Structural, optical, and magnetic properties of Zn-doped CoFe2O4CoFe_2O_4 nanoparticles

The effect of Zn-doping in CoFe(2)O(4) nanoparticles (NPs) through chemical co-precipitation route was investigated in term of structural, optical, and magnetic properties. Both XRD and FTIR analyses confirm the formation of cubic spinel phase, where the crystallite size changes with Zn content from 46 to 77 nm. The Scherrer method, Williamson-Hall (W-H) analysis, and size-strain plot method (SSPM) were used to study of crystallite sizes. The TEM results were in good agreement with the results of the SSP method. SEM observations reveal agglomeration of fine spherical-like particles. The optical band gap energy determined from diffuse reflectance spectroscopy (DRS) varies increases from 1.17 to 1.3 eV. Magnetization field loops reveal a ferromagnetic behavior with lower hysteresis loop for higher Zn content. The magnetic properties are remarkably influenced with Zn doping; saturation magnetization (M(s)) increases then decreases while both coercivity (H(C)) and remanent magnetization (M(r)) decrease continuously, which was associated with preferential site occupancy and the change in particle size

Electrocardiogram reading : a randomized study comparing 2 e-learning methods for medical students

Interpretation of the electrocardiogram (ECG) is an essential skill in most medical specialties; however, the best method of teaching how to read ECGs has not been determined. The aim of the study was to compare the effectiveness of collaborative (C‑eL) and self (S‑eL) e‑learning of ECG reading among medical students. A total of 60 fifth‑year medical students were randomly assigned to the C‑eL and S‑eL groups. S‑eL students received 15 ECG recordings with a comprehensive description by email (one every 48 hours), while C‑eL students received the same ECG recordings without description. C‑eL students were expected to analyze each ECG together within the subgroups using an internet platform and to submit the interpretation within 48 hours. Afterwards, they received a description of each ECG. C‑eL students' activity was assessed based on the number of words written on the internet platform during discussion. A final test consisted of 10 theoretical questions and 10 ECG recordings. The final score was a sum of points obtained for the interpretation of ECG recordings. The main endpoint of the study was the number of students whose final score was 56% or higher. The final test was completed by 53 students (88.3%). The main endpoint was achieved in 20 C‑eL students (77%) and in 13 S‑eL students (48.1%), P = 0.03. The final score was 6.4 (interquartile range [IQR], 5.8-7.6) in the C‑eL group and 5.6 (IQR, 4.2-7.2) in the S‑eL group, P = 0.04. It correlated with the results of the theoretical test and students’ activity during C‑eL (r = 0.42, P = 0.002 and r = 0.4, P = 0.04, respectively). C‑eL of ECG reading among fifth‑year medical students is superior to S‑eL

Activation of O2O_2, H2H_2O and H2O2H_2O_2 in photoinduced electron transfer processes

