BW as compatibiliser of PCL/PLA blends

Posljednjih godina, povećanjem brige za okoliš, povećala se i svijest o utjecaju plastičnog otpada na onecišćenje okoliša. Kao najbolja metoda za obradu plastičnog otpada pokazalo se kompostiranje, što je utjecalo na povećanje primjene biorazgradivih polimera. S druge strane, iscrpljivanje fosilnih izvora potaknulo je proizvodnju biopolimera, odnosno polimera na bazi obnovljivih izvora, tj. biomase, za koje se pokazalo i da imaju bolji učinak na okoliš. Unatoč povećanju proizvodnje, biopolimeri su i dalje skuplji u odnosu na širokoprimjenjive polimere te su njihova svojstva često slabija ili ne odgovaraju zahtjevima potrošača. Upravo zbog toga bi miješanje, kao relativno brza i jeftina metoda prilagodbe svojstava polimera, moglo imati ključnu ulogu u povećanju konkurentnosti biopolimera. Polilaktid (PLA) je biopolimer dobiven iz biološkog supstrata kukuruza, šećerne trske, manioke, itd., te su njegova mehanička svojstva slična onima širokoprimjenjivih polimera. Kako bi se proširilo područje primjene, PLA se često miješa s polikaprolaktonom (PCL). PLA/PCL mješavine pokazuju široku paletu fizikalnih svojstava i biorazgradivosti, koja se mogu kontrolirati promjenom udjela komponenata i uvjetima miješanja. Kako su PLA i PCL međusobno nemješljivi polimeri, dodatkom kompatibilizatora moguće je povećati njihovu mješljivost, a time i poboljšati svojstva dobivenih mješavina. U ovome radu proučavane su PLA/PCL mješavine različitih omjera komponenata uz pčelinji vosak (BW) kao kompatibilizator. Istraženo je kako pčelinji vosak utječe na slobodnu površinsku energiju, mehanička i toplinska svojstva te morfologiju PLA/PCL mješavina. Utvrđeno je kako dodatak BW u PCL/PLA mješavine značajno utječe na konačna svojstva mješavina.Increasing environmental concerns have also increased the awareness of the impact of plastic waste on environmental pollution. Composting proved to be the most advantageous method for the treatment of plastic waste, thus biodegradable and compostable polymers have found application in various fields. On the other hand, bio-based polymers, i.e. polymers produced from renewable feedstock, biomass in general, might replace fossil sources and also have considerable environmental benefits. In spite of increasing production capacity, biopolymers are still quite expensive compared to commodity polymers and their properties are also often inferior or do not correspond to the expectation of converters or users. Blending is a relatively cheap and fast method to tailor the properties of plastics. As a result, this approach may play a crucial role in increasing the competitiveness of biopolymers. Polylactide (PLA) is a biopolymer derived from from biological substrate of maize, cassava, sugar cane, etc., and its mechanical properties resemble that of present day commodity plastics. In order to broaden the area of application, PLA is often blended with polycaprolactone (PCL). PLA/PCL blends show a wide variety of physical properties and biodegradability, which can be controlled by adjusting the blending ratio and preparation conditions to meet various applications. PLA and PCL are immiscible polymers, therefore compatibilizers can be used to improve their miscibility. In this study, PLA/PCL blends of different compositions were prepared with and without beeswax (BW) as a compatibilizer. The effect of beeswax on surface free energy, morphology, mechanical and thermal properties of the blends was examined. It was found that the addition of BW in PCL/PLA blends significantly affects the final properties of the blends

