# Development of Polymer-Cored Akaganeite Adsorbent for Phosphate Adsorption
## 3 Results and Discussion
### Granulation of Akaganeite  
#### 3.2.1 Optimum Granulation Condition for Iron Oxyhydroxide Powder  
Time variation with PES polymer exposure to the air during the process of granulation was monitored, and corresponding SEM images of cross-sections were obtained. Only granular PES without powdered akaganeite showed that bulky pores were located in internal granules and fine pores were located at the edge (Figure 4a). SEM images (b)-(f) suggest that powdered akaganeite was immobilized around the edge of the PES polymer. Though (a) and (b) appear similar, the latter has a rough surface on the edge when compared to blank (a), where the powdered akaganeite attaches to the PES polymer. With increasing the exposure time, a pore in an internal granule was converted to a huge hole, and the akaganeite layer formed a thin layer (Figure 4b-f). The reason for phase inversion has been attributed to the non-solvent/solvent exchange rate, with DI water as the non-solvent and the DMF as the solvent; this parameter plays the role of drying phase inversion phenomena that control the phase of the PES polymer in a membrane field [30]. The DMF solvent dissolved in water when immersed, and the position was filled with water by allowing water to form empty pores in the internal PES. Moreover, images (b)-(f) explain why more pores were produced with decreasing exposure time and the non-solvent/solvent exchange rate of water was faster than that of natural volatilization. These results suggest that a granule with much higher exposure time had a big hole, not a pore, and that the drying phase inversion did occur, which did not allow PES enough time to form pores (f); thus, PES polymer formed a much denser non-porous structure. Because of this, a granule of (f) must form a hole in the internal granule. As a result, granular akaganeite at 30 s of exposure time, which does not float on water, was selected and carefully analyzed.  
To analyze the components of the granule surface, an edge was analyzed through field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FESEM-EDS). Akaganeite formed the chemical constituents of FeOOH:H\({}_{2}\)O (Fe 52.2%, H\({}_{2}\)O 25.0%) [22], and polyethersulfone was used to immobilize particle forms (C\({}_{12}\)H\({}_{8}\)O\({}_{3}\)S) [31].  
According to the results obtained from qualitative analysis (Table 1), the S element existed only in the PES polymer, not in akaganeite. Thus, the S element can be a reference for the existence of PES. In order to measure the distribution of akaganeite powder in the akaganeite granule, EDS mapping was performed on the surface of the granule where the akaganeite was immobilized (#1 in Figure 5b) and the inside of the granule (#2 in Figure 5b). The O and Fe contents in #1 were higher than those in #2 (Figure 5a,b). Moreover, the EDS mapping results (red dot in (b) and white dot in (c) in Figure 5) confirmed that the Fe and O elements were situated close to the edge (left side in boundary). In contrast, the S element ((white dot) in (d)) was detected far from the edge. Thus, these data suggest that akaganeite was doped onto the PES polymer scaffolds and that the Fe was gradually distributed from the inner area to the edge of the granularity. These data verify the immobilization of the akaganeite particles from the PES polymer scaffolds.  
Figure 4: SEM images of cross-section area for synthesized granular akaganeite depending on the exposure time in the air. The samples are named as follows: blank (**a**), 30 s (**b**), 60 s (**c**), 120 s (**d**), 300 s (**e**), and 1440 s (**f**).  
Figure 5: SEM images of cross-sections of granular akaganeite (**a**), EDS mapping of Fe (**b**), EDS mapping of O (**c**) and EDS mapping of S (**d**).