W ramach rozprawy doktorskiej "Aktywacja cząsteczek O2, H2O i H2O2 w procesach fotoindukowanego przeniesienia elektronu" przeprowadzono badania mające na celu poznanie różnych aspektów aktywacji tytułowych cząsteczek w obecności komercyjnych materiałów TiO2 o strukturze anatazu, rutylu oraz kompozytów anatazu i rutylu, a także materiałów zsyntetyzowanych o określonej ekspozycji płaszczyzn krystalograficznych lub zmodyfikowanych powierzchniowo wybranymi grupami związków organicznych i nieorganicznych. W przypadku form anatazu i rutylu określono wpływ obecności tlenu i nadtlenku wodoru w naświetlanym układzie na generowane reaktywne formy tlenu. Wykazano lepsze właściwości redukcyjne rutylu w porównaniu z anatazem w procesach redukcji tlenu oraz nadtlenku wodoru. Wynikają one częściowo z lepszej adsorpcji tlenu na powierzchni rutylu, ale przede wszystkim z silniej redukujących właściwości wzbudzonego rutylu w porównaniu z anatazem. Zbadano również wpływ zwiększonej ekspozycji wybranych płaszczyzn krystalograficznych na właściwości utleniająco-redukujące materiału. Zsyntezowano i poddano badaniom materiały na bazie anatazu o zwiększonej ekspozycji płaszczyzn (101), (100) i (001). Uszeregowano płaszczyzny względem aktywności w procesach aktywacji cząsteczek H2O i H2O2. Przebadane zostały również materiały monokrystalicznego rutylu o niemal stuprocentowym udziale płaszczyzn (110), (101) i (001). W przypadku rutylu zaobserwowano wzrost właściwości redukcyjnych materiału wraz ze wzrostem energii powierzchniowej najbardziej eksponowanej płaszczyzny a właściwościami redukcyjnymi materiału, a w przypadku anatazu zaobserwowany został odwrotny trend. Kolejno przebadano materiały TiO2 modyfikowane powierzchniowo. Określono zdolności do adsorpcji tlenu dla materiałów modyfikowanych heksafluorometalanami i fluorkami oraz aktywność tych materiałów w procesach aktywacji H2O i O2. Ustalono prawidłowy sposób postępowania przy wyznaczaniu wartości EBG w przypadku materiałów absorbujących światło o energii mniejszej niż szerokość przerwy wzbronionej. Zbadano również aktywność materiałów modyfikowanych związkami organicznymi koordynującymi do powierzchni TiO2 i tworzącymi barwne kompleksy charge transfer. Przebadano również serię innych materiałów półprzewodnikowych i określono ich wydajność w procesach aktywacji cząsteczek H2O oraz H2O2. Jednym z niezbędnych etapów pracy była weryfikacja przydatności dostępnych metod detekcji i oznaczania reaktywnych form tlenu generowanych w układach zawierających fotokatalizator heterogeniczny. Wiele z dostępnych metod nie nadaje się do bezpośredniego wykorzystania w obecności fotokatalizatora heterogenicznego ze względu na jego zdolności do m.in. bezpośredniego utlenienia lub redukcji cząsteczek sond używanych do analizy. Wykazano, że metody bazujące na prostych reakcjach utleniania i redukcji nie są selektywne w stosunku do konkretnych reaktywnych form tlenu, na przykład anionorodnika ponadtlenkowego. Wykazano wady metod opartych na redukcji XTT i chemiluminescencji luminolu. Potwierdzono za to wysoką selektywność i czułość metody detekcji rodnika hydroksylowego opartej na utlenianiu kwasu tereftalowego. Za pomocą spektroskopii EPR potwierdzono bardzo dobre właściwości EDTA do wygaszania dziur elektronowych generowanych na powierzchni półprzewodnika, bez wygaszania rodników hydroksylowych powstających na drodze innych ścieżek reakcji.As part of the dissertation "Activation of O2, H2O and H2O2 in photoinduced electron transfer processes" research was carried to recognize various aspects of activation of the title molecules in the presence of commercially available TiO2 anatase, rutile and mixed phase materials, as well as self-synthesized facet tailored materials, or modified with selected organic and inorganic compounds. In the case of anatase and rutile the influence of oxygen and hydrogen peroxide presence on the reactive oxygen species in the irradiated system was determined. It was proven that rutile, compared to anatase, performs better in both oxygen and hydrogen peroxide reduction. It is due to the better adsorption of oxygen on rutile, but the most important factor is that the excited rutile is a better reductant compared to anatase. The influence of the exposed crystal facets on redox properties of materials were also investigated. Materials with larger content of (101), (100) and (001) facets were synthesized and tested. The facets were put in an order (101) > (100) > (001) according to their activity in the H2O2 molecule activation via reduction processes, and contra wise according to activity in H2O activation process in the oxidative pathway. Monocrystalline rutile materials, containing almost 100% of the selected (110), (101) or (001) facets were also tested. In the case of rutile with increasing surface energy of the most exposed facet the reduction properties increased, while in the presence of anatase they behaved inversely. The next step involved tests on surface modified TiO2 materials. Oxygen adsorption properties of materials modified with hexafluorometallates and fluorides, as well as their activity in H2O and O2 activation processes were investigated. A proper approach to determining the EBG in the case of surface modified materials that absorb light of energy lower than EBG. Activity of materials modified with organic compounds coordinating to the surface of TiO2, resulting in a formation of color charge transfer complexes, was tested. Additionally, a series of other semiconductors were investigated in terms of H2O and H2O2 activation properties. One of the crucial parts of this work was to verify the suitability of available ROS detection and determination methods in the systems containing heterogeneous photocatalysts. Many of the available methods cannot be used directly in the presence of a heterogeneous photocatalyst due to its ability to oxidize or reduce the probe molecules directly. It has been shown that methods based on simple oxidation and reduction reactions are not selective towards specific reactive oxygen species, i.e., superoxide anion. Weaknesses of methods based on reduction of XTT and chemiluminescence of luminol have been shown. Both high selectivity and sensitivity of the method to analyze production of hydroxyl radicals based on the oxidation of terephthalic acid was confirmed. By means of EPR spectroscopy, EDTA has been confirmed to have very good holes quenching properties, while this compound does not quench hydroxyl radicals generated by other reaction pathways

