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  • 101. Sun, Rui
    et al.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Strømme, Maria
    Cheung, Ocean
    Hierarchical Porous Carbon Synthesized from Novel Porous Amorphous Calcium or Magnesium Citrate with Enhanced SF6 Uptake and SF6/N-2 Selectivity2019Ingår i: Acs Applied Nano Materials, ISSN 2574-0970, Vol. 2, nr 2, s. 778-789Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The emission of greenhouse gases such as CO2 and SF6 is believed to contribute significantly toward global warming. One way to reduce their release is by adsorption at point sources using a suitable adsorbent. In this work we present the synthesis of two hierarchical porous carbon materials (referred to as PC-CaCit and PC-MgCit) with a high uptake of SF 6 (5.23 mmol/g, 0 degrees C, 100 kPa) and a reasonable uptake of CO2 (>3 mmol/g). PC-CaCit and PC-MgCit were obtained by pyrolysis of the most porous calcium citrate and magnesium citrate ever reported, which were synthesized by us. The Langmuir specific surface area of PC-CaCit and PC-MgCit was over 2000 m(2)/g (BET surface area also close to 2000 m(2)/g). We characterized PC-CaCit and PC-MgCit using a range of advanced characterization techniques including N-2 adsorption, high-resolution electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. PC-CaCit and PC-MgCit also showed a SF6-over-N-2 selectivity of similar to 33 at 0 degrees C (100 kPa), good cyclic performance, and moderately low heat of adsorption. The porous carbons synthesized in this work are good candidate adsorbents for greenhouse gases.

  • 102. Sun, Rui
    et al.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Strømme, Maria
    Cheung, Ocean
    The effects of additives on the porosity and stability of amorphous calcium carbonate2019Ingår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 292, artikel-id 109736Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amorphous calcium carbonate (ACC) stabilized by various carboxylic additives was synthesized by incorporating the additives into an ACC suspension in methanol. The additives studied included polyacrylic acid, citric acid, adipic acid, 6-aminocaproic acid, 4-aminobutyric acid and hexanoic acid. The stabilized ACC samples (ACC-additives) exhibited similar characteristics to ACC alone. They appeared X-ray amorphous, contained characteristic infrared bands and had the same nanoparticle aggregated microstructure as ACC. The porosity of the ACC-additives was, however, markedly improved, with Brimauer-Emmett-Teller (BET) surface areas of up to similar to 640 m(2)/g. The BET surface area of ACC-citric acid was close to double that of a highly porous ACC sample. The structure and amount of the additive had a noticeable effect on the porosity of the ACC-additives. When the additive was adsorbed onto the surface of the ACC nanoparticles, their growth was restricted. The restricted growth reduced the size of the ACC nanoparticles, which increased the BET surface area of ACC. Finally, the long-term stability study revealed that the stability of all the ACC-additives was markedly enhanced when stored in ambient or semi-airtight conditions (in a closed falcon tube). In particular, ACC stabilized with adipic acid (ACC-AA-267) had excellent stability, remaining in an amorphous phase for more than one year under ambient conditions and retaining similar to 87% porosity for 48 weeks under semi-airtight conditions. The extremely high porosity and excellent long-term stability make these ACC-additives promising candidates for applications where porosity and stability are critical, such as those involving adsorption, bone regeneration or drug delivery.

  • 103. Sun, Rui
    et al.
    Zhang, Peng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Uppsala University, Sweden.
    Bajnócz, Éva G.
    Neagu, Alexandra
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Persson, Ingmar
    Strømme, Maria
    Cheung, Ocean
    Amorphous Calcium Carbonate Constructed from Nanoparticle Aggregates with Unprecedented Surface Area and Mesoporosity2018Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, nr 25, s. 21556-21564Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amorphous calcium carbonate (ACC), with the highest reported specific surface area of all current forms of calcium carbonate (over 350 m(2) g(-1)), was synthesized using a surfactant-free, one-pot method. Electron microscopy, helium pycnometry, and nitrogen sorption analysis revealed that this highly mesoporous ACC, with a pore volume of similar to 0.86 cm(3) g(-1) and a pore-size distribution centered at 8-9 nm, is constructed from aggregated ACC nanoparticles with an estimated average diameter of 7.3 nm. The porous ACC remained amorphous and retained its high porosity for over 3 weeks under semi-air-tight storage conditions. Powder X-ray diffraction, large-angle X-ray scattering, infrared spectroscopy, and electron diffraction exposed that the porous ACC did not resemble any of the known CaCO3 structures. The atomic order of porous ACC diminished at interatomic distances over 8 angstrom. Porous ACC was evaluated as a potential drug carrier of poorly soluble substances in vitro. Itraconazole and celecoxib remained stable in their amorphous forms within the pores of the material. Drug release rates were significantly enhanced for both drugs (up to 65 times the dissolution rates for the crystalline forms), and supersaturation release of celecoxib was also demonstrated. Citric acid was used to enhance the stability of the ACC nanoparticles within the aggregates, which increased the surface area of the material to over 600 m(2) g(-1). This porous ACC has potential for use in various applications where surface area is important, including adsorption, catalysis, medication, and bone regeneration.

