1,721,144 research outputs found
Aqueous Acid Orange 7 dye removal by clay and red mud mixes
No full textIn this study, Portuguese clay, Fe-impregnated clay, red mud and clay/red mud mixtures were used in the removal of Acid Orange 7 by Fenton and photo-Fenton (under UV light) oxidation processes. In comparison with pure adsorption, the catalytic activity of Fe-loaded clay showed an optimum removal rate (98%). This photo-assisted Fenton degradation of Acid Orange 7 azo-dye molecules was exploiting HO radicals from generated H2O2 and clay supported iron species, following the pseudo-first order kinetic mechanism.By using red mud pre-calcined at 400 °C, 10% improvement in overall discolouration was observed in comparison to the untreated clay. This improvement is attributed to the partial reduction of Fe3+ to Fe2+ species on the surface of the catalyst, and to the reaction with H2O2 to generate highly oxidative hydroxyl radicals. It was seen that the synergistic effect of photocatalysis due to the presence of TiO2 in the red mud also contributed in this photo-Fenton process. Furthermore, the use of red mud/clay catalyst mixes assured 38% dye discolouration at pH 7, but a lowering of solution pH to 3 resulted in a much higher discolouration rate (over 80% after 1 h). The good fitting with a pseudo-second-order kinetic model (R2 equals to 0.99) shows that adsorption processes could strongly contribute in the dye removal efficiency
Geopolymer foams: An overview of recent advancements
Full text linkGeopolymer foams (highly porous materials) have emerged as one of the most exciting materials over the past few years due to their remarkable properties, low cost and green synthesis protocol, enabling their use in various high added-value applications. Review papers on porous geopolymers are uncommon, and the emphasis has been given to materials processing and properties, while the applications were only briefly addressed. This review aims to fill this gap by presenting a comprehensive literature survey and critical analysis of the most recent and exciting research carried out on geopolymer foams. Up to now, these bulk-type (not powders) materials have been mainly considered as thermal and acoustic insulators. However, besides addressing their use as building material, this review also shows that their use in less investigated, but environmentally and economically relevant applications (e.g. bulk-type adsorbents, pH buffering agents and catalysts), is feasible and might ensure performance and technical advantages over their powdered counterparts. The limitations, challenges and future prospects associated with the different applications are presented. This review shows the remarkable potential of geopolymer foams in high added-value applications, far beyond their historical use as Portland cement replacement, which may encourage the widespread technological use of these materials
Chromatic properties of industrial solid waste based ferrites
No full textThe hexaferrite and monoferrite powders were prepared by the common solid state reaction method. Similar formulations have been prepared but using chemically- pure commercial reagents or by using a sludge generated by steel wiredraw process as source of iron oxide. This iron-rich industrial waste is mainly composed of Fe2O3 (62 wt%). Zinc and calcium are present in minor quantities and can form complexes such as franklinite (ZnFe2O4) and apatite (Ca5(PO4) 3(OH,F,Cl)). Ni/Cr galvanising sludge was also used to enhance the black coloration of monoferrite. After calcination of the mixtures at 1,000 °C and 1,050 °C, typical X-ray diffraction patterns of the expected SrFe12O19 and NiFe2O4 phases were obtained, together with minor peaks of spinel-type (SrFe2O 4 and ZnFe2O4) and Fe2O3 phases. Anyway, this resulted in a black pigment with chromatic properties comparable to those of commercial formulations, such as iron cobalt chromite (Fe,Co)(Fe,Cr)2O4 (DCMA 13-40-9), chrome iron nickel (Ni,Fe)(Fe,Cr)2O2 (DCMA 13-50-9), and manganese ferrite (Fe,Mn)(Fe,Mn)2O4 (DCMA 13-41-9). © Springer Science+Business Media B.V. 2012
Magnetic wood-based biomorphic Sr3Co2Fe24O41 Z-type hexaferrite ecoceramics made from cork templates
Full text linkEcoceramics (environmentally conscious ceramics) are biomimetic/biomorphic ceramics, which use a naturally occurring and sustainable material as a template for their unique morphology and structure. Usually woods (or lignocellulosics) are used, due to the inherent cellular nature of their microstructures. The wood is pyrolised and the resulting carbon skeleton impregnated with a fluid, and this is then heated to combust the carbon template and convert the fluid precursor into a ceramic, while maintaining the structure of the original natural template. For the first time, ecoceramics have been made from cork, a totally sustainable wood that is harvested without harming the tree. Also for the first time, ecoceramics have been made of soft magnetic Z-type hexaferrites, in this case the room temperature multiferroic strontium Z ferrite Sr3Co2Fe24O41 (SrZ). Cork powder was pyrolised at 1000 degrees C, infiltrated with an aqueous sol-gel SrZ precursor, and then heated at 1200 degrees C/2 h to produce the ecoceramic. The cellular structure of the cork was maintained, with a small reduction in the hexagonal cell dimension to 10 mu m diameter, but the cell walls remained 1-2 mu m thick, of a similar magnitude to the hexaferrite grain size. Both magnetic and XRD data agreed that there was a small portion of the SrW phase present in these ecoceramics as well, and the magnetic loop showed a magnetically soft ecoceramic with M-s = 59.5 A m(2) kg(-1) (at 3 T), and a low H-c of 16 kA m(-1). (C) 2015 Elsevier Ltd. All rights reserved
