Amino- and ionic liquid-functionalised nanocrystalline ZnO via silane anchoring - an antimicrobial synergy

Temperature has critical impact on food quality and safety within food supply chain, therefore, food should be kept at the defined storage temperature range. Final consumer should be assured when buying food about actual temperature and thermal history of the selected food product and this is why it should be indicated on the packed or prepacked item. The chromogenic temperature indicator for cold food chain was prepared from suitable active material packed in the properly structured holder. When temperature rises above the defined storage temperature, the active material changes colour and physical state (solid/liquid). Simultaneously, special packaging structure enables irreversible recording of the time exposed to the elevated temperature. The active material was made of thermochromic composite, consisting of dye, developer and solvent. It changes colour at its melting point, being coloured below and discoloured above it. The temperature is called activation temperature of the composite. Its value was adjusted by appropriate solvent and additives used for preparation of the composite, to reach the desired value. The temperature dependent colour change of the composite was determined by colorimetric measurements. The conditions for best observation of the change by naked eye were also examined. The structure of the active material’s holder was analyzed for best displaying of the time spend at high temperature (above the activation temperature). Functioning of the indicator was examined with growth of pathogens as a function of migration of the active material at temperature above the required storage temperature of the food. It was found out that the described chromogenic temperature indicator for cold food chain shows the thermal history of food storage by colour-, phase- and migration changes of the active composite material and consequently would be reliable as indicator in cold food chain to indicate temperature abuse and would disclose potential growth of psychrophilic microorganisms

TEM and DFT Study of Basal-plane Inversion Boundaries in SnO2-doped ZnO

In our recent study (Ribie et al. 2020) we reported the structure of inversion boundaries (IBs) in Sb2O3 -doped ZnO. Here, we focus on IBs that form in SnO2-doped ZnO. Using atomic resolution scanning transmission electron microscopy (STEM) methods we confirm that in SnO2-doped ZnO the IBs form in head-to-head configuration, where ZnO4 tetrahedra in both ZnO domains point towards the IB plane composed of a close packed layer of octahedrally coordinated Sn and Zn atoms. The in-plane composition is driven by the local charge balance, following Pauling's principle of electroneutrality for ionic crystals, according to which the average oxidation state of cations is 3+. To satisfy this condition, the cation ratio in the IB-layer is Sn4+ : Zn2+ =1:1. This was confirmed by concentric electron probe analysis employing energy dispersive spectroscopy (EDS) showing that Sn atoms occupy 0.504 +/- 0.039 of the IB layer, while the rest of the octahedral sites are occupied by Zn. IBs in SnO2-doped ZnO occur in the lowest energy, IB3 translation state with the cation sublattice expansion of Delta IB(zn-zn) of +91 pm with corresponding O-sublattice contraction Delta IB(O-O) of -46 pm. Based on quantitative HRTEM and HAADF-STEM analysis of in-plane ordering of Sn and Zn atoms, we identified two types of short-range distributions, (i) zigzag and (ii) stripe. Our density functional theory (DFT) calculations showed that the energy difference between the two arrangements is small (similar to 6 meV) giving rise to their alternation within the octahedral IB layer. As a result, cation ordering intermittently changes its type and the direction to maximize intrinsic entropy of the IB layer driven by the in-plane electroneutrality and 6-fold symmetry restrictions. A long-range in-plane disorder, as shown by our work would enhance quantum well effect to phonon scattering, while Zn2+ located in the IB octahedral sites, would modify the the bandgap, and enhance the in-plane conductivity and concentration of carriers

Hierarchical ZnO/SnO2 heterostructures via hydrothermally assisted electrospinning technique: synthesis and photocatalytic performances