Titanium dioxide nanoparticles stabilized with polyelectrolytes

Celem pracy było zbadanie stabilności zoli TiO2 w szerokim zakresie pH oraz przetestowanie ich aktywności fotokatalitycznej.Dodatkowo uzupełnieniem części badawczej było zsyntetyzowanie powłok tlenku tytanu(IV) na podłożu metalicznym oraz zbadanie wpływu modyfikatora na właściwości fizykochemiczne otrzymanych powłok. Przeprowadzono również próbę fotosensybilizacji układów stabilnych, oraz przetestowano ich aktywność fotokatalityczną w warunkach naświetlania światłem widzialnym.Przetestowano 5 substancji (PEG1500, PEG4000, PEG6000, SDS oraz Tween ® 80) w 7 różnych stężeniach (0,1, 0,2, 0,5, 1,0 2,0 5,0 10,0 g/L) pod kątem stabilizacji zolu (cTiO2 )=1 g⁄L). Jedynie układ zawierający 10-krotnie wyższe stężenie wagowe Tweenu ® 80 względem tlenku tytanu(IV) okazał się stabilny w warunkach pH = 7. Przeprowadzono dla tego układu testy aktywności fotokatalitycznej (degradacja barwników: oranżu metylowego i azuru B) w zakresie światła ultrafioletowego, jednakże układy w trakcie naświetlania ulegały destabilizacji.Podjęte zostały próby fotosensybilizacji powyższego układu za pomocą 2,3-naftalenodiolu, a następnie przetestowano aktywność fotokatalityczną. Układ ten charakteryzował się wysoką wydajnością w procesie degradacji azuru B. Nie ulegał on również destabilizacji w trakcie naświetlania i był stabilny w szerokim zakresie pH.The aim of this work was to investigate stability of nanocrystalline titanium dioxide in wide pH range, and to test its photocatalytic activity.Additionally several attempts to synthesize titanium dioxide coatings on metallic surfaces were made. Also the impact of the stabilizer on physicochemical properties of obtained films was investigated. Attempts to photosensitize stable systems and test their photocatalytic activity upon visible light irradioation were also made.In terms of sol stabilization (cTiO2 )=1 g⁄L) 5 different substances (PEG1500, PEG4000, PEG6000, SDS and Tween ® 80) at 7 different concentrations (0,1, 0,2, 0,5, 1,0 2,0 5,0 10,0 g/L) were tested. Only the system with 10 fold excess (mass concentration) of Tween ® 80 was found to be stable at pH = 7. Photocatalytic activity tests towards degradation of organic dyes (methylene orange and azure B) in UV light range were carried out, however during the irradiation the system loses its stability. Photosensitization attempts with 2,3-naphthalenediol were carried out. Photosensitized system showed a very high activity in azure B degradation process, remained stable during irradiation, and was found stable in a wide pH range

UV and visible light active aqueous titanium dioxide colloids stabilized by surfactants

