Comparative study of physical properties of hydroxyapatite derived from Asian moon scallop and batik shells using sol–gel techniques for producing inorganic membrane plate

Approximately 33% of organic waste generated in Indonesia is food waste. The waste such as animal bones, seashells, and eggshells with CaCO₃ are unavoidable. To add technological values to the unused waste, Asian moon scallop shell and batik shell that contained high CaCO₃ were used as calcium precursors for synthesizing hydroxyapatite (HAp). Asian moon scallop shell and batik shell powder were obtained by size reduction using a concentric ball mill (CBM) and planetary ball mill (PBM). HAp was synthesized by a sol–gel method followed by calcination at 800 °C to 1000 °C. The characterization data of the HAP with respect to functional groups, microstructure, particle size, and structural analysis were presented. It was found that the presence of CO₃²⁻ groups was due to the interaction of the samples with CO₂ in the atmosphere during synthesis. PO₄³⁻ and OH⁻ groups were present in the HAp. The X-ray diffraction (XRD) analyses show that the product was pure HAp with no other phases present. Its crystallinity index (CI) of 86% indicated a high degree of crystallization. The crystallinity of powder improved with an increasing temperature, while there was non-uniformity in the morphology of HAp due to the increased temperature during calcination. Based on the scanning electron microscope (SEM) analysis, the resulting HAp had a reasonable purity and a nanostructured morphology. According to XRD results, the crystal structure of HAp was hexagonal, confirmed by ICDD card No. 01-084-1998. The lattice structure at peak 31.763° (211) was 2.815 Å. Based on X-ray fluorescence (XRF) analysis, calcium was the most predominant component in both calcined Asian moon scallop shell and batik shell powder (over 98% (w/w)). It is expected that this work contributes to the progress of sol–gel technique for HAp synthesis and the development of eco-friendly materials from unused waste for constructing inorganic membrane plates that can be used for wastewater treatment.