Effect of Fe3+Fe^{3+} ions present in the structure of poly(acrylic acid) / montmorillonite composites on their thermal decomposition

Poly(acrylic acid)/montmorillonite (MMT) composites with various polymer contents were synthesized by in situ polymerization technique. The structure of obtained materials was characterized by powder X-ray dif- fraction and infrared spectroscopy (FTIR). It was found that only a limited amount of hydrogel could be introduced between the clay layers. The remaining part of polymer was deposited on the external surface of clay particles. The introduction of the polymer modifier significantly increased the adsorption capacity of MMT in the elimination of $Fe^{3+}$ ions from aqueous solution. The thermal behavior of the samples before and after the $Fe^{3+}$ adsorption was examined by thermogravimetry and differential thermal analysis. Moreover, the composition of gaseous products evolved during decomposition was determined by FTIR. The mate- rials after $Fe^{3+}$ adsorption exhibited different thermal sta- bility in oxidizing atmosphere than the fresh samples. $Fe^{3+}$ cations, forming $FeO_x$ species during thermal treatment, appeared to be effective catalysts of polymer oxidation

Funkcjonalizacja mezoporowatej krzemionki SBA-15 w wyniku szczepienia poliwinyloaminy na powierzchni modyfikowanej grupami epoksydowymi

Mesoporous SBA-15 silica was modified by grafting of 3-glycidoxypropyltrimethoxysilane (GPTMS). An influence of GPTMS/SBA-15 mass ratio used during this pre-functionalization step on the real amount of epoxy-silane grafted on the SBA-15 surface was studied by thermogravimetry and elemental analysis. The pre-functionalized SBA-15 was subsequently used to attach polyvinylamine (PVAm) chains by the opening of oxirane rings and the formation of bonds with NH2 groups from PVAm. The yield of this process was determined. Furthermore, SEM (scanning electron microscopy), DRIFT (diffuse reflectance infrared Fourier transform spectroscopy) and XPS (X-ray photoelectron spectroscopy) as well as zeta potential measurements were applied to observe the changes in the chemical composition of SBA-15 surface and morphology of the synthesized materials. Various types of organic functionalities present on the modified SBA-15 were identified and analyzed quantitatively.Powierzchnię mezoporowatej krzemionki SBA-15 zmodyfikowano na drodze szczepienia 3-glicydoksypropylotrimetoksysilanu (GPTMS). Z wykorzystaniem metod analiz elementarnej oraz termograwimetrycznej badano wpływ stosunku masowego GPTMS/SBA-15 zastosowanego we wstępnej modyfikacji na rzeczywistą zawartość wprowadzonych na powierzchnię krzemionki grup epoksydowych. Do powierzchni zmodyfikowanego SBA-15 przyłączono następnie łańcuchy poliwinyloaminy (PVAm) w wyniku reakcji otwierania pierścieni oksiranowych połączonej z utworzeniem wiązań z grupami NH2 pochodzącymi od PVAm. Określono wydajność tego procesu. Badania SEM (skaningowej mikroskopii elektronowej), DRIFT (spektroskopii odbicia rozproszonego w podczerwieni), XPS (spektroskopii fotoelektronów) oraz pomiary potencjału zeta pozwoliły na ocenę zmian składu chemicznego powierzchni SBA-15 oraz morfologii zsyntetyzowanych materiałów. Zidentyfikowano oraz oznaczono ilościowo różne rodzaje grup funkcyjnych obecnych na powierzchni modyfikowanej krzemionki SBA-15

Rola obróbki plazmą MV na odporność korozyjną stali stopowych

Obróbkę powierzchni wysokostopowych stali chromowo-niklowej typu duplex S32404 i austenitycznej S32615 przeprowa- dzono poprzez węgloazotowanie przy użyciu techniki próżniowej z mikrofalowym wspomaganiem plazmowym o częstotliwości 2.45GHz i mocy generatora 350W. Zastosowano reaktywną mieszaninę gazową zawierającą CH4 i N2 w warunkach niskiego ciśnienia 0.2 Tr. przy niskiej temperaturze 400°C. Oceniono wpływ składu chemicznego i struktury stopów na tworzącą się war- stwę wierzchnią podczas obróbki. Strukturę powierzchni analizowano za pomocą rentgenowskiej spektroskopii fotoelektronów (XPS). Odporność korozyjną próbek określano na podstawie krzywych polaryzacyjnych LSV w 3% roztworze chlorku sodu przy temperaturze 37°C. Powierzchnie stali poddane obróbce wykazały wyższą skłonność do pasywacji w oraz podwyższały odporność na korozję wżerową w porównaniu z powierzchniami niemodyfikowanymi.Two stainless steels (S32404 duplex and S32615 austenitic) were subject to the carbon/nitrogen plasma treatment to examine the role of alloy composition and structure in the behavior of surface during modification. The modification process was performed in the electron cyclotron resonance (ECR) micro wave plasma system, with the frequency of 2.45 GHz and the generator power of 350 W, and with the use of reactive gas mixtures containing CH4 and N2, at the low temperature of 400°C and under pressure of 0.2Tr. The treated surface was analyzed by means of X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the samples was determined on the basis of LSV polarization curves in 3% sodium chloride solution at 37°C. The treated steel surfaces showed a higher tendency for passivation and higher pitting corrosion resistance compared to the non-modified surfaces

