Recent progress and comprehensive review of hydroxyapatite-based materials for adsorption, photocatalysis, and oil separation from wastewater

Hydroxyapatite (HAP), chemically denoted as ${\left(\mathrm{Ca}\right)}_{10}{{(\mathrm{PO}}_4)}_6{\left(\mathrm{OH}\right)}_2$, is an environmentally friendly calcium phosphate material known for its exceptional versatility and structural adaptability. Widely present in natural forms as a principal component of bone, teeth, and phosphate mineral rocks, HAP’s notable structural and surface properties make it highly reactive, biocompatible, and stable. This inherent adaptability allows for modifications that result in advanced HAP-based materials with enhanced functionalities. HAP’s relevance extends across various applications, particularly in environmental remediation as an adsorbent for heavy metals and organic pollutants, as well as in catalysis and oil/water separation processes. This review comprehensively explores the preparation and synthesis methods of HAP and their effect on its surface and morphological properties. Additionally, it discusses HAP's various properties, including dielectric, mechanical, and thermal characteristics. The review delves into structural modifications, such as metal doping, non-metal substitutions, and hybridization with organic substances like polymers and other adsorbent-based materials, and their impacts on environmental applications.