A facile synthesis of hydroxyapatite for effective removal strontium ion

Enhanced sorption of strontium radionuclides onto a modified molybdenum titanate composite

A study was conducted to investigate the sorption of 85Sr from aqueous solutions using a fabricated magnesium molybdenum titanate (MgMoTi) composite. The MgMoTi composites were synthesized through the co-precipitation technique and characterized using different analytical tools, including FT-IR, XRD, SEM, and EDX. The sorption studies focused on 85Sr and examined factors such as shaking time, pH, ionic strength, temperature, initial ion concentration, and saturation capacity. The results obtained from the study indicated that, under optimum sorption conditions, the saturation capacity for 85Sr onto S-4 and S-5 was determined to be 23.31 and 37.72 mg g-1, respectively. The sorption of 85Sr exhibited dependence on pH and ionic strength. The kinetics of the sorption process followed the pseudo-2nd-order model, while the thermodynamics revealed an endothermic and spontaneous nature. Desorption studies revealed that 0.1 M HCl was the most effective eluent for the complete recovery of 85Sr. Furthermore, the recycling results demonstrated the excellent recyclability of MgMoTi, suggesting its potential application as a sorbent for the removal of 85Sr from aqueous solutions. Overall, the study highlights MgMoTi as a promising composite with practical utility in the sorption of 85Sr from aqueous solutions.

Selective Adsorption of Sr(II) from Aqueous Solution by Na3FePO4CO3: Experimental and DFT Studies

The efficient segregation of radioactive nuclides from low-level radioactive liquid waste (LLRW) is paramount for nuclear emergency protocols and waste minimization. Here, we synthesized Na3FePO4CO3 (NFPC) via a one-pot hydrothermal method and applied it for the first time to the selective separation of Sr2+ from simulated LLRW. Static adsorption experimental results indicated that the distribution coefficient Kd remained above 5000 mL·g-1, even when the concentration of interfering ions was more than 40 times that of Sr2+. Furthermore, the removal efficiency of Sr2+ showed no significant change within the pH range of 4 to 9. The adsorption of Sr2+ fitted the pseudo-second-order kinetic model and the Langmuir isotherm model, with an equilibrium time of 36 min and a maximum adsorption capacity of 99.6 mg·g-1. Notably, the adsorption capacity was observed to increment marginally with an elevation in temperature. Characterization analyses and density functional theory (DFT) calculations elucidated the adsorption mechanism, demonstrating that Sr2+ initially engaged in an ion exchange reaction with Na+. Subsequently, Sr2+ coordinated with four oxygen atoms on the NFPC (100) facet, establishing a robust Sr-O bond via orbital hybridization.

Recent advances of application of bentonite-based composites in the environmental remediation

Bentonite-based composites have been widely utilized in the removal of various pollutants due to low cost, environmentally friendly, ease-to-operate, whereas the recent advances concerning the application of bentonite-based composites in environmental remediation were not available. Herein, the modification (i.e., acid/alkaline washing, thermal treatment and hybrids) of bentonite was firstly reviewed; Then the recent advances of adsorption of environmental concomitants (e.g., organic (dyes, microplastics, phenolic and other organics) and inorganic pollutants (heavy metals, radionuclides and other inorganic pollutants)) on various bentonite-based composites were summarized in details. Meanwhile, the effect of environmental factors and interaction mechanism between bentonite-based composites and contaminants were also investigated. Finally, the conclusions and prospective of bentonite-based composites in the environmental remediation were proposed. It is demonstrated that various bentonite-based composites exhibited the high adsorption/degradation capacity towards environmental pollutants under the specific conditions. The interaction mechanism involved the mineralization, physical/chemical adsorption, co-precipitation and complexation. This review highlights the effect of different functionalization of bentonite-based composites on their adsorption capacity and interaction mechanism, which is expected to be helpful to environmental scientists for applying bentonite-based composites into practical environmental remediation.