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

BW as compatibiliser of PCL/PLA blends

Posljednjih godina, povećanjem brige za okoliš, povećala se i svijest o utjecaju plastičnog otpada na onecišćenje okoliša. Kao najbolja metoda za obradu plastičnog otpada pokazalo se kompostiranje, što je utjecalo na povećanje primjene biorazgradivih polimera. S druge strane, iscrpljivanje fosilnih izvora potaknulo je proizvodnju biopolimera, odnosno polimera na bazi obnovljivih izvora, tj. biomase, za koje se pokazalo i da imaju bolji učinak na okoliš. Unatoč povećanju proizvodnje, biopolimeri su i dalje skuplji u odnosu na širokoprimjenjive polimere te su njihova svojstva često slabija ili ne odgovaraju zahtjevima potrošača. Upravo zbog toga bi miješanje, kao relativno brza i jeftina metoda prilagodbe svojstava polimera, moglo imati ključnu ulogu u povećanju konkurentnosti biopolimera. Polilaktid (PLA) je biopolimer dobiven iz biološkog supstrata kukuruza, šećerne trske, manioke, itd., te su njegova mehanička svojstva slična onima širokoprimjenjivih polimera. Kako bi se proširilo područje primjene, PLA se često miješa s polikaprolaktonom (PCL). PLA/PCL mješavine pokazuju široku paletu fizikalnih svojstava i biorazgradivosti, koja se mogu kontrolirati promjenom udjela komponenata i uvjetima miješanja. Kako su PLA i PCL međusobno nemješljivi polimeri, dodatkom kompatibilizatora moguće je povećati njihovu mješljivost, a time i poboljšati svojstva dobivenih mješavina. U ovome radu proučavane su PLA/PCL mješavine različitih omjera komponenata uz pčelinji vosak (BW) kao kompatibilizator. Istraženo je kako pčelinji vosak utječe na slobodnu površinsku energiju, mehanička i toplinska svojstva te morfologiju PLA/PCL mješavina. Utvrđeno je kako dodatak BW u PCL/PLA mješavine značajno utječe na konačna svojstva mješavina.Increasing environmental concerns have also increased the awareness of the impact of plastic waste on environmental pollution. Composting proved to be the most advantageous method for the treatment of plastic waste, thus biodegradable and compostable polymers have found application in various fields. On the other hand, bio-based polymers, i.e. polymers produced from renewable feedstock, biomass in general, might replace fossil sources and also have considerable environmental benefits. In spite of increasing production capacity, biopolymers are still quite expensive compared to commodity polymers and their properties are also often inferior or do not correspond to the expectation of converters or users. Blending is a relatively cheap and fast method to tailor the properties of plastics. As a result, this approach may play a crucial role in increasing the competitiveness of biopolymers. Polylactide (PLA) is a biopolymer derived from from biological substrate of maize, cassava, sugar cane, etc., and its mechanical properties resemble that of present day commodity plastics. In order to broaden the area of application, PLA is often blended with polycaprolactone (PCL). PLA/PCL blends show a wide variety of physical properties and biodegradability, which can be controlled by adjusting the blending ratio and preparation conditions to meet various applications. PLA and PCL are immiscible polymers, therefore compatibilizers can be used to improve their miscibility. In this study, PLA/PCL blends of different compositions were prepared with and without beeswax (BW) as a compatibilizer. The effect of beeswax on surface free energy, morphology, mechanical and thermal properties of the blends was examined. It was found that the addition of BW in PCL/PLA blends significantly affects the final properties of the blends

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 reaction 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 temperatures ceria nanoparticles are very prone to coarsening. In order to increase the thermal stability of CeO2 nanoparticles, 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 copper addition has a positive effect on the thermal stability of CeO2

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

Sol-gel Synthesis and Characterization of Lithium and Cerium Codoped Perovskite

Perovskites are an important group of ceramic materials with a structural formula ABO3 and wide array of potential applications in electronics, superconductors, catalysis, etc. CaTiO3, by which the whole group was named for, is particularly significant due to its use in catalysis, but its photocatalytic activity is limited by a large band gap value (~3.5 eV). A possible solution is the substitution of A and B cations with foreign cations which causes the alteration of properties, including photocatalytic efficiency. The aim of this work was the sol-gel synthesis of lithium and cerium codoped CaTiO3, characterization of the prepared gel and ceramics obtained by its thermal treatment. Samples of codoped perovskite, Ca1-xLixCexTiO3, where x = 0, 0.01, 0.02, 0.03 and 0.04, were prepared and characterized using powder X–ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), differential thermal and thermo- gravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Photocatalytic activity was evaluated through the study of methylene blue photocatalytic degradation. XRD analysis showed that the prepared samples consisted of calcium nitrate and titanium chelate. In accordance with the established thermal evolution path, all samples were thermally treated at 500 °C for 2 hours. Beside perovskite, Ca2Ti2O6 appeared as a secondary phase in all thermally treated samples. SEM analysis of thermally treated samples showed the presence of agglomerates of irregular morphology and the decrease of primary particles size with the increase of dopants concentration. The sample with x=0.04 showed an increased photocatalytic activity

Measurement and Control: Determination of the Semiconductors Band Gap by UV-Vis Diffuse Reflectance Spectroscopy

