Applied Chemical Engineering

Synthesis of Hydroxyapatite/Chitosan–Glutamic Acid Nanocomposite for Highly Efficient Removal of Congo Red Dye from Water

Huda Mahdi

Department of Chemistry, College of Science, University of Thi-Qar, Al-Nasyriah, Thi Qar, 64001, Iraq

Saher Ali

Department of Chemistry, College of Science, University of Thi-Qar, Al-Nasyriah, Thi Qar, 64001, Iraq

Safa Ali

Department of Physics, College of Education, Al-Shatrah University, Al-Shatrah, Thi Qar, 64007, Iraq

DOI: https://doi.org/10.59429/ace.v9i1.5854

Keywords: Hydroxyapatite, chitosan, glutamic acid, Congo red, adsorption, isotherm, thermodynamics

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Abstract

Water pollution by synthetic dyes from industrial effluents poses serious environmental and health risks. This study reports the synthesis, characterization, and application of a novel hydroxyapatite/chitosan-glutamic acid composite (HAP-Cs-Glu) for Congo red (CR) dye removal from aqueous solutions. The composite was synthesized via chemical precipitation at 80°C and pH 10 with 5 hours aging. Characterization was performed using XRD, FESEM, TEM, BET, and FTIR techniques. XRD confirmed hydroxyapatite formation with low crystallinity and 12.27 nm average crystal size. FESEM and TEM revealed spherical particles (~45.77 nm) composed of needle-like nanocrystals. BET analysis showed a surface area of 58.958 m²/g, pore volume of 0.5538 cm³/g, and average pore diameter of 37.572 nm. FTIR confirmed successful functionalization with characteristic phosphate, amino, and carboxyl bands. Batch adsorption experiments investigated effects of contact time (15-75 min), adsorbent dose (0.03-0.15 g), pH (3-9), initial concentration (200-600 mg/L), and temperature (313-333 K). Optimum conditions were: 600 mg/L CR concentration, pH 3, 0.03 g adsorbent, 45 min contact time, and 60°C, achieving maximum adsorption capacity of 833.33 mg/g. Kinetic data followed pseudo-second-order model (R² = 0.9996). Langmuir isotherm provided better fit than Freundlich, indicating monolayer adsorption. Thermodynamic analysis revealed spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) adsorption with positive entropy change. The HAP-Cs-Glu composite demonstrates excellent potential as an eco-friendly adsorbent for CR removal from contaminated water.

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References

[1]. Tahira, I.; Aslam, Z.; Abbas, A.; Monim-Ul-Mehboob, M.; Ali, S.; Asghar, A. Adsorptive removal of acidic dye onto grafted chitosan: A plausible grafting and adsorption mechanism. Int. J. Biol. Macromol. 2019, 136, 1209–1218. https://doi.org/10.1016/j.ijbiomac.2019.06.173.

[2]. Kim, H.; Park, C.; Choi, N.; Cho, K. Congo red dye degradation using Fe-containing mineral as a reactive material derived from waste foundry dust. Environ. Sci. Pollut. Res. 2024, 31 (19), 28443–28453. https://doi.org/10.1007/s11356-024-33064-9.

[3]. Ali, N. M. Removal of (Crystal Violet, Janus Green) dyes by poly acrylic acid hydrogel beads. Univ. Thi-Qar J. Sci. 2023, 10 (1), 48–54. https://doi.org/10.32792/utq/utjsci/v10i1.925.

[4]. Ali, S. A. K. Dye removal from wastewater. IJSRSET 2017, IJSRSET1731130, 3 (5). ISSN 2395-1990 (Print); 2394-4099 (Online).

[5]. Hernández-Zamora, M.; Martínez-Jerónimo, F. Congo red dye diversely affects organisms of different trophic levels: A comparative study with microalgae, cladocerans, and zebrafish embryos. Environ. Sci. Pollut. Res. 2019, 26 (12), 11743–11755. https://doi.org/10.1007/s11356-019-04589-1.

