TY - JOUR A1 - Pilar Yeste, Maria A1 - Carlos Hernandez-Garrido, Juan A1 - Kumke, Michael Uwe A1 - Alvarado, Sarah A1 - Cauqui, Miguel Angel A1 - Juan Calvino, Jose A1 - Primus, Philipp-Alexander T1 - Low-temperature growth of reactive pyrochlore nanostructures on Zirconia-supported ceria BT - implications for improved catalytic behavior JF - ACS applied nano materials N2 - The use of a catalyst support for the design of nanoscale heterogeneous catalysts based on cerium oxide offers vast possibilities for future catalyst development, particularly with regard to an increased focus on the use of renewable biogas and an emerging hydrogen economy. In this study, zirconia-supported ceria catalysts were synthesized, activated by using different thermochemical treatments, and characterized by way of temperature-programmed reduction (TPR), oxygen storage capacity, Xray diffraction, electron microscopy, and luminescence spectroscopy using Eu3+ as a spectroscopic probe. Through reduction-oxidation pretreatment routines, reactive pyrochlore structures were created at temperatures as low as 600 degrees C and identified through TPR and electron microscopy experiments. A structural relationship and alignment of the crystal planes is revealed in high-resolution scanning transmission electron microscopy experiments through the digital diffraction patterns. Low-temperature pretreatment induces the formation of reactive pyrochlore domains under retention of the surface area of the catalyst system, and no further morphological changes are detected. Furthermore, the formation of pyrochlore domains achieved through severe reduction and mild reoxidation (SRMO) treatments is reversible. Over multiple alternating SRMO and severe reduction and severe reoxidation (SRSO) treatments, europium spectroscopy and TPR results indicate that pyrochlore structures are recreated over consecutive treatments, whenever the mild oxidation step at 500 degrees C is the last treatment (SRMO, SRMO-SRSO-SRMO, etc.). KW - pyrochlore KW - nanocomposite KW - ceria KW - zirconia KW - supported catalyst KW - oxygen KW - storage capacity Y1 - 2022 U6 - https://doi.org/10.1021/acsanm.2c00416 SN - 2574-0970 VL - 5 IS - 5 SP - 6316 EP - 6326 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Primus, Philipp-Alexander A1 - Menski, Antonia A1 - Yeste, Maria Pilar A1 - Cauqui, Miguel Angel A1 - Kumke, Michael Uwe T1 - Fluorescence Line-Narrowing Spectroscopy as a Tool to Monitor Phase Transitions and Phase Separation in Efficient Nanocrystalline CexZr1-xO2:Eu3+ Catalyst Materials JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Despite the wide range of industrial applications for ceria-zirconia mixed oxides (CexZr1-xO2), the complex correlation between their atomic structure and catalytic performance is still under debate. Catalytically interesting CexZr1-xO2 nanomaterials can form homogeneous solid solutions and, depending on the composition, show phase separation under the formation of small domains. The characterization of homogeneity and atomic structure of these materials remains a major challenge. High-resolution emission spectroscopy recorded under cryogenic conditions using Eu3+ as a structural probe in doped CeZrO2 nanoparticles offers an effective way to identify the different atomic environments of the Eu3+ dopants and, subsequently, to monitor structural parameters of the ceria-zirconia mixed oxides. It is found that, in stoichiometric CeZrO2:Eu3+, phase separation occurs at elevated temperatures beginning with the gradual formation of (pseudo)cubic crystallites in the amorphous materials at 500 degrees C and a sudden phase separation into tetragonal, zirconia-rich and cubic, ceria-rich domains over 900 degrees C. The presented technique allows us to easily monitor subtle changes even in amorphous, high surface area samples, yielding structural information not accessible by conventional techniques such as X-ray diffraction (XRD) and Raman. Moreover, in reference experiments investigating the reducibility of largely unordered Ce0.2Zr0.8O2:Eu3+, the main reduction peak in temperature-programmed reduction measurements appeared at exceptionally low temperatures below 200 degrees C, thus suggesting the outstanding potential of this oxide to activate catalytic oxidation reactions. This effect was found to be dependent on the amount of Eu3+ dopant introduced into the CeZrO2 matrix as well as to be connected to the atomic structure of the catalyst material. Y1 - 2015 U6 - https://doi.org/10.1021/acs.jpcc.5b01271 SN - 1932-7447 VL - 119 IS - 19 SP - 10682 EP - 10692 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Primus, Philipp-Alexander A1 - Ritschel, Thomas A1 - Sigueenza, Pilar Y. A1 - Cauqui, Miguel Angel A1 - Hernandez-Garrido, Juan Carlos A1 - Kumke, Michael Uwe T1 - High-resolution spectroscopy of europium-doped ceria as a tool to correlate structure and catalytic activity JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Site-selective emission spectra of Eu3+-doped CeO2 nanoparticles up to the D-5(0) - F-7(5) transition were recorded under cryogenic conditions to identify the local structure around the Eu3+ dopants in ceria. It is found that pretreatment conditions are crucial for the redistribution of dopants from a broad variety of environments to six well-defined lattice sites. The influence of the dopant and the host structure on the catalytic activity was investigated. A relationship between structure and reactivity is discussed. It is shown that oxygen transport is most efficient in particles with a pronounced