Magnetic Properties of "As-Prepared" and Chemically Modified Multiwalled Carbon Nanotubes

In this work we have studied the structural and magnetic properties of "as-prepared" multiwalled carbon nanotubes, synthesized by the chemical vapor deposition method, and chemically modified multiwalled carbon nanotubes. Transmission electron microscopy was used to show multiwalled carbon nanotubes structure. The results of systematic magnetic property measurements on multiwalled carbon nanotubes are presented. The static and dynamic magnetic responses, such as the temperature dependence of the linear AC susceptibility and DC magnetization up to 9 T were studied. We have observed significant changes in magnetic AC susceptibility and magnetization for "as-prepared" and chemically modified multiwalled carbon nanotubes samples

Distribution of heavy metals in sediments of Dobczyce reservoir

Osady denne stanowią istotny składnik środowiska wodnego, akumulując składniki mineralne, w tym metale ciężkie. Zbiornik Dobczycki, będąc rezerwuarem wody pitnej dla aglomeracji krakowskiej, spełnia bardzo ważną funkcję gospodarczą. W badaniach osadów dennych Zbiornika Dobczyckiego wykonano analizę wierzchniej ich warstwy w 17 punktach pomiarowych. Pozwoliło to na opisanie dystrybucji metali w czaszy zbiornika oraz ocenę czynników warunkujących tę dystrybucję. Analizę wykonano dwoma metodami: metodą atomowej spektrometrii absorpcyjnej oraz metodą PIXE. Stwierdzono, z wykorzystaniem narzędzi statystycznych, że ze względu na stężenie metali, punkty poboru próbek można podzielić na dwie grupy: leżące poza dawnym nurtem rzeki Raby (niższe stężenia metali ciężkich) oraz usytuowane w dawnym nurcie rzeki (wyższe stężenia). Odpowiada to zmieniającym się właściwościom sorpcyjnym osadów, zależnym m.in. od uziarnienia, składu chemicznego i mineralnego oraz zawartości materii organicznej. Zastosowanie metody PIXE umożliwiło wykonanie wielopierwiastkowej analizy składu bez wstępnej procedury przygotowania próbek, z wystarczającą czułością oznaczeń, lecz mniejszą precyzją niż metoda ASA. Metody te mogą być komplementarne z punktu widzenia potrzeb analiz środowiskowych.Sediments constitute important part of water systems, accumulating mineral compounds, such as heavy metals. Dobczyce Reservoir, being the main drinking water source for the city of Krakow, is important from the economical point of view. In the present research, analysis of elemental composition of sediment samples (upper 10 cm layer) in 17 sampling points was performed. It enabled us to analyse distribution of analysis of elements in Dobczyce Reservoir and to assess what factors influenced that distribution. The analysis was carried out by means of two instrumental methods, namely PIXE and ASA. Based on the statistical analysis of the results, it was found that all the sampling points could be divided into two groups – one situated out of the Raba river current (characterized by lower concentration of elements) and the other along the river current (higher concentration of elements). Such a division results from the differences in chemical and mineralogical composition of sediments as well as from their organic matter content and physical properties. The use of PIXE method makes it possible to analyze sediments in a multielemental mode without sample pretreatment, obtaining satisfactory sensitivity but less precision than with the use of AAS method. Both methods could be considered as complementary in environmental analysis

Direct support mixture painting, using Pd(0) organo-metallic compounds - an easy and environmentally sound approach to combine decoration and electrode preparation for fuel cells

An inventive, fast and straight-forward approach for the direct preparation of fuel cell electrodes has been developed and tested. Our approach avoids long catalyst preparation and post-synthesis treatment. It reduces the use of chemicals and thereby concomitantly lowers the environmental impact and improves cost efficiency. It combines decoration of the support by palladium nanoparticles with electrode preparation through a simple one-step ink-painting and annealing process. Composites have been investigated by high resolution transmission electron microscopy, scanning electron microscopy, and Xray diffraction. Crystalline particles are well-attached and well-distributed on the support. Particles are of few nanometers in size and spherical for decorated Vulcan whereas they are larger and irregularly shaped for decorated helical carbon nanofibers (HCNFs). Electrodes with a metal loading of 0.8 mg cm(-2) have been tested in a direct formic acid fuel cell. Both the Vulcan and the HCNF electrodes show a similar and high power output of up to 120 mW mg(-1). They also show similar performances in deactivation experiments conducted at 200 mA cm(-2) even when using only high purity grade formic acid. After deactivation the electrodes show no structural damage, making them superior to most commercial catalysts. The electrodes can be completely regenerated to initial activity by simple treatment with water. The easy regeneration process indicates that CO-adsorption on the fuel cell anode catalyst is not the main poisoning mechanism responsible for electrode degeneration