1,721,038 research outputs found
Cork-derived hierarchically porous hydroxyapatite with different stoichiometries for biomedical and environmental applications
No full textHydroxyapatite (HA, Ca10(PO4)6(OH)2) is the major mineral component of human bone, but has a wide range of interesting and useful properties, and many applications beyond biomedicine. Here we produce HA-based materials from a naturally templated precursor which can have a variety of tailored microstructures and hierarchical porosities, and we investigate their use as designed functional materials for several applications. HA-based materials with different stoichiometries of Ca/P = 1.67 (HA) and 1.5 (Ca-deficient HA) were successfully synthesised from a previously prepared and reported cork-derived CaCO3. The CaCO3 was reacted with a phosphorus containing precursor solution at 60 °C, and also successively recalcined at 700 °C. The samples prepared at 60 °C maintained the 3D honeycomb structure of ∼20 μm hexagonal cells typical of cork, and showed high specific surface areas (SSA > 85 m2 g-1) and a high mesoporosity (average mesopores ∼10-15 nm). These features made them suitable for environmental remediation applications such as heavy metals (i.e. lead) removal from water, with calcium-deficient HA (higher degree of mesoporosity) adsorbing >99% of Pb(ii) ions from solutions containing up to 1.5 g of lead per L. Recalcined samples (SSA = 29 m2 g-1), on the other hand, had very low cytotoxicity towards MG-63 osteoblasts, showing them to be biocompatible for biomaterials. All had cell viabilities of over 70% against a control, and the calcium-deficient HA proved to be even less cytotoxic than the control (>100% viability after 24 and 48 h). Therefore, cork was shown to be an excellent template agent for the design of HA materials with varied properties, tailored for different applications in the environmental and biomedical fields. This journal i
Photocatalytic nano-composite architectural lime mortar for degradation of urban pollutants under solar and visible (interior) light
No full textRecent advances in nano-technology and nano-additives can give enhanced properties to natural hydraulic lime (NHL), creating a multifunctional material. We have prepared a novel nanocomposite, made of a commercial mortar with 1 wt% and 5 wt% added titania nanoparticles (NPs). These TiO2 NPs are themselves doped with 1 mol% silver, to give the material enhanced photocatalytic and antimicrobial properties. The Ag-doped TiO2 NPs were made from a simple, costs effective, aqueous green nanosynthesis process, and the end material only contains 0.01–0.05% Ag. As this mortar is intended to both combat atmospheric pollution, and create more durable/lower maintenance building façades (plastering and finishing) by limiting attack from microorganisms and pollutants, its photocatalytic anti-pollution activity under solar and visible (no UV) light for nitrous oxide (NOx) and volatile organic compound (VOC) removal was studied. The addition of dopants did not significantly alter the physical properties or curing of the mortar, while it showed excellent photocatalytic activity under sunlight, The mortars with only 1 and 5 wt% additives degraded 10.6% and 21% NOx after 45 mins, respectively, comparing well to a value of 50% for a pure TiO2/Ag+ sample. They also degraded VOCs under visible light, of the kind used for lighting inside buildings, with no UV component. As the NPs are contained in the whole of the mortar layer, not just as a coating, if the surface is chipped or damaged this mortar will not loose its photocatalytic capabilities
Truncated tetragonal bipyramidal anatase nanocrystals formed without use of capping agents from the supercritical drying of a TiO2sol
No full textTitanium dioxide (TiO2) nanoparticles are extremely attractive materials for numerous applications, especially in the anatase form. We have made these shaped, <10 nm anatase nanoparticles (NPs) via the supercritical (SC) drying of a titania sol, made by a "green" aqueous sol-gel nanosynthesis route. The SC drying was carried out in alcohol at 255-260 °C, and no further heating or processing of the NPs was required. The true phase composition (crystalline and amorphous phases) and the microstructure of the NPs was thoroughly characterised by the advanced X-ray methods, such as Rietveld-reference intensity ratio (RIR) and the whole powder pattern modelling (WPPM) technique, and HR-TEM analysis. Furthermore, the NPs were also characterised by Raman, FT-IR and optical spectroscopy. These anatase NPs showed themselves to exhibit a truncated tetragonal bipyramidal shape, exposing the {101} (side) and {001} (top) faces. They had a euhedral crystal habit, with sharply defined and easily recognised faces, and were very homogeneous and monodisperse in both shape and size. The photocatalytic activity (PCA) of the samples was assessed in gas-solid phase by monitoring the degradation of nitrogen oxides (NOx), a major atmospheric pollutant. Results showed that the particular shape of these anatase NPs played a key role in their photocatalytic behaviour. In fact, these truncated tetragonal bipyramidal nanocrystals exhibited an enhanced photocatalytic activity, double that of spherical anatase NPs of a similar size reported previously by the authors. This was attributed to the exposure of mainly the {101} and, to a lesser extent, {001} crystal faces, which are more reactive under photocatalysis for redox reactions