Phosphination of amino-modified mesoporous silica for the selective separation of strontium

Radioactive strontium (90Sr) is considered as one of the most dangerous radionuclides due to its high biochemical toxicity. For the efficient and selective separation of Sr from acidic environments, a novel functional adsorbent CEPA@SBA-15-APTES was prepared in this work through the phosphorylation of amino-modified mesoporous silica with organic content of approximately 20 wt%. CEPA@SBA-15-APTES was characterized by TEM, SEM, EDS, TG-DSC, BET, FTIR, and XPS techniques, revealing its characteristics of an ordered hexagonal lattice-like structure and rich functional groups. The experimental results demonstrated that the adsorbent exhibited good adsorption capacity for Sr over a wide acidity range (i.e., from 10-10 M to 4 M HNO3). The adsorption equilibriums of Sr by CEPA@SBA-15-APTES in 10-6 M and 3 M HNO3 solutions were reached within 30 and 5 min, respectively, and the adsorption capacities at 318 K were 112.6 and 71.8 mg/g, respectively. Furthermore, by combining the experimental and characterization results, we found that the adsorption mechanism consisted of ion exchange between Sr(II) and H+ (in P-OH) in the 10-6 M HNO3 solution and coordination between the Sr(II) and oxygen-containing (CO and P = O) functional groups in the 3 M HNO3 solution.

Hydroxyapatite and its composite in heavy metal decontamination: Adsorption mechanisms, challenges, and future perspective

Nanohydroxyapatite (n-HAP), recognized by its peculiar crystal architecture and distinctive attributes showcased the underlying potential in adsorbing heavy metal ions (HMI). In this paper, the intrinsic mechanism of HMI adsorption by n-HAP was first revealed. Subsequently, the selectivity and competitiveness of n-HAP for HMI in a variety of environments containing various interferences from cations, anions, and organic molecules are elucidated. Next, n-HAP was further categorized according to its morphological dimensions, and its adsorption properties and intrinsic mechanisms were investigated based on these different morphologies. It was shown that although n-HAP has excellent adsorption capacity and cost-effectiveness, its application is often challenging to realize due to its inherent fragility and agglomeration, the technical problems required for its handling, and the difficulty of recycling. Finally, to address these issues, this paper discusses the tendency of n-HAP and its hybridized/modified materials to adsorb HMI as well as the limitations of their applications. By summarizing the limitations and future directions of hybridization/modification HAP in the field of HMI contamination abatement, this paper provides insightful perspectives for its gradual improvement and rational application.

Sequestration of strontium, nickel, and cadmium on glomalin-related soil protein: Interfacial behaviors and ecological functions

Glomalin-related soil protein (GRSP) is a widespread recalcitrant soil protein complex that promotes the immobilization of metals in soils. Herein, we combined indoor simulation and field investigation to reveal the interfacial behaviors and ecological functions of GRSP to the three typical metals (Sr(II), Ni(II), and Cd(II)). The kinetic and isotherm data suggested that GRSP had a strong ability to adsorb the metals, which was closely related to the Hard-Soft-Acid-Base theory and the film diffusion mechanisms. Regarding environmental factors, the higher solution pH was beneficial to the adsorption of the metals onto GRSP, while the adsorption capacity decreased at lower or higher salinity due to the salting-out and Na⁺ competition effects. Moreover, Sr(II), Ni(II), and Cd(II) showed competitive adsorption onto GRSP, which was associated with the spatial site resistance effect. By comparing the retention factors of seven natural and artificial particles, GRSP had elevated distribution coefficients in high metal concentration, while its retention factors showed a relatively lower decrease, suggesting that GRSP had excellent buffer performance for a potential metal pollution emergency. Through the continental-scale coastal regions investigation, GRSP sequestered 1.05-3.11 μmol/g Ni, 0.31-1.49 μmol/g Sr, and 0.01-0.06 μmol/g Cd with 0.54-0.91 % of the sediment mass, demonstrating its strong ability to adsorb the metals. Therefore, we advocate that GRSP, as a recalcitrant protein complex, can be considered an effective tool for buffering capacity of metal pollution and environmental capacity within coastal wetlands.