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
Compositional and chromatic properties of strontium hexaferrite as pigment for ceramic bodies and alternative synthesis from wiredrawing sludge
No full textThis paper reports a new black pigment based on strontium M-type hexaferrite (SrM) obtained from pure reagents or by the inclusion of Fe-rich wiredrawing sludge. The fired powders show a clear predominance of SrFe 12O19. Also, haematite (α-Fe2O 3) and iron spinel were detected in variable amounts. These two phases are present in higher amounts (57 wt.%) in the sludge-based pigment, due to the interference of contaminants. The optical measurements illustrated that the prepared pigments displayed good colorimetric properties, close to those shown by a black commercial pigment. However, the addition of Fe-rich sludge slightly reduced this black colour by increasing the L* and b* colour coordinates. Since the variance is slight, further trials were carried out by minor addition of chromophores (Co, Mn and Ni). The chromatic measurements showed that the best pigment was obtained by adding cobalt. Nevertheless, in ceramic porcelainized bodies, the combination of Co and Mn assured the nearest hue to the commercial pigment. Nickel was not effective in the colouration because it was mostly assimilated by the spinel (trevorite) phase and was not inserted in the hexaferrite phase. Other trials with non-stoichiometric formulations showed a bleaching of the black colouration in stoneware supports, especially on sludge-containing formulations, along with an apparent increasing of the green hue. © 2012 Elsevier Ltd. All rights reserved
Magnetic properties of ferrite ceramics made from wastes
No full textIron-rich industrial waste sludge (62 % Fe2O3) was processed to produce recycled chromatic and magnetic materials. In this paper we report on combining the waste with stoichiometric amounts of oxides, which were then fired to produce SrM hexagonal ferrite (SrFe12O19) based ceramic powders. A series of powders were made from pure oxides for comparison. All samples were fired in air at 1,050-1,150 °C, and analysed by use of XRD (X-ray diffraction) and VSM (vibrating sample magnetometry). The firing of SrM stoichiometric mixtures derived from Fe-rich waste sludge did not result in a hard SrM ferrite product, but instead resulted in strongly magnetic but soft ferrites, which were a mixture of SrM and spinel phases, along with nonmagnetic α-Fe2O3. XRD and VSM data strongly suggested that the 21% volatile organic fraction of the waste was burnt out during firing, reducing some of the Fe3+ to form magnetite, Fe 3O4, which was then oxidised on cooling in air to form maghemite, γ-Fe2O3, which is magnetically soft, with Ms and Hc values lower than those of SrM. The recycled waste magnetic materials had Ms values of 37-59 A m2 kg-1, and Hc values of 13-40 kA m-1. Thus, a highly magnetic soft-magnet ceramic is made from the simple thermal remediation of these wastes. © Springer Science+Business Media Dordrecht 2013
Sustainable and efficient cork - inorganic polymer composites: An innovative and eco-friendly approach to produce ultra-lightweight and low thermal conductivity materials
No full textIn this investigation cork was used as a low density aggregate in the production of ultra-lightweight and low thermal conductivity inorganic polymer (geopolymer) composites. This novel and highly sustainable material, synthesised at room temperature (23 °C), may decrease the energy losses inside buildings, thus contributing to the United Nations development goals regarding energy and climate change. The ultra-low density (260 kg/m3) and low thermal conductivity (72 mW/m K) shown by the cork-composites are the second lowest ever reported for inorganic polymer composites, only being surpassed by that of polystyrene-inorganic polymer composites. However, cork is a fully renewable and sustainable resource, while polystyrene is manufactured from non-renewable fossil fuels, and for that reason our strategy has an additional sustainability advantage. Moreover, the cork-inorganic polymer composites do not release any toxic fume when under fire conditions, which is a major advantage over polymeric-based foams
Highly efficient lead extraction from aqueous solutions using inorganic polymer foams derived from biomass fly ash and metakaolin
Full text linkThis work reports a simple and safe, but powerful, route to depollute lead-containing aqueous solutions. Inorganic polymer foams (cm-size) were used as bulk-type adsorbents. The influence of the specimens' porosity and activator molarity on the foams' physical properties and on their lead extraction ability was studied. Then, the best performing samples were deeply evaluated as lead adsorbents by studying the impact of pH, lead concentration, contact time, ionic strength and solution volume. Lead sorption kinetics is strongly affected by the pollutant concentration, pH and the solution ionic strength. Under the most favourable conditions the foams showed an impressive removal capacity (105.9 mg/g at pH 5, 23 °C, C0 = 800 ppm, deionised water), surpassing all other reported values on the use of bulk-type inorganic polymers. The foams’ lead uptake is 2.3 times higher than the previous best performing bulk-type specimens (mm-size spheres), and sorption is 12.5–15 times faster. The foams can be easily regenerated using mild acidic conditions, and then reused as adsorbent, suggesting that the main adsorption mechanism is ion exchange
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
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