Mikolaj Lewandowski

Preparation and Characterization of Carbon Nano-Onion/ PEDOT:PSS Composites

Composites of unmodified or oxidized carbon nano-onions (CNOs/ox-CNOs) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are prepared with different compositions. By varying the ratio of PEDOT:PSS relative to CNOs, CNO/PEDOT:PSS composites with various PEDOT:PSS loadings are obtained and the corresponding film properties are studied as a function of the polymer. X-ray photoelectron spectroscopy characterization is performed for pristine and ox-CNO samples. The composites are characterized by scanning and transmission electron microscopy and differential scanning calorimetry studies. The electrochemical properties of the nanocomposites are determined and compared. Doping the composites with carbon nanostructures significantly increases their mechanical and electrochemical stabilities. A comparison of the results shows that CNOs dispersed in the polymer matrices increase the capacitance of the CNO/PEDOT:PSS and ox-CNO/PEDOT:PSS composites.

Acid−base properties and the hydrofining activity of NiMo catalysts incorporated on alumina modified with F− and Cl−

A series of studies on NiMo catalysts incorporated on to Al2O3 modified with chloride and fluoride ions was carried out. As the test reactions, the reactions of decomposition of 2-propanol and diacetone alcohol as well as of ethylbenzene were employed. The obtained catalysts were also tested in hydrofining of coal liquid. It was observed that modification of the support with fluoride and chloride ions in the studied range of concentrations increases the acidity of the catalyst. A distinctly higher increase in acidity was obtained for the modification with F− ions than with Cl− ions. The applied modifiers, on the one hand, lead to the increase in the activity of the catalysts in the reactions of decomposition of 2-propanol to propene, ethylbenzene to styrene, but on the other hand, reduce their activity in the decomposition of diacetone alcohol to acetone. Modification with Cl− and F− ions only insignificantly affects the activity of catalysts in hydrodesulfurization (HDS) of coal liquid. Introduction of fluoride ions on the support of NiMo catalyst leads to a quite large increase of the activity in hydrodenitrogenation (HDN) of coal liquid, whereas, when modified with chloride ions, these catalysts bring about a decrease in the activity of the discussed reaction. The properties of catalysts generated by ions of the modifiers, in particular the type and strength of acid centers, play a significant role in the HDN of coal liquid.

CO+NO versus CO+O2 Reaction on Monolayer FeO(111) Films on Pt(111)

Thin oxide films grown on metal single crystals are used in many “surface science” research groups in attempts to understand the surface chemistry of metal oxides. In addition, these films are employed as suitable supports for modeling highly dispersed metal catalysts (for reviews, see Refs. [1]–[4]). However, in the case of ultrathin films that are only a few angstroms in thickness, the metal substrate underneath the film often affects the properties of metal clusters by charge transfer through the film. These observations can, in principle, be traced back to the so-called “electronic theory of catalysis” developed in the 1950s and 1960s, and are primarily based on a Schottky barrier model, which predicts, in particular, that by varying the thickness of oxide films, the reactivity of heterogeneous catalysts can be controlled. However, these ideas faded away, primarily because of a lack of successful examples of the promotional effects of thin oxide films on catalytic activity and/or selectivity. Recently, it has been demonstrated that a thin oxide film grown on a metal may exhibit higher catalytic activity than the metal substrate under the same reaction conditions. Indeed, a thin FeO(111) film grown on Pt(111) is active for CO oxidation at 450 K, a temperature far below that at which Pt(111) itself is active. Furthermore, the rate enhancement was observed on Fe3O4-supported Pt nanoparticles, [13] which underwent encapsulation by an FeO(111) film as a result of the strong metal– support interaction. It has been suggested that, in the millibar pressure range (1 mbar=100 Pa) of O2, the bilayer Fe–O film on Pt(111) transforms into a trilayer O–Fe–O film that catalyzes CO oxidation according to a Mars–van Krevelen-type mechanism. A density functional theory (DFT) study corroborated this scenario. The DFT results showed that, by overcoming a small energy barrier of about 0.3 eV, O2 is chemisorbed on the Fe atom, which is pulled out of the pristine FeO film. In the chemisorbed state, electrons are transferred from the oxide/metal interface to oxygen, resulting in a O2 2 species, which then dissociates, thus forming a local O–Fe–O trilayer structure. Further DFT studies revealed that the reaction is site-specific within the large Moir unit cell formed due to an approximately 10% mismatch between the FeO(111) and Pt(111) lattices. This mismatch explains scanning tunneling microscopy (STM) results that showed the formation of close-packed O–Fe–O islands rather than a continuous FeO2 film. [15]

Synthesis and characterization of magnetite/silver/antibiotic nanocomposites for targeted antimicrobial therapy