NaOH-assisted H2O2 post-modification as a novel approach to enhance adsorption capacity of residual coffee waste biochars toward radioactive strontium: Experimental and theoretical studies

In this study, NaOH-assisted H₂O₂ post-modification was proposed as a novel strategy to enhance the adsorption of radioactive strontium (Sr) onto residual coffee waste biochars (RCWBs). To validate its viability, the adsorption capacities and mechanisms of Sr(II) using pristine (RCWB_P), H₂O₂ post-modified (RCWB_HP), and NaOH-assisted H₂O₂ post-modified residual coffee waste biochars (RCWB_NHP) were experimentally and theoretically investigated. The highest adsorption capacity of Sr(II) for RCWB_NHP (10.91 mg/g) compared to RCWB_HP (5.57 mg/g) and RCWB_P (5.07 mg/g) was primarily attributed to higher negative surface zeta potential (RCWB_NHP = -5.66 → -30.97 mV; RCWB_HP = -0.31 → -11.29 mV; RCWB_P = 1.90 → -10.40 mV) and decoration of Na on the surfaces of RCWB_P via NaOH-assisted H₂O₂ post-modification. These findings agree entirely with the theoretical observations that the adsorption of Sr(II) onto RCWB_P and RCWB_HP was controlled by electrostatic interactions involving carbonyls whereas enriched carboxylic acids and decorated Na on the surfaces of RCWB_NHP through the replacement of Mg and K by NaOH-assisted H₂O₂ modification stimulated electrostatic interactions and cation exchanges governing the adsorption of Sr(II). Hence, NaOH-assisted H₂O₂ post-modification seemed to be practically applicable for improving the adsorption capacity of Sr(II) using RCWB-based carbonaceous adsorbents in real water matrices.

Post-substitution of magnesium at CaI of nano-hydroxyapatite surface for highly efficient and selective removal of radioactive 90Sr from groundwater

We have modified the ion-exchange affinity of nano-Hydroxyapatite (Ca₅(PO₄)₃OH, HAP) surface for the rapid and selective adsorption of ⁹⁰Sr from groundwater. The modification was achieved by the post-substitution of cations (Na⁺, Mg²⁺, Cu²⁺, Ba²⁺, Fe³⁺, and Al³⁺) for parent Ca²⁺ within surface structure of HAP. The diffraction patterns of modified HAP showed a slight shift of the (002) peak between 25° and 27° 2θ depending the ionic radius of the substituted cation. Magnesium substituted HAP, Mg-HAP, exhibited the highest removal efficiency (>95%) for 10 ppm of Sr²⁺, which is attributable to the higher ion-exchange affinity of substituted Mg²⁺ than parent Ca²⁺ toward Sr²⁺. The results of various analyses revealed that Mg substitution dominantly occurred at the Ca^I site of HAP, which enabled the Mg-HAP to adsorb Sr²⁺ at both of Ca^I and Ca^II sites whereas bare HAP could adsorb Sr²⁺ mainly at Ca^II site. Adsorption isotherms and the kinetics of Mg-HAP for Sr²⁺ were evaluated using a bi-Langmuir isotherm and a pseudo-second-order kinetic model, which demonstrated the Mg-HAP exhibited the highest adsorption capacity (64.69 mg/g) and fastest adsorption kinetics (0.161-1.714 g/(mg·min)) than previously modified HAPs. In the presence of competing cations at circumneutral pHs, the enhanced performance of the Mg-HAP led to a greater than 97% reduction of ⁹⁰Sr (initial radioactivity = 9500 Bq/L) within 1 h. The distribution coefficient of Mg-HAP was 1.3-6.6 × 10³ mL/g while that of bare HAP was 1.2-6.6 × 10² mL/g. The findings in the present study highlight that the ion-exchange affinity of Ca^I and Ca^II sites on HAP surface plays a key-role in ⁹⁰Sr uptake. The proposed modification method can simply increase the affinity of HAP surface, therefore, this work can further improve the deployment of an in situ remediation technology for ⁹⁰Sr contaminated groundwater, i.e., Mg-HAP-based permeable reactive barrier.

Highly enhanced adsorption performance to uranium(VI) by facile synthesized hydroxyapatite aerogel

In order to protect environment and save uranium resources, it was necessary to find a highly efficient adsorbent for uranium recovery from wastewater. In this work, we used a freeze-drying-calcination method to synthesize HAP aerogel to effectively remove uranium. Compared with commercially available nano-hydroxyapatite, HAP aerogel presented better adsorption performance. This was because the as-prepared HAP aerogel presented continuous porous structure, which could provide more active sites for the adsorption to uranium. The uranium removal efficiency of HAP aerogel arrived 99.4% within 10 min and the maximum adsorption capacity was up to 2087.6 mg g^-1 at pH = 4.0 and 298 K. In addition, the immobilization of uranium on HAP aerogel was chemisorption, which was probably due to adsorption, dissolution-precipitation and ions exchange. These results indicated that the as-prepared HAP aerogel could be widely used as a high efficiency and potential adsorbent for the treatment of uranium-containing wastewater in the future.

