Composites of hydroxyapatite, recognized by its peculiar crystal architecture and distinctive attributes showcased the potential in adsorbing heavy metal ions and radioactive elements as well as selected organic substances. In this paper, the intrinsic mechanism of adsorption by composites hydroxyapatite was proved for the first time. Subsequently, selectivity and competitiveness of composites of hydroxyapatite for a variety of environments containing various interferences from cations, anions, and organic molecules are elucidated. Next, composites of hydroxyapatite were further categorized according to their morphological dimensions. Adsorption properties and intrinsic mechanisms were investigated based on different morphologies. It was shown that although composites of hydroxyapatite were characterized by excellent adsorption capacity and cost-effectiveness, their application is often challenging due to inherent fragility and agglomeration, technical problems required for their handling as well as difficulty in recycling. Finally, to address these issues, the paper discusses the tendency of hydroxyapatite composites to adsorb heavy metal ions and radioactive elements as well as the limitations of their applications. Summarizing the limitations and future directions of modification of HAP in the field of heavy metal ions and different substances contamination abatement, the paper provides insightful perspectives for its gradual improvement and rational application.

The sustainable microwave (MW) synthesis of hydroxyapatite (HAp) from decarbonized eggshells was investigated. Decarbonization of eggshells, as a natural source of calcium carbonate (CaCO3), was carried out in the current study at ambient conditions to reduce the footprint of CO2 emissions on our environment where either calcination or acidic direct treatments of eggshells produce CO2 emissions, which is a major cause for global warming. Eggshell decarbonization was carried out via the chemical reaction with sodium hydroxide (NaOH) alkaline solution in order to convert eggshell waste into calcium hydroxide (Ca(OH)2) and simultaneously store CO2 as a sodium carbonate (Na2CO3) by-product which is an essential material in many industrial sectors. The produced Ca(OH)2 was mixed with ammonium dihydrogen phosphate (NH4H2PO4) reagent at pH~11 before being subjected to MW irradiation at 2.45 GHz frequency for 5 min using 800 Watts to prepare HAp. The prepared Nano-HAp was characterized using X-ray diffraction (XRD) where the crystal size was ~28 nm using the Scherrer equation. The elongated rod-like nano-HAp crystals were characterized using scanning electron microscopy (SEM) equipped with dispersive energy X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). MW synthesis of decarbonized eggshells is considered as a sustainable and environmentally friendly route to produce promising bioceramics such as nano-HAp. Concurrently, decarbonization of eggshells offers the ability to store CO2 as a high value-added Na2CO3 material.

Nanomaterials in particular the magnetic nanoparticles (MNPs) offer tremendous potential for cancer treatment due to their unique intrinsic properties. Combining materials with a variety of functional groups, and forming a multifunctional nanosystem to overcome the limitations of monotherapy for cancer treatment has always been a research focus with notable difficulties. Considering the many challenges faced by radiotherapy and hyperthermia, in this study, we designed a rational strategy for magnetic hyperthermia using Fe3O4@SiO2@Sec2@FA nanoparticles as a novel nano-radiosensitizer to simultaneously enhance the therapeutic effects of radiotherapy in the future. Fe3O4@SiO2 core-shell structured nanoparticles were synthesized with an appropriate silica layer thickness to maintain good saturation magnetization. The as-prepared Fe3O4@SiO2@Sec2@FA nanoparticles had the specific absorption rate (SAR)value of 57 W/g, which was below the clinically acceptable alternating magnetic field value of 4.9 × 109 Am-1s-1, indicating good heat generation efficiency (the temperature level ΔT=6-10 °C). Moreover, Folate-modified nanoparticles exhibited approximately 6-fold higher cellular internalization of Hela cells with no obvious cytotoxicity for the Hela and MDA-MB-231 cells, and lower cytotoxicity for the HUVECs in a concentration range of 0-150 µg/mL. In addition, these nanoparticles were modified on the silica surface by L-selenocystine, which could enhance the elimination of tumor cells by producing reactive oxygen species under X-rays, resulting in a novel radiosensitization effect. Therefore, the as-prepared Fe3O4@SiO2@Sec2@FA nanoparticles with good biocompatibility and active targeting would possess synergistic magnetic hyperthermia/radiotherapy effect.