Carbon Cryogel Magnetite Composites-Effective Adsorbents for the Phosphate and Phenol Removal from Water

Carbon cryogel (CC) was impregnated with magnetite to produce a multifunctional magnetic adsorbent capable of removing phenoles and phosphates from water. Adsorbents were prepared via co-precipitation of Fe2+ and Fe3+ ions in aqueous solution in the presence of CC. Non-treated or acid-activated CC was used. The CC: Fe3O4 ratios of 1:1 and 3:1 were applied. The addition of HCl in the synthesis process was also investigated. XRD confirmed the formation of nanocrystalline magnetite. BET analysis showed that the pre-treatment diminished the CC porous structure, reducing also specific surface area (Sp). Formation of magnetite decreases Sp and total volume of micro and meso pores, but their distribution remained unchanged. FTIR spectra revealed that magnetite was attached to the surface of the acid activated CC via C═O bond. DTA-TGA and SEM indicated that acid treatment and presence of HCl were beneficial for homogeneous nucleation and distribution of magnetite, increasing adsorption properties of composite. Batch adsorption proved that the maximum adsorption capacity for phenoles was accomplished with 3:1 ratio with non-treated CC. Samples synthesized with pre- treated CC, under 1:1 ratio, gave the best results for phosphate removal. The CC/magnetite composite was found as promising adsorbent for the simultaneous removal of both polutants.The book of abstract available at: [http://conf.univerzitetpim.com/wp-content/uploads/2022/06/Book-of-Abstracts_2022-1.pdf

Tm(III)-doped d-Bi2O3 for solid - oxide fuel cells

The oxide ion conductors have widely been investigated because of their application in many devices with high economical and ecological interests, such as solid oxide fuel cells (SOFC). -Bi2O3 polymorph possesses the highest known O2– ion conductivity, which is one to two orders of magnitude higher than that of stabilized zirconia at corresponding temperatures [1]. At the moment, the application of this high-temperature polymorph as an electrolyte in SOFC requires temperatures above 730 °C. However, the doping allows -Bi2O3 stabilization to room temperature and opens the possibility for construction of SOFC that will operate at intermediate temperatures (ca. 350 °C) [2]. As it is found that some lanthanides are suitable dopants [3], the possibility to stabilize O2– ion conductors related to the -Bi2O3 polymorph in the Bi2O3–Tm2O3 system was investigated. Two starting mixtures with compositions (Bi1–xTmx )2O3 (x = 0.04 and 0.20) were homogenized in an agate mortar, heat treated at 750 °C for 3 h and then slowly furnace cooled. The samples were characterized by XRPD, DTA and SEI techniques. Based on XRPD, the single-phase tetragonal β-Bi2O3 was identified in the sample with x = 0.04. Its unit cell parameters, a = 7.742(2) and c = 5.650(2) Å, well-correspond to those of undoped β-Bi2O3 [4]. On the other hand, the cubic -Bi2O3 phase was obtained in the sample with x = 0.20. Its unit cell parameter was greater than the value reported for Tm-doped -Bi2O3 sample with x = 0.25 [3] (5.5033(9) vs. 5.478 Å). Both values are smaller than reported for undoped -Bi2O3 [4]. This means that the unit cell parameter of cubic -Bi2O3 decreases as Tm-content increases and it is in accordance with Tm3+ and Bi3+ ionic radii [5]. For the sample with x = 0.04, cyclic DTA curves showed one reversible β-Bi2O3 ↔ -Bi2O3 transition with corresponding temperatures: on heating, 660 °C, and, on cooling, 600 °C. Surprisingly, no phase transitions were observed in the sample with x = 0.20 which indicates that the obtained -Bi2O3 is stable within the whole investigated interval, i.e., from room temperature to 1000 °C. Electrochemical impedance of -Bi2O3 phase was measured in the following temperature range: 300 – 800 °C. At higher temperatures (600 – 800 °C) the conductivities are similar (0.11 – 0.32 S cm –1 ), but with lowering temperature they rapidly decrease, and amount, for example, 2.1·10–5 S cm–1 at 300 °C. As a consequence, two activation energies are found: 0.45(4) eV (600 – 800 °C), and 1.33(2) eV (300 – 600 °C). References: [1] P. Shuk, H.-D. Wiemhöfer, U. Guth, W. Göpel, M. Greenblatt, Solid State Ionics 89 (1996) 179 [2] E. D. Wachsman, K.T. Lee, Science 334 (2011) 935 [3] H. T. Cahen, T. G. M. Van Den Belt, J. H. W. De Wit, G. H. J. Broers, Solid State Ionics 1 (1980) 411 [4] H. A. Harwig, Z. anorg. allg. Chem. 444 (1978) 151 [5] R. D. Shannon, Acta Cryst. A 32 (1976) 75