Degradation of methylene blue using Co-dopant of Mg and Se into hydroxyapatite composite

In this work, a comparative study of different Magnesium ions content was incorporated into hydroxyapatite (HAP) modified with selenite ions aiming to develop the degradation performance of methylene blue. Although the dopant metal (Mg²⁺ ) has a relatively low ratio, it makes a change in microstructure, morphology, surface area, external surface charge, particle size, and degradation performance. The effect of magnesium and selenium binary doping on microstructural and degradation of methylene blue has been evaluated. The external surface charge measured by zeta potential clarified that the highest negativity was -11.8 mV and it was accomplished in 1.0Mg/Se-HAP. Also, the roughness average grew from 36.8 nm reaching 59.2 nm upon the additional Mg (II). Moreover, TEM micrographs showed that compositions were formed in rod shapes. The process of degradation are optimized, showing effectiveness in methylene blue (MB) degradation of 62.4 % after 150 min of exposure to visible light. Electrostatic attraction and H-bonding and coordination have a vital role in the adsorption process. The recyclability of the as-prepared compositions exhibited that the effectiveness has been reduced to be about 54.2 % after five times of re-using.

Recent Progress in the Application of Hydroxyapatite for the Adsorption of Heavy Metals from Water Matrices

Wastewater treatment remains a critical issue globally, despite various technological advancements and breakthroughs. The study of different materials and technologies gained new valences in the last years, in order to obtain cheap and efficient processes, to obtain a cleaner environment for future generations. In this context, the present review paper presents the new achievements in the materials domain with highlights on apatitic materials used for decontamination of water loaded with heavy metals. The main goal of this review is to present the adsorptive removal of heavy metals using hydroxyapatite-based adsorbents, offering a general overview regarding the recent progress in this particular area. Developing the current review, an attempt has been made to give appropriate recognition to the most recent data regarding the synthesis methods and targeted pollutants, including important information regarding the synthesis methods and precursors, morphological characteristics of the adsorbent materials and effectiveness of processes.

Fast and Efficient Removal of Uranium onto a Magnetic Hydroxyapatite Composite: Mechanism and Process Evaluation

The exploration and rational design of easily separable and highly efficient sorbents with satisfactory capability of extracting radioactive uranium (U)-containing compound(s) are of paramount significance. In this study, a novel magnetic hydroxyapatite (HAP) composite (HAP@ CoFe2O4), which was coupled with cobalt ferrite (CoFe2O4), was rationally designed for uranium(VI) removal through a facile hydrothermal process. The U(VI) ions were rapidly removed using HAP@ CoFe2O4 within a short time (i.e., 10 min), and a maximum U(VI) removal efficiency of 93.7% was achieved. The maximum adsorption capacity (Qmax) of the HAP@CoFe2O4 was 338 mg/g, which demonstrated the potential of as-prepared HAP@CoFe2O4 in the purification of U(VI) ions from nuclear effluents. Autunite [Ca(UO2)2(PO4)2(H2O)6] was the main crystalline phase to retain uranium, wherein U(VI) was effectively extracted and immobilized in terms of a relatively stable mineral. Furthermore, the reacted HAP@CoFe2O4 can be magnetically recycled. The results of this study reveal that the suggested process using HAP@CoFe2O4 is a promising approach for the removal and immobilization of U(VI) released from nuclear effluents.