Tailoring properties of resol resin-derived spherical carbons for adsorption of phenol from aqueous solution

The polycondensation of resorcinol and formaldehyde in a water–ethanol mixture using the adapted Stöber method was used to obtain resol resins. An optimization of synthesis conditions and the use of an appropriate stabilizer (e.g., poly(vinyl alcohol)) resulted in spherical grains. The resins were carbonized in the temperature range of 600–1050 °C and then chemically activated in an aqueous HNO3 solution, gaseous ammonia, or by an oxidation–reduction cycle (soaking in a HNO3 solution followed by treatment with NH3). The obtained carbons were characterized by XRD, the low-temperature adsorption of nitrogen, SEM, TGA, and XPS in order to determine degree of graphitization, porosity, shape and size of particles, and surface composition, respectively. Finally, the materials were tested in phenol adsorption. The pseudo-second order model perfectly described the adsorption kinetics. A clear correlation between the micropore volume and the adsorption capacity was found. The content of graphite domains also had a positive effect on the adsorption properties. On the other hand, the presence of heteroatoms, especially oxygen groups, resulted in the clogging of the pores and a decrease in the amount of adsorbed phenol

Pyrolytic carbons derived from water soluble polymers

Conductive pyrolytic carbon materials were obtained in wet impregnation process followed by controlled pyrolysis. Poly- N -vinylformamide (PNVF) as well as mix- ture of PNVF and pyromellitic acid (PMA) were applied as carbon precursors. Composition of carbon precursors was optimized in terms to obtain best electrical properties of pyrolytic carbons. Mixture of PNVF and PMA as well as pure PNVF were deposited on the model alumina ( a -Al 2 O 3 ) support to form conductive carbon layers (CCL). The opti- mal composition of the polymer precursors was determined by Raman spectra and electrical conductivity measurements. The carbonization conditions were optimized using com- plementary thermal analysis methods (EGA(FTIR)–TG/ DTG/STDA). It was found that the addition of PMA to polymer precursor PNVF decreases temperature of forma- tion of condensed graphene structures, domains of electrical conductivity, thus, the formation temperature of pyrolytic carbons with desired electrical properties may be decreased

Catalytic behavior of chromium oxide supported on nanocasting-prepared mesoporous alumina in dehydrogenation of propane

Mesoporous alumina with narrow pore size distribution centered in the range of 4.4–5.0 nm and with a specific surface area as high as 270 m2·g−1 was prepared via the nanocasting approach using a CMK-3 carbon replica as a hard template. Based on this support, a series of catalysts containing 1, 5, 10, 20 and 30 wt % of chromium was prepared by incipient wetness impregnation, characterized, and studied in the dehydrogenation of propane to propene (PDH). Cr species in three oxidation states—Cr(III), Cr(V) and Cr(VI)—were found on the oxidized surface of the catalysts. The concentration of these species varied with the total Cr loading. Temperature-programmed reduction (H2-TPR) and UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS) studies revealed that Cr(VI) species dominated at the lowest Cr content. An increase in the Cr loading resulted in an appearance of an increasing amount of Cr(III) oxide. UV-Vis-DRS measurements performed in situ during the PDH process showed that at the beginning of the catalytic test Cr(VI) species were reduced to Cr(III) redox species. A crucial role of the redox species in the PDH process over the catalysts with the low Cr content was confirmed. The stability test for the catalyst containing 20 wt % of Cr showed that this sample exhibited the reproducible catalytic performance after the first four regeneration–dehydrogenation cycles. Moreover, this catalyst had higher resistance on deactivation during the PDH process as compared to the reference catalyst with the same Cr loading, but was supported on commercially available alumina

Thermal transformation of polyacrylonitrile deposited on SBA-15 type silica : effect on adsorption capacity of methyl-ethyl ketone vapor

Thermogravimetry, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used for the studying of ther- mally induced structural changes of polyacrylonitrile (PAN) deposited on the surface of SBA-15 type meso- porous silica. Polymer was introduced onto the support by the precipitation polymerization of acrylonitrile in aqueous suspension of SBA-15. Low temperature transformation (to 723 K) of the deposited PAN was analyzed. It was found that at about 523 K, exothermic cyclization of polymer chains to the so-called ladder form of PAN occurred. However, the total cyclization of PAN required higher carbonization temperatures, at which gradual dehydroge- nation followed by graphitization was initiated. XPS revealed that the cyclic form of PAN and a relatively large amount of carbonyl species, formed during the carboniza- tion of the PAN/SBA-15 composite at 623 K, were responsible for the high sorption capacity in the methyl– ethyl ketone (MEK) vapor elimination. The efficiency in the MEK adsorption was also influenced by the content of PAN-derived carbon deposited on the SBA-15 surfac