Attempts to increase the stability of photocatalytically active nanodispersions of titanium dioxide over a wide range of pH (3 – 10) were undertaken. Polyethylene glycols (PEGs) with di ff erent molecular weights and polyoxyethylenesorbitan monooleate (Tween® 80) were tested as stabilizing agents of TiO 2 nano- particles. The results of DLS measurements proved the stabilizing e ff ect of Tween® 80 while the systems involving PEGs, independently of the polymer concentration, showed a tendency to form aggregates in neutral solutions. The colloids stabilized with Tween® 80 were photosensitized with 2,3-naphthalenediol (nd) or 2-hydroxy-3-naphthoic acid (hn) or catechol (cat). The photocatalytic activity of such colloids has been assessed in an azure B degradation reaction using both UV and visible light. The nd@TiO 2 + Tween colloid appeared particularly photoactive upon visible light irradiation. Moreover, the comparison of activi- ties of nd@TiO 2 + Tween and TiO 2 + Tween revealed a signi fi cantly better performance of the former nanodispersion, independently of the irradiation conditions (UV or visible light). This e ff ect has been explained by di ff erent structures of micelles formed in the case of TiO 2 and nd@TiO 2 stabilized with Tween® 80

Rac1 regulates lipid droplets formation, nanomechanical, and nanostructural changes induced by TNF in vascular endothelium in the isolated murine aorta

Endothelial inflammation is recognized as a critical condition in the development of cardiovascular diseases. TNF-induced inflammation of endothelial cells is linked to the formation of lipid droplets, augmented cortical stiffness, and nanostructural endothelial plasma membrane remodelling, but the insight into the mechanism linking these responses is missing. In the present work, we determined the formation of lipid droplets (LDs), nanomechanical, and nanostructural responses in the model of TNF-activated vascular inflammation in the isolated murine aorta using Raman spectroscopy, fluorescence imaging, atomic force microscopy (AFM), and scanning electron microscopy (SEM). We analysed the possible role of Rac1, a major regulator of cytoskeletal organization, in TNF-induced vascular inflammation. We demonstrated that the formation of LDs, polymerization of F-actin, alterations in cortical stiffness, and nanostructural protuberances in endothelial plasma membrane were mediated by the Rac1. In particular, we revealed a significant role for Rac1 in the regulation of the formation of highly unsaturated LDs formed in response to TNF. Inhibition of Rac1 also downregulated the overexpression of ICAM-1 induced by TNF, supporting the role of Rac1 in vascular inflammation. Altogether, our results demonstrate that LDs formation, an integral component of vascular inflammation, is activated by Rac1 that also regulates nanomechanical and nanostructural alterations linked to vascular inflammation

Lead molybdate : a promising material for optoelectronics and photocatalysis

The growing interest in the use of light as an information and energy carrier has led to an increasing demand for new materials, characterised by particular photoelectrochemical properties. The aim of this work is to introduce a wide band gap semiconductor – PbMoO4 with a detailed description of its synthesis procedure and product characterisation. The emphasis was put on its electronic structure and photoelectrochemical properties in order to evaluate the mechanism of the photoelectrochemical photocurrent switching effect (the PEPS effect). This phenomenon may be utilized in the construction of simple logic devices (e.g. logic gates or switches) or more complex optoelectronic circuits. Lead molybdate in the form of fine powder was obtained via a microwave assisted hydrothermal route. It was found that the composition of the reaction mixture (i.e. the ratio between lead and molybdate ions) influences the morphology and the electronic structure of the semiconductor. The photoelectrochemical characterization revealed that PbMoO4 in the presence of the Ce4+/Ce3+ redox couple exhibits the PEPS effect regardless of the presence of oxygen in the electrolyte. This may be explained in terms of oxidation/reduction processes of cerium(III)/cerium(IV) species. An attempt to modify the surface via the adsorption of alizarin onto PbMoO4 was also made. The spectroscopic characterization and DFT calculations performed for such an organic–inorganic hybrid material revealed that the dye binds to MoVI centres which are exposed on the surface. Alizarin adsorbed onto PbMoO4 strongly enhances the cathodic photocurrent generation. At the same time, however, the anodic photocurrent diminishes. Therefore, literally no switching effect occurs for such a system. Nonetheless, the generation of intense cathodic photocurrent may be utilized in photocatalysis, e.g. during the photoreduction of metal ions or the generation of reactive oxygen species and/or solar fuels