U radu je dan pregled pojmova i jednadžbi vezanih uz određivanje zabranjene zone metodom difuzne refleksijske spektroskopije i uporabu Taucova grafičkog prikaza. Kako bi se demonstrirao postupak i vrednovala sama metoda, primjenom metode određena je zabranjena zona komercijalnih uzoraka anatasa, rutila, cinkita i hematita. Na temelju eksperimentalno dobivenih vrijednosti širine zabranjene zone komentirana je točnost metode te osjetljivost pri razlikovanju poluvodiča s direktnim i indirektnim prijelazima. Pokazano je da Taucova metoda nije besprijekorna niti u pogledu točnosti niti razlikovanja indirektnih i direktnih elektronskih prijelaza u poluvodičkim materijalima, ali je vrlo praktičan način određivanja širine zabranjene zone poluvodiča budući da ne zahtijeva pretjerano skupu instrumentaciju a obrada eksperimentalnih podataka relativno je jednostavna. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.For the application of semiconductors, an important factor is the band gap, i.e., the minimum energy required for the transfer of electrons from the valence to the conduction band. One of the possible methods for band gap determination is diffuse reflectance spectroscopy and Tauc plot. In this paper, an overview of the terms and equations related to the said method is given, as well as its utilization in the determination of band gaps of commercial samples of various metal oxides. Thus, the procedure is demonstrated and evaluated through the determination of indirect and direct band gap values of anatase (TiO2), rutile (TiO2), zincite (ZnO), and hematite (Fe2O3). All samples were beforehand analysed and identified by X-ray powder diffraction on Shimadzu XRD 6000 diffractometer with CuKα radiation working in a step scan mode with steps of 0.02° and counting time of 0.6 s. It was determined that all samples are well crystallized with relatively large crystallite sizes. UV-Vis spectra of the samples, as well as barite, which was used as a reference, were obtained on the UV-Vis spectrometer with an integrating sphere in total reflectance mode. The UV-Vis DRS spectra were transformed to Kubelka-Munk function, after which Tauc plot was used for the determination of the indirect and direct band gap values of all samples. The obtained values for anatase were 3.20 eV for indirect transition and 3.41 eV for direct transition, and for rutile 3.00 eV for indirect transition and 3.11 eV for direct transition. The zincite sample showed an indirect band gap of 3.19 eV and direct band gap of 3.25 eV, while the obtained indirect band gap value for hematite was 1.96 eV and direct band gap value 2.15 eV. As may be seen, the method is not particularly useful when distinguishing direct from indirect semiconductors, since, for all samples, the curves in Tauc plot for both indirect and direct electron transitions possess a linear dependence region from which the band gap value is estimated. However, the obtained band gap values for all the studied semiconductors are in relatively good concordance with literature references. The method is perhaps most useful in monitoring the variation of band gap depending on the dopant content. Namely, the studied metal oxides are used in photocatalysis where the addition of dopants is expected to reduce the band gap to visible light area, and thus improve the photocatalytic activity of the semiconductor. It can be concluded that the Tauc method is not perfect in terms of accuracy and differentiation between indirect and direct electron transitions in semiconductors. Nevertheless, it is a very practical way of band gap assessment for semiconducting materials, because it requires no excessively expensive instrumentation, and the processing of experimental data is rather simple. This work is licensed under a Creative Commons Attribution 4.0 International License

Humidity sensing ceria thin-films

Lowering the constitutive domains of semiconducting oxides to the nano-range has recently opened up the possibility of added benefit in the research area of sensing materials, in terms both of greater specific surface area and pore volume. Among such nanomaterials, ceria has attracted much attention ; therefore, we chemically derived homogeneous ceria nanoparticle slurries. One set of samples was tape-casted onto a conducting glass substrate to form thin-films of various thicknesses, thereby avoiding demanding reaction conditions typical of physical depositions, while the other was pressed into pellets. Structural and microstructural features, along with electrical properties and derivative humidity-sensing performance of ceria thin-films and powders pressed into pellets, were studied in detail. Particular attention was given to solid- state impedance spectroscopy (SS-IS), under controlled relative humidity (RH) from 30%– 85%, in a wide temperature and frequency range. Moreover, for the thin-film setup, measurements were performed in surface-mode and cross-section- mode. From the results, we extrapolated the influence of composition on relative humidity, the role of configuration and thin-film thickness on electrical properties, and derivative humidity- sensing performance. The structural analysis and depth profiling both point to monophasic crystalline ceria. Microstructure analysis reveals slightly agglomerated spherical particles and thin-films with low surface roughness. Under controlled humidity, the shape of the conductivity spectrum stays the same along with an increase in RH, and a notable shift to higher conductivity values. The relaxation is slow, as the thickness of the pellet slows the return of conductivity values. The increase in humidity has a positive effect on the overall DC conductivity, similar to the temperature effect for semiconducting behavior. As for the surface measurement setup, the thin-film thickness impacts the shape of the spectra and electrical processes. The surface measurement setup turns out to be more sensitive to relative humidity changes, emphasized with higher RH, along with an increase in thin-film thickness. The moisture directly affects the conductivity spectra in the dispersion part, i.e., on the localized short-range charge carriers. Moisture sensitivity is a reversible process for thin-film samples, in contrast to pellet form samples

Ružička days : International conference 16th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: open lecture (1), chemical analysis and synthesis (3), chemical and biochemical engineering (8), food technology and biotechnology (8), medical chemistry and pharmacy (3), environmental protection (11) and meeting of young chemists (2)