  • 104. Sun, Rui
    et al.
    Åhlén, Michelle
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bajnóczi, Éva G.
    de Kleijne, Fenne
    Ferraz, Natalia
    Persson, Ingmar
    Strømme, Maria
    Cheung, Ocean
    Highly Porous Amorphous Calcium Phosphate for Drug Delivery and Bio-Medical Applications2020Ingår i: Nanomaterials, E-ISSN 2079-4991, Vol. 10, nr 1, artikel-id 20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amorphous calcium phosphate (ACP) has shown significant effects on the biomineralization and promising applications in bio-medicine. However, the limited stability and porosity of ACP material restrict its practical applications. A storage stable highly porous ACP with Brunauer-Emmett-Teller surface area of over 400 m(2)/g was synthesized by introducing phosphoric acid to a methanol suspension containing amorphous calcium carbonate nanoparticles. Electron microscopy revealed that the porous ACP was constructed with aggregated ACP nanoparticles with dimensions of several nanometers. Large angle X-ray scattering revealed a short-range atomic order of <20 angstrom in the ACP nanoparticles. The synthesized ACP demonstrated long-term stability and did not crystallize even after storage for over 14 months in air. The stability of the ACP in water and an alpha-MEM cell culture medium were also examined. The stability of ACP could be tuned by adjusting its chemical composition. The ACP synthesized in this work was cytocompatible and acted as drug carriers for the bisphosphonate drug alendronate (AL) in vitro. AL-loaded ACP released 25% of the loaded AL in the first 22 days. These properties make ACP a promising candidate material for potential application in biomedical fields such as drug delivery and bone healing.

  • 105. Svensson, Fredric G. G.
    et al.
    Daniel, Geoffrey
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Seisenbaeva, Gulaim A. A.
    Kessler, Vadim G. G.
    Titanium phosphonate oxo-alkoxide clusters: solution stability and facile hydrolytic transformation into nano titania2020Ingår i: RSC Advances, E-ISSN 2046-2069, Vol. 10, nr 12, s. 6873-6883Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Titanium (oxo-) alkoxide phosphonate complexes were synthesized using different titanium precursors and tert-butylphosphonic acid (tBPA) as molecular models for interaction between phosphonates and titania surfaces and to investigate the solution stability of these species. Reflux of titanium(iv) ethoxide or titanium(iv)(diisopropoxide)bis(2,4-pentadionate) with tert-butylphosphonic acid in toluene-ethanol mixture or acetone yielded seven titanium alkoxide phosphonate complexes; [Ti-5(mu(3)-O)(mu(2)-O)(mu-HOEt)(2)(mu-OEt)(3)(mu(2)-OEt)(mu(3)-tBPA)(3)(mu(3)-HtBPA)(mu(2)-tBPA)(2)(mu(2)-HtBPA)]center dot 3EtOH, 1, [Ti4O(mu-OEt)(5)(mu(2)-OEt)(7)(mu(3)-tBPA)], 2, [Ti-4(mu(2)-O)(2)(mu-OEt)(2)(mu-HOEt)(2)(mu(2)-tPBA)(2)(mu(2)-HtPBA)(6)]center dot 4EtOH, 3, [Ti-4(mu(2)-O)(2)(mu-OEt)(2)(mu-HOEt)(2)(mu(2)-tPBA)(2)(mu(2)-HtPBA)(6)]center dot 2EtOH, 4, [Ti-6(mu(2)-O)(mu(3)-O)(2)(mu(2)-OEt)(5)(mu-OEt)(6)(mu(3)-tBPA)(3)(mu(3)-HtBPA)], 5, [Ti-4(mu-(OPr)-O-i)(4)(acac)(4)(mu(2)-tBPA)(4)], 6 and [Ti-5(mu(4)-O)(mu(2)-O)(3)(mu(2)-OEt)(4)(mu-OEt)(6)(mu-HOEt)(mu(3)-tBPA)](2), 7. The binding mode of tBPA to the titanium oxo-core were either double or triple bridging or a combination of the two. No monodentate or chelating coordination was observed. P-31 NMR spectrometry of dissolved single crystals indicates that 1 and 5 retain their solid-state structures in solution, the latter even on moderate heating, while 6 and 7 dissolved into several other forms. The complexes were found to be sensitive towards hydrolysis, proceeding in a topotactic fashion with densification of the material into plates and lamellae resulting finally in core-shell nanoparticles with a crystalline core (anatase) and an amorphous outer shell upon contact with water at room temperature as observed by HRTEM and AFM analyses. P-31 NMR data supported degradation after addition of water to solutions of the complexes. Hydrolysis under different conditions affords complex oxide structures of different morphologies.

  • 106.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Diffuse scattering in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3 relaxor solid solutions2013Ingår i: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 18, nr 2, s. 1900-1901Artikel i tidskrift (Refereegranskat)
  • 107.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ferroelectric domain morphology, electrical and electromechanical properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics2011Ingår i: Ferroelectric and Multiferroic Materials, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics were fabricated by mixed-oxide route. The compositions along morphotropic phase boundary were investigated. Dielectric properties and piezoelectric coefficient were measured. The maximum relative permittivity is 33600 found in the (PIN-PT)x(PMN-PT)1-x ceramics with x = 0.1 at 167 °C. When increasing the amount of Pb(In1/2Nb1/2)O3, the piezoelectric coefficient of the ceramics decreases but the phase transition temperature increases. The selected-area electron diffraction patterns show the pseudo-cubic perovskite symmetry. Diffuse scattering is found in the diffraction pattern taken at higher order zone axis. Transmission electron microscopy study shows that the morphology of ferroelectric/ferroelastic domains is neither tetragonal nor rhombohedral configuration

  • 108.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Morphological study of soot particles by off-axis electron holography2010Ingår i: Proceedings of 17th International Microscopy Congress, Rio de Janeiro,Brazil, 2010, s. M22.2-Konferensbidrag (Refereegranskat)
    Abstract [en]

     

     

     

