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  • 1.
    Bergström, Lennart
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sörensen, Malin H
    Boon Sing Ng, Jovice
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Alberius, Peter C.A.
    Improved enzymatic activity of Thermomyces lanuginosus lipase immobilized in a hydrophobic particulate mesoporous carrier2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 343, p. 359-365Article in journal (Other academic)
    Abstract [en]

    Lipase from Thermomyces lanuginosus has been immobilized within particulate mesoporous silica carriers, with either hydrophilic or hydrophobic supporting surfaces, produced by the newly developed emulsion and solvent evaporation (ESE) method. The Michaelis–Menten model was used to calculate the parameters related to the enzymatic activity of lipase i.e. the turnover number, kcat, and the specific activity. The specific activity was improved by immobilization of lipase onto the hydrophobic support, compared to lipase immobilized onto the hydrophilic support and lipase free in solution. The enhanced enzymatic activity of lipase onto a hydrophobic support was attributed to interfacial activation of the Thermomyces lanuginosus lipase when it is attached to a hydrophobic surface and a reduced denaturation. Confocal scanning laser microscopy (CLSM) studies, of fluorescently tagged lipase, showed that leakage of the lipase from the mesoporous particles was limited to an initial period of only a few hours. Both the rate and the amount of lipase leached were reduced when the lipase was immobilized onto the hydrophobic support.

  • 2. Burks, T.
    et al.
    Avila, M.
    Akhtar, Farid
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gothelid, M.
    Lansaker, P. C.
    Toprak, M. S.
    Muhammed, M.
    Uheida, A.
    Studies on the adsorption of chromium(VI) onto 3-Mercaptopropionic acid coated superparamagnetic iron oxide nanoparticles2014In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 425, p. 36-43Article in journal (Refereed)
    Abstract [en]

    Chromium (Cr) in the form of Cr(VI) is deemed toxic in water due to its mutagenic and carcinogenic properties. For the successful removal of Cr(VI), we demonstrate a novel adsorbent consisting of superparamagnetic iron oxide nanoparticles (SPION) functionalized with 3-Mercaptopropionic acid (3-MPA). Fourier transform infrared spectroscopy (FT-IR) confirmed the functionalization of nanoparticles and presence of sulfonate groups. Batch adsorption experiments showed that the functionalized adsorbent recovered 45 mg of Cr(VI)/g of 3-MPA coated SPION at initial concentration of 50 mg/L aqueous solution at pH 1 with less than 1% of Fe dissolution from SPION. The results from X-ray photoelectron spectroscopy confirmed that Cr(VI) chemisorbed onto the adsorbent. Hence, the XPS spectra did not indicate any reduction of Cr(VI) to Cr(III) upon adsorption. The adsorption data were better fitted for the Freundlich model. Moreover, the Cr(VI) adsorption kinetics on functionalized SPION followed a pseudo-second order rate, revealing chemisorption as the dominant mechanism. The high Cr(VI) removal, rapid adsorption kinetics and stability of adsorbent indicate that 3-MPA coated SPION could be an efficient adsorbent for the removal of Cr(VI).

  • 3.
    Gordeyeva, Korneliya S.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hall, Stephen
    Wicklein, Bernd
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stabilizing nanocellulose-nonionic surfactant composite foams by delayed Ca-induced gelation2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 472, p. 44-51Article in journal (Refereed)
    Abstract [en]

    Aggregation of dispersed rod-like particles like nanocellulose can improve the strength and rigidity of percolated networks but may also have a detrimental effect on the foamability. However, it should be possible to improve the strength of nanocellulose foams by multivalent ion-induced aggregation if the aggregation occurs after the foam has been formed. Lightweight and highly porous foams based on TEMPO-mediated oxidized cellulose nanofibrils (CNF) were formulated with the addition of a nonionic surfactant, pluronic P123, and CaCO3 nanoparticles. Foam volume measurements show that addition of the non-ionic surfactant generates wet CNF/P123 foams with a high foamability. Foam bubble size studies show that delayed Ca-induced aggregation of CNF by gluconic acid-triggered dissolution of the CaCO3 nanoparticles significantly improves the long-term stability of the wet composite foams. Drying the Ca-reinforced foam at 60 degrees C results in a moderate shrinkage and electron microscopy and X-ray tomography studies show that the pores became slightly oblate after drying but the overall microstructure and pore/foam bubble size distribution is preserved after drying. The elastic modulus (0.9-1.4 MPa) of Ca-reinforced composite foams with a density of 9-15 kg/m(3) is significantly higher than commercially available polyurethane foams used for thermal insulation.

