Engenharia de Materiais e Cerâmica (demac)

A quaternary bioactive sol-gel glass of high silica content was heat treated at different temperatures, and then wet ball milled under different balls-to-powder ratios. A total of sixteen experiments were performed to study in detail the effects of both experimental variables on the structure, morphology, particle size distributions and nitrogen adsorption isotherms. The balls–to–powder ratio exerts a tremendous influence on the final particle size distribution of the powders, while its effects on the pore volume and morphology are minimal. These structural features are mostly governed by the changes in calcination temperature. Therefore, understanding the specific roles of each experimental parameter is of paramount importance towards achieving optimum powders with the desired properties. This work sheds light on the importance of using a suitable combination of these two parameters for tuning the morphology and the granulometry of the sol-gel derived bioactive glass powders.

Magnetic particles were successfully synthesised by a new and simple one-step auto-ignition method, with octylamine as organic fuel and iron nitrate nonahydrate as an oxidant, both in an aqueous solution. After synthesis and stabilising at 550 °C in reduced atmosphere, the samples consisted of mostly well crystalline magnetite (Fe3O4), with a small amount of hematite present, in the form of micron–scale agglomerations of nanoparticles. A noticeable reduction of crystallite size of magnetite (42–28 nm) and an increase in the hematite crystallite sizes were observed with increasing octylamine addition, although the actual observed nanoparticle size increased slightly from ∼30 up to 50 nm. The magnetic properties were assessed at room temperature, and all were found to be strongly ferrimagnetic with very narrow hysteresis loops. The saturation magnetisation at 4 T was 77.2–91.6 A m2 kg−1, and coercivity was only 10.03–11.30 kA m−1 (126–142 Oe). These results are also compared to the few previous studies on using octylamine to produce magnetite nanoparticles, which were all purely organic hydrothermal processes, and produced materials with lower magnetisation values and comparable coercivity in similarly sized particles.

We show the influence of two functional ions (Cu2+ and La3+), incorporated into a quaternary (Si, Ca, Na, P) sol‐gel derived bioactive glass system, on its particle size, cytotoxicity, and bioactivity. By doping the parent glass with the two ions in singular or combined forms, 15 doped glasses were prepared by a rapid sol‐gel technique. The influence of the combined doping on the particle size and cell viability was successfully evaluated by the aid of signal‐to‐noise‐ratio (S/N), using Taguchi analysis. This allowed us to analyze the complex interplay of effects between these ions, and the marked differences in biocompatibility between the three cell types studied. Cu addition had a significant effect on reducing the glass particle size, while both increased density. Cell viability was significantly improved for some doping combinations, demonstrating that while combined Cu–La doping was beneficial for biocompatibility with lymphoblasts, individual high‐Cu or low‐La doping was better with fibroblasts, and either high‐Cu or low‐La doping, or certain combined Cu–La combinations, were the optimum for osteoblasts. However, the bioactivity of doped samples was generally similar to that of the parent glass, although both La, and particularly Cu, did appear to aid dissolution of ions when immersed in SBF, act as glass modifiers, and encourage HAp crystallization. The results reveal that potential synergistic benefits can be obtained by combining the effects on the mean particle size, density, cytotoxicity, and bioactivity of the glasses. The greatly improved biocompatibility of some of the doped glasses makes them promising candidates for biomedical applications.

To highlight the effect of salt precursors on the final properties, bioactivity and biocompatibility, five quaternary (Si–Ca–P–Na) glass compositions were successfully prepared through two distinct rapid sol–gel routes; one using acetate salt precursors (A) catalysed by nitric acid, and the other using nitrate salts (N) and citric acid as a catalyst. The sols dried rapidly, and stabilised at 550 & 800 °C to be characterised by X–ray diffraction (XRD), Magic angle spinning–Nuclear magnetic resonance (29Si MAS–NMR) and Fourier transform infra–red spectroscopy (FTIR). Upon immersion in simulated body fluid (SBF), hydroxyapatite (HAp) formation was initially enhanced by increasing Ca–content up to 40 mol%, but the formation of calcite was favoured with further increments of Ca to 45 and 48 mol%. The A–glasses exhibited lower density and lower network connectivity compared with N–glasses. The chemical surface modifications after 4 h in SBF were more evident for N–glasses in comparison to A–glasses. The biocompatibility is favoured for the samples treated at 800 °C and for the samples of the higher silica contents.

ABSTRACT kappa-Carrageenan coated magnetic iron oxide nanoparticles (NPs) were synthesized and tested as adsorbents for the magnetically assisted removal of methylene blue (MB) from aqueous solutions, a cationic dye commonly present in wastes from the textile industry. The resulting composite NPs were superparamagnetic and contained ca. 12 wt% carrageenan. The MB uptake ability was found to vary with the pH solution and was larger in alkaline conditions. Both pseudo-first-order and pseudo-second-order equations predicted well the kinetics with the maximum adsorption achieved very fast, within 5 min. The MB adsorption has shown an unusual Z-type isotherm which suggests the generation of new adsorbing sites with increasing MB initial concentration. Under the experimental conditions used (23 degrees C, pH 9) the materials presented here displayed MB adsorption capacity (185.3 mg/g) higher than other magnetic sorbents previously reported. Thus x-carrageenan coated magnetic NPs are very promising eco-friendly materials for removing MB from wastewater using magnetic separation. (c) 2013 Elsevier B.V. All rights reserved.

ABSTRACT This work describes the synthesis of ZnS powders in high yield and via a straightforward process, under ambient conditions (temperature and pressure), by adding to aqueous zinc (II) a nutrient solution containing biologically generated sulfide from sulfate-reducing bacteria (SRB). The powders obtained as above were composed mainly of ZnS (sphalerite) nanoparticles (NP's) exhibiting a spheroidal morphology (20–30 nm). The NP's morphological properties and crystalline phase were not markedly altered by the SRB growth media composition neither by the presence of bacterial cells. The relevance of this method to obtain ZnS supported solid substrates has been demonstrated by performing the synthesis in the presence of TiO2 and SiO2 submicron particles.

This work describes the synthesis of CuS powders in high yield and via an environmentally friendly and straightforward process, under ambient conditions (temperature and pressure), by adding to aqueous copper (II) a nutrient solution containing biologically generated sulfide from sulfate-reducing bacteria (SRB). The powders obtained were composed of CuS (covellite) nanoparticles (NPs) exhibiting a spheroid morphology (<5 nm). The relevance of this method to obtain CuS supported solid substrates has been demonstrated by performing the synthesis in the presence of TiO2 and SiO2 submicron particles. We further extended the work carried out, which substantiates the potential of using biogenic sulfide for the production of covellite nanocrystals and composites, using the effluent of a bioremediation column. Hence, such process results in the synthesis of added value products obtained from metal rich effluents, such as metallurgical and industrial ones, or Acid Mine Drainage (AMD), when associated with bioremediation processes.

This work describes the synthesis of ZnS powders in high yield and via a straightforward process, under ambient conditions (temperature and pressure), by adding to aqueous zinc (II) a nutrient solution containing biologically generated sulfide from sulfate-reducing bacteria (SRB). The powders obtained as above were composed mainly of ZnS (sphalerite) nanoparticles (NP's) exhibiting a spheroidal morphology (20–30 nm). The NP's morphological properties and crystalline phase were not markedly altered by the SRB growth media composition neither by the presence of bacterial cells. The relevance of this method to obtain ZnS supported solid substrates has been demonstrated by performing the synthesis in the presence of TiO2 and SiO2 submicron particles.