Magnetic solid-phase extraction of U(VI) in aqueous solution by Fe3O4@hydroxyapatite

Composites of hydroxyapatite and their application in adsorption, medicine and as catalysts

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.

High efficiency adsorption of uranium by magnesia-silica-fluoride co-doped hydroxyapatite

Hydroxyapatite has a high affinity to uranium, and element doping can effectively improve its adsorption performance. In this study, magnesia-silica-fluoride co-doped hydroxyapatite composite was prepared by hydrothermal method, and the effect of single-phase and multiphase doping on the structure and properties of the composites was investigated. The results showed that the specific surface area of Mg-Si-F-nHA composites increased by 63.01% after doping. Comparing with nHA, U(VI) adsorption capacity of Si-nHA, Mg-Si-nHA and Mg-Si-F-nHA composites increased by 13.01%, 17.39% and 22.03%, respectively. The adsorption capacity of Mg-Si-F-nHA composite reached 1286.76 mg/g. Adsorbent dosage and pH obviously affected U(VI) adsorption, and the experimental data can be fitted well by PSO and Sips models. The physicochemical characterization before and after adsorption suggested that complexation, ion exchange and precipitation participated in uranium adsorption. In conclusion, different elements doping can effectively improve the uranium adsorption properties of hydroxyapatite composites.

Magnetic Hydroxyapatite Nanoparticles in Regenerative Medicine and Nanomedicine

This review focuses on the latest advancements in magnetic hydroxyapatite (mHA) nanoparticles and their potential applications in nanomedicine and regenerative medicine. mHA nanoparticles have gained significant interest over the last few years for their great potential, offering advanced multi-therapeutic strategies because of their biocompatibility, bioactivity, and unique physicochemical features, enabling on-demand activation and control. The most relevant synthetic methods to obtain magnetic apatite-based materials, either in the form of iron-doped HA nanoparticles showing intrinsic magnetic properties or composite/hybrid compounds between HA and superparamagnetic metal oxide nanoparticles, are described as highlighting structure-property correlations. Following this, this review discusses the application of various magnetic hydroxyapatite nanomaterials in bone regeneration and nanomedicine. Finally, novel perspectives are investigated with respect to the ability of mHA nanoparticles to improve nanocarriers with homogeneous structures to promote multifunctional biological applications, such as cell stimulation and instruction, antimicrobial activity, and drug release with on-demand triggering.

Magnetite/β-cyclodextrin/fly ash composite as an effective and recyclable adsorbent for uranium(VI) capture from wastewater

As a novel adsorbent for the separation of uranium(VI) from wastewater, Magnetite/β-cyclodextrin/fly ash composite (Fe₃O₄/β-CD/FA) was first prepared via a chemical coprecipitation technology. The characterization results indicated that Fe₃O₄ and β-CD had been successfully loaded on FA, which had brought abundant oxygen-containing functional groups, providing numerous adsorptive sites for the removal of uranium(VI). At pH = 5.0 and T = 25 °C, the maximum uranium(VI) removal efficiency and capacity of Fe₃O₄/β-CD/FA were higher to 97.8% and 444.4 mg g^-1, respectively. Pseudo-second-order and Langmuir models fitted better with the experimental data, illustrating that chemical adsorption dominated the uranium(VI) removal process. In addition, Fe₃O₄/β-CD/FA showed good anti-interference ability and recoverability. After five cycles, the removal rate of uranium(VI) on Fe₃O₄/β-CD/FA was still higher to 90.4%. The immobilization of uranium(VI) on Fe₃O₄/β-CD/FA was mainly ascribed to the synergism of redox reaction, complex reaction, chemical reaction and electrostatic interaction. Given the above, Fe₃O₄/β-CD/FA would be regarded as an efficacious, green and promising adsorbent for uranium(VI) separation from wastewater.

In situ synthesis of magnesium-doped hydroxyapatite aerogel for highly efficient U(VI) separation with ultra high adsorption capacity and excellent recyclability

Mg-doped HAP aerogel (MHAPA) was firstly in situ prepared via freeze-drying-calcination technology to capture U(VI). The U(VI) removal capacity by MHAPA even arrived 2685.6 mg g^-1, which was about 2 times over purchased HAP, illustrating that the incorporation of Mg ions could greatly enhance the U(VI) removal capacity. Compared with HAP, MHAPA also showed better anti-ion interference ability and dynamic removal performances. In comparison with other HAP-based adsorbents, MHAPA possessed good recyclability and its desorption rate was up to 93.4% in the first cycle. The excellent U(VI) removal performances of MHAPA might be owing to its low crystallinity and grain size, fast ion exchange rate and partial ionization under acidic conditions, which would accelerate the process of electrostatic attraction, ion-exchange, and complexation to immobilize U(VI). To sum up, the prepared MHAPA was expected to be an environmentally friendly, recyclable and effective adsorbent to immobilize U(VI) in actual wastewater.

