Facile synthesis of bismuth and iron co-doped hydroxyapatite nanomaterials for high-performance fluoride ions adsorption

Fluoride is essential, but excessive intake of it in drinking water can have adverse effects. Thus, it must be removed using routine techniques and novel nanomaterials that are environmentally friendly. In this study, we present a facile synthesis of bismuth and iron co-doped hydroxyapatite nanomaterials for high-performance fluoride ions adsorption. The crystal size and degree of crystallinity of the nanomaterials were controlled by the ratios of iron and bismuth precursors. The morphology analysis confirmed the presence of rod-like structures of variable sizes. Calcium, phosphorous, oxygen, bismuth, and iron were detected with the expected elemental state in the co-doped hydroxyapatite material. Batch adsorption experiments showed excellent fluoride ion adsorption performance for bismuth and iron co-doped hydroxyapatite nanomaterials. Pseudo-second order and Langmuir models better describe the experimental findings. This denotes that fluoride uptake through the synthesized material is a chemical process that forms a monolayer, and the surface is homogenous. Thermodynamic data showed that the defluoridation process absorbs heat energy but is spontaneous. Furthermore, in the regeneration and reuse analysis, 74.3% of 10 mg/L fluoride ions were removed even in the fifth cycle, which ensured the nanomaterial's reusability. The proposed defluoridation mechanisms were electrostatic interaction and ion exchange. Insertions of bismuth and iron ions into hydroxyapatite structure provided a potent sorbent for fluoride removal. Fluoride adsorption performance and the ease of synthesis make this bismuth and iron codoped hydroxyapatite nanomaterials attractive for water treatment and environmental remediation applications.