[6]. Majeed, H. A. S. A. Synthesis, characterization, and study of the spectral and electronic properties of a new azo dyes compounds. J. Thi-Qar Sci. 2013, 4 (1). ISSN 1991-8690.

[7]. Farooq, M.; Ramli, A.; Naeem, A.; Shah, L. A.; Mahmood, T.; Tariq, M.; Khan, J.; Perveen, F.; Humayun, M. Photocatalytic degradation of Acid Yellow 17 azo dye using ZrO2–CeO2 hollow macrospheres as a catalyst. Desalin. Water Treat. 2019, 170, 318–324. https://doi.org/10.5004/dwt.2019.24685.

[8]. Obaid, H. T. Study the effect of changing positions on some of the spectral properties of the new azo dye [sodium (E)-7-amino-3-((2-(hydrogenarsonato)phenyl)diazenyl)-3-hydroxynaphthalene-1-sulfonate] and compare it with other azo dye prepared in advance [sodium (Z)-4-amino-2-((2-(hydrogenarsonato)phenyl)diazenyl)-4-hydroxynaphthalene-2-sulfonate]. J. Thi-Qar Sci. 2017, 6 (2). ISSN 1991-8690.

[9]. Siddiqui, S. I.; Allehyani, E. S.; Al-Harbi, S. A.; Hasan, Z.; Abomuti, M. A.; Rajor, H. K.; Oh, S. Investigation of Congo Red toxicity towards different living organisms: A review. Processes 2023, 11 (3), 807. https://doi.org/10.3390/pr11030807.

[10]. Rao, T. M.; Rao, V. V. B. Biosorption of Congo Red from aqueous solution by crab shell residue: A comprehensive study. SpringerPlus 2016, 5 (1). https://doi.org/10.1186/s40064-016-2113-9.

[11]. Chatterjee, S.; Lee, D. S.; Lee, M. W.; Woo, S. H. Congo red adsorption from aqueous solutions by using chitosan hydrogel beads impregnated with nonionic or anionic surfactant. Bioresour. Technol. 2009, 100 (17), 3862–3868. https://doi.org/10.1016/j.biortech.2009.03.023.

[12]. Sivarajasekar, N.; Baskar, R. Adsorption of basic red 9 on activated waste Gossypium hirsutum seeds: Process modeling, analysis and optimization using statistical design. J. Ind. Eng. Chem. 2013, 20 (5), 2699–2709. https://doi.org/10.1016/j.jiec.2013.10.058.

[13]. Velkova, Z. Y.; Kirova, G. K.; Stoytcheva, M. S.; Gochev, V. Biosorption of Congo Red and Methylene Blue by pretreated waste Streptomyces fradiae biomass—Equilibrium, kinetic and thermodynamic studies. J. Serb. Chem. Soc. 2017, 83 (1), 107–120. https://doi.org/10.2298/jsc170519093v.

[14]. Rani, K. C.; Naik, A.; Chaurasiya, R. S.; Raghavarao, K. S. M. S. Removal of toxic Congo red dye from water employing low-cost coconut residual fiber. Water Sci. Technol. 2017, 75 (9), 2225–2236. https://doi.org/10.2166/wst.2017.109.

[15]. Adly, E. R.; Shaban, M. S.; El-Sherbeeny, A. M.; Zoubi, W. A.; Abukhadra, M. R. Enhanced Congo Red adsorption and photo-Fenton oxidation over an iron-impeded geopolymer from ferruginous kaolinite: Steric, energetic, oxidation, and synergetic studies. ACS Omega 2022, 7 (35), 31218–31232. https://doi.org/10.1021/acsomega.2c03365.

[16]. Zouboulis, A.; Zamboulis, D.; Szymanska, K. Hybrid membrane processes for the treatment of surface water and mitigation of membrane fouling. Sep. Purif. Technol. 2014, 137, 43–52. https://doi.org/10.1016/j.seppur.2014.09.023.