High-speed and efficient removal of uranium (VI) from aqueous solution by hydroxyapatite-modified ordered mesoporous carbon (CMK-3)

In recent years, the synthesis and application of green, cost-effective, and sustainable materials for uranium (VI) removal was significant to environmental protection. The ordered mesoporous carbon (CMK-3) supported different mass of hydroxyapatite materials (HAP@CMK-3) were facilely synthesized via hydrothermal method. The resultant materials were characterized by XRD, FT-IR, BET, SEM, TEM mapping, and XPS, and implemented for immobilizing U(VI). Not only the specific surface area of HAP (7.01 m²/g) was increased by the loading on CMK-3 (818.37 m²/g), but also the adsorption capacity of CMK-3 was increased by HAP modification. Impressively, HAP@CMK-3 exhibited highly adsorption capacity of U(VI) with the increase of HAP deposition and was capable of achieving fast reaction. Therein to, the specific surface area of HAP@CMK-3(2:1) was 253.68 m²/g, as well as the adsorption capacity was up to 1072 mg/g (fitted by Langmuir isotherm, at pH=3.0, 298 K) and the adsorption process was completed in 30 min (followed by pseudo-second-order kinetic). The adsorption mechanisms of U(VI) on HAP@CMK-3 involved electrostatic forces, ionic interactions, and chemical complexation. This work offered new avenues to address the limitations of cost and less secondary pollution for the removal of U(IV) from wastewater.

Surfactant-assisted adsorption of uranyl ions in aqueous solution on TiO2/polythiophene nanocomposite

In this work, hexadecyltrimethylammonium-bromide (HTAB)-modified polythiophene (PTh)/TiO₂ nanocomposite (HTAB/PTh/TiO₂) was applied to remove uranyl ions (UO₂²⁺). FT-IR, XRD, ζ potential, TGA, SEM, and XPS were utilized to obtain the chemical and physical properties of HTAB/PTh/TiO₂. The effects of HTAB content, preparation temperature, and adsorption conditions on UO₂²⁺ removal were investigated comprehensively. And the UO₂²⁺ adsorption process on HTAB/PTh/TiO₂ was fitted to the Sips model with a saturated adsorption capacity of 234.74 mg/g, which was 6 times over TiO₂. The results suggested that the surfactant of HTAB can significantly improve the adsorption ability of TiO₂ for UO₂²⁺ ions. This work provides a strategy of surfactant modification for enhancing the separation and recovery ability of adsorbent toward UO₂²⁺ in the radioactive wastewater.

Hydroxyapatite with magnetic core: Synthesis methods, properties, adsorption and medical applications

This review presents the actual state of knowledge and recent research results on the magnetic composite synthesized from iron oxide (γ-Fe₂O₃ or Fe₃O₄) and hydroxyapatite. It can be obtained applying some methods, i.e. chemical precipitation, hydrothermal, sol-gel, and biomimetic or combined techniques which exhibit characteristic properties affecting the form of the prepared product. More specific details are discussed in this paper. A comparison of the discussed synthesis methods is presented. On the basis of selected publications, a comparison of the results of the analysis by XRD, FTIR, SEM and EDX methods for hydroxyapatite with a magnetic core was also presented. Moreover, the characteristics large adsorption capacity and specific area allow employing nanocomposites as adsorbents particularly in removal of toxic metal ions. Nowadays this issue is extremely vital due to large amounts of pollutants in the environment and greater ecological awareness of people. Moreover, magnetic hydroxyapatite can be also applied as a catalyst in various syntheses or oxidation reactions as well as in medicine in magnetic resonance imaging, hyperthermia treatment, drug delivery and release, bone regeneration or cell therapy.

Synthesis and characterization of γ-MnO2/chitosan/Fe3O4 cross-linked with EDTA and the study of its efficiency for the elimination of zinc(II) and lead(II) from wastewater

In this research, a novel γ-MnO₂/chitosan/Fe₃O₄ nanocomposite was synthesized and modified by ethylenediaminetetraacetic acid (EDTA) for the separation and simultaneous elimination of Zn(II) and Pb(II) ions from aqueous solutions in a batch system. The magnetic nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and elemental analysis (EDAX). The results demonstrated that the magnetic nanocomposite was successfully synthesized and cross-linked. The predominant influential experimental parameters including pH, contact time, initial concentration, and temperature were analyzed in relation to the adsorption capacity. The experimental data were well converged with the double exponential kinetic model. Also, the results were well matched with the Langmuir isotherm, where the maximum adsorption values were 310.4 and 136 mg g^-1 for Pb(II) and Zn(II), respectively. On the other hand, in the binary-component system, the Langmuir-Freundlich model dominated the experimental data. The thermodynamic results (ΔG° < 0, ΔH° > 0, and ΔS° > 0) within the temperature range of 25-40 °C showed that the nature of adsorption by the nanocomposite for both ions was spontaneous and endothermic and was favored at higher temperatures. The simultaneous removal of two ions, the excellent magnetic separation, and the high efficiency in reuse (five effective recovery cycles) indicated the high capability of the EDTA-modified γ-MnO₂/chitosan/Fe₃O₄ nanocomposite in the treatment of industrial effluents from Pb(II) and Zn(II).