Synthesis of Hydroxyapatite Porous Microspheres forEfficient Adsorption of Copper Ion from Water

Abstract

Copper is a common heavymetal contamination source for water bodies, and achieving sustainable andcost-effective removal of Cu²⁺ from Cu-containing wastewater remainsa challenge. In this study, an economical and eco-friendly adsorbent-hydroxyapatite (HA) porous microspheres-was synthesized via a simple one-step hydrothermal method. Adsorption experiments demonstratedthat the maximum adsorption capacity of HA porous microspheres for Cu²⁺ is 116 mg/g, approximately 3.74 times that of reported HA nanosheet adsorbents.The adsorption process follows the pseudo-second-order kinetic model and theSips isotherm model. Thecorrelation coefficient R² = 0.9997. Linear fitting of the amounts of Cu²⁺ removed and Ca²⁺ leached at the same time revealed an R² value as high as0.997, indicating that ion exchange is the dominant adsorption mechanism.Therefore, the excellent adsorption performance is attributed to the highspecific surface area (207 m²/g) and mesoporous structure ofthe spherical HA adsorbent, which provides abundant active sites and promotesefficient ion diffusion. These structural advantagessignificantly enhanced the two primary adsorption mechanisms: ion exchange andsurface complexation. Furthermore, the effects of adsorbent dosage, solutionpH, reaction time, initial Cu²⁺ concentration, and temperature onadsorption performance were systematically investigated. Finally, the adsorption mechanism wasinvestigated by characterizing the adsorbed material using XRD, FTIR, and XPS.It was determined that ion exchange, complexation, and electrostatic attraction are the main adsorptionmechanisms.This study enhances the adsorptioncapacity of HA materials for Cu²⁺ by controlling morphology,offering new perspectives for developing high-performance, economical,eco-friendly, and sustainable adsorbents.

Keywords

Adsorption / Hydroxyapatite / Heavy metal / Ion exchange / Microsphere

Statement of the Use of Generative AI and AI-Assisted Technologies in the Writing Process

During the preparation of this manuscript, the authors used DeepSeek in order to improve the readability and language quality of the manuscript. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.

Author Contributions

Conceptualization, Q.Z.; Methodology, T.D.; Software, T.D.; Validation, R.C., J.Y. and W.Y.; Formal Analysis, T.D.; Investigation, T.D.; Resources, Q.Z.; Data Curation, T.D.; Writing—Original Draft Preparation, T.D.; Writing—Review & Editing, Z.H.; Visualization, J.Y.; Supervision, Q.Z.; Project Administration, R.C.; Funding Acquisition, Q.Z.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Funding

The financial support from Natural Science Foundation of Hubei Province (No. 2024AFD141 and 2024AFD146) is acknowledged. The financial support from National Natural Science Foundation of China through grant No. 52372120 is acknowledged. This work was supported by the Wuhan Institute of Technology startup funding (No. 23QD40). This work was financially supported by the research funds of Key Laboratory of Textile Fiber and Products (Ministry of Education) through grant No. Fzxw2024009. This work was supported by Ministry of Education’s Industry-University-Research Collaborative Education Program (No. 2408074419).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

[1] Ma WC, Han R, Zhang W, Zhang H, Chen L, Zhu L. Magnetic biochar enhanced copper immobilization in agricultural lands: Insights from adsorption precipitation and redox. J. Environ. Manage.2024, 352, 120058. DOI:10.1016/j.jenvman.2024.120058

[2] Ozdemir S, Turkan Z, Kilinc E, Bayat R, Soylak M, Sen F. Preconcentrations of Cu (II) and Mn (II) by magnetic solid-phase extraction on Bacillus cereus loaded γ-Fe₂O₃ nanomaterials. Environ. Res. 2022, 209, 112766. DOI: 10.1016/j.envres.2022.112766

[3] Hopkins DT, MacQuarrie S, Hawboldt KA. Removal of copper from sulfate solutions using biochar derived from crab processing by-product. J. Environ. Manage. 2022, 303, 114270. DOI: 10.1016/j.jenvman.2021.114270

[4] Wei YF, Chen T, Qiu ZY, Liu H, Xia Y, Wang Z, et al. Enhanced lead and copper removal in wastewater by adsorption onto magnesium oxide homogeneously embedded hierarchical porous biochar. Bioresour. Technol. 2022, 365, 128146. DOI: 10.1016/j.biortech.2022.128146

