Fish scale-extracted hydroxyapatite/chitosan composite scaffolds fabricated by freeze casting-An innovative strategy for water treatment.

In this study, low-cost and eco-friendly hydroxyapatite (HA) minerals were extracted from scales of Tilapia fish (Oreochromis mossambicus). After calcination, fish-scale extracted powder was further confirmed to be HA by X-ray diffraction with mean particle size of 5.96 μm determined by particle size analyzer. The calcined powder was utilized as the raw material and combined with chitosan (CS) to synthesize composite scaffolds by freeze casting and cross-linking. Mercury porosimetry results showed that the scaffolds possessed hierarchical porous structure. Microstructural features characterized by SEM revealed unidirectional channel structures with channel sizes ranged from 10 to 100 μm and 1 to 50  μm for scaffolds freeze-casted at 2 ℃/min and 5 ℃/min cooling rates, respectively. The adsorption kinetics of HA/CS composite scaffolds with varying channel sizes were investigated by both batch and fixed-bed processes with different Pb(П) initial concentrations (100 and 1000 mg/L). The adsorption capability was optimized by tuning the cooling rates and the maximum adsorption amount could reach 75-570 mg/g in batch process and 94 mg/g in fixed bed process. In summary, the HA/CS composite scaffolds showed great capability to remove heavy metal ions from waste water and their tunable channel sizes could be applied in suitable fields under both statistic and flowing conditions.