Paper A-068

In this study, we investigated the synthesis of nano-size iron particle using a borohydride reduction of ferric ion in the presence of solvent containing carbonyl groups. When we varied the contents of solvent, there is a corresponding variation of synthesis and iron form. Each sample of synthesized iron particles was characterized by transmission electron microscope (TEM) and powder X-ray diffractometer (XRD). The contents of zero-valent iron (ZVI) in the synthesized particles were measured to investigate the effect of solvent proportions in aqueous-organic solvent system reducing iron particles. As the solvent added, ZVI proportion in the synthesized particle was decreased forming well dispersed iron particle suspension. Their dispersity were also characterized by light scattering particle size analyzer, which led us to confirm the change of dispersing characteristics of wet synthesized iron particles in multi component system. INTRODUCTION Iron nanoparticles have been synthesized to form magnetic recording media, ferrofluids, medical contrast agent, and environmental remediants (Li et al., 2006; Lu et al., 2007; Masciangioli and Zhang, 2003). In environmental field, iron has been widely used as reactive catalyst on account of its effectiveness, non-toxic, ubiquitous, and low price. Among the various synthetic methods, wet-chemical synthesis using borohydride has been the most common ways to synthesize nano-scale transitional metal. In recent, several results reported ferric salt reducing method using borohydride derivatives to get a simple and controllable fabrication of environmental nanoiron (Wang and Zhang, 1997). These nanostructures have become the focus of intensive research because nanostructures provide a better system to the mechanical properties on size reduction (Cain et al., 1996). However, synthesized nanomaterials faced great challenge for applications due to their strong tendency of agglomeration and consequently occuring consolidation (Bonini et al., 2007; Kantrell et al. 1997). In field application, Saleh et al. reported the problem of conventionally reduced nano-scale iron which occurs pore plugging (Saleh et al., 2007). Various efforts have been attributed to prepare a stable suspension of reactive nano-scale iron (Bonder et al., 2007; Cha et al., 2007). Although these dispersing methods using additives can partially reduce the aggregation and sedimentation of particles, method of preparing stabilized iron particle dispersion is still necessary. Because dispersing step and additives could occur deformation or wasteful reaction before the expected reaction. Furthermore, additives can make secondary pollution during the remediation. The goal of this research would be to develop a process that would get the enhanced colloidal nanoiron for in situ remediation with water-solvent system. MATERIALS AND METHODS Reagents. The following chemicals were used without further purification: FeCl3•6H2O (extra pure, Kanto chemical, Japan), NaBH4 (98%, Aldrich, USA), acetone (HPLC grade, J-T baker, USA). All aqueous stock solutions were prepared using Ar purged DI water. In a typical process, 0.1M ferric solution (solution 1) and 0.15M borohydride was prepared. Excessive borohydride is typically deployed to perform the perfect synthesis reaction. Solution 1 was aerated with Ar gas before the reaction. For modification, solvent should be added and mixed with solution during the bubbling of solution 1. To make enhanced dispersity and reduced particle size, additives would be aprotic, containing carbonyl group that would disturb the reduction reaction, and well mixed with water. In this paper, acetone was added to solution 1. After addition, under the Ar flow, borohydride solution was added at rates of smaller than 0.02 mL/s for the mild synthesis. During the addition, the solutions were mixed by mechanical stirrer and shaken by hand to reduce induced aggregation during the synthesis. Procedure. Ferric ion is reduced by mixing sodium borohydride as the reductant, following the reaction (Glavee et al., 1995). 4Fe(aq) + 3BH4 + 9H2O → 4Fe(s) + 3H2BO3 + 12H(aq) + 6H2(g) (1) The black precipitates on the surface after (1) reaction, they were allowed to settle down. The separated black precipitates were washed with deionized water and acetone with triplicate. Finally precipitates were dried under Ar flow. Characterization. The amount of zero-valent iron species in synthesized iron particle was measured using inductively coupled plasma-atomic emission spectrometry (ICPAES; IRIS-AP, Thermo Elemental). Excessive Fe ions were quantified by classical chemical titration method using o-Phenanthroline. The pH and reduction potential was measured using a pH-ORP meter (Orion, ROSS ultra combination electrode: 8102BNUWP). X-ray powder diffraction patterns were obtained on a RIGAKU X-ray diffractometer with Cu Kα radiation. The microstructures of synthesized particles were characterized using a Philips CM-200. An electophoretical light scattering measurement (Photal, Otsuka Electronics) provided particle size distributions in the submicron range. RESULTS AND DISSCUSION Reduction of iron ion with borohydride derivatives in solvent is a simple and mild reaction which can be done safely. Moreover, a key advantage of this reaction is that various iron sources can be used for the intended reaction. The different conditions for preparing the nanoiron particles with multi-component solvent system were listed in Table 1. Several parameters could significantly affect the formation of nanoiron. Arriagada and OsseoAsare summarized five aspects to be taken into consideration for particle synthesis, which are phase behavior and solubilization, average concentration of the reacting species in the aqueous phase, intermolecular interactions, dynamic behavior of the multicomponent system, and water to co-solvent ratio (Arriagada and Osseo-Asare; 1992). TABLE 1. Multi-component system of nano iron sythesis. Trial Water (wt%) Acetone (wt%) W