Hierarchical nanostructures with multiporous tin oxide nanofibers (SnO2- MPNFs) and zinc oxide nanorods (ZnO-NRs) have been synthesized by combining electrospinning technique and hydrothermal method. A solution containing uniformly distributed tin (Sn) and silicon (Si) species of precursors, as well as a sacrificial polymer (PVP) was electrospun using a single-nozzle spinneret to fabricate nanofibers. In virtue of the Kirkendall effect driven by calcination at 550 °C, the SiO2-cored SnO2 nanofibers (SnO2-SiO2-NFs) deliberated from PVP were formed and used as backbones for further hydrothermal growth of ZnO-NRs. By varying the hydrothermal reaction time (0.5–2 h) at the constant concentration of SnO2-SiO2-NFs, zinc (Zn) precursor, directing agent (hexamethylenetetramine, HMT) and aqueous ammonia, the density, length and thickness of ZnO-NRs were controlled. Nanofibers and ZnO-NRs/SnO2-MPNFs heterostructures are confirmed by X-ray diffraction (XRD), field-emission scanning electron microcopy (FE-SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and elemental mapping analysis. The hydrothermal treatment conducted at 90 °C in aqueous ammonia allowed: a) selective etching of SiO2 from the SnO2-SiO2-NFs core and SiO2 trapped between SnO2 particles, and b) effective growth of ZnO-NRs. The process resulted in ZnO-NRs/SnO2-MPNFs heterostructures with ZnO-NRs of 1–5 μm in length attached to SnO2-MPNFs, the shell of which was composed of ultra-fine SnO2 crystallites (~5 nm in size) and where the four porous channels create the core instead of SiO2. Photocatalytic performance of the heterostructures was investigated toward different organic azo-dyes (methylene blue, methyl orange) and obvious enhancement was demonstrated in degradation of the organic pollutant, compared to primary SnO2-based nanofibers

The influence of spark plasma sintering temperature on the properties of Sb-doped barium stannate ceramics

Barium-stannate (BaSnO3, BSO) is a member of the perovskite-type alkaline earth stannates ASnO3 (A = Ca, Sr, Ba) with an ideal cubic crystal structure (space group: ). Doping with antimony (Sb5+) can change this wide band-gap semiconductor (Eg = 3.1-3.4 eV) into an n-type semiconductor with high electrical conductivity at room temperature. The major drawbacks in the BSO-based ceramics synthesis are phase composition and low density of final ceramic materials. These problems could be solved using spark plasma sintering (SPS), a current and pressure-assisted technique, which enables the preparation of dense ceramics at significantly lower temperatures and for a shorter time. To investigate the influence of spark plasma sintering temperature on the structural, microstructural and electrical properties of BaSn1-xSbxO3 (BSSO, x = 0.00; 0,04; 0.06; 0.08; and 0.10) ceramics samples, BSSO powders were spark plasma sintered at 1100 °C, 1200 °C and 1250 °C for 5 min. X-ray diffraction (XRD) analysis confirmed that all ceramic samples sintered at 1100 °C crystallized in a single-phased cubic BSO structure. Their relative densities were in the range of 72–82% ρt. Sintering at 1200 °C increased the samples’ relative densities to 79–96% ρt, but also induced the formation of a barium-rich secondary phase, Ba2SnO4. Rising the sintering temperature further to 1250 °C induced the melting of all samples except BaSn0.92Sb0.08O3. Field emission scanning electron microscopy (FE-SEM) revealed that doping with antimony decreased the grain sizes in BSSO samples sintered at 1100 °C and 1200 °C up to the concentration x = 0.08. Electrical measurements revealed the typical semiconductor behavior of the undoped samples, showing nonlinear current-voltage characteristic and the existence of one semicircle in their impedance spectra, characteristic for materials with double Schottky barrier at the grain boundaries. However, samples with higher dopant concentrations (x = 0.08 and 0.10) showed significantly lower electrical resistivity and linear current-voltage characteristic. The lowest and almost constant value of electrical resistivity in the temperature range of 25–150 °C, and complete loss of the semicircle in its impedance spectrum revealed the metallic-like behavior of sample BaSn0.92Sb0.08O3 sintered at 1200 °C

The influence of sintering processing on microstructural, optical and electrical properties of zinc oxide ceramics doped with Al3+, B3+, Mg2+

