# Development of Polymer-Cored Akaganeite Adsorbent for Phosphate Adsorption
## 4 Conclusions  
In this study, akaganeite with an FeOOH structure in iron oxyhydroxide was synthesized, and reusable materials were developed. Immobilization with the core-shell method using polyethersulfone was applied as a strategy to recover phosphate anions from a trace of phosphate solution. The synthesized granular akaganeite was successfully investigated through various analyses, such as SEM/TGA/BET, to understand its physical properties.  
The XRD analysis of the powder form of the synthesized akaganeite showed a blunt peak, while TEM showed an aggregated millet grain shape with an average size of 5 nm. The SAD patterns of akaganeite verified the amorphous form owing to scattering patterns; these data were supported by the results from XRD analysis. Powdered akaganeite had a surface area of 231 mg\({}^{2}\)/g and was estimated as a superior material given that the zeta potential of akaganeite was higher than that of goethite and lepidocrocite at pH 6-7, with 5 mg/L of phosphate. In the granulation process, to prevent the dispersion of the powder, granular akaganeite was synthesized using polyethersulfone as a scaffold. The granulation of akaganeite was carried out to improve the field applicability of intrinsic akaganeite. In the analysis of its characteristics, the result of the SEM images of the cross-section area of granular akaganeite depending on the exposure time was explained by the dry phase inversion due to DMF volatility participating in forming holes in an internal granule. SEM/EDS analyses of the edge surface of granular akaganeite suggest that akaganeite particles are well immobilized onto PES polymer scaffolds. Moreover, based on the pore size data, the physical properties were found to have remained unchanged. Finally, the surface area of granular akaganeite decreased by 4-5 times compared to powdered akaganeite. The adsorption kinetic of granular akaganeite was well fitted by the pseudo-second-order model (R\({}^{2}\) > 0.99 for adsorption and R\({}^{2}\) > 0.99 for desorption). The adsorption equilibrium time for granular akaganeite reached 12 h, while the desorption equilibrium time reached 6 h. Furthermore, the equilibrium adsorption capacity (q\({}_{e}\)) was calculated as 2.71 mg/g using the pseudo-second-order kinetic model, while the desorption capacity was calculated as 2.53 mg/g. The Freundlich and the Langmuir isotherm models were applied using granular akaganeite as well.  
Powdered akaganeite showed a high removal efficiency in affinity with phosphate anions. On the other hand, granular akaganeite showed a lower affinity. This suggests that the granulation of akaganeite with the PES polymer did not change its adsorption property. As a result, the maximum adsorption capacities calculated were 21.27 mg/g for powdered akaganeite and 3.65 mg/g for granular akaganeite.  
Conceptualization, J.B.; methodology, H.W. and S.K.; validation, S.B. and J.B.; investigation, S.O.; data curation, J.B.; writing--original draft preparation, H.W. and J.B.; writing--review and editing, S.O., S.K. and S.B.; supervision, J.B.; project administration, S.B.; funding acquisition, J.B. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Korea Ministry of Environment under the Aquatic Ecosystem Conservation Research Program (No. 20230206-001). The authors are very grateful for the funds (Project #20230160-001) provided by the \"Korea Institute of Civil Engineering and Building Technology\" (KICT), Republic of Korea.  
Not applicable for studies not involving humans or animals.  
Not applicable for studies not involving humans.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
The authors declare no conflicts of interest.