Phase composition, crystal structure and microstructure of silver and tungsten doped TiO2 nanopowders with tuneable photochromic behaviour
No full textTitanium dioxide exists in a large number of polymorphs, the most common ones being, in order of abundance, rutile, anatase and brookite. Recently, there has been an increasing degree of attention on TiO2, due to its photocatalytic and antibacterial properties. In this work, titania nanopowders synthesized via an aqueous sol-gel method were modified with silver and/or tungsten, with potential application as photocatalysts and antibacterial agents. The dried gels were thermally treated at two temperatures, and the occurrence of amorphous phase - in both dried and calcined gels - was obtained using the Rietveld method. In powders calcined at 600 C, the crystal structure of rutile was determined with the Rietveld method on the full profile fitting of the X-ray powder diffraction patterns, while microstructural information was achieved by means of Williamson-Hall plots and line broadening analysis methods. The photochromic property of the Ag and W/Ag modified samples - when subjected to both UV- and visible-light irradiation and for different time exposures - was also investigated via UV-Vis spectroscopy. Powders were shown to possess a tuneable photochromism due to the surface plasmon resonance of the added silver, depending on the firing temperature, light (and time) exposure, and on whether or not tungsten was present in the nanopowders. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Silver-containing calcium phosphate materials of marine origin with antibacterial activity
No full textAbstract Hydroxyapatite (Ca10(PO4)6(OH)2 - HAp) is a common material for bone replacement in artificial implants and prostheses, due to its high biocompatibility. In this work we report about the preparation of HAp-based materials of marine origin with antibacterial properties. Bones from cod fish (Gadhus morua) were treated with a dilute AgNO3 solution, to obtain HAp-containing samples with silver as a minor component. The samples were characterised by XRD, FT-IR spectroscopy and SEM, indicating the presence of HAp, β-TCP and some metallic silver. The determination of unit cell parameters, however, indicated that the majority of silver is substituted in the β-TCP lattice in ionic form. The antibacterial activity of these materials was tested towards both Gram-positive and Gram-negative bacterias; results showed that the material is very effective with Gram-negative strains such as Escherichia coli (inactivation rates of 99.82% and 99.999% after 2 and 5 h, respectively) and had a smaller but still significant effect on Gram-positive MRSA (91% inactivation rate). These results show the potentials of these samples as infection-resistant bone replacement materials
Pseudobrookite ceramic pigments: Crystal structural, optical and technological properties.
No full textPseudobrookite pigments were synthesized by the conventional ceramic route, calcining at 1300 C four mixts., with a Fe2O3:TiO2 ratio ranging from 47:53 to 40:60, and were characterised by XRPD, DRS and coloring performance in several ceramic matrixes. Titania in moderate excess of the Fe2TiO5 stoichiometry, necessary to minimise the occurrence of unreacted precursors, induced lattice parameters smaller than ideal pseudobrookite, in agreement with the different radii of Ti4+ and Fe3+ ions. These pigments exhibit a peculiar, intensely brown coloration originated by several light absorptions in the visible spectrum due to both d5 electronic transitions and a magnetically-coupled paired transition between iron ions in adjacent lattice sites. A doubling of the 6A1 4T1 and 4T2 bands is related to the occurrence of Fe3+ in both octahedral sites of pseudobrookite. Besides, distinct metal-oxygen distances imply different energy absorptions in good accordance with the crystal field theory, despite the strongly covalent character of the Fe-O bonding. Although an entropy-stabilized phase, pseudobrookite persists dispersed in glazes and glassy coatings even after fast firing at 1200 C, so being suitable as ceramic pigment. However, its coloring performance depends on the chemico-phys. properties of ceramic matrixes: satd. brown shades achieved in low temp. glasses shift to a lighter brown in opacified glazes and fade to a light gray in wall tile glazes, where the high CaO and ZnO content contributes to rapidly dissolve pseudobrookite