Zinc oxide (ZnO) is a versatile functional material, widely employed in industry and technology as varistor ceramics, transparent conducting films, surface acoustic wave resonators etc. ZnO-based conductive ceramics, attractive for various applications, should have low electrical resistivity and good linearity. The n-type conductivity of wide band gap (3.37 eV) ZnO semiconductor could be enhanced by multiple doping with trivalent metals (B3+, Al3+, Ga3+, In3+), as shallow donors. The intrinsic defects, zinc vacancies and interstitial oxygen, exist in the grain boundaries of n-type ZnO ceramics as localized acceptor states. These states attract charge carriers, creating a depletion region around the grain boundaries and energy potential barrier, which hinder the motion of the electrons [1]. In this work, zinc oxide ceramics doped with Al3+, B3+ and Mg2+ was prepared using solid-state reaction technique from ZnO powder obtained in solvothermal synthesis and Al2O3, MgO and B2O3 (H3BO3) commercial powders. Al2O3 was used as a donor dopant to increase the carrier concentration, B2O3 was added to enhance densification and grain growth, and MgO – to decrease the thermal conductivity [2,3]. The pressed ZnO (0.25 % Al2O3, 0.5 % B2O3, 1 % MgO) pellets were sintered by conventional (CS) and spark plasma (SPS) method. The ceramic samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis spectroscopy and current-voltage (I–U) measurements. The correlation between the sintering processing, microstructure and electrical properties of multiple doped ZnO-based ceramics was investigated. The electrical performances of ZnO (0.25 % Al2O3, 0.5 % B2O3, 1 % MgO) ceramics were strongly dependent on composition and microstructure (density, grain size, segregation of secondary phase in grain boundaries). The electrical resistivity of SPS sample was an order of magnitude lower than electrical resistivity of CS sample and it showed almost linear I-U characteristics in temperature range of (25–150) C. 1. T.K. Gupta, W.G. Carlson, J. Mater. Sci., 20 (1985) 3487 2. T. Tian, L. Cheng, J. Xing, L. Zheng, Z. Man, D. Hu, S. Bernik, J. Zeng, J. Yang, Y. Liu, G. Li, Mater. Design, 132 (2017) 479 3. B. Yuksel, T. O. Ozkan, Mater. Sci. – Poland, 33 (2015) 22

Zirconia-toughened alumina ceramic wear particles do not elicit inflammatory responses in human macrophages

Ten percent of patients undergoing total hip arthroplasty (THA) require revision surgery. One of the reasons for THA are wear particles released from the implants that can activate the immune defense and cause osteolysis and failure of the joint implant. The discrepancies between reports on toxicity and immunogenicity of the implant materials led us to this study in which we compared toxicity and immunogenicity of well-defined nanoparticles from Al2O3, zirconia-toughened alumina (ZTA), and cobalt chrome (CoCr), a human THP-1 macrophage cell line, human PBMCs, and therefrom-derived primary macrophages. None of the tested materials decreased the viability of THP-1 macrophages nor human primary macrophages at the 24 h time point, indicating that at concentrations from 0.05 to 50 µm3/cell the tested materials are non-toxic. Forty-eight hours of treatment of THP-1 macrophages with 5 µm3/cell of CoCr and Al2O3 caused 8.3-fold and 4.6-fold increases in TNF-α excretion, respectively, which was not observed for ZTA. The comparison between THP-1 macrophages and human primary macrophages revealed that THP-1 macrophages show higher activation of cytokine expression in the presence of CoCr and Al2O3 particles than primary macrophages. Our results indicate that ZTA is a non-toxic implant material with no immunogenic effects in vitro.Slovenian Research Agency (ARRS

Effect of the sintering technique on the properties of Sb-doped BaSnO3 ceramics

Barium stannate, BaSnO3 (BSO), a cubic perovskite-type oxide with its interesting structural, optical and electrical properties has wide application as an electrode material, thermally stable capacitor, transparent conductive oxide, photocatalyst, humidity and gas sensor material [1]. Partial substitution of Sn by Sb in BSO leads to drastic changes primarily in its electrical properties, resulting in metallic-like conductivity of doped ceramics. Major problems concerning the synthesis of Sb doped BSO (BSSO) are connected to the phase composition and density of final ceramic material. This study covers the comprehensive investigation of structural, microstructural and electrical properties of the Sb-doped BaSn1-xSbxO3 (x = 0.00, 0.04 and 0.08, BSSO) ceramic materials obtained by two different sintering techniques: conventional sintering (CS) and Spark Plasma sintering (SPS). The relative densities of the BSSO-CS ceramic samples sintered at 1600 °C for 3 h was in the range of 79– 96 %. On the other side, the relative densities of BSSO-SPS ceramic samples in the range of 86–96 % were obtained at 1200 °C, with sintering time of only 5 minutes. The XRD analysis confirmed that cubic BaSnO3 is a major phase in all BSSO samples. The presence of tetragonal Ba2SnO4 as a secondary phase was detected in BSSO-SPS ceramic samples, with its content decreasing upon Sb-doping. As expected, the grain size of the samples sintered at higher temperatures (BSSO-CS) is larger in comparison with BSSO-SPS ceramic samples, which was confirmed by Scanning Electron Microscopy (SEM). SEM analysis also revealed the layered structure within the grains of BaSn0.92Sb0.08O3-CS sample while HRTEM analysis confirmed the existence of the low angle grain boundaries (LAGBs) in the SPSed sample with the same composition. The electrical resistivity decreased upon Sb doping, and all doped BSSO samples showed the linear I-U characteristic in the temperature range of 25–150 °C. The semiconductor behavior of all BSSO-CS and BSSO-SPS (x = 0.00 and 0.04) ceramic samples was confirmed through the existence of semicircles in their impedance spectra. On the other hand, the BaSn0.92Sb0.08O3 sample showed the metallic-like behavior resulting from the loss of the electrostatic barriers at LAGBs, which is manifested through the absence of the semicircle in its impedance spectra