Changes in adsorption mechanisms of radioactive barium, cobalt, and strontium ions using spent coffee waste biochars via alkaline chemical activation: Enrichment effects of O-containing functional groups

The single adsorption of radioactive barium (Ba(II)), cobalt (Co(II)), and strontium (Sr(II)) ions using pristine (SCWB-P) and chemically activated spent coffee waste biochars with NaOH (SCWB-A) were thoroughly explored in order to provide deeper insights into the changes in their adsorption mechanisms through alkaline chemical activation. The greater removal efficiencies of SCWB-A (76.6-97.3%) than SCWB-P (45.6-75.2%) and the consistency between the adsorptive removal patterns (Ba(II) > Sr(II) > Co(II)) and oxygen bond dissociation enthalpies (BaO (562 kJ/mol) > SrO (426 kJ/mol) > CoO (397 kJ/mol)) of radioactive species supported the assumption that the adsorption removal of radioactive species with spent coffee waste biochars highly depended on the abundances of O-containing functional groups. The calculated R² values of the pseudo-first-order (SCWB-P = 0.998-0.999; SCWB-A = 0.850-0.921) and pseudo-second-order kinetic models (SCWB-P = 0.988-0.998; SCWB-A = 0.935-0.966) are evident that the physisorption mainly controlled the adsorption of radioactive species toward SCWB-P and the chemisorption played a crucial role in their adsorptive removal with SCWB-A. From the calculated intra-particle diffusion, isotherm, thermodynamic parameters, it can be concluded that the intra-particle diffusion and monolayer adsorption primarily governed the adsorption of radioactive species using SCWB-P and SCWB-A, and their adsorption processes occurred spontaneously and endothermically. The dominant adsorption mechanism of spent coffee waste biochars was changed from physisorption (ΔH° of SCWB-P = 21.6-29.8 kJ/mol) to chemisorption (ΔH° of SCWB-A = 42.4-81.3 kJ/mol) through alkaline chemical activation. The distinctive M-OH peak in the O1s XPS spectra of SCWB-A directly corresponding to the decrease in the abundances of O-containing functional groups confirms again that the enrichment of O-containing functional groups markedly facilitated the adsorption removal of radioactive species by chemisorption occurred at the inner and outer surfaces of spent coffee waste biochars.

Facile fabrication of BiOCl nanoplates with high exposure {001} facets for efficient photocatalytic degradation of nitro explosives

BiOCl nanoplates with highly exposed {001} facets displayed excellent photocatalytic activity on the degradation of nitro explosives.

Superadsorbents for Strontium and Cesium Removal Enriched in Amidoxime by a Homo-IPN Strategy Connected with Porous Silica Texture

In light of the fact that two with good compatibility are better than one, the homo-interpenetrating polymer network (IPN) strategy was used in this work to design novel amidoxime (AOX)-interpenetrating networks into porous silica (PSi) with the final aim to enhance the sorption performances of composite sorbents toward Cs⁺ and Sr²⁺. To achieve this goal, first, a homo-IPN of poly(acrylonitrile) (PAN) was constructed inside the channels of two kinds of porous silica, one mesoporous (PSi1) and one macroporous (PSi2), the textural properties of silica being exploited in controlling the sorption performances of the composites. The novel composites were fully characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and the nitrogen sorption/desorption isotherms (Brunauer-Emmett-Teller (BET) analysis). The sorption properties of the PSi1/AOX and PSi2/AOX composite sorbents for Sr²⁺ and Cs⁺ were investigated in the batch mode to determine the effect of solution pH, contact time, initial metal ion concentration, temperature, and the presence of competitive ions on the adsorption performances. The fast kinetics of sorption was supported by the fact that ∼80% of Sr²⁺ and ∼65% of Cs⁺ were adsorbed in the first 30 min, the kinetic data being better described by the pseudo-second-order kinetic model. The experimental isotherms were well fitted by the Langmuir and Sips isotherm models. The superadsorption of Sr²⁺ and Cs⁺ is demonstrated by the values of the maximum sorption capacity of the best sorbent constructed with mesoporous silica (PSi1/IPN-AOX), which were 344.23 mg Cs⁺/g and 360.23 mg Sr²⁺/g. The sorption process was spontaneous and endothermic for both metal ions. The presence of interfering cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺), at a concentration of 10^-2 M, only slightly influenced the sorption capacity for the main cation. The composite sorbents were still highly efficient after five sorption/desorption cycles.