[5] Shrestha R, Ban S, Devkota S, Sharma S, Joshi R, Tiwari AP, et al. Technological trends in heavy metals removal from industrial wastewater: A review. J. Environ. Chem. Eng. 2021, 9, 105688. DOI: 10.1016/j.jece.2021.105688

[6] Babeker TMA, Lv S, Khalil MN, Hao Z, Chen Q. Biochar modified by ammonium pyrrolidine dithiocarbamate for high selective adsorption of copper in wastewater. Sep. Purif. Technol. 2025, 354, 129436. DOI: 10.1016/j.seppur.2024.129436

[7] Lin SY, Liu XY, Ma HQ, Liu YZ, Wang Y, Liu H, et al. Fe/Mn/Zr ternary electrode facilitates ultra-low-resistance electrocatalysis for closed-loop electrochemical removal of heavy metals from industrial wastewater. Chem. Eng. J. 2025, 525, 170397. DOI: 10.1016/j.cej.2025.170397

[8] Cao QQ, Huang ZH, Liu SG, Wu YP. Potential of Punica granatum biochar to adsorb Cu (II) in soil. Sci. Rep. 2019, 9, 11116. DOI: 10.1038/s41598-019-46983-2

[9] Shen XY, Chi YK, Xiong KN. The effect of heavy metal contamination on humans and animals in the vicinity of a zinc smelting facility. PLoS ONE 2019, 14, e0207423. DOI: 10.1371/journal.pone.0207423

[10] Pu XQ, Yao L, Yang L, Jiang WJ, Jiang X. Utilization of industrial waste lithium-silicon-powder for the fabrication of novel nap zeolite for aqueous Cu (II) removal. J. Clean. Prod. 2020, 265, 121822. DOI: 10.1016/j.jclepro.2020.121822

[11] Guemiza K, Coudert L, Metahni S, Mercier G, Besner S, Blais J-F. Treatment technologies used for the removal of As, Cr, Cu, PCP and/or PCDD/F from contaminated soil: A review. J. Hazard. Mater. 2017, 333, 194-214. DOI: 10.1016/j.jhazmat.2017.03.021

[12] Wang C, Xiong C, He YL, Yang C, Li X, Zheng J, et al. Facile preparation of magnetic Zr-MOF for adsorption of Pb (II) and Cr (VI) from water: Adsorption characteristics and mechanisms. Chem. Eng. J. 2021, 415, 128923. DOI: 10.1016/j.cej.2021.128923

[13] Zhang Z, Wang T, Zhang HX, Liu Y, Xing B. Adsorption of Pb (II) and Cd (II) by magnetic activated carbon and its mechanism. Sci. Total Environ. 2021, 757, 143910. DOI: 10.1016/j.scitotenv.2020.143910

[14] White RL, White CM, Turgut H, Massoud A, Tian ZR. Comparative studies on copper adsorption by graphene oxide and functionalized graphene oxide nanoparticles. J. Taiwan Inst. Chem. Eng. 2018, 85, 18-28. DOI: 10.1016/j.jtice.2018.01.036

[15] Rodríguez RP, Alfonso Herrera LÁ, Cervantes JM, Tapia AM, Chiñas Rojas LE, Rivera Villanueva JM. Highly efficient adsorption of aqueous heavy metals by Co-derived metal-organic framework. Synergistic mechanism for enhanced water purification. J. Solid State Chem. 2024, 338, 124833. DOI: 10.1016/j.jssc.2024.124833

[16] Nasir A, Inaam-ul-Hassan M, Raza A, Tahir M, Yasin T. Removal of copper using chitosan beads embedded with amidoxime grafted graphene oxide nanohybids. Int. J. Biol. Macromol. 2022, 222, 750-758. DOI: 10.1016/j.ijbiomac.2022.09.188

[17] Li ZL, Qiu Y, Zhao DY, Li J, Li G, Jia H, et al. Application of apatite particles for remediation of contaminated soil and groundwater: A review and perspectives. Sci. Total Environ. 2023, 904, 166918. DOI: 10.1016/j.scitotenv.2023.166918

[18] Zhou CL, Zhou QQ, Yu Y, Ge SF. Spongy magnetic hydroxyapatite for the enhanced Pb²⁺ removal and its dynamic sorption mechanism. J. Environ. Chem. Eng. 2023, 11, 110213. DOI: 10.1016/j.jece.2023.110213

