Synthesis and characterization of bismuth-doped hydroxyapatite nanorods for fluoride removal

Abstract

Even if limited amount of fluoride is vital, excessive accumulation of it has a serious health effect to human. Thus fluoride ions need to be removed using an environmentally friendly method and cost-effective material. Bismuth-doped hydroxyapatite nanorod was synthesized using co-precipitation technique and characterized by XRD, FT-IR, FE-SEM and EDS. XRD data revealed that the synthesized materials are hydroxyapatite having hexagonal structure with a space group of P63/m. Crystallite size and degree of crystallinity were increased as the amount of bismuth doped increased. Characteristics peaks of hydroxyapatite were observed in the FT-IR analysis. Energy dispersive spectroscopic analysis indicates that calcium, phosphorous, oxygen and bismuth are available in the synthesized product. In addition, the result indicates that the molar ratio of calcium to phosphorous reduced due to substitution of calcium by bismuth. Morphology analysis shows the presences of an aggregates of rod-like structure having diameters in the range of 10.06 – 31.93 nm. Batch adsorption experimental data were well fitted to pseudo-second order and Langmuir models, which implies that the sorption process is chemisorption through a monolayer on homogenous surface. The maximum adsorption capacity of bismuth doped hydroxyapatite nanorod was 60.67 mg/g using Langmuir model at room temperature. Thermodynamic data revealed that the adsorption process is endothermic and spontaneous. Regeneration and reuse analysis insured that the materials have good potential for reuse. The adsorption mechanism was inferred as chemisorption through electrostatic interaction and ion exchange. The modification of hydroxyapatite with bismuth can be considered a competent sorbent for removing fluoride ions.

Keywords

• Hydroxyapatite
• Precipitation
• Characterization
• Nanorods
• Synthesis