Browsing by Author "Abitaev, Karina"

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Open Access
Adjustable polystyrene nanoparticle templates for the production of mesoporous foams and ZnO inverse opals
(2020) Abitaev, Karina; Qawasmi, Yaseen; Atanasova, Petia; Dargel, Carina; Bill, Joachim; Hellweg, Thomas; Sottmann, Thomas
The manifold applications of porous materials, such as in storage, separation, and catalysis, have led to an enormous interest in their cost-efficient preparation. A promising strategy to obtain porous materials with adjustable pore size and morphology is to use templates exhibiting the appropriate nanostructure. In this study, close-packed polystyrene (PS) nanoparticles, synthesized by emulsion polymerization, were used to produce porous PS and ZnO inverse opals. The size and distribution of the polystyrene nanoparticles, characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), and scanning electron microscopy (SEM), were controlled via the concentration of sodium dodecyl sulfate (SDS). Systematic measurements of the water/styrene-interfacial tension show that the critical micelle concentration (CMC) of the ternary water–styrene–SDS system, which determines whether monodisperse or polydisperse PS particles are obtained, is considerably lower than that of the binary water–SDS system. The assemblies of close-packed PS nanoparticles obtained via drying were then studied by small-angle X-ray scattering (SAXS) and SEM. Both techniques prove that PS nanoparticles synthesized above the CMC result in a significantly unordered but denser packing of the particles. The polystyrene particles were subsequently used to produce porous polystyrene and ZnO inverse opals. While the former consists of micrometer-sized spherical pores surrounded by extended open-cellular regions of mesopores (Rpore ≈ 25 nm), the latter are made of ZnO-nanoparticles forming a structure of well-aligned interconnected pores.
Open Access
From macro to mesoporous ZnO inverse opals : synthesis, characterization and tracer diffusion properties
(2021) Kousik, Shravan; Sipp, Diane; Abitaev, Karina; Li, Yawen; Sottmann, Thomas; Koynov, Kaloian; Atanasova, Petia
Oxide inverse opals (IOs) with their high surface area and open porosity are promising candidates for catalyst support applications. Supports with confined mesoporous domains are of added value to heterogeneous catalysis. However, the fabrication of IOs with mesoporous or sub-macroporous voids (<100 nm) continues to be a challenge, and the diffusion of tracers in quasi-mesoporous IOs is yet to be adequately studied. In order to address these two problems, we synthesized ZnO IOs films with tunable pore sizes using chemical bath deposition and template-based approach. By decreasing the size of polystyrene (PS) template particles towards the mesoporous range, ZnO IOs with 50 nm-sized pores and open porosity were synthesized. The effect of the template-removal method on the pore geometry (spherical vs. gyroidal) was studied. The infiltration depth in the template was determined, and the factors influencing infiltration were assessed. The crystallinity and photonic stop-band of the IOs were studied using X-Ray diffraction and UV-Vis, respectively. The infiltration of tracer molecules (Alexa Fluor 488) in multilayered quasi-mesoporous ZnO IOs was confirmed via confocal laser scanning microscopy, while fluorescence correlation spectroscopy analysis revealed two distinct diffusion times in IOs assigned to diffusion through the pores (fast) and adsorption on the pore walls (slow).
Open Access
Hierarchical silica inverse opals as a catalyst support for asymmetric molecular heterogeneous catalysis with chiral Rh‐diene complexes
(2021) Deimling, Max; Kousik, Shravan R.; Abitaev, Karina; Frey, Wolfgang; Sottmann, Thomas; Koynov, Kaloian; Laschat, Sabine; Atanasova, Petia
The efficacy of heterogeneous catalysis relies heavily on diffusion and distribution of reactants within catalyst supports. However, the presence of confinement, essential for reaction selectivity, drastically slows down molecular transport. Here, macro‐mesoporous silica inverse opal (SiO2-IO) films were used as a model system to study the rather unexplored molecular infiltration behavior using a probe molecule resembling a catalyst via confocal laser scanning microscopy (CLSM). CLSM analysis revealed homogeneous tracer distribution in SiO2-IO and attachment to both transport and mesopores. Bulk macro‐mesoporous SiO2-IO support was used for the attachment of mono‐ and bis‐functionalized chiral Rh‐diene complexes, and the catalytic activity and selectivity with respect to the support was studied. Lower enantioselectivity was observed with the bis‐functionalized ligand due to ligand entanglement and reduced accessibility of the active site, while the mono‐functionalized ligand gave an excellent enantioselectivity of 94 %ee in the asymmetric 1,2‐addition of triphenylboroxine to N‐tosylimines and could be recycled up to three times.
Open Access
In situ ultra-small- and small-angle X-ray scattering study of ZnO nanoparticle formation and growth through chemical bath deposition in the presence of polyvinylpyrrolidone
(2023) Abitaev, Karina; Atanasova, Petia; Bill, Joachim; Preisig, Natalie; Kuzmenko, Ivan; Ilavsky, Jan; Liu, Yun; Sottmann, Thomas
ZnO inverse opals combine the outstanding properties of the semiconductor ZnO with the high surface area of the open-porous framework, making them valuable photonic and catalysis support materials. One route to produce inverse opals is to mineralize the voids of close-packed polymer nanoparticle templates by chemical bath deposition (CBD) using a ZnO precursor solution, followed by template removal. To ensure synthesis control, the formation and growth of ZnO nanoparticles in a precursor solution containing the organic additive polyvinylpyrrolidone (PVP) was investigated by in situ ultra-small- and small-angle X-ray scattering (USAXS/SAXS). Before that, we studied the precursor solution by in-house SAXS at T = 25 °C, revealing the presence of a PVP network with semiflexible chain behavior. Heating the precursor solution to 58 °C or 63 °C initiates the formation of small ZnO nanoparticles that cluster together, as shown by complementary transmission electron microscopy images (TEM) taken after synthesis. The underlying kinetics of this process could be deciphered by quantitatively analyzing the USAXS/SAXS data considering the scattering contributions of particles, clusters, and the PVP network. A nearly quantitative description of both the nucleation and growth period could be achieved using the two-step Finke–Watzky model with slow, continuous nucleation followed by autocatalytic growth.
Open Access
Preparation and characterization of mesoscale confined materials for asymmetric catalysis
(2024) Abitaev, Karina; Sottmann, Thomas (Apl. Prof. Dr.)