[19] Ibrahim M, Labaki M, Giraudon J-M, Lamonier J-F. Hydroxyapatite, a multifunctional material for air, water and soil pollution control: A review. J. Hazard. Mater. 2020, 383, 121139. DOI: 10.1016/j.jhazmat.2019.121139

[20] Wang T, Cao WY, Dong K, Li H, Wang D, Xu Y. Hydroxyapatite and its composite in heavy metal decontamination: Adsorption mechanisms, challenges, and future perspective. Chemosphere 2024, 352, 141367. DOI: 10.1016/j.chemosphere.2024.141367

[21] Wu HY, Ling LB, Wang T, Dong K, Xu Y, Yu G, et al. Temperature-Directed Morphological Tuning of Hydroxyapatite Nanowires and Dual-Stage Mechanism for Pb (II) Adsorption. Environ. Res. 2025, 287, 123145. DOI: 10.1016/j.envres.2025.123145

[22] Su YP, Wang J, Li S, Zhu JH, Liu WS, Zhang ZT. Self-templated microwave-assisted hydrothermal synthesis of two-dimensional holey hydroxyapatite nanosheets for efficient heavy metal removal. Environ. Sci. Pollut. Res. 2019, 26, 30076-30086. DOI: 10.1007/s11356-019-06160-4

[23] Lebre F, Sridharan R, Sawkins MJ, Kelly DJ, O’Brien FJ, Lavelle EC. The shape and size of hydroxyapatite particles dictate inflammatory responses following implantation. Sci. Rep. 2017, 7, 2922. DOI: 10.1038/s41598-017-03086-0

[24] Chen BY, Li CX, Song JQ, Dai XZ, Lu ZQ, Zhou ZH, et al. Removal of Cl-from contaminated acid by resin adsorption: Kinetics, isothermal model, approximate site energy distribution and adsorption mechanism. J. Environ. Chem. Eng. 2025, 13, 116656. DOI: 10.1016/j.jece.2025.116656

[25] Cheng XK, Huang ZL, Li JQ, Liu Y, Chen C, Chi R-A, et al. Self-assembled growth and pore size control of the bubble-template porous carbonated hydroxyapatite microsphere. Cryst. Growth Des. 2010, 10, 1180-1188. DOI: 10.1021/cg901088c

[26] Wang YC, Dai HL, Li ZH, Meng Z-Y, Xiao Y, Zhao Z. Mesoporous polydopamine-coated hydroxyapatite nano-composites for ROS-triggered nitric oxide-enhanced photothermal therapy of osteosarcoma. J. Mater. Chem. B 2021, 9, 7401-7408. DOI: 10.1039/D1TB01084K

[27] Stötzel C, Müller F, Reinert F, Niederdraenk F, Barralet J, Gbureck U. Ion adsorption behaviour of hydroxyapatite with different crystallinities. Colloids Surf. B 2009, 74, 91-95. DOI: 10.1016/j.colsurfb.2009.06.031

[28] Irawan V, Akaike K, Mizuno HL, Anraku Y, Sotome S, Okawa A, et al. Comparative study on the sintered porous A-type carbonate apatite, B-type carbonate apatite, and hydroxyapatite. J. Am. Ceram. Soc. 2025, 108, e20389. DOI: 10.1111/jace.20389

[29] Zhang JY, Xia X, Zeng LR, Zeng SY, Li KQ, Fang ZK, et al. New insights into the co-pyrolysis synergistic effect of pig bone-derived natural hydroxyapatite and sodium-rich Spartina alterniflora on forming highly active heterostructure sites for enhanced Cu²⁺ removal. Sep. Purif. Technol. 2025, 364, 132512. DOI: 10.1016/j.seppur.2025.132512

[30] Valenzuela EI, Sánchez-Urzúa JM, Mendoza PGY, Navarro-Márquez M, Zayas-Olivares A, Gutiérrez-Uribe JA, et al. Recovery of calcium from maize Lime-Cooking wastewater as hydroxyapatite for biomedical applications. Sep. Purif. Technol. 2025, 365, 132777. DOI: 10.1016/j.seppur.2025.132777

[31] Jung K-W, Lee SY, Choi J-W, Lee YJ. A facile one-pot hydrothermal synthesis of hydroxyapatite/biochar nanocomposites: Adsorption behavior and mechanisms for the removal of copper (II) from aqueous media. Chem. Eng. J. 2019, 369, 529-541. DOI: 10.1016/j.cej.2019.03.102