[17]. Fowsiya, J.; Madhumitha, G.; Al-Dhabi, N. A.; Arasu, M. V. Photocatalytic degradation of Congo red using Carissa edulis extract capped zinc oxide nanoparticles. J. Photochem. Photobiol. B 2016, 162, 395–401. https://doi.org/10.1016/j.jphotobiol.2016.07.011.

[18]. Kristianto, H.; Rahman, H.; Prasetyo, S.; Sugih, A. K. Removal of Congo red aqueous solution using Leucaena leucocephala seed’s extract as natural coagulant. Appl. Water Sci. 2019, 9 (4). https://doi.org/10.1007/s13201-019-0972-2.

[19]. Rambabu, K.; Bharath, G.; Monash, P.; Velu, S.; Banat, F.; Naushad, M.; Arthanareeswaran, G.; Show, P. L. Effective treatment of dye polluted wastewater using nanoporous CaCl2 modified polyethersulfone membrane. Process Saf. Environ. Prot. 2019, 124, 266–278. https://doi.org/10.1016/j.psep.2019.02.015.

[20]. Alotaibi, N. F.; Nassar, A. M.; Alrwaili, G. M.; Elnasr, T. A. S.; Zeid, E. F. A. Selective, efficient and complete precipitation of anionic dyes in aqueous solutions using Ag@PbCO3 nanocomposite. Inorg. Nano-Met. Chem. 2019, 49 (11), 395–400. https://doi.org/10.1080/24701556.2019.1661463.

[21]. Nodehi, R.; Shayesteh, H.; Kelishami, A. R. Enhanced adsorption of congo red using cationic surfactant functionalized zeolite particles. Microchem. J. 2019, 153, 104281. https://doi.org/10.1016/j.microc.2019.104281.

[22]. Silva, E. R.; Dall’Oglio, E. L.; Vasconcelos, L. G.; Morais, E. B. Decolorization of the benzidine-based azo dye Congo red by the new strain Shewanella xiamenensis G5-03. Braz. J. Biol. 2021, 82. https://doi.org/10.1590/1519-6984.237386.

[23]. Thamer, A.N.; Turki, H.J.; Hassan, A.H.; Jasim, L.S.; Haider, M.N. Stimuli-Responsive Nano Hydrogels for Sustainable Water Pollution Reduction: A Comprehensive Review of Design, Performance, and Industrial Translation. Journal of Nanostructures 2026, 16 (1), 568-584. https://doi.org/10.22052/JNS.2026.01.051

[24]. Karimi, H.; Ghaedi, M. Application of artificial neural network and genetic algorithm to modeling and optimization of removal of methylene blue using activated carbon. J. Ind. Eng. Chem. 2013, 20 (4), 2471–2476. https://doi.org/10.1016/j.jiec.2013.10.028.

[25]. Harja, M.; Lupu, N.; Chiriac, H.; Herea, D.; Buema, G. Studies on the removal of congo red dye by an adsorbent based on Fly-Ash@Fe3O4 mixture. Magnetochemistry 2022, 8 (10), 125. https://doi.org/10.3390/magnetochemistry8100125.

[26]. Tor, A.; Cengeloglu, Y. Removal of congo red from aqueous solution by adsorption onto acid activated red mud. J. Hazard. Mater. 2006, 138 (2), 409–415. https://doi.org/10.1016/j.jhazmat.2006.04.063.

[27]. Imessaoudene, A.; Cheikh, S.; Hadadi, A.; Hamri, N.; Bollinger, J.; Amrane, A.; Tahraoui, H.; Manseri, A.; Mouni, L. Adsorption performance of zeolite for the removal of Congo red dye: Factorial design experiments, kinetic, and equilibrium studies. Separations 2023, 10 (1), 57. https://doi.org/10.3390/separations10010057.

[28]. Aminu, I.; Gumel, S. M.; Ahmad, W. A.; Idris, A. A. Adsorption isotherms and kinetic studies of Congo-Red removal from waste water using activated carbon prepared from jujube seed. Am. J. Anal. Chem. 2020, 11 (1), 47–59. https://doi.org/10.4236/ajac.2020.111004.