The article is devoted to preparation and characterization of magnetite/silver/antibiotic nanocomposites for targeted antimicrobial therapy. Magnetite nanopowder was produced by thermochemical technique; silver was deposited on the magnetite nanoparticles in the form of silver clusters. Magnetite/silver nanocomposite was investigated by XRD, SEM, TEM, AFM, XPS, EDX techniques. Adsorptivity of magnetite/silver nanocomposite towards seven antibiotics from five different groups was investigated. It was shown that rifampicin, doxycycline, ceftriaxone, cefotaxime and doxycycline may be attached by physical adsorption to magnetite/silver nanocomposite. Electrostatic surfaces of antibiotics were modeled and possible mechanism of antibiotic attachment is considered in this article. Raman spectra of magnetite, magnetite/silver and magnetite/silver/antibiotic were collected. It was found that it is difficult to detect the bands related to antibiotics in the magnetite/silver/antibiotic nanocomposite spectra due to their overlap by the broad carbon bands of magnetite nanopowder. Magnetic measurements revealed that magnetic saturation of the magnetite/silver/antibiotic nanocomposites decreased on 6-19 % in comparison with initial magnetite nanopowder. Pilot study of antimicrobial properties of the magnetite/silver/antibiotic nanocomposites were performed towards Bacillus pumilus.

Influence of silver content on rifampicin adsorptivity for magnetite/Ag/rifampicin nanoparticles

Magnetite nanoparticles (NPs) decorated with silver (magnetite/Ag) are intensively investigated due to their application in the biomedical field. We demonstrate that the increase of silver content on the surface of nanoparticles improves the adsorptivity of antibiotic rifampicin as well as antibacterial properties. The use of ginger extract allowed to improve the silver nucleation on the magnetite surface that resulted in an increase of silver content. Physicochemical and functional characterization of magnetite/Ag NPs was performed. Our results show that 5%-10% of silver content in magnetite/Ag NPs is already sufficient for antimicrobial properties against Streptococcus salivarius and Staphylococcus aureus. The rifampicin molecules on the magnetite/Ag NPs surface made the spectrum of antimicrobial activity wider. Cytotoxicity evaluation of the magnetite/Ag/rifampicin NPs showed no harmful action towards normal human fibroblasts, whereas the effect on human embryonic kidney cell viability was time and dose dependent.

Structure of Fe3O4(111) Films on Pt(111) and Ru(0001): The Role of Epitaxial Strain at the Iron Oxide/Metal Single Crystal Interface

Thin oxide films epitaxially grown on metal single crystal surfaces may exhibit structural properties that differ from the corresponding bulk oxide materials. The structure of the films is often rendered by their thickness, the structure and properties of the substrate and by the nature of the oxide/substrate interface. We prepared thin iron oxide films on Pt(111) and Ru(0001) and studied their structure using STM, LEED and XPS. The structure of FeO(111) – the iron oxide phase that forms at the interface with the metal single crystal – depends on the parameters of the support and is believed to further influence the structure of thicker iron oxide films, such as Fe3O4(111), that are being grown on top of it. In this article we discuss the role of one of the important parameters that may determine this structure – the epitaxial strain at the iron oxide/metal single crystal interface.

Anchoring Fe3O4 nanoparticles in a reduced graphene oxide aerogel matrix via polydopamine coating

Reduced graphene oxide–magnetite hybrid aerogels attract great interest thanks to their potential applications, e.g., as magnetic actuators. However, the tendency of magnetite particles to migrate within the matrix and, ultimately, escape from the aerogel structure, remains a technological challenge. In this article we show that coating magnetite particles with polydopamine anchors them on graphene oxide defects, immobilizing the particles in the matrix and, at the same time, improving the aerogel structure. Polydopamine coating does not affect the magnetic properties of magnetite particles, making the fabricated materials promising for industrial applications.

On the Structure of Ultrathin FeO Films on Ag(111)

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moiré superstructure with 45 Å periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films’ preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form.

Symmetry-Induced Structuring of Ultrathin FeO and Fe3O4 Films on Pt(111) and Ru(0001)

Iron oxide films epitaxially grown on close-packed metal single crystal substrates exhibit nearly-perfect structural order, high catalytic activity (FeO) and room-temperature magnetism (Fe3O4). However, the morphology of the films, especially in the ultrathin regime, can be significantly influenced by the crystalline structure of the used support. This work reports an ultra-high vacuum (UHV) low energy electron/synchrotron light-based X-ray photoemission electron microscopy (LEEM/XPEEM) and electron diffraction (µLEED) study of the growth of FeO and Fe3O4 on two closed-packed metal single crystal surfaces: Pt(111) and Ru(0001). The results reveal the influence of the mutual orientation of adjacent substrate terraces on the morphology of iron oxide films epitaxially grown on top of them. On fcc Pt(111), which has the same mutual orientation of adjacent monoatomic terraces, FeO(111) grows with the same in-plane orientation on all substrate terraces. For Fe3O4(111), one or two orientations are observed depending on the growth conditions. On hcp Ru(0001), the adjacent terraces of which are ‘rotated’ by 180° with respect to each other, the in-plane orientation of initial FeO(111) and Fe3O4(111) crystallites is determined by the orientation of the substrate terrace on which they nucleated. The adaptation of three-fold symmetric iron oxides to three-fold symmetric substrate terraces leads to natural structuring of iron oxide films, i.e., the formation of patch-like magnetite layers on Pt(111) and stripe-like FeO and Fe3O4 structures on Ru(0001).