[32] Yang X, Zhang XL, Wang ZW, Li S, Zhao J, Liang G, et al. Mechanistic insights into removal of norfloxacin from water using different natural iron ore–biochar composites: more rich free radicals derived from natural pyrite-biochar composites than hematite-biochar composites. Appl. Catal. B Environ. 2019, 255, 117752. DOI: 10.1016/j.apcatb.2019.117752

[33] Allen SJ, Mckay G, Porter JF. Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems. J. Colloid Interface Sci. 2004, 280, 322-333. DOI: 10.1016/j.jcis.2004.08.078

[34] Syafiuddin A, Salmiati S, Jonbi J, Fulazzaky MA. Application of the kinetic and isotherm models for better understanding of the behaviors of silver nanoparticles adsorption onto different adsorbents. J. Environ. Manage. 2018, 218, 59-70. DOI: 10.1016/j.jenvman.2018.03.066

[35] Dwivedi AD, Dubey SP, Gopal K, Sillanpää M. Strengthening adsorptive amelioration: Isotherm modeling in liquid phase surface complexation of Pb (II) and Cd (II) ions. Desalination 2011, 267, 25-33. DOI: 10.1016/j.desal.2010.09.002

[36] Du BY, Chai LF, Li W, Wang X, Chen XH, Zhou JH, et al. Preparation of functionalized magnetic graphene oxide/lignin composite nanoparticles for adsorption of heavy metal ions and reuse as electromagnetic wave absorbers. Sep. Purif. Technol. 2022, 297, 121509. DOI: 10.1016/j.seppur.2022.121509

[37] Lü LL, Jiang XJ, Jia L, Ai T, Wu H. Kinetic and thermodynamic studies on adsorption of Cu²⁺, Pb²⁺, methylene blue and malachite green from aqueous solution using AMPS-modified hazelnut shell powder. Chem. Res. Chin. Univ. 2017, 33, 112-118. DOI: 10.1007/s40242-017-6243-6

[38] Günay A, Arslankaya E, Tosun I. Lead removal from aqueous solution by natural and pretreated clinoptilolite: Adsorption equilibrium and kinetics. J. Hazard. Mater. 2007, 146, 362-371. DOI: 10.1016/j.jhazmat.2006.12.034

[39] Shi TZ, Xie ZF, Zhu Z, Shi W, Liu Y, Liu M. Highly efficient and selective adsorption of heavy metal ions by hydrazide-modified sodium alginate. Carbohydr. Polym. 2022, 276, 118797. DOI: 10.1016/j.carbpol.2021.118797

[40] Zhang JY, Xia X, Li KQ, Shen YF, Xue Y. New insights into temperature-induced mechanisms of copper adsorption enhancement on hydroxyapatite-in situ self-doped fluffy bread-like biochar. Chem. Eng. J. 2024, 479, 147657. DOI: 10.1016/j.cej.2023.147657

[41] Bazargan-Lari R, Zafarani HR, Bahrololoom ME, Nemati A. Removal of Cu (II) ions from aqueous solutions by low-cost natural hydroxyapatite/chitosan composite: Equilibrium, kinetic and thermodynamic studies. J. Taiwan Inst. Chem. Eng. 2014, 45, 1642-1648. DOI: 10.1016/j.jtice.2013.11.009

[42] Liu XF, Yin H, Liu H, Cai YH, Qi X, Dang Z. Multicomponent adsorption of heavy metals onto biogenic hydroxyapatite: Surface functional groups and inorganic mineral facilitating stable adsorption of Pb (Ⅱ). J. Hazard. Mater. 2023, 443, 130167. DOI: 10.1016/j.jhazmat.2022.130167

[43] Dou DT, Wei DL, Guan X, Liang ZJ, Lan LH, Lan XD, et al. Adsorption of copper (II) and cadmium (II) ions by in situ doped nano-calcium carbonate high-intensity chitin hydrogels. J. Hazard. Mater. 2022, 423, 127137. DOI: 10.1016/j.jhazmat.2021.127137

[44] Yin H, Xiong QQ, Zhang M, Wang BW, Zhang FG. Multi-principles analysis of Cu (II) adsorption in water on magnetic microspheres and modified Chitosan. J. Environ. Chem. Eng. 2023, 11, 111285. DOI: 10.1016/j.jece.2023.111285

[45] Marrane SE, Danoun K, Allouss D, Sair S, Channab B-E, Rhihil A, et al. A novel approach to prepare cellulose-g-hydroxyapatite originated from natural sources as an efficient adsorbent for heavy metals: Batch adsorption optimization via response surface methodology. ACS Omega 2022, 7, 28076-28092. DOI: 10.1021/acsomega.2c02108