[29]. Javed, T.; Thumma, A.; Uddin, A. N.; Akhter, R.; Taj, M. B.; Zafar, S.; Baig, M. M.; Shah, S. S. A.; Wasim, M.; Abid, M. A.; Masood, T.; Jilani, M. I.; Batool, M. Batch adsorption study of Congo Red dye using unmodified Azadirachta indica leaves: Isotherms and kinetics. Water Pract. Technol. 2024, 19 (2), 546–566. https://doi.org/10.2166/wpt.2024.020.

[30]. Ali, I. H. Removal of congo red dye from aqueous solution using eco-friendly adsorbent of nanosilica. Baghdad Sci. J. 2021, 18 (2), 0366. https://doi.org/10.21123/bsj.2021.18.2.0366.

[31]. Ga, A. B. Hydroxyapatite-based materials for heavy metal removal in wastewater treatment. Pet. Petrochem. Eng. J. 2020, 4 (2), 1–5. https://doi.org/10.23880/ppej-16000227.

[32]. Hughes, J. M.; Rakovan, J. F. Structurally robust, chemically diverse: Apatite and apatite supergroup minerals. Elements 2015, 11 (3), 165–170. https://doi.org/10.2113/gselements.11.3.165.

[33]. Tas, A. C. Synthesis of biomimetic Ca-hydroxyapatite powders at 37 °C in synthetic body fluids. Biomaterials 2000, 21, 1429–1438.

[34]. Pokhrel, S. Hydroxyapatite: Preparation, properties and its biomedical applications. Adv. Chem. Eng. Sci. 2018, 8 (4), 225–240. https://doi.org/10.4236/aces.2018.84016.

[35]. Bose, S.; Ke, D.; Sahasrabudhe, H.; Bandyopadhyay, A. Additive manufacturing of biomaterials. Prog. Mater. Sci. 2017, 93, 45–111. https://doi.org/10.1016/j.pmatsci.2017.08.003.

[36]. Avram, A.; Frentiu, T.; Horovitz, O.; Mocanu, A.; Goga, F.; Tomoaia-Cotişel, M. Hydroxyapatite for removal of heavy metals from wastewater. Studia Univ. Babeș-Bolyai Chem. 2017, 62 (4), 93–104. https://doi.org/10.24193/subbchem.2017.4.08.

[37]. Zhou, C.; Wang, X.; Wang, Y.; Song, X.; Fang, D.; Ge, S. The sorption of single- and multi-heavy metals in aqueous solution using enhanced nano-hydroxyapatite assisted with ultrasonic. J. Environ. Chem. Eng. 2021, 9 (3), 105240. https://doi.org/10.1016/j.jece.2021.105240.

[38]. Billah, R. E. K.; Ayouch, I.; Abdellaoui, Y.; Kassab, Z.; Khan, M. A.; Agunaou, M.; Soufiane, A.; Otero, M.; Jeon, B. A novel chitosan/nano-hydroxyapatite composite for the adsorptive removal of Cd(II) from aqueous solution. Polymers 2023, 15 (6), 1524. https://doi.org/10.3390/polym15061524.

[39]. Ragab, A.; Ahmed, I.; Bader, D. The removal of Brilliant Green dye from aqueous solution using nano hydroxyapatite/chitosan composite as a sorbent. Molecules 2019, 24 (5), 847. https://doi.org/10.3390/molecules24050847.

[40]. Hou, H.; Zhou, R.; Wu, P.; Wu, L. Removal of Congo red dye from aqueous solution with hydroxyapatite/chitosan composite. Chem. Eng. J. 2012, 211–212, 336–342. https://doi.org/10.1016/j.cej.2012.09.100.

[41]. Chahkandi, M. Mechanism of Congo red adsorption on new sol-gel-derived hydroxyapatite nanoparticle. Mater. Chem. Phys. 2017, 202, 340–351. https://doi.org/10.1016/j.matchemphys.2017.09.047.