amorphous character. Y1 - 2014 U6 - https://doi.org/10.1021/jp505467r SN - 1932-7447 VL - 118 IS - 40 SP - 23349 EP - 23360 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Primus, Philipp-A. A1 - Kumke, Michael Uwe T1 - Flash photolysis study of complexes between salicylic acid and lanthanide ions in water JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - In the natural environment humic substances (HS) represent a major factor determining the speciation of metal ions, e.g., in the context of radionuclide migration. Here, due to their intrinsic sensitivity and selectivity, spectroscopic methods are often applied, requiring a fundamental understanding of the photophysical processes present in such HS-metal complexes. Complexes with different metal ions were studied using 2-hydroxybenzoic acid (2HB) as a model compound representing an important part of the chelating substructures in HS. In flash photolysis experiments under direct excitation of 2HB in the absence and the presence of different lanthanide ions, the generation and the decay of the 2HB triplet state, of the phenoxy radical, and of the solvated electron were monitored. Depending on the lanthanide ion different intracomplex processes were observed for these transient species including energy migration to and photoreduction of the lanthanide ion. The complexity of the intracomplex photophysical processes even for small molecules such as 2HB underlines the necessity to step-by-step approach the photochemical reactivity of HS by using suitable model compounds. Y1 - 2012 U6 - https://doi.org/10.1021/jp2043575 SN - 1089-5639 VL - 116 IS - 4 SP - 1176 EP - 1182 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Eisold, Ursula A1 - Kupstat, Annette A1 - Klier, Dennis Tobias A1 - Primus, Philipp-A. A1 - Pschenitza, Michael A1 - Niessner, Reinhard A1 - Knopp, Dietmar A1 - Kumke, Michael Uwe T1 - Probing the physicochemical interactions of 3-hydroxy-benzo[a]pyrene with different monoclonal and recombinant antibodies by use of fluorescence line-narrowing spectroscopy JF - Analytical & bioanalytical chemistry N2 - Characterization of interactions between antigens and antibodies is of utmost importance both for fundamental understanding of the binding and for development of advanced clinical diagnostics. Here, fluorescence line-narrowing (FLN) spectroscopy was used to study physicochemical interactions between 3-hydroxybenzo[a]pyrene (3OH-BaP, as antigen) and a variety of solvent matrices (as model systems) or anti-polycyclic aromatic hydrocarbon antibodies (anti-PAH). We focused the studies on the specific physicochemical interactions between 3OH-BaP and different, previously obtained, monoclonal and recombinant anti-PAH antibodies. Control experiments performed with non-binding monoclonal antibodies and bovine serum albumin (BSA) indicated that nonspecific interactions did not affect the FLN spectrum of 3OH-BaP. The spectral positions and relative intensities of the bands in the FLN spectra are highly dependent on the molecular environment of the 3OH-BaP. The FLN bands correlate with different vibrational modes of 3OH-BaP which are affected by interactions with the molecular environment (pi-pi interactions, H-bonding, or van-der-Waals forces). Although the analyte (3OH-BaP) was the same for all the antibodies investigated, different binding interactions could be identified from the FLN spectra on the basis of structural flexibility and conformational multiplicity of the antibodies' paratopes. KW - FLNS KW - Antibody KW - Paratope KW - Hapten KW - Polycyclic aromatic hydrocarbons Y1 - 2014 U6 - https://doi.org/10.1007/s00216-013-7584-8 SN - 1618-2642 SN - 1618-2650 VL - 406 IS - 14 SP - 3387 EP - 3394 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Chemura, Sitshengisiwe A1 - Haubitz, Toni A1 - Primus, Philipp A. A1 - Underberg, Martin A1 - Hülser, Tim A1 - Kumke, Michael Uwe T1 - Europium-doped Ceria-Gadolinium mixed oxides BT - PARAFAC analysis and high-resolution emission spectroscopy under cryogenic conditions for structural analysis JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 <= x <= 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at lambda(ex) = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the D-5(0)-F-7(0) transition at lambda(ex) = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the D-5(0)-F-7(0) excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum. Y1 - 2020 U6 - https://doi.org/10.1021/acs.jpca.0c03188 SN - 1089-5639 SN - 1520-5215 VL - 124 IS - 24 SP - 4972 EP - 4983 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Matthes, Philipp R. A1 - Schönfeld, Fabian A1 - Nitsch, Jörn A1 - Steffen, Andreas A1 - Primus, Philipp-Alexander A1 - Kumke, Michael Uwe A1 - Müller-Buschbaum, Klaus A1 - Holdt, Hans-Jürgen T1 - White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a–d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+. Y1 - 2015 U6 - https://doi.org/10.1039/C4TC02919D SN - 2050-7534 SN - 2050-7526 VL - 18 IS - 3 SP - 4623 EP - 4631 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Matthes, Philipp R. A1 - Schönfeld, Fabian A1 - Nitsch, Jörn A1 - Steffen, Andreas A1 - Primus, Philipp-Alexander A1 - Kumke, Michael Uwe A1 - Müller-Buschbaum, Klaus A1 - Holdt, Hans-Jürgen T1 - White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ JF - Journal of materials chemistry : C, Materials for optical and electronic devices Y1 - 2015 U6 - https://doi.org/10.1039/c4tc02919d SN - 2050-7526 SN - 2050-7534 VL - 3 IS - 18 SP - 4623 EP - 4631 PB - Royal Society of Chemistry CY - Cambridge ER -