  • 109.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Oxygen octahedral tilting and ferroelectric domain morphology in lead-free Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3-BaTiO3 ceramics2010Ingår i: Proceedings of the 17th International Microscopy Congress, Rio de Janeiro, Brazil, 2010, s. M9.12-1-M9.12-2Konferensbidrag (Refereegranskat)
    Abstract [en]

     

     

  • 110.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Synthesis and characterization of carbon nanotubes decorated with gold nanoparticles2010Ingår i: Acta Physica Polonica. A, ISSN 0587-4246, E-ISSN 1898-794X, Vol. 118, nr 3, s. 483-486Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In presented work we report results of simple and viable method for producing Au/CNT composites. Chemicalcomposition and crystallographic structure of the Au/CNT composites was confirmed by X-ray diffractionmeasurements, while transmission and scanning electron microscopy were used to characterize the morphology ofnanocrystals as well as the distribution of nanocrystals in the composite. The obtained particles with relativelysmall diameter (less than 9 nm) were found to be spatially well dispersed on the carbon nanotubes. The densityof attached Au–nanoparticles is not sufficient, and cannot be improved by simple increasing gold loading.

  • 111.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    TEM sample preparation by facile ion-milling - Ion Slicer2014Konferensbidrag (Övrigt vetenskapligt)
  • 112.
    Tai, Cheuk-Wai
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Santosh, Mysore Sridhar
    Microwave assisted systhesis and magnetics studies of cobalt oxide nanoparticles2010Ingår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 125, s. 347-350Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An efficient microwave-assisted route has been used to synthesize nanoparticles of cobalt oxide. The particles were well characterized by transmission electron microscopy (TEM) which showed that the average diameter of the particles is around 6 nm. X-ray diffraction (XRD) studies further confirmed the formation of the spinel Co3O4. Purity of the products was detected by Fourier transform infrared spectroscopy (FTIR) combined with thermal gravimetric analysis (TG/DTG). The magnetic measurements revealed a small hysteresis loop at room temperature indicating a weak ferromagnetic nature of the synthesized Co3O4 nanoparticles. The magnetic moment of the particles was measured to be 4.27 μeff.

  • 113. Talyzin, A. V.
    et al.
    Luzan, S. M.
    Leifer, K.
    Akhtar, S.
    Fetzer, J.
    Cataldo, F.
    Tsybin, Y. O.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Dzwilewski, A.
    Moons, E.
    Coronene Fusion by Heat Treatment: Road to Nanographenes2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 27, s. 13207-13214Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500-700 degrees C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530-550 degrees C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550-600 degrees C by oligomerization into larger molecules. Above 600 degrees C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.

  • 114.
    Thersleff, Thomas
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Schönström, Linus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Uppsala University, Sweden.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Adam, Roman
    Bürgler, Daniel E.
    Schneider, Claus M.
    Muto, Shunsuke
    Rusz, Ján
    Single-pass STEM-EMCD on a zone axis using a patterned aperture: progress in experimental and data treatment methods2019Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 9, artikel-id 18170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measuring magnetic moments in ferromagnetic materials at atomic resolution is theoretically possible using the electron magnetic circular dichroism (EMCD) technique in a (scanning) transmission electron microscope ((S)TEM). However, experimental and data processing hurdles currently hamper the realization of this goal. Experimentally, the sample must be tilted to a zone-axis orientation, yielding a complex distribution of magnetic scattering intensity, and the same sample region must be scanned multiple times with sub-atomic spatial registration necessary at each pass. Furthermore, the weak nature of the EMCD signal requires advanced data processing techniques to reliably detect and quantify the result. In this manuscript, we detail our experimental and data processing progress towards achieving single-pass zone-axis EMCD using a patterned aperture. First, we provide a comprehensive data acquisition and analysis strategy for this and other EMCD experiments that should scale down to atomic resolution experiments. Second, we demonstrate that, at low spatial resolution, promising EMCD candidate signals can be extracted, and that these are sensitive to both crystallographic orientation and momentum transfer.

  • 115.
    Tinnis, Fredrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Verho, Oscar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient Palladium-Catalyzed Aminocarbonylation of Aryl Iodides Using Palladium Nanoparticles Dispersed on Siliceous Mesocellular Foam2014Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, nr 20, s. 5885-5889Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A highly dispersed nanopalladium catalyst supported on mesocellular foam (MCF), was successfully used in the heterogeneous catalysis of aminocarbonylation reactions. During the preliminary evaluation of this catalyst it was discovered that the supported palladium nanoparticles exhibited a “release and catch” effect, meaning that a minor amount of the heterogeneous palladium became soluble and catalyzed the reaction, after which it re-deposited onto the support.

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  • 116.
    Tran, Dung
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    TEM-based pair distribution function study of bimetallic nanoparticles2014Ingår i: XV International Conference on Electron Microscopy, 2014Konferensbidrag (Övrigt vetenskapligt)
  • 117.
    Tran, Dung Trung
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    SUePDF: a program to obtain quantitative pair distribution functions from electron diffraction data2017Ingår i: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 50, s. 304-312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    SUePDF is a graphical user interface program written in MATLAB to achieve quantitative pair distribution functions (PDFs) from electron diffraction data. The program facilitates structural studies of amorphous materials and small nanoparticles using electron diffraction data from transmission electron microscopes. It is based on the physics of electron scattering as well as the total scattering methodology. A method of background modeling is introduced to treat the intensity tail of the direct beam, inelastic scattering and incoherent multiple scattering. Kinematical electron scattering intensity is scaled using the electron scattering factors. The PDFs obtained after Fourier transforms are normalized with respect to number density, nanoparticle form factor and the non-negativity of probability density. SUePDF is distributed as free software for academic users.