[42]. Lee, W.; Loo, C.; Van, K.; Zavgorodniy, A.; Rohanizadeh, R. Regulating protein adsorption onto hydroxyapatite: Amino acid treatment. Key Eng. Mater. 2011, 493–494, 666–671. https://doi.org/10.4028/www.scientific.net/kem.493-494.666.

[43]. Lee, W.; Loo, C.; Zavgorodniy, A. V.; Rohanizadeh, R. High protein adsorptive capacity of amino acid-functionalized hydroxyapatite. J. Biomed. Mater. Res. A 2012, 101A (3), 873–883. https://doi.org/10.1002/jbm.a.34383.

[44]. Bumajdad, A.; Hasila, P. Surface modification of date palm activated carbonaceous materials for heavy metal removal and CO2 adsorption. Arab. J. Chem. 2022, 16 (1), 104403. https://doi.org/10.1016/j.arabjc.2022.104403.

[45]. Uskoković, V.; Uskoković, D. P. Nanosized hydroxyapatite and other calcium phosphates: Chemistry of formation and application as drug and gene delivery agents. J. Biomed. Mater. Res. B 2010, 96B (1), 152–191. https://doi.org/10.1002/jbm.b.31746.

[46]. El Boujaady, H.; Mourabet, M.; EL Rhilassi, A.; Bennani-Ziatni, M.; El Hamri, R.; Taitai, A. Adsorption of a textile dye on synthesized calcium deficient hydroxyapatite (CDHAp): Kinetic and thermodynamic studies. J. Mater. Environ. Sci. 2016, 7 (11), 4049–4063.

[47]. Chen, F.; Wang, Z.-C.; Lin, C.-J. Preparation and characterization of nano-sized hydroxyapatite particles and hydroxyapatite/chitosan nanocomposite for use in biomedical materials. Mater. Lett. 2002, 57, 858–861.

[48]. Lowry, N.; Han, Y.; Meenan, B.; Boyd, A. Strontium and zinc co-substituted nanophase hydroxyapatite. Ceram. Int. 2017, 43 (15), 12070–12078. https://doi.org/10.1016/j.ceramint.2017.06.062.

[49]. Galotta, A.; Rubenis, K.; Locs, J.; Sglavo, V. M. Dissolution-precipitation synthesis and cold sintering of mussel shells-derived hydroxyapatite and hydroxyapatite/chitosan composites for bone tissue engineering. Open Ceram. 2023, 15, 100418. https://doi.org/10.1016/j.oceram.2023.100418.

[50]. Kuriakose, T.; Kalkura, S.; Palanichamy, M.; Arivuoli, D.; Dierks, K.; Bocelli, G.; Betzel, C. Synthesis of stoichiometric nanocrystalline hydroxyapatite by ethanol-based sol–gel technique at low temperature. J. Cryst. Growth 2004, 263 (1–4), 517–523. https://doi.org/10.1016/j.jcrysgro.2003.11.057.

[51]. Panda, R. N.; Hsieh, M. F.; Chung, R. J.; Chin, T. S. FTIR, XRD, SEM and solid state NMR investigations of carbonate-containing hydroxyapatite nanoparticles synthesized by hydroxide-gel technique. J. Phys. Chem. Solids 2003, 64, 193–199.

[52]. Ma, M. Hierarchically nanostructured hydroxyapatite: Hydrothermal synthesis, morphology control, growth mechanism, and biological activity. Int. J. Nanomedicine 2012, 1781. http://dx.doi.org/10.2147/IJN.S29884.

[53]. Dreghici, D. B.; Butoi, B.; Predoi, D.; Iconaru, S. L.; Stoican, O.; Groza, A. Chitosan–hydroxyapatite composite layers generated in radio frequency magnetron sputtering discharge: From plasma to structural and morphological analysis of layers. Polymers 2020, 12 (12), 3065. https://doi.org/10.3390/polym12123065.

