Thermal evolution process, properties and photocatalytic activity of sol-gel derived nanocrystalline anatase in dye degradation process

Nanocrystalline anatase aimed to be used as a photocatalyst for dye degradation processes in industrial effluents and has been prepared and investigated. Amorphous titania gel has been prepared using sol–gel process by slow hydrolysis of titanium n–butoxide. The prepared gel has been investigated using Fourier–Transformed Infra–Red Spectroscopy (FTIR), Powder X–ray Diffraction (PXRD), Differential Thermal Analysis (DTA), Thermo–Gravimetric Analysis (TGA), N2 gas adsorption–desorption isotherms and Diffuse Reflectance UV–Vis Spectroscopy (DRS). It was determined that the amorphous gel was comprised of non-hydrolyzed butoxy groups as well as hydroxyl groups bonded to titanium. The thermal evolution of gel is consisted of five steps: elimination of adsorbed water and butanol in temperature range between room temperature and 200 °C, decomposition and elimination of butoxy groups between 200 and 300°C. The crystallization of anatase centered at 404°C, transformation to rutile starting from 540 °C and oxidation of char and tar above 600°C. Thermal treatment of gel at 350 °C for 2 h yields with pure nanocrystalline anatase with average crystallite size of 13.2±0.2 nm, specific surface area of 65.48 m2 g–1 and bandgap, of 3.24 eV. The preliminary assessment of prepared catalyst photocatalytic activity was obtained through degradation process of methylene blue dye under UV light and the 99 % degradation of dye took place within 150 min

On the Temperature Corresponding to a = 0.632 in Non-isothermal JMA Kinetics

The expression for rate, da/dT, of the nucleation and growth (NG) process under non-isothermal conditions, as described by the Johnson-Mehl-Avrami (JMA) kinetic model, served as the basis for a detailed study of a class of functions F(m) = (da/dT)Tm, where m ÎÂ. Studies of the fractional conversion, a, of the NG process at the temperature of the maximum of function F(m), T = T(m), have shown that when reduced activation energy, x = E/RT, approaches infinity (x®¥), fractional conversion, a, at the temperature corresponding to the maximum of function F(m), a(m), converges to a = 0.632, for any value of m. It has been further shown that fractional conversion, a, for the NG process is equal to a = 0.632 at the temperature corresponding to the maximum of function F(m) = (da/dT)Tm for the particular value of parameter m from the interval: 1 £ m £ 2

Application of a Numerical Method for the Analysis of Metglas 2826 MB Crystallization Kinetics

Crystallization kinetics of y-FeNiMo solid solution in Metglas 2826 MB was studied by isothermal differential scanning calorimetry (DSC). The Johnson-Mehl-Avrami (JMA) equation was used to describe the crystallization process. In order to calculate the kinetic parameters, a new model of the numerical analysis of isothermally obtained DSC data was successfully applied. For the purposes of method evaluation, the classical analytical method of data analysis was also performed. The apparent activation energies obtained were (280 ± 22) kJ mol-1 and (296 ± 23) kJ mol-1 for the analytical and numerical methods, respectively. The Avrami exponents obtained by both methods lie between 1.75 and 1.95

Electrochemical and catalytic applications of cerium(IV) oxide

Cerium(IV) oxide is one of the most important rare earth metal oxides owing to its high oxygen storage and release capacity, as well as thermal and mechanical stability. Its various applications range from sensors, solid oxide fuel cells and supercapacitors to the most important catalytic application in three-way catalytic converters, oxidation of volatile organic molecules, water-gas shift reaction, etc. This short review article gives a brief introduction to rare earth metals, then describes in detail the properties of cerium(IV) oxide and ways to improve them, as well as presents an overview of the most important and current applications of cerium(IV) oxide. Finally, it gives an overview of the results obtained by our group regarding pure and doped cerium(IV) oxide for various applications

Tla in sedimenti zaledja Proščanskega jezera kot možen terigen doprinos v jezerski sistem