  • 118.
    Tran, Dung-Trung
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Atomistic computation of the finite size effect in pair distribution function of nanoparticlesManuskript (preprint) (Övrigt vetenskapligt)
  • 119.
    Tran, Dung-Trung
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    TEM-based total scattering method for studying disorder of nanoparticles2014Konferensbidrag (Övrigt vetenskapligt)
  • 120.
    Trushkina, Yulia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Salazar-Alvarez, German
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Fabrication of Maghemite Nanoparticles with High Surface Area2019Ingår i: Nanomaterials, E-ISSN 2079-4991, Vol. 9, nr 7, artikel-id 1004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Maghemite nanoparticles with high surface area were obtained from the dehydroxylation of lepidocrocite prismatic nanoparticles. The synthesis pathway from the precursor to the porous maghemite nanoparticles is inexpensive, simple and gives high surface area values for both lepidocrocite and maghemite. The obtained maghemite nanoparticles contained intraparticle and interparticle pores with a surface area ca. 30 x 10(3) m(2)/mol, with pore volumes in the order of 70 cm(3)/mol. Both the surface area and pore volume depended on the heating rate and annealing temperature, with the highest value near the transformation temperature (180-250 degrees C). Following the transformation, in situ X-ray diffraction (XRD) allowed us to observe the temporal decoupling of the decomposition of lepidocrocite and the growth of maghemite. The combination of high-angle annular dark-field imaging using scanning transmission electron microscopy (HAADF-STEM) and surface adsorption isotherms is a powerful approach for the characterization of nanomaterials with high surface area and porosity.

  • 121.
    Valiente, Alejandro
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Carrasco, Sergio
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sanz-Marco, Amparo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bermejo Gómez, Antonio
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Sprint Bioscience, Sweden.
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Aerobic Homocoupling of Arylboronic Acids Catalyzed by Regenerable Pd(II)@MIL-88B-NH2(Cr)2019Ingår i: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 11, nr 16, s. 3933-3940Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fast and operationally simple method for the aerobic homocoupling of arylboronic acids is described. The process is catalyzed by Pd(II) complexes supported on the metal-organic framework MIL-88B-NH2(Cr). The benefits of this approach include the use of a benign oxidant/solvent mixture at room temperature with catalytic amounts of base, easy recovery of the catalyst, and easy isolation of the products. Very high conversions and good yields were achieved for a variety of substrates, and the process was also carried out on a larger scale with the same efficiency. The catalyst was found to suffer deactivation due to progressive reduction and agglomeration of palladium into inactive metal clusters/particles. An innovative procedure for the oxidative redispersion and regeneration of the active Pd(II)@MOF species is presented. 

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  • 122.
    Valiente, Alejandro
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    S. G. Ahlquist, Mårten
    Martín-Matute, Belen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tetrameric Aryl Palladium Bromide Intermediates Leading to Easy Transmetalation in Suzuki – Miyaura Cross-Couplings with Pd @ MIL-101-NH2Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The composition and structure of catalytic intermediates in the context of the Suzuki – Miyaura cross-coupling reaction catalyzed by Pd @ MIL-101-NH2 has been investigated. Trimeric and tetrameric palladium species with formula [Br-Pd-Ar] n Br -(n = 3–4) have been identified by electrospray ionization mass spectrometry (ESI-MS) and density-functional theory (DFT) calculations, and their role in the transmetalation step has been studied. The weak nature of the bonds between Pd and the bridging halides in these species enables a very easy transmetalation step, with an estimated activation free energy of only 10 kcal / mol. Further experimental support for Pd speciation was obtained using scanning transmission electron microscopy (STEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and fluorine-19 nuclear magnetic resonance spectroscopy (19 F NMR). 

  • 123. Valvo, Mario
    et al.
    Chien, Yu-Chuan
    Liivat, Anti
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Detecting voltage shifts and charge storage anomalies by iron nanoparticles in three-electrode cells based on converted iron oxide and lithium iron phosphate2023Ingår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 440, artikel-id 141747Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Noticeable voltage shifts have been observed in the charge/discharge profiles of a three-electrode cell with a lithium metal reference electrode and having a deeply lithiated iron oxide (Fe/Li2O) negative electrode galvanostatically cycled in a limited potential range against a positive LiFePO4 counterpart. The origin of such shifts has been attributed to charge storage anomalies in the Fe/Li2O nanocomposite due to characteristic reduced Fe nanoparticle sizes. These shifts also affected the extreme points of the voltage profiles of the positive electrode, which was also independently monitored. A combined evaluation of voltage profile slippages with possible changes in internal resistance and/or Li+ inventory loss, including an aimed analysis of current interruptions at the end of each lithiation/de-lithiation half-cycle to monitor the internal resistance and diffusion resistance coefficient of the Fe/Li2O electrode, has enabled a clarification of its altered charge storage. An asymmetric behaviour of the Fe/Li2O electrode during Li+ uptake/release has been revealed, highlighting a progressive, diffusion-controlled-type voltage drift at low potentials vs. Li+/Li, and an unusual tendency to slight oxidation with capacitive variations during the reverse electrochemical processes at higher voltages, instead.

