial ratio of the fibrils and strong covalent interactions; (b) the avoidance of drying before and during processing, a subtle but critical aspect in nanomanufacturing with biobased materials; and (c) ice templating, which makes the hydrogels and cryogels suitable for advanced biobased materials.
  • Highly efficient cathode catalyst layer based on nitrogen-doped carbon nano-tubes for the alkaline direct methanol fuel cell
    (2014-09) Kanninen, Petri; Borghei, Maryam; Sorsa, Olli; Pohjalainen, Elina; Kauppinen, Esko; Ruiz, Virginia; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The performance of a direct methanol alkaline anion-exchange membrane (Fumatech FAA3) fuel cell with Pt-free nitrogen-doped few-walled carbon nanotubes (N-FWCNT) as the cathode catalyst is compared with a commercial supported Pt catalyst. The ionomer content of the N-FWCNT cathode catalyst layer is therefore optimized and it is shown to be 40 wt% of FAA3. Scanning electron microscopy images of the catalyst layer show that the ionomer forms aggregates with N-FWCNTs probably due to their charged nature and that the catalyst layer structure is remarkably open even with high ionomer contents facilitating the mass transfer of reactants and products to the active sites. With oxygen as the oxidant, the maximum power density obtained with our Pt-free N-FWCNTs (0.78 mW cm-2) is slightly higher than with the Pt catalyst (0.72 mW cm-2). However, when more practical air is used as the oxidant, the N-FWCNTs (0.73 mW cm-2) show clearly superior performance compared to the Pt catalyst (0.18 mW cm-2). The lower performance with the Pt catalyst is attributed to the denser electrode layer structure resulting in higher mass transport resistance and to the presence of methanol in the cathode, which poisons the Pt but not the N-FWCNTs.
  • Immobilized cellulose nanospheres enable rapid antigen detection in lateral flow immunoassays
    (2023-03) Solin, Katariina; Beaumont, Marco; Borghei, Maryam; Orelma, Hannes; Mertens, Pascal; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Rapid diagnostic systems are essential in controlling the spread of viral pathogens and efficient patient management. The available technologies for low-cost viral antigen testing have several limitations, including a lack of accuracy and sensitivity. Here, we introduce a platform based on cellulose II nanoparticles (oppositely charged NPan and NPcat) for effective control of surface protein interactions, leading to rapid and sensitive antigen tests. Passivation against non-specific adsorption and augmented immobilization of sensing antibodies is achieved by adjusting the electrostatic charge of the nanoparticles. The interactions affecting the performance of the system are investigated by microgravimetry and confocal imaging. As a proof-of-concept test, SARS-CoV-2 nucleocapsid sensing was carried out by using saliva-wicking by channels that were stencil-printed on paper. We conclude that inkjet-printed NPcat elicits strong optical signals, visible after a few minutes, opening the opportunity for cost-effective and rapid diagnostic. Graphical abstract: [Figure not available: see fulltext.]