In this study, the adsorption capacity of bio-hydroxyapatite (Bio-HAp) from devilfish for the removal of F^- and Cd(II) from aqueous solutions was investigated. This material was synthesized according to a 2FI factorial experimental design by varying the extraction conditions for Bio-HAp, including the type of pretreatment (alkaline and peroxide), the calcination temperature from 550 to 850 °C, and the sonication process. The maximum adsorption capacities were 8.48 and 83.56 mg g^-1 for F^- and Cd(II), respectively. Statistical analysis showed the importance of the type of pretreatment, temperature, and sonication for adsorption. The predicted optimal conditions were Bio-HAp extracted from bone with peroxide pretreatment, calcination at 550 °C and sonication. The surface of the Bio-HAp was found to be mesoporous and basic in character. TGA, FT-IR and SEM-EDS characterizations confirmed the presence of F^- and Cd(II) on the Bio-HAp surface and confirmed the adsorption mechanisms by electrostatic forces, ion exchange, and chemisorption. The Praunitz-Rake model of adsorption isotherm showed better agreement with the equilibrium adsorption data of F^- and Cd(II) at pH 7. Furthermore, photodegradation experiments showed 100% degradation methylene blue (MB) under natural sunlight. This study indicates an effective photodegradation process, suggesting high adsorption capacity of the samples. The use of devilfish as an adsorbent promises to be a viable and sustainable option for the removal of fluoride and cadmium from water, and for use in photodegradation experiments.

The aim of this work was the development and characterization of iron oxide nanoparticles with magnetite phases (IONPs)-hydroxyapatite (HAp) composites. In this article, the chemical coprecipitation method was used to synthesize three different nanomaterials: IONPs, HAp, and IONPs-HAp composite. Rietveld analysis of the X-ray diffraction (XRD) revealed the crystal lattice parameters and presence of HAp and IONPS after synthesis, which was carried out at a temperature of 120 °C inductively coupled plasma (ICP) was used to identify the trace elements present, Fourier transform infrared (FTIR) spectroscopy to verify the functional groups present in each material and efficiency of washes for the composite material, transmission electron microscopy (TEM) to observe the morphology and nanoparticle size for IONPs 11 nm and IONPs-HAp 15 nm. ζ potential measurements to investigate the surface charges for all samples had a positive value, the apatite samples showed a very stable behavior, and vibrating sample magnetometry (VSM) to evaluate the magnetic properties showed that IONPs and IONPs-HAp composite exhibit superparamagnetic behavior, while HAp nanoparticles show diamagnetic behavior. It was also shown that the saturation magnetization and magnetic moments of the IONPs do not change upon formation of the IONPs-HAp composite.