[46] Gibert O, Valderrama C, Martínez MM, Darbra RM, Moncunill JO, Martí V. Hydroxyapatite coatings on calcite powder for the removal of heavy metals from contaminated water. Water 2021, 13, 1493. DOI: 10.3390/w13111493

[47] Chen YN, Li ML, Li YP, Liu YH, Chen YR, Li H, et al. Hydroxyapatite modified sludge-based biochar for the adsorption of Cu²⁺ and Cd²⁺: Adsorption behavior and mechanisms. Bioresour. Technol. 2021, 321, 124413. DOI: 10.1016/j.biortech.2020.124413

[48] Ma N, Li K, Xu B, Tian HF, Ma SB, Li JL, et al. Zein/polyvinyl alcohol-based electrospun nanofibrous films reinforced with nano-hydroxyapatite for efficient Cu (II) adsorption. J. Appl. Polym. Sci. 2024, 141, e55086. DOI: 10.1002/app.55086

[49] Yamsomphong K, Xu H, Yang P, Setyawan MIB, Yotpanya N, Yokoi T, et al. Excellent but strange adsorption performance of shrimp shell-derived adsorbent for anionic pollutant removal. Chem. Eng. J. 2025, 515, 163683. DOI: 10.1016/j.cej.2025.163683

[50] Kayalvizhi K, Alhaji N, Saravanakkumar D, Mohamed SB, Kaviyarasu K, Ayeshamariam A, et al. Adsorption of copper and nickel by using sawdust chitosan nanocomposite beads–A kinetic and thermodynamic study. Environ. Res. 2022, 203, 111814. DOI: 10.1016/j.envres.2021.111814

[51] Liao J, Xiong T, Ding L, Xie Y, Zhang Y, Zhu W. Design of a renewable hydroxyapatite-biocarbon composite for the removal of uranium (VI) with high-efficiency adsorption performance. Biochar 2022, 4, 29. DOI: 10.1007/s42773-022-00154-1

[52] Pavithra S, Thandapani G, Alkhamis HH, Alrefaei AF, Almutairi MH. Batch adsorption studies on surface tailored chitosan/orange peel hydrogel composite for the removal of Cr (VI) and Cu (II) ions from synthetic wastewater. Chemosphere 2021, 271, 129415. DOI: 10.1016/j.chemosphere.2020.129415

[53] Xu CQ, Liu Q, Han YW, Hu S, Xu S. Efficient adsorption of Cu²⁺ using ZnCo bimetallic organic frameworks loaded cellulose-based modified aerogel: Adsorption behavior and mechanism. Environ. Res. 2025, 269, 120877. DOI: 10.1016/j.envres.2025.120877

[54] Xiao X, Yang L, Zhou DL, Zhou JB, Tian YP, Song CS, et al. Magnetic γ-Fe₂O₃/Fe-doped hydroxyapatite nanostructures as high-efficiency cadmium adsorbents. Colloid Surf. Physicochem. Eng. Asp. 2018, 555, 548-557. DOI: 10.1016/j.colsurfa.2018.07.036

[55] Zhan YH, Lin JW, Li J. Preparation and characterization of surfactant-modified hydroxyapatite/zeolite composite and its adsorption behavior toward humic acid and copper (II). Environ. Sci. Pollut. Res. 2013, 20, 2512-2526. DOI: 10.1007/s11356-012-1136-1

[56] Yang L, Wei ZG, Zhong WH, Cui J, Wei W. Modifying hydroxyapatite nanoparticles with humic acid for highly efficient removal of Cu (II) from aqueous solution. Colloid Surf. Physicochem. Eng. Asp. 2016, 490, 9-21. DOI: 10.1016/j.colsurfa.2015.11.039

[57] Liao J, Ding L, Zhang Y, Zhu W. Efficient removal of uranium from wastewater using pig manure biochar: Understanding adsorption and binding mechanisms. J. Hazard. Mater. 2022, 423, 127190. DOI: 10.1016/j.jhazmat.2021.127190

[58] Zheng T, Wang T, Ma RQ, Liu W, Cui F, Sun W. Influences of isolated fractions of natural organic matter on adsorption of Cu (II) by titanate nanotubes. Sci. Total Environ. 2019, 650, 1412-1418. DOI: 10.1016/j.scitotenv.2018.09.152