  • 124. Valvo, Mario
    et al.
    Liivat, Anti
    Eriksson, Henrik
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Edström, Kristina
    Iron-Based Electrodes Meet Water-Based Preparation, Fluorine-Free Electrolyte and Binder: A Chance for More Sustainable Lithium-Ion Batteries?2017Ingår i: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, nr 11, s. 2431-2448Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Environmentally friendly and cost-effective Li-ion cells are fabricated with abundant, non-toxic LiFePO4 cathodes and iron oxide anodes. A water-soluble alginate binder is used to coat both electrodes to reduce the environmental footprint. The critical reactivity of LiPF6-based electrolytes toward possible traces of H2O in water-processed electrodes is overcome by using a lithium bis(oxalato) borate (LiBOB) salt. The absence of fluorine in the electrolyte and binder is a cornerstone for improved cell chemistry and results in stable battery operation. A dedicated approach to exploit conversion-type anodes more effectively is also disclosed. The issue of large voltage hysteresis upon conversion/de-conversion is circumvented by operating iron oxide in a deeply lithiated Fe/Li2O form. Li-ion cells with energy efficiencies of up to 92% are demonstrated if LiFePO4 is cycled versus such anodes prepared through a prelithiation procedure. These cells show an average energy efficiency of approximately 90.66% and a mean Coulombic efficiency of approximately 99.65% over 320 cycles at current densities of 0.1, 0.2 and 0.3 mAcm(-2). They retain nearly 100% of their initial discharge capacity and provide an unmatched operation potential of approximately 2.85 V for this combination of active materials. No occurrence of Li plating was detected in three-electrode cells at charging rates of approximately 5C. Excellent rate capabilities of up to approximately 30C are achieved thanks to the exploitation of size effects from the small Fe nanoparticles and their reactive boundaries.

  • 125. Valvo, Mario
    et al.
    Philippe, Bertrand
    Lindgren, Fredrik
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Edström, Kristina
    Insight into the processes controlling the electrochemical reactions of nanostructured iron oxide electrodes in Li- and Na-half cells2016Ingår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 194, s. 74-83Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The kinetics and the processes governing the electrochemical reactions of various types of iron oxide nanostructures (i.e., nanopowders, nanowires and thin-films) have been studied via cyclic voltammetry in parallel with Li- and Na-half cells containing analogous electrolytes (Li+/Na+, ClO4- in EC:DEC). The particular features arising from each electrode architecture are discussed and compared to shed light on the associated behaviour of the reacting nanostructured active materials. The influence of their characteristic structure, texture and electrical wiring on the overall conversion reaction upon their respective lithiation and sodiation has been analyzed carefully. The limiting factors existing for this reaction upon uptake of Li+ and Na+ ions are highlighted and the related issues in both systems are addressed. The results of this investigation clearly prove that the conversion of iron oxide into metallic Fe and Na2O is severely impeded compared to its analogous process upon lithiation, independently of the type of nanostructure involved in such reaction. The diffusion mechanisms of the different ions (i.e., Li+ vs. Na+) through the phases formed upon conversion, as well as the influence of various interfaces on the resulting reaction, appear to pose further constraints on an efficient use of these compounds.

  • 126.
    Verho, Oscar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nagendiran, Anuja
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mild and Selective Hydrogenation of Nitro Compounds using Palladium Nanoparticles Supported on Amino-Functionalized Mesocellular Foam2014Ingår i: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, nr 11, s. 3153-3159Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the utilization of a heterogeneous catalyst comprised of Pd nanoparticles supported on aminopropyl-functionalized siliceous mesocellular foam (Pd-0-AmP-MCF) for the selective hydrogenation of aromatic, aliphatic, and heterocyclic nitro compounds to the corresponding amines. In general, the catalytic protocol exclusively affords the desired amine products in excellent yields within short reaction times with the reactions performed at room temperature under ambient pressure of H-2. Moreover, the reported Pd nanocatalyst displayed excellent structural integrity for this transformation as it could be recycled multiple times without any observable loss of activity or leaching of metal. In addition, the Pd nanocatalyst could be easily integrated into a continuous-flow device and used for the hydrogenation of 4-nitroanisole on a 2.5 g scale, where the product p-anisidine was obtained in 95% yield within 2 h with a Pd content of less than 1 ppm.

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  • 127.
    Verho, Oscar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kärkäs, Markus
    Åkermark, Torbjörn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Johnston, Eric V.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Svengren, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Well-Defined Palladium Nanoparticles Supported on Amino-Functionalized Siliceous Mesocellular Foam: An Efficient Heterogeneous Catalyst for Chemically-Induced H2O OxidationManuskript (preprint) (Övrigt vetenskapligt)
  • 128.
    Verho, Oscar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nagendiran, Anuja
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johnston, Eric V.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nanopalladium on Amino-Functionalized Mesocellular Foam: An Efficient Catalyst for Suzuki Reactions and Transfer Hydrogenations2013Ingår i: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, nr 2, s. 612-618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The applications of a heterogeneous Pd0-AmP-MCF nanoparticle catalyst in Suzuki cross-coupling reactions and transfer hydrogenations of alkenes are described. The catalyst was highly efficient for both transformations, resulting in 1)coupling of a wide range of aryl halides with various boronic acids in high yields and 2)chemoselective reduction of a variety of alkenes with the use of 1-methyl-1,4-cyclohexadiene as hydrogen donor. Moreover, the catalyst can be recycled several times without any significant decrease in activity or leaching of metal into solution, making the protocol economical and environmentally friendly. In the case of the Suzuki cross-coupling, a 15-fold increase in reaction rate was observed if the reaction was performed under microwave irradiation compared to conventional heating in an oil bath.

  • 129.
    Verho, Oscar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nagendiran, Anuja
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Johnston, Eric V.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nanopalladium on Amino-Functionalized Mesocellular Foam as an Efficient and Recyclable Catalyst for the Selective Transfer Hydrogenation of Nitroarenes to Anilines2014Ingår i: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, nr 1, s. 205-211Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, we report on the use of nanopalladium on amino-functionalized siliceous mesocellular foam as an efficient heterogeneous catalyst for the transfer hydrogenation of nitroarenes to anilines. In all cases, the protocol proved to be highly selective and favored the formation of the desired aniline as the single product in high yields with short reaction times if naturally occurring and renewable -terpinene was employed as the hydrogen donor. Furthermore, the catalyst displayed excellent recyclability over five cycles and negligible leaching of metal into solution, which makes it an eco-friendly and economic catalyst to perform this transformation. The scalability of the protocol was demonstrated with the reduction of 4-nitroanisole on a 2g scale, in which p-anisidine was isolated in 98% yield.