Brushite-infused polyacrylonitrile nanofiber adsorbent for strontium removal from water

The Fukushima Daiichi nuclear disaster and the decommissioning of over a hundred nuclear reactors worldwide led to the increase in the demand for efficient water treatment technologies to remove radionuclides, such as ⁹⁰Sr. Brushite or dicalcium phosphate dihydrate (DCPD) is a potential adsorbent to remove strontium from water. In this study, composite poly(acrylonitrile) (PAN) nanofiber (NF) adsorbents with DCPD (PAN/DCPD) were prepared, characterized, and investigated for strontium adsorption in water. Material characterization revealed mechanically suitable, hydrophilic, and macroporous composite NF adsorbents with average fiber diameters of <500 nm. As-prepared DCPD powder exhibited a superior strontium uptake capacity of 81.7 mg g^-1 at pH ≅ 10 of aqueous Sr²⁺ solution over its biogenic and synthetic predecessor, hydroxyapatite. Increased DCPD loading resulted in higher adsorption. Maximum Sr²⁺ uptake of PAN/DCPD NF with 70 wt% DCPD loading (PAN/70DCPD NF) was 146 mg g^-1 considering the Sips isotherm model. Kinetic studies revealed that Sr²⁺ removal by PAN/DCPD NF was a chemisorption process which involved ion exchange and surface complexation. PAN/70DCPD NF as a dead-end membrane filter exhibited superior removal efficiency over pure PAN NF. The overall results of this study revealed the potential application of PAN/DCPD NF adsorbent for ⁹⁰Sr removal from water.

One-pot synthesis of sodium lauryl sulfate-loaded polyacrylonitrile solid-phase extractor for investigating the adsorption behavior of radioactive strontium(II) from aqueous solutions

Sodium lauryl sulfate-loaded polyacrylonitrile (SLSLPAN) was synthesized in the present investigation using an in-situ one step process through gamma radiation-induced polymerization. The structure, composition, surface area and pore size and volume of the employed adsorbent were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption-desorption measurements. Adsorption of radioactive strontium(II) onto SLSLPAN was studied in the pH range 3-13. Batch kinetic data showed that the equilibrium was attained at 840 min and the pseudo-first-order was the best kinetic model for describing the kinetic data of the present adsorption process. The diffusion of strontium(II) into SLSLPAN was deeply studied using four diffusion models, namely, Bangham, Boyd, Weber-Morris and Mathewas-Weber models. Two-parameter (Freundlich, Langmuir and Temkin) and three-parameter (Redlich-Peterson, Toth and Generalized) isotherm models were used to analyze the adsorption equilibrium data of strontium(II) onto SLSLPAN. The maximum adsorption capacity calculated by the Generalized isotherm model is found to be 0.391 mmol strontium(II) per gram of SLSLPAN. The estimated mean free energy (E = 2.151 kJ/mol) indicated that strontium(II) radionuclides were physically adsorbed onto SLSLPAN. The value of enthalpy change (ΔH^o = 35.325 kJ/mol) and those of free energy change (ΔG^o = -15.278, -16.948, -18.619 and -20.288 at 303, 313, 323 and 333 K, respectively) confirmed that adsorption of strontium(II) radionuclides on SLSLPAN was endothermic and spontaneous process.

Mussel Shell-Derived Macroporous 3D Scaffold: Characterization and Optimization Study of a Bioceramic from the Circular Economy

Fish industry by-products constitute an interesting platform for the extraction and recovery of valuable compounds in a circular economy approach. Among them, mussel shells could provide a calcium-rich source for the synthesis of hydroxyapatite (HA) bioceramics. In this work, HA nanoparticles have been successfully synthesized starting from mussel shells (Mytilus edulis) with a two steps process based on thermal treatment to convert CaCO3 in CaO and subsequent wet precipitation with a phosphorus source. Several parameters were studied, such as the temperature and gaseous atmosphere of the thermal treatment as well as the use of two different phosphorus-containing reagents in the wet precipitation. Data have revealed that the characteristics of the powders can be tailored, changing the conditions of the process. In particular, the use of (NH4)2HPO4 as the phosphorus source led to HA nanoparticles with a high crystallinity degree, while smaller nanoparticles with a higher surface area were obtained when H3PO4 was employed. Further, a selected HA sample was synthesized at the pilot scale; then, it was employed to fabricate porous 3D scaffolds using the direct foaming method. A highly porous scaffold with open and interconnected porosity associated with good mechanical properties (i.e., porosity in the range 87-89%, pore size in the range 50-300 μm, and a compressive strength σ = 0.51 ± 0.14 MPa) suitable for bone replacement was achieved. These results suggest that mussel shell by-products are effectively usable for the development of compounds of high added value in the biomedical field.