[54]. Drabczyk, A.; Kudłacik-Kramarczyk, S.; Głąb, M.; Kędzierska, M.; Jaromin, A.; Mierzwiński, D.; Tyliszczak, B. Physicochemical investigations of chitosan-based hydrogels containing aloe vera designed for biomedical use. Materials 2020, 13 (14), 3073. https://doi.org/10.3390/ma13143073.

[55]. Gadda, N.; Benabdallah, G. A.; et al. Investigation of equilibrium and kinetics in the removal of Methylene Blue from aqueous solutions using Chamaerops humilis fruit. Morocc. J. Chem. 2024, 12 (4), 1446–1461. https://doi.org/10.48317/IMIST.PRSM/morjchem-v12i4.46755.

[56]. Chen, Q.; He, Q.; Lv, M.; Xu, Y.; Yang, H.; Liu, X.; Wei, F. Selective adsorption of cationic dyes by UiO-66-NH2. Appl. Surf. Sci. 2014, 327, 77–85. https://doi.org/10.1016/j.apsusc.2014.11.103.

[57]. Bhattacharyya, K. G.; Gupta, S. S. Adsorptive accumulation of Cd(II), Co(II), Cu(II), Pb(II), and Ni(II) from water on montmorillonite: Influence of acid activation. J. Colloid Interface Sci. 2007, 310 (2), 411–424. https://doi.org/10.1016/j.jcis.2007.01.080.

[58]. Mohammad, A. M.; Eldin, T. A. S.; Hassan, M. A.; El-Anadouli, B. E. Efficient treatment of lead-containing wastewater by hydroxyapatite/chitosan nanostructures. Arab. J. Chem. 2015, 10 (5), 683–690. https://doi.org/10.1016/j.arabjc.2014.12.016.

[59]. Adeogun, A. I.; Babu, R. B. One-step synthesized calcium phosphate-based material for the removal of alizarin S dye from aqueous solutions: Isothermal, kinetics, and thermodynamics studies. Appl. Nanosci. 2015, 11 (7), 1–13. https://doi.org/10.1007/s13204-015-0484-9.

[60]. Mall, I.; Srivastava, V.; Kumar, G.; Mishra, I. Characterization and utilization of mesoporous fertilizer plant waste carbon for adsorptive removal of dyes from aqueous solution. Colloids Surf. A 2006, 278 (1–3), 175–187. https://doi.org/10.1016/j.colsurfa.2005.12.017.

[61]. Sakkayawong, N.; Thiravetyan, P.; Nakbanpote, W. Adsorption mechanism of synthetic reactive dye wastewater by chitosan. J. Colloid Interface Sci. 2005, 286 (1), 36–42. https://doi.org/10.1016/j.jcis.2005.01.020.

[62]. Kaur, S.; Rani, S.; Mahajan, R. K. Adsorption kinetics for the removal of hazardous dye congo red by biowaste materials as adsorbents. J. Chem. 2013, 628582. https://doi.org/10.1155/2013/628582.

[63]. Chiou, M.; Li, H. Equilibrium and kinetic modeling of adsorption of reactive dye on cross-linked chitosan beads. J. Hazard. Mater. 2002, 93 (2), 233–248. https://doi.org/10.1016/S0304-3894(02)00030-4.

[64]. Wong, S.; Tumari, H. H.; Ngadi, N.; Mohamed, N. B.; Hassan, O.; Mat, R.; Amin, N. A. S. Adsorption of anionic dyes on spent tea leaves modified with polyethyleneimine (PEI-STL). J. Clean. Prod. 2018, 206, 394–406. https://doi.org/10.1016/j.jclepro.2018.09.201.

[65]. Duranoğlu, D.; Trochimczuk, A. W.; Beker, U. Kinetics and thermodynamics of hexavalent chromium adsorption onto activated carbon derived from acrylonitrile-divinylbenzene copolymer. Chem. Eng. J. 2012, 187, 193–202. https://doi.org/10.1016/j.cej.2012.01.120.

