Preparation and application of hydroxyapatite extracted from fish scale waste using deep eutectic solvents

Abstract

In this study, we propose a green and environmentally-friendly method to extract hydroxyapatite (HAP) from crucian carp scales by a deep eutectic solvent (choline chloride/1,4-butanediol). The optimal conditions for the extraction were as follows: an extraction temperature of 65 °C, an extraction time of 2 h, and a solid:liquid ratio of 1:15 (g:g). Under these conditions, the extraction rate of HAP was 40.58% ± 0.14%. The functional groups and crystallinity of the hydroxyapatite obtained were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The chemical composition was determined by energy dispersive X-ray spectrometry (EDX) and inductively coupled plasma emission spectrometry (ICP-MS). The surface morphology and particle size distribution were observed by scanning electron microscopy (SEM). The thermal stability was analyzed by thermogravimetric analysis (TGA). The adsorption capacity was determined by metal ion adsorption experiments. The results show that the extracted HAP has a heterogeneous morphology and is a mixture of the phosphates of carbonic acid and phosphoric acid, with high purity and excellent thermal stability. HAP has a good adsorption capacity for metal ions such as lead, copper, silver, and zinc.