The Plitvice Lakes National Park is in the northwestern part of the Dinaric Karst in central Croatia. An important role of the soil in the karst is to purify the waters before they reach the phreatic zone. The soil is also a zone of accumulation, transformation, retardation and dilution of a potential pollutant. Knowing soil mineralogical composition is an important factor in understanding fate and transport of contaminants throughout lakes system. Samples of soil, peat and stream sediment were collected in the Prošće lake catchment and partly in the assumed zone of influence, X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR) analysis of samples was performed to determine dominant mineral species in samples. XRD analysis showed predominance of lowquartz, which was found in all samples, most often as dominant phase. Dolomite was found in half of the samples, almost always as a significant phase while calcite was dominant phase in one of the samples. In most of the samples, members of the feldspars and chlorites groups, as well as muscovite, were present as minor phases. The absorption bands in the range of 2800-3000 cm-1 due to the organic matter are visible in spectra of all samples. These minerals can enter lakes system by surface waters, primarily streams and overland flow during snow thawing and rain, and also in cases of shore erosion. Terrigenic input in lakes is small but cannot be neglected due to the longlasting preservation efforts of the Prošće Lake recharge area, and the Plitvice Lakes National Park in general, terrigenous intake still does not pose a threat to water quality and tufa production. Considering the analyzed samples and characteristics of detected soil constituents, soils and sediments in the Prošće Lake catchment have the ability to retain and purify water on its way to the lakes. On the other hand, in case of the possible contamination in the recharge area of the lakes system, the pollutants can enter the system adsorbed on the soil particles. Learning more about the soils surrounding lakes gives valuable insight into their possible influence on lakes water chemistry and adds one piece of the puzzle into understanding this kind of a natural phenomenon.Narodni park Plitviška jezera se nahaja v severozahodnem delu Dinarskega krasa v osrednji Hrvaški. Pomembna vloga tal v krasu je, da čistijo vodo, preden doseže freatično cono. Tla so tudi območje, kjer se potencialna onesnaževala kopičijo, preoblikujejo in redčijo. Tla ta onesnaževala tudi zadržijo. Poznavanje mineraloške sestave tal je pomemben dejavnik pri razumevanju prenosa onesnaževal v jezerskem sistemu. Tla, šoto in sedimente smo vzorčili v neposrednem zaledju in na vplivnem območju Prošćankega jezera. Mineralne vrste smo določili z rentgensko difrakcijo (XRD) in infrardečo spektroskopijo s Fourierjevo transformacijo (FTIR). Analiza XRD je pokazala, da v vzorcih prevladuje kremen, ki je bil v vseh vzorcih ugotovljen kot prevladujoč mineral. Dolomit je bil najden v polovici vzorcev, skoraj vedno kot pomemben mineral, medtem ko je kalcit prevladoval samo v enem od vzorcev. V večini vzorcev so bili v manjšini še glinenci, kloritni minerali in muskovit. Absorpcijski pasovi na območju 2800-3000 cm-1 so bili zaradi organske snovi vidni v vseh spektrih. Minerale lahko v jezerski sistem prinesejo površinske vode, predvsem med taljenjem snega in ob padavinah ali obalnih erozijskih procesi. Terigeni vnos je majhen, vendar ga zaradi dolgotrajnih prizadevanj za ohranitev in obnovo območja Prošćanskega jezera ni mogoče prezreti. Verjetno pa še ne ogroža kakovosti vode in nastajanja lehnjaka. Rezultati kažejo, da tla in sedimenti v zaledju Proščanskega jezera učinkovito zadržijo in čistijo vodo na poti do jezera. Vseeno lahko ob morebitnem onesnaženju v zaledju onesnaževala dosežejo jezerski sistem, če so adsorbirana na delce tal. Poznavanje tal v okolici in širšem zaledju jezera omogoča dragocen vpogled na njihov morebitni vpliv na kemijo vode v jezerih in prispeva k razumevanju tovrstnega naravnega pojava

Effect of copper on thermal stability of nanocrystalline ceria

Cerium (IV) oxide (CeO2) is extensively used as a catalyst because it has numerous advantages over conventional catalysts, like low cost, better poisoning resistance, high catalytic activity due to the facile Ce4+ / Ce3+ redox reac-tion and high oxygen storage capacity. CeO2 nanoparticles have higher specific surface area and better redox properties, and thus an increased catalytic activity in comparison to bulk materials. However, at elevated tem-peratures ceria nanoparticles are very prone to coarsening. In order to increase the thermal stability of CeO2 na-noparticles, but also improve its catalytic properties, metal ions are incorporated into the CeO2 crystal structure. The aim of this study was to compare coarsening kinetics of nanocrystalline CeO2 and nanocrystalline CeO2 doped with 10 mol. % of copper in order to determine the effect of doping on thermal stability. Samples were prepared by hydrothermal synthesis and thermally treated at different temperatures and processing times. The samples were analyzed by X-ray diffraction analysis and the crystallite sizes were calculated using the Scherrer’s equation. Based on the obtained crystallite sizes, kinetic parameters were determined and it was found that cop-per addition has a positive effect on the thermal stability of CeO2