Published: April 25, 2011 r2011 American Chemical Society 2264 dx.doi.org/10.1021/cg1016802 | Cryst. Growth Des. 2011, 11, 2264–2272 ARTICLE pubs.acs.org/crystal Fast Precipitation of Acicular Goethite from Ferric Hydroxide Gel under Moderate Temperature (30 and 70 °C) G. Montes-Hernandez,* ,† P. Beck, ‡ F. Renard, †,§ E. Quirico, ‡ B. Lanson, † R. Chiriac, || and N. Findling † † CNRS and University Joseph Fourier-Grenoble 1, Institute of Earth Sciences (ISTerre), OSUG/INSU, BP 53, 38041 Grenoble Cedex 9, France ‡ CNRS and University Joseph Fourier-Grenoble 1, IPAG, OSUG/INSU, BP 53, 38041 Grenoble Cedex 9, France § Physics of Geological Processes, University of Oslo, Norway ) Universit  e de Lyon, Universit  e Lyon 1, Laboratoire des Multimat  eriaux et Interfaces UMR CNRS 5615, 43 bd du 11 novembre 1918, 69622 Villeurbanne Cedex, France b S Supporting Information 1. INTRODUCTION Iron oxides, hydroxides, and oxy-hydroxides represent effi- cient sorbents for organic and inorganic species and have a great potential in industrial applications. They are also of substantial interest in environmental sciences, since some of them are frequently occurring in soils and have significant impact on the fate of pollutants. 1 Among iron oxy-hydroxides, goethite (R-FeOOH) is an abundant constituent of terrestrial soils, sediments, and oolitic iron ores and a major weathering product of ferrous silicates (via oxidation and hydrolysis processes). It is predominant in younger sedimentary deposits, giving them a yellowish color. 2À5 Goethite particles have high specific surface areas and strong affinities for oxyanions and heavy metals. 6,7 Recently, the mineral goethite has also been suspected as a constituent of the Martian dusts and dark asteroids. 8 The mineral goethite has a long history of applications, since it was used as a dark-yellow ochre pigment in paleolithic cave painting over 30 000 years ago. As a colloidal system, it readily forms crystallites of colloidal dimensions, which can be stabilized in water at pH below about 4. 9 It is also a model adsorbent in soils and environmental applications (see ref 10 and references therein). Moreover, goethite finds application as a precursor in magnetic carrier systems, where it can be transformed by thermal treatment into maghemite (γ-Fe 2 O 3 ) or into metallic particles. 6,11 The synthesis of goethite has been studied for decades (e.g., refs 12À20), and studies to improve the existing methods Received: December 18, 2010 Revised: April 13, 2011 ABSTRACT: The present study describes a simple and novel synthesis route for submicrometric acicular goethite (R-FeOOH) using high OH/Fe molar ratio (=5) and moderate temperature (30 and 70 °C). Two different alkaline sources (NaOH and Ca(OH) 2 ) and two iron(III) sources (FeCl 3 3 6H 2 O and Fe- (NO 3 ) 3 .9H 2 O) were investigated. FESEM, XRD, FTIR, N 2 sorp- tion isotherms, color evolution, and pH monitoring have been used to determine the formation mechanism, the particle size, specific surface area, and morphology of goethite particles. Three pH regions were determined during goethite formation, and each of them was qualitatively associated to (I) the formation of a ferric hydroxide gel, leading to acid conditions (pH < 2.5); (II) the spontaneous nucleation of goethite, leading to alkaline conditions (pH > 11) and fine sedimentable particles; and (III) the growth of goethite in alkaline conditions (11 < pH < 13.5). Both the temperature and the Fe(III) source have a significant effect on the particle size, specific surface area, and morphology of goethite. High acicular goethite particles (<1 μm in length, moderate specific surface area, S BET = 31.2 m 2 /g) were produced after 7 h of reaction at 70 °C, while about 24 h of reaction are required to produce low acicular goethite particles (<0.5 μm in length, high specific surface area, S BET = 133.8 m 2 /g) at 30 °C, using in both cases iron chloride. When Ca(OH) 2 particles are used as alkaline source, a complex mineral composite with high specific surface area (87.3 m 2 /g) was synthesized; it was mainly composed of unreacted Ca(OH) 2 coated with nanosized particles (possibly amorphous iron hydroxide), calcium iron oxide chloride hydrate, and calcite. Novel conditions to prepare uniform goethite particles, possibly with high potential as adsorbents or pigments, have been established.