  • 4.
    Kapuscinski, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Agthe, Michael
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Time-resolved viscoelastic properties of self-assembling iron oxide nanocube superlattices probed by quartz crystal microbalance with dissipation monitoring2018In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 522, p. 104-110Article in journal (Refereed)
    Abstract [en]

    Self-assembly of nanoparticles into superlattices can be used to create hierarchically structured materials with tailored functions. We have used the surface sensitive quartz crystal microbalance with dissipation monitoring (QCM-D) technique in combination with video microscopy (VM) to obtain time-resolved information on the mass increase and rheological properties of evaporation-induced self-assembly of nanocubes. We have recorded the frequency and dissipation shifts during growth and densification of superlattices formed by self-assembly of oleic acid capped, truncated iron oxide nanocubes and analyzed the time-resolved QCM-D data using a Kelvin-Voigt viscoelastic model. We show that the nanoparticles first assemble into solvent-containing arrays dominated by a viscous response followed by a solvent releasing step that results in the formation of rigid and well-ordered superlattices. Our findings demonstrate that QCM-D can be successfully used to follow self-assembly and assist in the design of optimized routes to produce well-ordered superlattices.

  • 5.
    Korolev, Nikolai
    et al.
    Nanyang Technological University, Singapore.
    Lyubartsev, Alexander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Nordenskiöld, Lars
    Nanyang Technological University, Singapore.
    Cation-indiced polyelectrolyte-polyelectrolyte attraction in solutions of DNA and nucleosome core particles2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 158, p. 32-47Article in journal (Refereed)
    Abstract [en]

    The paper reviews our current studies on the experimentally induced cation compaction and aggregation in solutions of DNA and nucleosome core particles and the theoretical modelling of these processes using coarse-grained continuum models with explicit mobile ions and with all-atom molecular dynamics (MD) simulations. Recent experimental results on DNA condensation by cationic oligopeptides and the effects of added salt are presented. The results of MD simulations modelling DNA–DNA attraction due to the presence of multivalent ions including the polyamine spermidine and fragments of histone tails, which exhibit bridging between adjacent DNA molecules, are discussed. Experimental data on NCP aggregation, using recombinantly prepared systems are summarized. Literature data and our results of studying of the NCP solutions are compared with predictions of coarse-grained MD simulations, including the important ion correlation as well as bridging mechanisms. The importance of the results to chromatin folding and aggregation is discussed.

  • 6. Liu, Peng
    et al.
    Oksman, Kristiina
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Surface adsorption and self-assembly of Cu(II) ions on TEMPO-oxidized cellulose nanofibers in aqueous media2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 464, p. 175-182Article in journal (Refereed)
    Abstract [en]

    TEMPO-mediated oxidized cellulose nanofibers (TOCNFs) have shown potential in the bioremediation of metal ions from contaminated water due to their interaction with positively charged metal ions via electrostatic interactions involving surface carboxyl groups. Copper is one of the most common pollutants in industrial effluents and is thus the target metal in the current study. The specific surface adsorption of Cu (II) was similar for TOCNFs with different degrees of functionalization and directly impacted the zeta potential. SEM imaging of the TOCNF after Cu(II) adsorption revealed interesting nanostructured clusters that were attributable to Cu(II) ions first being adsorbed by carboxylate groups on the TOCNF and subsequently being reduced and self-assembled to Cu(0) nanoparticles (NPs) or copper oxide NPs by microprecipitation. TOCNF turned superhydrophilic and resulted in faster water filtration after copper adsorption due to the stronger polarity of the copper ions or the self-assembled Cu(0) NPs creating voids or highly water-permeable channels at the interface between the interconnected TEMPO-oxidized nanofibers. Thus, the adsorption of Cu(II) ions and self-assembly into the Cu NPs on TOCNF favors a faster water purification process and provides a viable route to reuse/recycle TOCNFs studded with Cu nanoparticles as biocidal materials.