Sintering of alumina doped with different oxides, followed by sensitive dilatometer

Sintered alumina powder represents suitable material for usage in various industry fields (e.g., as chip carriers in electronics, microwaves, jewelry production), due to convenient physical properties, such as sinterability, electrical and mechanical features. Those properties can be modified by addition of different oxides and/or mechanical treatment. Therefore, in this investigation the alumina was doped with 1 wt. % of Cr2O3, Mn2O3 and NiO, respectively, followed by 1 hour of mechanical activation at 400 rpm in planetary ball mill. Sintering of powder mixtures was tracked by sensitive dilatometer up to 1400 °C. The final density values varied from cca. 2 ̶ 3.2 g/cm3. Changes in microstructure were observed by means of SEM. The influence of additives along with mechanical activation is monitored trough changes in electrical permittivity and loss tangent. Compared to pure alumina, the additives lower the relative permittivity and increase dielectric losses. For a given mixture, the sintering increases the relative permittivity and decreases losses

Physical Properties of Sintered Alumina Doped with Different Oxides

Corundum (alpha-alumina) is a suiTab. material for usage in various industry fields owing to its chemical stability, electrical and mechanical features. It is known that properties of ceramics could be modified by addition of different oxides, as well as by changing the consolidation parameters. In this respect, alumina was doped with 1 wt.% of Cr2O3, Mn2O3 and NiO, followed by 1 hour of mechanical activation in a high-energy planetary ball mill. A sensitive dilatometer was used for sintering of powder mixtures up to 1400 degrees C and recording the obtained dilatation. The final density varied between cca. 1.9 and 3.3 g/cm(3). Microstructural changes were detected by SEM measurements. Changes in electrical permittivity and loss tangent were associated with the preparation conditions (types of additives, duration of mechanical activation). For a given mixture, the sintering increases the relative permittivity and decreases losses, exhibiting the optimal values of 8.32 and 0.027, respectively, for the sample activated 60 minutes and sintered, with the addition of MnO2. Mechanical measurements indicate significant differences in strength with the addition of different transition metal oxides. Samples with Mn and Ni, activated and sintered, with strength of 121 and 86 MPa, respectively, have a significantly higher tensile strength than the other tested samples, due to their more compact microstructures

Effects of ball-milling on properties of sintered alumina doped with Mn2O3

Recently, with the huge use of smart gadgets, developing of smart jewelry represents a very interesting segment in material science, as well as in electronic science. Alumina is widely used ceramic in many industrial fields as pigments, catalysis, microelectronics, etc., mostly because of its low cost and appropriate mechanical and electrical properties, high surface area and thermal stability. Also, modified alumina could be applied in production of smart jewelry. Thus, the main objectives of this investigation is to improve features of sintered alumina doped with Mn2O3 along with mechanical treatment, in order to obtain strong ceramic with low values of dielectric loss and low relative dielectric permittivity, as well as esthetic. Commercial alumina powder was doped with 1 wt % of manganese oxide and treated in planetary ball mill for an hour. Characteristic temperatures of both powders (non-activated and activated one) were investigated in detail by DTA and TG analyses. After sintering at 1200, 1300, and 1400 oC for 2 h, XRD patterns and SEM images were recorded. Furthermore, mechanical and electrical properties were examined for all sintered samples

