**6. Acknowledgment**

We would like to thank the National Science Fund for Distinguished Young Scholars of China (50925521), the Natural Science Foundation of China (51075092), the Natural Science Foundation of Heilongjiang Province in China (E200903) and China Postdoctoral Science Foundation (20100471020), and Harbin Innovative Talents Fund (2011RFQXG017) for their financial supports.

### **7. References**

	- A. Gannepalli, and S. K. Mallapragada, Physics Review B, 66 (2002) 104103.

**10** 

*Japan* 

**Novel Mechanochemical Process for Aqueous -** 

Nano-sized magnetite (Fe3O4) powder has been widely used in various industrial products: for instance, pigments, recording materials, printing and electrophotography such as copying toner and carrier powders, etc. (Buxbaum & Pfaff, 2005; Hakata, 2002; Ochiai et al., 1994) because of the excellent physicochemical properties. In particular, Fe3O4 nanoparticles with a size of smaller than about 20 nm exhibit a unique magnetic property, namely, superparamagnetism. In recent years, its non-toxicity property and high chemical stability have attracted much attention, and the use of superparamagnetic Fe3O4 nanoparticles have rapidly expanded in biomedical fields, such as magnetic resonance imaging (Hu et al., 2010; Lee et al., 2009), drug delivery (Guo et al., 2009; Zhou et al., 2009), hyperthermia (Gao et al., 2010; Muzquiz-Ramos et al., 2010), immobilization of enzymes (Wang et al., 2008) and

For industrial production of superparamagnetic Fe3O4 nanoparticles, chemical coprecipitation is often employed (Buyukhatipoglu et al., 2009; Compeán-Jasso et al., 2008; Iwasaki et al., 2011a; Mizutani et al., 2010; Yang et al., 2009; Yu et al., 2010). In coprecipitation methods, ferrous and ferric ions are simultaneously precipitated as ferrous hydroxide (Fe(OH)2) and goethite (α-FeOOH) in an alkaline solution, respectively, resulting in the formation of Fe3O4. In order to prepare superparamagnetic Fe3O4 nanoparticles with good dispersibility, not only the primary size of Fe3O4 nanoparticles must be controlled but also the aggregation of Fe3O4 nanoparticles must be avoided. Thus, anti-aggregation agents (e.g., surfactant) and toxic organic solvents are added to the staring solution in many cases (Cheng et al., 2005; Ge et al., 2007; Hua et al., 2008; Wan et al., 2007; Wen et al., 2008). Therefore, the Fe3O4 suspensions thus obtained should be washed enough before its use in the applications. In addition, for improving the crystallinity, heating treatments such as annealing and hydrothermal treatment are often performed, leading to the enhancement of the ferromagnetism (Mizutani et al., 2008; Wu et al., 2007, 2008; Zheng et al., 2006). Unfortunately, these required treatments complicate the preparation process and may

In order to overcome these problems, a novel synthesis method using a mechanochemical effect has been developed for the production of superparamagnetic Fe3O4 nanoparticles with

proteins (Can et al., 2009), and magnetic separation of cells (Li et al., 2009).

increase the environmental impact and the production cost.

**1. Introduction** 

**Phase Synthesis of Superparamagnetic** 

**Magnetite Nanoparticles** 

*Department of Chemical Engineering,* 

Tomohiro Iwasaki

*Osaka Prefecture University* 