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  • 130.
    Verho, Oscar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Torbjörn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johnston, Eric V.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svengren, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Kärkäs, Markus D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Well-Defined Palladium Nanoparticles Supported on Siliceous Mesocellular Foam as Heterogeneous Catalysts for the Oxidation of Water2015Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, nr 15, s. 5909-5915Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, we describe the use of Pd nanoparticles immobilized on an amino-functionalized siliceous mesocellular foam for the catalytic oxidation of H2O. The Pd nanocatalyst proved to be capable of mediating the four-electron oxidation of H2O to O-2, both chemically and photochemically. The Pd nanocatalyst is easy to prepare and shows high chemical stability, low leaching, and recyclability. Together with its promising catalytic activity, these features make the Pd nanocatalyst of potential interest for future sustainable solar-fuel production.

  • 131.
    Volkov, Alexey
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Verho, Oscar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mild Deoxygenation of Aromatic Ketones and Aldehydes over Pd/C Using Polymethylhydrosiloxane as the Reducing Agent2015Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 54, nr 17, s. 5122-5126Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, a practical and mild method for the deoxygenation of a wide range of benzylic aldehydes and ketones is described, which utilizes heterogeneous Pd/C as the catalyst together with the green hydride source, polymethylhydrosiloxane. The developed catalytic protocol is scalable and robust, as exemplified by the deoxygenation of ethyl vanillin, which was performed on a 30 mmol scale in an open-to-air setup using only 0.085 mol% Pd/C catalyst to furnish the corresponding deoxygenated product in 93% yield within 3 hours at room temperature. Furthermore, the Pd/C catalyst was shown to be recyclable up to 6 times without any observable decrease in efficiency and it exhibited low metal leaching under the reaction conditions.

  • 132. Wei, Wei
    et al.
    Oltean, Gabriel
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Edström, Kristina
    Björefors, Fredrik
    Nyholm, Leif
    High energy and power density TiO2 nanotube electrodes for 3D Li-ion microbatteries2013Ingår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 1, nr 28, s. 8160-8169Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Highly ordered anodic TiO2 nanotube arrays with a tube length of 9 mm are shown to provide areal capacities of 0.24 mA h cm(-2) (i.e. 96 mA h g(-1)) at a charge/discharge current density of 2.5 mA cm(-2) (corresponding to a rate of 5 C) and 0.46 mA h cm(-2) (i.e. 184 mA h g(-1)) at 0.05 mA cm(-2), when used as 3D free-standing anodes in Li-ion microbatteries. The present nanotube electrodes, which could be cycled for 500 cycles with only 6% loss of capacity, exhibited significantly higher energy and power densities, as well as an excellent cycling stability compared to previously reported TiO2-based Li-ion microbattery electrodes. The influence of parameters such as ordering, geometry and crystallinity of the nanotubes on the microbattery performance was investigated. A two-step anodization process followed by annealing of the nanotubes was found to yield the best microbattery performance. It is also demonstrated that the rate capability of the electrode depends mainly on the rate of the structural rearrangements associated with the lithiation/delithiation reaction and that the areal capacity at various charge/discharge rates can be increased by increasing the tube wall thickness or the length of the nanotubes, up to 0.6 mA h cm(-2) for 100 cycles.

  • 133.
    Wetterskog, Erik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Salazar-Alvarez, German
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Anomalous Magnetic Properties of Nanoparticles Arising from Defect Structures: Topotaxial Oxidation of Fe1-xO|Fe3-δO4 Core|Shell Nanocubes to Single-Phase Particles2013Ingår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, nr 8, s. 7132-7144Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here we demonstrate that the anomalous magnetic properties of iron oxide nanoparticles are correlated with defects in their interior. We studied the evolution of microstructure and magnetic properties of biphasic core|shell Fe1–xO|Fe3−δO4 nanoparticles synthesized by thermal decomposition during their topotaxial oxidation to single-phase nanoparticles. Geometric phase analysis of high-resolution electron microscopy images reveals a large interfacial strain at the core|shell interface and the development of antiphase boundaries. Dark-field transmission electron microscopy and powder X-ray diffraction concur that, as the oxidation proceeds, the interfacial strain is released as the Fe1–xO core is removed but that the antiphase boundaries remain. The antiphase boundaries result in anomalous magnetic behavior, that is, a reduced saturation magnetization and exchange bias effects in single-phase nanoparticles. Our results indicate that internal defects play an important role in dictating the magnetic properties of iron oxide nanoparticles.

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    ACSNano-Core|shell
  • 134.
    Wetterskog, Erik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Salazar-Alvarez, German
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Strain relief during stepwise oxidation of monodisperse Fe1-xO/Fe3-xO4 nanocubes. Influence on their structure and magnetic properties.2011Konferensbidrag (Övrigt vetenskapligt)
  • 135. Wikberg, J. Magnus
    et al.
    Knut, Ronny
    Bhandary, Sumanta
    di Marco, Igor
    Ottosson, Mikael
    Sadowski, Janusz
    Sanyal, Biplab
    Palmgren, Pal
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Eriksson, Olle
    Karis, Olof
    Svedlindh, Peter
    Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 2, s. 024417-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature (T(c)), and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants, the enhancement of the magnetic moment at saturation is significant. Results of x-ray magnetic circular dichroism show a behavior of the spin and orbital moment that is consistent with a structural transition at T(c). In particular, we find that the ratio of the orbital to the spin moment shows a marked increase in the coexistence region of the ferromagnetic alpha- and paramagnetic beta-phases a result that is well in accord with the observed increase in the c/a ratio in the same temperature region. The ab initio density functional calculations reveal that the magnetic properties are more sensitive towards change in the ab-plane compared to change in the c-axis which is explained by the analysis of band structures. The effects of electron correlation in MnAs using ab initio dynamical mean field theory are also presented.