HIGHLY CONDUCTIVE LANTHANOIDE STABILIZED δ-Bi2O3 PHASES

Due to the increasing demands for new highly efficient and environmentally friendly energy conversion technologies, the oxide ion conductors applicable in solid oxide fuel cells (SOFCs) have widely been investigated. The aim is to find a suitable electrolyte with the ionic conductivity high enough at intermediate temperatures in order to reduce the operating temperature of SOFCs. The high temperature δ-Bi2O3 phase has been proposed as a good candidate for electrolyte in SOFCs because it is the fastest known ionic conductor. In this study, the possibility to stabilize O 2– ion conductors related to the -Bi2O3 polymorph in Bi2O3–Tm2O3 and Bi2O3–Lu2O3 systems was investigated. Six starting mixtures with the following compositions (Bi1–xTmx)2O3, x = 0.11, 0.14 and 0.20, and (Bi1–yLuy)2O3, y = 0.15, 0.20 and 0.25, were dry homogenized in an agate mortar, heat treated at 750 °C for 3 h and then slowly furnace cooled. The samples were characterized by XRD, TEM/SAED, SEM, DTA and SEI techniques. Based on XRD and TEM/SAED, the targeted cubic δ-Bi2O3 single-phase samples (space group Fm3m ) were successfully obtained within all six systems. The unit cell parameter of both Tm- and Lu-doped -Bi2O3 decreases as dopant content increases. By comparing Tm- and Lu-doped δ-Bi2O3 phases mutually, an expected increase of the unit cell parameters with larger ionic radii of dopant was found [ri(Tm3+) = 0.88 Å, and ri(Lu3+) = 0.86 Å in the octahedral environment1 ]. Electrochemical impedance of -Bi2O3 phases was measured between 300 and 800 °C. At temperatures 550 – 800 °C the conductivities are of the same order of magnitude (0.1 – 0.4 S cm –1 ), but with lowering temperature they rapidly decrease resulting in two activation energies. This is due to the changes in conductivity mechanism which will be discussed.According to the cyclic DTA curves, no phase transitions were observed in the following samples: (Bi0.8Tm0.2)2O3, (Bi0.8Lu0.2)2O3 and (Bi0.75Lu0.25)2O3, indicating that these -Bi2O3 phases are stable within the whole investigated interval, i.e., from room temperature to 985 °C. This means that the application of these electrolyte materials could result not only in the significant enhancement of IT-SOFC electrochemical performance, but also in their good structural stability over long time service in a wide temperature range. 1. R. D. Shannon, Acta Cryst. A, 32 (1976) 75

Structural, thermal and surface characterization of thermoplastic polyurethanes based on poly(dimethylsiloxane)

In this study, the synthesis, structure and physical properties of two series of thermoplastic polyurethanes based on hydroxypropyl-terminated poly(dimethylsiloxane) (HP-PDMS) or hydroxyethoxypropyl-terminated poly(dimethylsiloxane) (EO-PDMS) as soft segments, and 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments were investigated. The polyurethanes were synthesized by two-step polyaddition in solution. The effects of the type and content of PDMS segments on the structure, thermal and surface properties of copolymers were studied by H-1-, C-13-nuclear magnetic resonance (NMR) spectroscopy and two-dimensional NMR spectroscopies (heteronuclear multiple bond correlation (HMBC) and rotating-frame nuclear Overhauser effect (ROESY)), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide-angle X-ray scattering (WAXS), scanning electron microscopy (SEM) and water contact angle and water absorption measurements. Thermal properties investigated by DSC indicated that the presence of soft PDMS segments lowers the glass transition and melting temperatures of the hard phase as well as the degree of crystallinity. SEM analysis of the copolymers with a lower soft segment content confirmed the presence of spherulite superstructures, which arise from the crystallization of the hard segments. When compared with polyurethanes prepared from HP-PDMS, the copolymers synthesized from EO-PDMS with the same content of the soft segments had a higher degree of crystallinity, better thermal stability and a less hydrophobic surface. The obtained results showed that the synthesized polyurethanes had good thermal and surface properties, which could be further modified by changing the type or content of the soft segments

Uticaj postupka sinteze na aktivnost platinskih katalizatora za reakciju elektrooksidacije etanola