Correlation between the microstructure and electrical properties of Sb-doped BaSnO3 ceramics

The non-magnetic, non-inductive electroconductive materials with linear current-voltage characteristic and low and almost constant electrical resistivity in the wide temperature range could be used in conditions unfavorable for metals and alloys. Particular emphasis is placed on the performance and endurance of these materials in conditions at constant high voltage, current, and energy, as well as operating in acidic and humid environmental conditions. The aim of this work was to investigate the influence of antimony concentration and sintering parameters on the structure, microstructure, and electrical properties of antimony-doped barium stannate, BaSn1-xSbxO3 (BSSO, x = 0,00; 0,04; 0,06; 0,08 and 0,10) to obtain conductive electroceramic samples with linear current-voltage (I- U) characteristics and low electrical resistivity. For this purpose three different sintering techniques were used: conventional, spark plasma and cold sintering. According to the X-ray diffraction (XRD) analysis, single-phase ceramic mater- ials with cubic BaSnO3 structure were obtained by conventional sintering at 1600 °C for 3 h and spark plasma sintering at 1100 °C for 5 min. Raising the spark plasma sintering temperature to 1200 °C induced the formation of Ba-rich secondary phase, Ba2SnO4. XRD analysis confirmed the presence of unreacted SnO2 and BaCO3 in cold sintered BaSn0.92Sb0.08O3 sample (310 °C for 5 min, 20 wt.% 1 M acetic acid). Scanning electron microscopy (SEM) indicates a significant decrease in grain size upon doping, regardless of the sintering technique. High-resolution transmission electron microscopy (HRTEM) revealed the presence of low angle grain boundaries (LAGBs) in conventionally and spark plasma sintered (1200 °C for 5 min) samples with x = 0.08. The results of electrical measurements confirmed the semiconducting properties of all BSSO, except the spark plasma sintered BaSn0.92Sb0.08O3 (1200 °C for 5 min) sample. This sample showed linear current-voltage characteristic, the lowest and almost constant electrical resistivity in the temperature range of 25–150 °C resulting from the loss of potential barriers at grain boundaries due to the large fraction of LAGBs present in BaSn0.92Sb0.08O3 ceramic sample

The structural, electrical and optical properties of spark plasma sintered BaSn1-xSbxO3 ceramics

Antimony doped barium-stannate dense ceramic materials were synthesized using spark plasma sintering technique out of mechanically activated precursor powders. The influence of various Sb concentrations (x =0.00 – 0.10) on properties of BaSn1-xSbxO3 ceramics was investigated. Relative densities of prepared samples were in the range of (79–96) %. TEM analysis revealed the presence of many dislocations in undoped BaSnO3, and their significant reduction upon doping with Sb. All samples except BaSn0.92Sb0.08O3 exhibit non-linear I-U characteristic, typical for semiconductors with potential barrier at grain boundaries. Low angle grain boundaries found only in BaSn0.92Sb0.08O3 caused the loss of potential barrier at grain boundaries which was confirmed by AC impedance spectroscopy measurements. Consequently, BaSn0.92Sb0.08O3 showed the lowest electrical resistivity and linear I-U characteristic. UV–vis analysis confirmed the increasing of band gap (Burstein–Moss shift) values in all doped samples.This is the peer-reviewed version of the manuscript: Vukasinovic J, Pocuca-Nesic M, Golic DL, Ribic V, Brankovic Z, Savic SM, Dapcevic A, Bernik S, Podlogar M, Kocen M, Rapljenovic Z, Ivek T, Lazovic V, Dojcinovic B, Brankovic G, The structural, electrical and optical properties of spark plasma sintered BaSn1-xSbxO3 ceramics, Journal of the European Ceramic Society (2020), 40, 15, 5566-5575, doi: [https://doi.org/10.1016/j.jeurceramsoc.2020.06.062]The published version: [http://cer.ihtm.bg.ac.rs/handle/123456789/3628