  • 136.
    Xu, Chao
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Afewerki, Samson
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Mid Sweden University, Sweden.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Córdova, Armando
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Cyclopalladated Azo-linked Porous Polymers in C-C Bond Forming Reactions2016Ingår i: ChemistrySelect, ISSN 2365-6549, Vol. 1, nr 18, s. 5801-5804Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We designed a new cyclopalladated porous polymer (cyclo-Pd (II)/PP-2) with up to 20.7 wt% of Pd and investigated it as a heterogeneous catalyst for C-C bond-forming transformations. It was also shown to be an effective scavenger for Pd2+ in solution. The palladacycles formed along the backbone of the azo-linked porous polymer (PP-2) with (Pd-N) and (Pd-C) bonds as were confirmed by a combination of spectroscopies. The cyclo-Pd(II)/PP-2 decomposed when used for Suzuki and Heck cross-coupling reactions, and acyclic-Pd/PP-2 formed with Pd nanoparticles (NPs) bound to the PP-2. The Suzuki couplings were highly efficient in water and exhibited excellent recyclability. The cyclo-Pd(II)/PP-2 was also an effective heterogeneous Lewis-acid catalyst for stereoselective carbocyclization reactions.

  • 137.
    Yuan, Ning
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Swedish University of Agricultural Sciences, Sweden.
    Gudmundsson, Arnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Oschmann, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Persson, Ingmar
    Zou, Xiaodong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Verho, Oscar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Uppsala University, Sweden.
    Bajnóczi, Éva G.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Mid Sweden University, Sweden.
    Investigation of the Deactivation and Reactivation Mechanism of a Heterogeneous Palladium(II) Catalyst in the Cycloisomerization of Acetylenic Acids by In Situ XAS2021Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 11, nr 5, s. 2999-3008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A well-studied heterogeneous palladium(II) catalyst used for the cycloisomerization of acetylenic acids is known to be susceptible to deactivation through reduction. To gain a deeper understanding of this deactivation process and to enable the design of a reactivation strategy, in situ X-ray absorption spectroscopy (XAS) was used. With this technique, changes in the palladium oxidation state and coordination environment could be studied in close detail, which provided experimental evidence that the deactivation was primarily caused by triethylamine-promoted reduction of palladium(II) to metallic palladium nanoparticles. Furthermore, it was observed that the choice of the acetylenic acid substrate influenced the distribution between palladium(II) and palladium(0) species in the heterogeneous catalyst after the reaction. From the mechanistic insight gained through XAS, an improved catalytic protocol was developed that did not suffer from deactivation and allowed for more efficient recycling of the catalyst.

  • 138. Zeng, Lunjie
    et al.
    Tran, Dung Trung
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Olsson, Eva
    Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions2016Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 6, artikel-id 29679Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

  • 139. Zhang, Leiting
    et al.
    Müller Gubler, Elisabeth Agnes
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Kondracki, Łukasz
    Sommer, Heino
    Novák, Petr
    El Kazzi, Mario
    Trabesinger, Sigita
    Elucidating the Humidity-Induced Degradation of Ni-Rich Layered Cathodes for Li-Ion Batteries2022Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 14, nr 11, s. 13240-13249Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ni-rich layered oxides, in a general term of Li(NixCoyMn1–x–y)O2 (x > 0.5), are widely recognized as promising candidates for improving the specific energy and lowering the cost for next-generation Li-ion batteries. However, the high surface reactivity of these materials results in side reactions during improper storage and notable gas release when the cell is charged beyond 4.3 V vs Li+/Li0. Therefore, in this study, we embark on a comprehensive investigation on the moisture sensitivity of LiNi0.85Co0.1Mn0.05O2 by aging it in a controlled environment at a constant room-temperature relative humidity of 63% up to 1 year. We quantitatively analyze the gassing of the aged samples by online electrochemical mass spectrometry and further depict plausible reaction pathways, accounting for the origin of the gas release. Transmission electron microscopy reveals formation of an amorphous surface impurity layer of ca. 10 nm in thickness, as a result of continuous reactions with moisture and CO2 from the air. Underneath it, there is another reconstructed layer of ca. 20 nm in thickness, showing rock salt/spinel-like features. Our results provide insight into the complex interfacial degradation phenomena and future directions for the development of high-performance Ni-rich layered oxides. 

  • 140. Zhang, Yunfan
    et al.
    Selvaraj, Rengaraj
    Kim, Younghun
    Sillanpaa, Mika
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Photo-corrosion inhibition of Ag3PO4 by polyaniline coating2016Ingår i: Desalination and Water Treatment, ISSN 1944-3994, E-ISSN 1944-3986, Vol. 57, nr 29, s. 13394-13403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, polyaniline-coated silver phosphate has been successfully prepared via a facile chemisorption method in order to improve the stability of Ag3PO4 under light irradiation. The crystalline phase, band gap energy, and microstructure of the obtained PANI/Ag3PO4 composites were characterized by X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, and transmission electron microscopy, respectively. The photocatalytic degradation of methlylene blue was performed to test the activities of PANI/Ag3PO4 composites with different coating amounts and the results indicate that the stabilities of PANI/Ag3PO4 composites were successfully enhanced. The correlation between photocatalytic performance and the properties of PANI/Ag3PO4 composites is discussed in detail.

