Hydroxyapatite was obtained by bone calcinations. To study the calcination process, bovine and porcine bones were first autoclaved to remove fat and other non-bone tissues. They were then heated in an alumina pan in an oxidizing atmosphere of air, where simultaneous thermal analysis curves were recorded. To prepare the hydroxyapatites, bone samples were calcined at 850 °C and 1000 °C using a muffle furnace for 1 h. The obtained materials were powdered using mortar and pestle, and sifted in a sieve (60 mesh) without any additional purification or chemical treatment. The materials obtained were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The antimicrobial properties of these materials were determined through direct contact tests against Staphylococcus aureus. The natural hydroxyapatites obtained by bone calcination inhibited S. aureus growth, with the material obtained by calcination of bovine bones at 1000 °C, showing the best antimicrobial activity. These results indicated that bone wastes can be used to obtain hydroxyapatites with antimicrobial activity.

Sodium smectite clays were enriched with ferric ions (Argel-Fe and Volclay-Fe) to convert the surface charge of the clays from negative to positive and to use the clays in the discolouration of a synthetic effluent composed of seven anionic dyes (mixed from tartrazine, Brilliant Blue FCF and amaranth). The iron content increased from 5.99% to 11.02% for Argel-Fe and from 5.39% to 10.54% for Volclay-Fe. The efficiency of the discolouration of the anion dye mixture was evaluated by measuring the absorbance of the mixture at 562 nm, where the band with the greatest intensity was found. The contact time required for the system to reach equilibrium was ~5 min for both adsorbents. The kinetic adsorption data supported a pseudo-second-order kinetic model. The experimental data support the dual-site Langmuir–Freundlich isotherm model. The maximum adsorption capacities were 88.68 mg g–1 for Argel-Fe and 392.21 mg g–1 for Volclay-Fe. The enrichment of clays with Fe(III) added functionality to the clays and generated adsorbents with rapid adsorption abilities and high discolouration capacities.

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Akaganéite is a very rare iron oxyhydroxide in nature. It can be obtained by many synthetic routes, but thermohydrolysis is the most common method reported in the literature. In this work, akaganéite-like materials were prepared through the thermohydrolysis of FeCl(3).6H(2)O in water and suspensions containing clay minerals. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) data show that the clays determine the crystal phase and size of the iron oxyhydroxide crystals. According to XRD and FTIR data, beta-FeO(OH) (akaganéite) is the main metal oxyhydroxide phase. Considering the small basal spacing (d(001)) displacement observed when comparing the XRD patterns of pristine clays with the composites containing beta-FeO(OH), the iron oxyhydroxide should be mostly located on the basal and edge surfaces of the clay minerals. UV-Vis electronic absorption spectra indicate that the preferred phase of the iron oxyhydroxide is determined by the nature of the clay minerals.

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Recebido em 15/6/08; aceito em 13/4/09; publicado na web em 17/9/09 CHARACTERIZATION AND PROPERTIES OF COLLOIDAL β-FeOOH/BENTONITE NANOSTRUCTURED MATERIAL. A new mixed material was obtained through the combination of the suspensions of iron oxy-hydroxide and bentonite clay, denoted BFe. Analysis of its structure (XRD, Mossbauer and TGA) and composition (AAS) suggests the maintenance of the layer structure of the clay and an increase in the thermal stability of the BFe. Electrochemical studies performed in different electrolytes show that only in an alkaline medium it is possible to observe the redox peaks relative to the processes involving Fe +2 /Fe +3 pair. Tests that evaluated the potential use of the photo-Fenton process showed an efficient degradation process of the dyes in significantly reduced reaction times.Keywords: iron hydroxide; bentonite clay; sol-gel materials. INTRODUÇÃOCompostos à base de ferro têm sido amplamente utilizados desde os primórdios da nossa história, desempenhando um importante papel em inúmeras áreas de relevância.1 Embora muitas espécies sejam classificadas como óxidos de ferro, apenas a hematita (Fe 2 O 3 ), maghemita (γ-Fe 2 O 3 ) e magnetita são de fato óxidos, correspondendo às principais formas de óxido encontradas na natureza. Muitos hidróxidos, como hidróxido férrico (Fe(OH) 3 ), e oxi-hidróxidos, como a goetita (α-FeOOH) e a limonita (FeOOH), também são de importância industrial, principalmente como precursores de óxidos puros ou complexos. 1De maneira geral, os óxidos e hidróxidos de ferro coloidal sempre foram objetos de estudo, o que proporcionou que algumas de suas fases fossem identificadas e caracterizadas. Essas fases compreendem um amplo grupo de compostos amorfos e cristalinos, que podem ser obtidos por vários métodos na forma de "óxidos férricos hidratados" ou "hidróxidos férricos".2 Assim, as estruturas e propriedades mais importantes de óxidos e hidróxidos de ferro têm sido discutidas e revisadas por vários grupos ao longo de décadas. 2Existem cerca de 17 óxidos, hidróxidos e oxi-hidróxidos de ferro, muitos dos quais são obtidos artificialmente.3 De maneira geral, estas espécies apresentam uma área de superfície muito grande e podem ser usados como agentes adsorventes e como catalisadores. Outros usos incluem a indústria de pigmentos, semicondutores, supercapacitores, dentre outros. 1,3-4Além de permitirem aplicações convencionais como as acima descritas, estes materiais podem ser utilizados na degradação oxidativa de substratos de relevância ambiental, por meio de processos Fenton (Equações 1-3). Em geral, admite-se que o sítio (≡Fe(III)), representado na Equação 1, pode ser regenerado através da reação representada na Equação 3, fechando-se um ciclo catalítico que opera enquanto existir peróxido de hidrogênio. Processos Fenton aplicados na presença de óxidos e oxihidróxidos de ferro têm sido abundantemente relatados na literatura recente, principalmente em estudos de degradação envolvendo espécies de relevância ambiental (ex. corantes têxteis).7-13 Em geral, o...