Carbon supported platinum catalysts for ethanol electrooxidation were synthesized by modified polyol synthesis method, assisted by microwave or reflux heating. Synthesized catalysts were characterized by XRD, STM and TGA techniques to determine their structural and morphological properties. STM and XRD investigations revealed small particle size (~3nm), while TGA showed Pt loading of 20% in both samples. Electrocatalytic activity of prepared catalysts was examined by potentiodynamic measurements and compared to commercial Pt catalyst (Pt/C-Tanaka). The highest activity for ethanol electrooxidation was observed with Pt catalyst prepared by microwave irradiation. The increase in activity can be assigned to the benefits of microwave assisted synthesis, such as small particle size and homogeneous particle distribution on the support.Platinski katalizatori na ugljeničnoj podlozi su sintetizovani korišćenjem modifikovanog poliol postupka uz primenu mikrotalasnog ili refluks zagrevanja za reakciju elektrooksidacije etanola. Dobijeni katalizatori su karakterisani strukturno i morfološki korišćenjem XRD, STM i TGA tehnika. STM i XRD ispitivanja su pokazala malu veličinu čestica (~3nm), dok je TGA pokazala da je sadržaj metala u katalizatoru 20%. Elektrokatalitička aktivnost sintetizovanih katalizatora je ispitivana potenciodinamičkim merenjima i upoređena sa komercijalnim platinskim katalizatorom (Pt/C-Tanaka). Najbolju aktivnost za elektrooksidaciju etanola pokazao je platinski katalizator sintetizovan uz korišćenje mikrotalasnog zagrevanja. Veća aktivnost se može pripisati prednostima mikrotalasnog zagrevanja u toku sinteze jer je dobijen katalizator sa malom veličinom i homogenom di stribucijom čestica

Characterization of MgAl₂O₄ Sintered Ceramics

Single phase MgAl2O4 was made from a one-to-one molar ratio of MgO and Al2O3 powders mixed using ball-milling. Mixtures of MgO and Al2O3 were subsequently treated in planetary ball mill for 30, 60, 90 and 120 minutes in air. The aim of this study was to examine phase composition, microstructure, and densification behavior of sintered specimens. After sintering in dilatometer at 1500 °C, the powder was converted to single phase MgAl2O4. The results show that mechanical activation improved the densification behavior of MgAl2O4 sintered specimens, and it reduced the onset temperature for sintering by approx. 100°C. Based on dilatometer data, powders were subsequently densified at 1450°C by hot pressing. Almost all specimens exhibited full density, while sample activated for 30 minutes showed the fastest densification rate

Towards understanding intermolecular interactions in hydantoin derivatives: the case of cycloalkane-5-spirohydantoins tethered with a halogenated benzyl moiety

A series of cycloalkane-5-spirohydantoins bearing a halogeno substituted benzyl group (X = Cl and Br) in position 3 has been synthesized and their structures (1-6) have been determined by a single crystal X-ray diffraction method. These compounds have multiple functional groups, which allow greater competition and/ or cooperation among the different intermolecular interactions in the formation of their crystal structures. The molecules are linked together by paired N-H... O hydrogen bonds in R22(8) rings, while the CH. O interactions lead to their further association into double chains. The contribution of the cycloalkyl ring depends on its conformational flexibility and the multiple C-H donor implications. In the case of compounds 1-4 bearing the cyclopentyl or the cyclohexyl ring, halogen bonding (X...O) interactions give rise to a supramolecular pseudo-hexagonal network. In addition, the C-H... X interactions with a higher degree of multifurcation at the halogen acceptor have an important role in the formation of the crystal structure. Regarding compounds 5 and 6 with the cycloheptane ring, the X. O interaction is absent, and along with the C-H. X interactions, these compounds realize an alternative crystal structure with an emphasis on the X. p interactions. The lattice energies of all these crystal structures, as well as the intermolecular pair energies, have been calculated using PIXEL and further partitioned into coulombic, dispersive, polarization and repulsive factors. The crystal structures have also been subjected to Hirshfeld surface analysis which reveals that approximately 75% of the close contacts correspond to relatively weak interactions. The application of both concepts has provided a new insight into the relationship between the molecular interactions and crystal structures of the hydantoin derivatives.This is the peer-reviewed version of the following article: Crystengcomm, 2017, 19, 3, 469-483 [https://dx.doi.org/10.1039/C6CE02210C][http://cer.ihtm.bg.ac.rs/handle/123456789/2204