Titanium dioxide modified with transition metals and rare earth elements: Phase composition, optical properties, and photocatalytic activity
No full textA series of titania-transition metal and titania-rare earth element mixtures, with the stoichiometry Ti1-xMxO2, where M=Ce, Eu, La, Nb, W, Y, and x ranging from 0 to 0.05 atoms per formula unit, were prepared via solid-state reaction of the precursor oxides. The products of the synthesis were thermally treated in air and two maximum temperatures (900 and 1000 °C) were reached. The addition of transition metal and rare earth ions to the TiO2 structure modified the anatase-to-rutile phase transition temperature, depending on the valence state of the ions added. Transition metals entered the titania structure, but essentially no solid solution between the rare earth elements and TiO 2 was detected. The photocatalytic activity of the powders was assessed in liquid-solid and gas-solid phases, under UVA and visible-light irradiation, monitoring the degradation of an organic dye and isopropanol, respectively. The results were explained by taking into account the relative amounts of anatase and rutile in the samples, the specific surface area of the powders, and their optical properties. © 2012 Elsevier Ltd and Techna Group S.r.l
Nanosized titania modified with tungsten and silver: Microstructural characterisation of a multifunctional material
No full textWith the ever-growing interest in nanotechnologies, the area of metal oxides is playing an increasingly dominant role. Amongst them, titanium dioxide (TiO 2 ) nanoparticles are attracting increasing interest, owing to their unique physicochemical properties, and widespread applications-i.e. photocatalysis, energy materials, antibacterial agents, gas-sensors. We characterised the microstructure of titania nanopowders-synthesised via an aqueous sol-gel method and modified with silver and/or tungsten-using XRD data, through the whole powder pattern modelling (WPPM) procedure. An overall linear dependence of the lattice volume expansion was observed-the volume increased with the lowering of the crystalline domain size. Concerning the dislocation density, no specific trend depending on the modifying cation was reported. However, for the samples fired at 600°C, the undoped titania sample had a much larger number of screw dislocations in the rutile phase, while the Ag-modified sample had a much greater number of edge dislocations in the anatase phase. © 2013 Elsevier B.V. All rights reserved
Fully quantitative X-ray characterisation of Evonik Aeroxide TiO 2 P25®
No full textPhotocatalysis with TiO2 is one of the most promising methods for combatting environmental pollution. Of commercially available photocatalysts, Evonik Aeroxide (formerly Degussa) P25® titania is probably the most extensively used. In this communication, we quantitatively characterise the full phase composition (both crystalline and amorphous content) of P25®, as well as the microstructure of individual phases (crystalline domain size distribution and dislocation density). This was achieved with advanced X-ray diffraction (XRD) methods: Rietveld-RIR and whole powder pattern modelling (WPPM). Quantitative phase analysis (QPA) showed the precise composition of P25 to be 76.3 wt% anatase, 10.6 wt% rutile and 13.0 wt% amorphous, and microstructural details are given for the two crystalline phases. © 2014 Elsevier B.V
Hydroxyapatite and chloroapatite derived from sardine by-products
No full textIn this paper, phosphate-based compounds used in biomedicine were extracted from bones and scales of European sardines (Sardina pilchardus); this is the first time that different parts of the same fish are used for the extraction of these kinds of materials. The bones and scales behave very differently with processing, producing different materials when annealed between 600 and 1000 °C. The bones formed a mixture of hydroxyapatite (Ca10(PO 4)6(OH)2, HAp) and β-tri-calcium phosphate (β-Ca3(PO4)2, β-TCP), with a higher content of β-TCP obtained with increasing temperature. This bi-phasic material has a high added value, as it is employed as a bioceramic; in fact HAp has good biocompatibility while β-TCP has better resorbability than HAp, despite being less biocompatible. With scales, on the other hand, either a HAp-based material or a chlorine-substitute HAp containing material (chloroapatite (Ca10(PO4)6Cl2, ClAp) were produced. HAp-based material was obtained with a simple annealing process; for ClAp, on the other hand, a combined washing-annealing process was used. ClAp is also used in biomedicine, due to its improved resorption, mechanical properties and bioactivity. This is the first time ClAp of marine origin was produced. © 2014 Elsevier Ltd and Techna Group S.r.l
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