  • 141. Zhang, Yunfan
    et al.
    Selvaraj, Rengaraj
    Sillanpaa, Mika
    Kim, Younghun
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    The influence of operating parameters on heterogeneous photocatalytic mineralization of phenol over BiPO42014Ingår i: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 245, s. 117-123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The photocatalytic mineralization of phenol was investigated in the presence of BiPO4 prepared by hydrothermal method. The crystal structure and morphology of synthesized sample was inspected with powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The photocatalytic activity of BiPO4 was evaluated by the degradation of phenol in a batch reactor under UV-C irradiation. In order to investigate the influence of catalyst dosage, pH value, initial concentration and additives on mineralization behavior, these key operating parameters were systematically changed during the photocatalytic process. The findings confirmed that the phenol was degraded by BiPO4 under UV-C irradiation, and the TOC (Total Organic Carbon) analysis proved that the mineralization was efficient under the optimized conditions. It is also found that the intermediate process between photocatalytic degradation and mineralization is negligibly short.

  • 142. Zhang, Yunfan
    et al.
    Selvaraj, Rengaraj
    Sillanpää, Mika
    Kim, Younghun
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Coprecipitates Synthesis of CaIn2O4 and Its Photocatalytic Degradation of Methylene Blue by Visible Light Irradiation2014Ingår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, nr 29, s. 11720-11726Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Visible light-activated photocatalyst calcium indate (CaIn2O4) has been successfully prepared by a new approach with lower temperature calcinations. The sub-micrometer-sized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. High-purity CaIn2O4 particles were synthesized by controlling the sintering temperature and their photocatalytic performance were evaluated. Under visible light irradiation, 10 ppm of methylene blue solution was effectively degraded in 3.0 h. The excellent photocatalytic activity of CaIn2O4 is attributed to the high purity, small particle size, and large surface area because of lower sintering temperature by thermal decomposition of metal oxalate precursor.

  • 143. Zhang, Yunfan
    et al.
    Selvaraj, Rengaraj
    Sillanpää, Mika
    Kim, Younghun
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Enhanced solar photocatalytic activity of Er3+: YAlO3-loaded BiPO4 composite2015Ingår i: Journal of Industrial and Engineering Chemistry, ISSN 1226-086X, E-ISSN 1876-794X, Vol. 24, s. 161-165Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Er3+:YAlO3 loaded BiPO4 were successfully synthesized by a simple heat treatment approach in order to enhance the photocatalytic efficiency of BiPO4. Comparing with the simple substance of BiPO4, the composite system showed the better efficiency on photodegradation of Methlyene Blue (MB) solution under a simulated solar light irradiation. The relationship between loading amount and degradation rate was also investigated. It is found that the optimal loading amount of Er3+:YAlO3 is 7 wt%. The recycling test of selected sample was carried out to study the stability of the Er3+:YAlO3 loaded BiPO4 system. The composite materials were finally characterized by field-emission scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible diffuse reflectance spectroscopy (UV-vis DRS). Based on the findings a possible mechanism has been proposed. The existence of luminescence agent (Er3+-doped YAlO3) and the occurrence of upconversion luminescence process have been related with the enhanced photodegradation of MB over composite system. (C) 2014 The Korean Society of Industrial and Engineering Chemistry.

  • 144.
    Zheng, Haoquan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Su, Jie
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zou, Xiaodong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gao, Feifei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ultra-small mesoporous silica nanoparticles as efficient carriers for pH responsive releases of anti-cancer drugs2015Ingår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, nr 46, s. 20186-20192Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mesoporous silica has emerged as one of the most promising carriers for drug delivery systems. However, the synthesis of ultra-small mesoporous silica nanoparticles (UMSNs) and their application in drug delivery remains a significant challenge. Here, spherical UMSNs (similar to 25 nm) have been synthesized and tested as drug carriers. Anti-cancer drugs mitoxantrone (MX), doxorubicin (DOX) and methotrexate (MTX) have been utilized as model drugs. The pH-responsive drug delivery system can be constructed based on electrostatic interactions between carriers and drug molecules. The UMSNs could store drugs under physiological conditions and release them under acidic conditions. Different pH-responsive release profiles were obtained in phosphate buffer solutions (PBSs) at the designed pH values (from 4.0 to 7.4). MX and DOX can be used in the pH-responsive delivery system, while MTX cannot be used. Furthermore, we found that the physiological stabilities of these drug molecules in UMSNs are in a decreasing order MX > DOX > MTX, which follows the order of their isoelectric point (pI) values.

  • 145.
    Zheng, Zhiyao
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Deiana, Luca
    Posevins, Daniels
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rafi, Abdolrahim A.
    Zhang, Kaiheng
    Johansson, Magnus J.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Córdova, Armando
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Mid Sweden University, Sweden.
    Efficient Heterogeneous Copper-Catalyzed Alder-Ene Reaction of Allenynamides to Pyrrolines2022Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 12, nr 3, s. 1791-1796Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, we describe an efficient nanocopper-catalyzed Alder-ene reaction of allenynamides. The copper nanoparticles were immobilized on amino-functionalized microcrystalline cellulose. A solvent-controlled chemoselectivity of the reaction was observed, leading to the chemodivergent synthesis of pyrrolines (2,5-dihydropyrroles) and pyrroles. The heterogeneous copper catalyst exhibits high efficiency and good recyclability in the Alder-ene reaction, constituting a highly attractive catalytic system from an economical and environmental point of view. 

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