A novel sorbent based on Ti-Ca-Mg phosphates: synthesis, characterization, and sorption properties

This work focuses on the synthesis procedure of a new sorbent based on a TiCaMg phosphate. The synthesis strategy includes stepwise interaction between solid precursors and phosphorus-containing agents. The solid precursors were ammonium titanyl sulfate and calcined dolomite, which were used as titanium, calcium, and magnesium sources. The effect of the nature and concentration of phosphoric agent on the sorbent composition and properties has been investigated using elemental analysis, TG, XRD, IR spectroscopy, BET, and SEM techniques. The novel sorbent has been demonstrated to be a composite material consisting of the following components: TiO(OH)H₂PO₄·H₂O, Ti(HPO₄)₂·H₂O, CaHPO₄·2H₂O, MgНPO₄·3H₂O, and NH₄MgPO₄·6H₂O. The ratio between these phases in the composite depends on synthesis conditions. The optimal conditions, ensuring full conversion of Ti, Ca, and Mg containing in the initial precursors into the final product, have been found. The sorption properties of the obtained composite sorbent towards Co²⁺, Cs⁺, and Sr²⁺ cations and their radionuclide analogues have been studied. The obtained data has indicated that the purification effect was based on both precipitation and ion exchange mechanism. The combined action of the individual components of the composite sorbent ensures its high sorption capacity towards different cations in a wide pH range. The new sorbent shows high sorption ability towards radionuclides in multicomponent liquid radioactive waste (LRW) systems, and the distribution coefficient of the studied radionuclides was found to be 10⁵ mL g^-1. The presence of different types of functional groups in the composite sorbent allows realizing the one-step purification process of LRW that, in turn, simplifies the sorption system design.

Unexpectedly High Adsorption Capacity of Esterified Hydroxyapatite for Heavy Metal Removal

Nanohydroxyapatite (n-HAP) as an environmentally friendly adsorbent of heavy metal ions still requires the rational design of the pore structure and surface characteristic for enhancing their adsorption capacity toward heavy metal ions. A novel one-step strategy was developed to regulate the pore structure and surface characteristic of esterified HAP (n-EHAP) nanocrystals (NCs) for enhancing the adsorption capacity by incorporation of 2-bromo-2-methylpropionate (2-BrMP) groups on the surface of n-EHAP NCs. When using water as the sole solvent, the aggregation of n-EHAP NCs became unavoidable because of incorporation of hydrophobic 2-BrMP groups on n-HAP particle surfaces. The synthesis of uniform and individual n-EHAP NCs was achieved by rational adjustment of the aqueous dispersion medium to avoid agglomeration and precipitation, which was induced by the changing surface characteristic of n-EHAP NCs during the continuing incorporation of hydrophobic 2-BrMP groups in the water/acetone system. The successful incorporation of hydrophobic 2-BrMP groups on the surface of n-EHAP NCs was characterized by X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and liquid nitrogen adsorption isotherms. To explore the potential application in water treatment, a series of systematically designed batch experiments were conducted to determine the influences of the adsorbent dosage, solution pH, and contact time on the adsorption behavior of n-EHAP NCs. Experimental results indicated that the addition of water-soluble acetone greatly promoted the formation of individual n-EHAP NCs without aggregation, and furthermore, the successful incorporation of hydrophobic 2-BrMP groups led to formation of porously structured n-EHAP NCs with a higher surface area and an increasing micro-/mesopore ratio. Compared with pristine n-HAP, n-EHAP NCs exhibited lower crystallinity with smaller crystallite size and demonstrated an ultrahigh adsorption capacity for Pb(II) in acidic solution with a record of close to 2400 mg/g. The improved performance of n-EHAP NCs originated from both the suitable porous structure with a higher micro-/mesoporosity ratio and the existing tethered 2-BrMP group-induced the ester bond, providing more adsorption active affinity sites for heavy metal ions. The highly efficient adsorption (99.99%) was further achieved using tap water spiked with traces of Pb(II) (63 ppb). The presented findings promise the application of n-EHAP NCs in water treatment as an alternative, low-cost, and ecofriendly adsorbent for environmental remediation.

