Frank Krumeich

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Krumeich

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Frank

ORCID

0000-0001-5625-1536

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Publications 1 - 10 of 136

Dissolution and storage stability of nanostructured calcium carbonates and phosphates for nutrition
Posavec, Lidija; Knijnenburg, Jesper T.N.; Hilty, Florentine M.; et al. (2016)
Journal of Nanoparticle Research
Rapid calcium (Ca) dissolution from nanostructured Ca phosphate and carbonate (CaCO3) powders may allow them to be absorbed in much higher fraction in humans. Nanosized Ca phosphate and CaCO3 made by flame-assisted spray pyrolysis were characterized by nitrogen adsorption, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. As-prepared nanopowders contained both CaCO3 and CaO, but storing them under ambient conditions over 130 days resulted in a complete transformation into CaCO3, with an increase in both crystal and particle sizes. The small particle size could be stabilized against such aging by cation (Mg, Zn, Sr) and anion (P) doping, with P and Mg being most effective. Calcium phosphate nanopowders made at Ca:P ≤ .5 were XRD amorphous and contained γ-Ca2P2O7 with increasing hydroxyapatite content at higher Ca:P. Aging of powders with Ca:P = 1.0 and 1.5 for over 500 days gradually increased particle size (but less than for CaCO3) without a change in phase composition or crystallinity. In 0.01 M H3PO4 calcium phosphate nanopowders dissolved ≈4 times more Ca than micronsized compounds and about twice more Ca than CaCO3 nanopowders, confirming that nanosizing and/or amorphous structuring sharply increases Ca powder dissolution. Because higher Ca solubility in vitro generally leads to greater absorption in vivo, these novel FASP-made Ca nanostructured compounds may prove useful for nutrition applications, including supplementation and/or food fortification.
Structure-Function Relationship of Highly Reactive CuOx Clusters on Co₃O₄ for Selective Formaldehyde Sensing at Low Temperatures
D'Andria, Matteo; Krumeich, Frank; Yao, Zhangyi; et al. (2024)
Advanced Science
Designing reactive surface clusters at the nanoscale on metal-oxide supports enables selective molecular interactions in low-temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here, the low-temperature oxidation of formaldehyde with CuOₓ clusters on Co₃O₄ nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology, such CuOₓ clusters are finely dispersed, while some Cu ions are incorporated into the Co₃O₄ lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X-ray absorption fine structure spectroscopy and temperature-programmed reduction in H₂ identified Cu⁺ and Cu²⁺ species in these clusters as active sites. Remarkably, the Cu⁺ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient rho = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts-per-billion (ppb) at 75 degrees C, superior to state-of-the-art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control.
SnP nanocrystals as anode materials for Na-ion batteries
Liu, Junfeng; Wang, Shutao; Kravchyk, Kostiantyn V.; et al. (2018)
Journal of Materials Chemistry A
Evidence of bifunctionality of carbons and metal atoms in catalyzed acetylene hydrochlorination
Giulimondi, Vera; Ruiz-Ferrando, Andrea; Giannakakis, Georgios; et al. (2023)
Nature Communications
Carbon supports are ubiquitous components of heterogeneous catalysts for acetylene hydrochlorination to vinyl chloride, from commercial mercury-based systems to more sustainable metal single-atom alternatives. Their potential co-catalytic role has long been postulated but never unequivocally demonstrated. Herein, we evidence the bifunctionality of carbons and metal sites in the acetylene hydrochlorination catalytic cycle. Combining operando X-ray absorption spectroscopy with other spectroscopic and kinetic analyses, we monitor the structure of single metal atoms (Pt, Au, Ru) and carbon supports (activated, non-activated, and nitrogen-doped) from catalyst synthesis, using various procedures, to operation at different conditions. Metal atoms exclusively activate hydrogen chloride, while metal-neighboring sites in the support bind acetylene. Resolving the coordination environment of working metal atoms guides theoretical simulations in proposing potential binding sites for acetylene in the support and a viable reaction profile. Expanding from single-atom to ensemble catalysis, these results reinforce the importance of optimizing both metal and support components to leverage the distinct functions of each for advancing catalyst design.
