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<p>In this study, the biosorption of methyl violet (MV) onto waste eggshells (ES) and hydroxyapatite (HAp), which was synthesized from these eggshells using chemical precipitation methods, was investigated for dye removal. Converting these materials into recyclable and cost-effective biosorbents offers long-term benefits. Optimum conditions (pH, biosorbent amount, contact time, temperature, and initial concentration) were obtained by using the central composite design method. Characterization of biosorbents was analyzed by X-ray diffraction, Fourier transform infrared, and scanning electron microscopy. The maximum biosorption capacities (<i>q</i><sub>max</sub>) of ES and HAp are 24.916&#xa0;mg/g and 47.069&#xa0;mg/g, respectively. The fitting isotherm model for ES was determined to be Langmuir while for HAp Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherm models were determined. It can be said that the kinetic model suitable for biosorbents is the pseudo-second-order kinetic model. Thermodynamic analysis showed that biosorption onto ES was spontaneous and endothermic (<i>ΔH</i>° = 86.52&#xa0;kJ/mol), while the biosorption onto HAp was spontaneous and slightly exothermic (<i>ΔH</i>° = −0.99&#xa0;kJ/mol). The <i>ΔG</i>° values ranged from −8.66 to −6.57&#xa0;kJ/mol for ES and −9.08 to −8.36&#xa0;kJ/mol for HAp across the studied temperature range (30–45&#xa0;°C), confirming the favorable nature of the biosorption processes. Phytotoxicity tests showed that biosorption significantly reduced the toxicity of MV solutions, and desorption studies demonstrated that both biosorbents could be reused for at least seven cycles with minimal capacity loss. These findings in this study enabled further explorations highlight the potential application of waste-derived ES and HAp as low-cost, efficient biosorbents for dye removal.</p>

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Methyl Violet Biosorption by Biochar Prepared from Synthesis of Hydroxyapatite Using Waste Eggshells: Kinetic, Equilibrium, Thermodynamics and Toxicity Studies

  • 期刊论文

  • 发表日期：

    2025年7月29日

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  • Nur Bayram,
  • Semra Malkoc,
  • Sedef Dikmen

摘要

In this study, the biosorption of methyl violet (MV) onto waste eggshells (ES) and hydroxyapatite (HAp), which was synthesized from these eggshells using chemical precipitation methods, was investigated for dye removal. Converting these materials into recyclable and cost-effective biosorbents offers long-term benefits. Optimum conditions (pH, biosorbent amount, contact time, temperature, and initial concentration) were obtained by using the central composite design method. Characterization of biosorbents was analyzed by X-ray diffraction, Fourier transform infrared, and scanning electron microscopy. The maximum biosorption capacities (qmax) of ES and HAp are 24.916 mg/g and 47.069 mg/g, respectively. The fitting isotherm model for ES was determined to be Langmuir while for HAp Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherm models were determined. It can be said that the kinetic model suitable for biosorbents is the pseudo-second-order kinetic model. Thermodynamic analysis showed that biosorption onto ES was spontaneous and endothermic (ΔH° = 86.52 kJ/mol), while the biosorption onto HAp was spontaneous and slightly exothermic (ΔH° = −0.99 kJ/mol). The ΔG° values ranged from −8.66 to −6.57 kJ/mol for ES and −9.08 to −8.36 kJ/mol for HAp across the studied temperature range (30–45 °C), confirming the favorable nature of the biosorption processes. Phytotoxicity tests showed that biosorption significantly reduced the toxicity of MV solutions, and desorption studies demonstrated that both biosorbents could be reused for at least seven cycles with minimal capacity loss. These findings in this study enabled further explorations highlight the potential application of waste-derived ES and HAp as low-cost, efficient biosorbents for dye removal.