[66]. Mahmoodi, N. M.; Sadeghi, U.; Maleki, A.; Hayati, B.; Najafi, F. Synthesis of cationic polymeric adsorbent and dye removal isotherm, kinetic and thermodynamic. J. Ind. Eng. Chem. 2013, 20 (5), 2745–2753. https://doi.org/10.1016/j.jiec.2013.11.002.

[67]. Gerçel, Ö.; Özcan, A.; Özcan, A. S.; Gerçel, H. F. Preparation of activated carbon from a renewable bio-plant of Euphorbia rigida by H2SO4 activation and its adsorption behavior in aqueous solutions. Appl. Surf. Sci. 2006, 253 (11), 4843–4852. https://doi.org/10.1016/j.apsusc.2006.10.053.

[68]. Al-Harby, N. F.; Albahly, E. F.; Mohamed, N. A. Kinetics, isotherm and thermodynamic studies for efficient adsorption of Congo Red dye from aqueous solution onto novel cyanoguanidine-modified chitosan adsorbent. Polymers 2021, 13 (24), 4446. https://doi.org/10.3390/polym13244446.

[69]. Mondal, N. K.; Samanta, A.; Chakraborty, S.; Shaikh, W. A. Enhanced chromium(VI) removal using banana peel dust: Isotherms, kinetics and thermodynamics study. Sustain. Water Resour. Manag. 2017, 4 (3), 489–497. https://doi.org/10.1007/s40899-017-0130-7.

[70]. El-Sharkawy, R.; El-Ghamry, H. A. Multi-walled carbon nanotubes decorated with Cu(II) triazole Schiff base complex for adsorptive removal of synthetic dyes. J. Mol. Liq. 2019, 282, 515–526. https://doi.org/10.1016/j.molliq.2019.02.137.

[71]. Vijayakumar, G.; Tamilarasan, R.; Dharmendirakumar, M. Adsorption, kinetic, equilibrium and thermodynamic studies on the removal of basic dye Rhodamine-B from aqueous solution by the use of natural adsorbent perlite. J. Mater. Environ. Sci. 2012, 3 (1), 157–170.

[72]. Mkelemi, M.; Mwaijengo, G. N.; Rwiza, M. “Tree of life”: How baobab seeds-derived biochar could lead to water safety for underprivileged communities through heavy metal (Fe) removal – SDG 6. Environ. Sci. Adv. 2024. https://doi.org/10.1039/d4va00205a.

[73]. Sobhi, H. R.; Yeganeh, M.; Ghambarian, M.; Fallah, S.; Esrafili, A. A new MOF-based modified adsorbent for the efficient removal of Hg(II) ions from aqueous media: Isotherms and kinetics. RSC Adv. 2024, 14 (24), 16617–16623. https://doi.org/10.1039/d4ra00770k.

[74]. Wu, X.; Hui, K.; Hui, K.; Lee, S.; Zhou, W.; Chen, R.; Hwang, D.; Cho, Y.; Son, Y. Adsorption of basic yellow 87 from aqueous solution onto two different mesoporous adsorbents. Chem. Eng. J. 2011, 180, 91–98. https://doi.org/10.1016/j.cej.2011.11.009.

[75]. Massad, Y.; Hanbali, G.; Jodeh, S.; Hamed, O.; Bzour, M.; Dagdag, O.; Samhan, S. The efficiency of removal of organophosphorus malathion pesticide using functionalized multi-walled carbon nanotube: Impact of dissolved organic matter (DOM). Sep. Sci. Technol. 2021, 57 (1), 1–12. https://doi.org/10.1080/01496395.2021.1881118.

[76]. Hanbali, G.; Jodeh, S.; Hamed, O.; Bol, R.; Khalaf, B.; Qdemat, A.; Samhan, S. Enhanced ibuprofen adsorption and desorption on synthesized functionalized magnetic multiwall carbon nanotubes from aqueous solution. Materials 2020, 13 (15), 3329. https://doi.org/10.3390/ma13153329.