ABSTRACT
Unique properties of iron oxide, nanoparticles make it most versatile candidate for application in catalysis, medical diagnostics and cell imaging, as well as corrosion inhibitor, pigments and gas sensors applications, etc. [1-2]. The number of methods reported for production of iron oxide nanoparticles, some of the important methods are metal salt reduction, thermal decomposition of organometallic precursor, sol-gel and co precipitation, etc. [3-7]. Presences of impurities, use of organic solvents for production, wide particle size distribution are some of limitations of these methods. Particle aggregation is one of the important pronounced effects during synthesis as the particle size decreases, the surface charges on the particle increases, the particles come together to minimize the surface energy and they agglomerate [8]. Hence, to decrease the effect of surface charges and to keep the particles stable in solution, above said processes, utilizes surfactant for stabilization of nanoparticles. In wet chemical synthesis processes, the nanocolloids will form, which may find application in polymer coatings, conductive inks and biosensors etc. Metal salt reduction method is most widely used for synthesis of colloidal nanoparticles because of its ease in processing and precise control on process conditions and finally on the particle size. Reduction of metal salt aqueous solutions by sodium borohydride at room temperature produces both monometallic and bimetallic nanoparticles as amorphous powders [9]. The reduction process of metal salt for synthesis of colloidal iron oxide nanoparticles is simple but the stability and reproducibility of colloid is a great challenge. [10] Sania Pervaiz et al. [11] used vitamin C, sodium borohydrate for reduction of ferric chloride to yield the zero valent iron nanoparticles. Blum et al. [12] used Tiron for synthesis of monodisperse iron oxide nanoparticles. Hematite, maghemite, wustite are the main forms of iron oxide nanoparticles [13]. Maiyong et al. [14] synthesized hematite (m-Fe2O3) form of iron oxide nanoparticles by hydrothermal route. Jing et al. [15] used anionic and cationic surfactant to modify the reaction conditions for preparation of m-Fe2O3 nanoparticles through hydrothermal route. The most conventional method for obtaining maghemite Fe2O3 is by coprecipitation, Jeong et al. [16] fabricated g-Fe2O3 nanoparticles by co precipitation. However other routes are also explored by researcher for synthesis of maghemite Fe3O4. Liu et al. [17] synthesized g-Fe2O3 nanoparticles by the microemulsion method. Shafi et al. [18] have used the principles of sonochemistry for synthesis of g-Fe2O3 nanoparticles and they reported that the size and morphology of nanoparticles are govern by the reaction parameter and reactor type. The batch and continuous reaction mode was intensively investigated to study effect of reactor type on nanoparticle size and morphology [19-21]. Microreactor was used for continuous synthesis of nanoparticles providing the fine control over the proper-
ties at nanoscale. Laminar flow conditions in microreactor due to low Reynolds number provide diffusion-based reaction condition [22-26]. Miniaturization of reaction volume provides the scope for easy and quick variation in process parameter to generate database of product properties with process parameters, which can be useful for invention of novel material [27, 28]. Microreactor was used for synthesis of metal, metal oxide, semiconductor, polymer nanoparticles by numerous researchers [29-31].