  • 7.
    Pai, Ranjith Krishna
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ng, Jovice B.S.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Pillai, Saju
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Temperature induced formation of strong gels of acrylamide-based polyelectrolyte2009In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 337, p. 46-53Article in journal (Refereed)
    Abstract [en]

    Very strong physical gels have been formed by moderate temperature increases in aqueous dispersions of acrylamide-based beads and dissolved polymeric molecules. Rheometry, confocal laser scanning microscopy,  and differential scanning calorimetric studies of acrylamide-based copolymers with acrylic acid, [Poly(AM-co-AA)], and 2-acrylamido-2-methylpropane acid, [Poly(AM-co-NaAMPS)], suggest that the temperature induced swelling of the polymer beads and chains, create strongly entangled polymer networks, above the upper critical solution temperature. Analyses of the viscoelastic response showed that the time-scale for the gelation process is about minutes to hours. The addition of high concentrations of Ca2+ resulted in a significant decrease in the gel strength

  • 8.
    Sörensen, Malin
    et al.
    YKI, Institute for Surface Chemistry.
    Ng, Jovice Boon Sing
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Alberius, Peter
    YKI, Institute for Surface Chemistry.
    Improved enzymatic activity of Thermomyces lanuginosus lipase immobilized in a hydrophobic particulate2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 343, no 1, p. 359-365Article in journal (Refereed)
    Abstract [en]

    Lipase from Thermomyces lanuginosus has been immobilized within particulate mesoporous silica carriers, with either hydrophilic or hydrophobic supporting surfaces, produced by the newly developed emulsion and solvent evaporation (ESE) method.  The Michaelis-Menten model was used to calculate the parameters related to the enzymatic activity of lipase i.e. the turnover number, kcat, and the specific activity. The specific activity was improved by immobilization of lipase onto the hydrophobic support, compared to lipase immobilized onto the hydrophilic support and lipase free in solution. The enhanced enzymatic activity of lipase onto a hydrophobic support was attributed to interfacial activation of the Thermomyces lanuginosus lipase when it is attached to a hydrophobic surface and a reduced denaturation. Confocal scanning laser microscopy (CLSM) studies, of fluorescently tagged lipase, showed that leakage of the lipase from the mesoporous particles was limited to an initial period of only a few hours. Both the rate and the amount of lipase leached were reduced when the lipase was immobilized onto the hydrophobic support.

  • 9.
    Vasiliev, Petr
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Faure, Bertrand
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ng, Boon Sing
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Colloidal aspects relating to direct incorporation of TiO2 nanoparticles into mesoporous spheres by an aerosol-assisted process2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 319, no 1, p. 144-151Article in journal (Refereed)
    Abstract [en]

    Titania nanoparticles have been incorporated into spherical mesoporous silica powders by an aerosol-assisted synthesis process from both aqueous and ethanol-based precursor dispersions. Transmission electron microscopy (TEM) showed that the titania nanoparticles exist as single particles or small aggregates within the mesoporous carrier particles and analysis of the nitrogen adsorption isotherms proved that the pore blocking of the particles is small. Particle size and zeta potential measurements showed that the addition of tetraethoxysiloxane (TEOS), and also hexadecyl trimethyl ammonium bromide (C16TAB) induced flocculation of the TiO2 nanoparticles. The higher yield and narrower size distribution of the composite powder produced from ethanol-based dispersions compared to the aqueous dispersions could be related to a smaller degree of aggregation, indicated by rheological measurements.

     

1 - 9 of 9
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