Comparative studies of ferric green rust and ferrihydrite coated sand: Role of synthesis routes Varsha Khare a, * , Martine Mullet a , Khalil Hanna a , Mathias Blumers b , Mustapha Abdelmoula a , Go ¨star Klingelho ¨fer b , Christian Ruby a a Laboratoire de Chimie Physique et Microbiologie pour L’Environnement (LCPME), UMR-7564 CNRS-UHP Nancy Universite ´, Equipe Microbiologie et Physique, 405 rue de Vandoeuvre, F-54600 Villers-les-Nancy, France b Institut fu ¨r Anorganische und Analytische Chemie, Universita ¨t Mainz, MIMOS Group, Staudinger Weg 9, D5509 Mainz, BRD Germany Received 4 October 2007; received in revised form 24 January 2008; accepted 31 January 2008 Available online 8 February 2008 Abstract A comparative study of ferrihydrite and ferric green rust coated sand prepared by three synthesis routes has been outlined in the present contribution. The two minerals displayed inverse properties in terms of quantity of deposited iron for all three methods investigated. For ferric green rust coating, a newly proposed synthesis route named as dry contact method was efficient for the maximum quantity of iron with almost full coverage area. Considering the similar parameters, the modified wet synthesis method designated as reactive method provides the optimum results for ferrihydrite coated sand. These coatings have been characterised by different surface analysis techniques. In particular, due to the excellent sensitivity of miniaturised Mo ¨ssbauer Spectrometer (MIMOS) it was possible to detect the lowest iron content (0.1 Fe w/w%). A distinct approach based on tribology between crystallised ferric green rust and sand has been proposed to explain the relatively high quality of coating using dry contact method. Ó 2008 Elsevier Masson SAS. All rights reserved. Keywords: Green rust; Ferrihydrite; Iron coated sand; Mo ¨ssbauer spectroscopy; MIMOS; X-ray photoelectron spectroscopy 1. Introduction Iron oxide coated sand materials exhibit coating of various chemically synthesised iron oxide onto natural sand substrates. These materials are promising candidates for the elimination and fixation of pollutants such as inorganic and organic com- pounds in soils, sediments and in contaminated water [1e6]. The coated sand materials are much more favourable over pure iron oxide and uncoated silica. As a result of bound iron oxides, an increase in the specific surface area of the resulted coated sand provides a better adsorption efficiency of organic compounds and heavy metals [7e9]. In addition, due to the surface charge modifications and grain size effect, resulting materials are more adapted for high scale applica- tions such as wastewater treatment/filtration. Iron oxide coated sand or clay prepared by addition of base to an acidified Fe(III) solution in the presence of respective particles results in different types of coatings such as amor- phous, poorly crystalline [10e12] or crystalline [13]. Further- more, Xu and Axe [14] have also suggested that the synthesis route affects the crystallinity of coating and the particle size of silica which influences the quality of coating. In addition, several studies have been done to evaluate the characteristics of coatings such as the formation of FeeOeSi bond at the oxideecoating interface [13], lack of repulsive forces on chemical interactions at the oxideequartz interface [15] and effect of particle size on the oxideesubstrate interaction [16]. Some interesting investigations on elemental determina- tion, distribution and the structure of coatings have also been carried out [17e19]. In addition to investigations on labora- tory made coatings imitating natural ones, studies that concern optimisation of the coating processes and examination of fun- damental questions regarding substrateecoating interactions, * Corresponding author. Tel.: þ33383685220; fax: þ33383275444. E-mail address: versha.khare@lcpme.cnrs-nancy.fr (V. Khare). 1293-2558/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2008.01.033 Available online at www.sciencedirect.com Solid State Sciences 10 (2008) 1342e1351 www.elsevier.com/locate/ssscie