The Link between ZSM‐5 Zeolite Crystallization and Mesopore Formation by Leaching
Li, Teng; Ihli, Johannes; Wennmacher, Julian T.C.; et al. (2019)
Chemistry - A European Journal
Scalable photonic sources using two-dimensional lead halide perovskite superlattices
Jagielski, Jakub; Solari, Simon F.; Jordan, Lucie; et al. (2020)
Nature Communications
Miniaturized photonic sources based on semiconducting two-dimensional (2D) materials offer new technological opportunities beyond the modern III-V platforms. For example, the quantum-confined 2D electronic structure aligns the exciton transition dipole moment parallel to the surface plane, thereby outcoupling more light to air which gives rise to high-efficiency quantum optics and electroluminescent devices. It requires scalable materials and processes to create the decoupled multi-quantum-well superlattices, in which individual 2D material layers are isolated by atomically thin quantum barriers. Here, we report decoupled multi-quantum-well superlattices comprised of the colloidal quantum wells of lead halide perovskites, with unprecedentedly ultrathin quantum barriers that screen interlayer interactions within the range of 6.5 Å. Crystallographic and 2D k-space spectroscopic analysis reveals that the transition dipole moment orientation of bright excitons in the superlattices is predominantly in-plane and independent of stacking layer and quantum barrier thickness, confirming interlayer decoupling.
Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study**
Sadykov, Ilia I.; Sushkevich, Vitaly L.; Krumeich, Frank; et al. (2023)
Angewandte Chemie. International Edition
Operando X-ray absorption spectroscopy identified that the concentration of Fe2+ species in the working state-of-the-art Pt−FeOx catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe2+ sites. The active Fe2+ species are presumably Fe+2O−2 clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe3+) and metallic iron (Fe0) partially alloyed with platinum. The concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe2+ is the resting state of the active sites in the preferential carbon monoxide oxidation cycle.
Tunability and Scalability of Single-Atom Catalysts Based on Carbon Nitride
Chen, Zupeng; Mitchell, Sharon; Krumeich, Frank; et al. (2019)
ACS Sustainable Chemistry & Engineering
Gold-Catalyzed Aerobic Oxidation of Benzyl Alcohol: Effect of Gold Particle Size on Activity and Selectivity in Different Solvents
Haider, Peter; Kimmerle, Bertram; Krumeich, Frank; et al. (2008)
Catalysis Letters
Stabilization of Lead-Reduced Metal Halide Perovskite Nanocrystals by High-Entropy Alloying
Solari, Simon F.; Poon, Lok-Nga; Wörle, Michael; et al. (2022)
Journal of the American Chemical Society
Colloidal metal halide perovskite (MHP) nanocrystals (NCs) are an emerging class of fluorescent quantum dots (QDs) for next-generation optoelectronics. A great hurdle hindering practical applications, however, is their high lead content, where most attempts addressing the challenge in the literature compromised the material's optical performance or colloidal stability. Here, we present a postsynthetic approach that stabilizes the lead-reduced MHP NCs through high-entropy alloying. Upon doping the NCs with multiple elements in considerably high concentrations, the resulting high-entropy perovskite (HEP) NCs remain to possess excellent colloidal stability and narrowband emission, with even higher photoluminescence (PL) quantum yields, ηPL, and shorter fluorescence lifetimes, τPL. The formation of multiple phases containing mixed interstitial and doping phases is suggested by X-ray crystallography. Importantly, the crystalline phases with higher degrees of lattice expansion and lattice contraction can be stabilized upon high-entropy alloying. We show that the lead content can be approximately reduced by up to 55% upon high-entropy alloying. The findings reported here make one big step closer to the commercialization of perovskite NCs.

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Frank Krumeich

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