Amidoxime Functionalization of Algal/Polyethyleneimine Beads for the Sorption of Sr(II) from Aqueous Solutions

There is a need for developing new sorbents that incorporate renewable resources for the treatment of metal-containing solutions. Algal-polyethyleneimine beads (APEI) (reinforced with alginate) are functionalized by grafting amidoxime groups (AO-APEI). Physicochemical characteristics of the new material are characterized using FTIR, XPS, TGA, SEM, SEM-EDX, and BET. AO-APEI beads are tested for the recovery of Sr(II) from synthetic solutions after pH optimization (≈ pH 6). Uptake kinetics is fast (equilibrium ≈ 60-90 min). Sorption isotherm (fitted by the Langmuir equation) shows remarkable sorption capacity (≈ 189 mg Sr g-1). Sr(II) is desorbed using 0.2 M HCl/0.5 M CaCl2 solution; sorbent recycling over five cycles shows high stability in terms of sorption/desorption performances. The presence of competitor cations is studied in relation to the pH; the selectivity for Sr(II) is correlated to the softness parameter. Finally, the recovery of Sr(II) is carried out in complex solutions (seawater samples): AO-APEI is remarkably selective over highly concentrated metal cations such as Na(I), K(I), Mg(II), and Ca(II), with weaker selectivity over B(I) and As(V). AO-APEI appears to be a promising material for selective recovery of strontium from complex solutions (including seawater).

Self-templated microwave-assisted hydrothermal synthesis of two-dimensional holey hydroxyapatite nanosheets for efficient heavy metal removal

Heavy metals have caused serious environmental problems and threat to human health. Ultrathin and holey two-dimensional (2D) nanosheets have recently drawn significant attention as superb adsorbent material to remove heavy metal ions due to their unique physicochemical properties. Herein, we report a self-template-directed ultrafast reaction route to synthesis porous hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanosheets via a microwave-assisted hydrothermal method using poly(allylamine hydrochloride) as an additive. The resulting hydroxyapatite nanosheets showed a high specific surface area (92.9 m² g^-1) and excellent adsorption performance for various heavy metal ions including Pb(II), Cu(II), and Cd(II), with maximum adsorption capacities of 210.5, 31.6, and 24.9 mg g^-1, respectively. The adsorption kinetics fitted well with the pseudo-second-order equation and the equilibrium data showed a high correlation coefficient with the Langmuir model. Based on the experimental results and analysis, we can conclude that the sorption of heavy metal ions with the hydroxyapatite nanosheets mainly attributes to surface complexation and cation exchange. The present synthetic strategy allows the fast and massive production of porous hydroxyapatite ultrathin nanosheets and may also potentially be applicable to the fabrication of other metal phosphates with assembled or hierarchical porous structures towards various applications such as water purification.

An ionic liquid functionalized polymer for simultaneous removal of four phenolic pollutants in real environmental samples

An ionic liquid functionalized polymer (IL-P) was prepared feasibly and simply by grafting1-butyl-3-vinylimidazolium bromide onto the silica surface. The IL-P was fully characterized, and the results showed that IL-P has a rough surface with a lower specific surface area (205.49 m² g^-1), and the involvement of ionic liquid significantly improved the adsorption performance of IL-P. The pH, initial concentration, adsorption time and temperature were investigated to discuss the adsorption behaviors of IL-P in aqueous solution. The adsorption process of 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA) and 2,4-dinitrophenol (2,4-DNP) onto IL-P better fitted the pseudo-second-order model, while that of 2-isonaphthol (2-NP) followed the pseudo-first-order model. The adsorption behaviors of IL-P towards 2,4-DCP and 2,4-DNP fitted well with Liu isotherm model, and that of BPA and 2-NP can be described by Langmuir model. The maximum adsorption capacities of 2,4-DCP, BPA, 2,4-DNP and 2-NP bound on IL-P was 239.7, 68.39, 56.86 and 64.28 mg g^-1, respectively, and the adsorption of IL-P is a spontaneous physical process. Comparing with other adsorbent, the as-prepared IL-P showed excellent recognition ability towards the phenolic compounds and can be applied to adsorb and remove trace 2,4-DCP, 2-NP, 2,4-DNP and BPA simultaneously in complicated wastewater and soil samples.