This study presents the utilization of Fe3O4-doped black tea waste (TW) as an efficient, sustainable, and cost-effective adsorbent for the extraction of MB dye from wastewater, alongside the formulation of composite microbeads created by incorporating varying ratios of the black tea-magnetite mixture into sodium alginate (SA), a natural biopolymer. The characterization of composite microbeads was performed using FTIR-ATR, SEM, EDX, and pHpzc analyses. The surface charge of the adsorbent surface was determined as 6.43 from pHpzc. From the optimum condition studies, the contact time (60 min), adsorbent dosage (0.1 g/50 mL), and the initial pH (≅ 7) were determined. The raw data were utilized in various non-linear isotherm and kinetic models. The correlation coefficients and error functions indicated that the Langmuir model is the most suitable isotherm model for the adsorption process, with a maximum adsorption capacity of 41.28 mg g−1 for the SA/TW/Fe3O4/30 composite microspheres at 298 K. The kinetic and error results indicated that the process adhered to a pseudo-second-order kinetic model. The thermodynamic characteristics indicated that the adsorption process was spontaneous (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10661_2025_14107_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="106" /> </InlineMediaObject> <EquationSource Format="TEX">${\Delta G}^{o}=-25.09$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi mathvariant="normal">Δ</mi> <mi>G</mi> </mrow> <mi>o</mi> </msup> <mo>=</mo> <mo>-</mo> <mn>25.09</mn> </mrow> </math></EquationSource> </InlineEquation> kJ mol−1) and endothermic (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10661_2025_14107_Article_IEq2.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="99" /> </InlineMediaObject> <EquationSource Format="TEX">${\Delta H}^{o}=+9.03$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi mathvariant="normal">Δ</mi> <mi>H</mi> </mrow> <mi>o</mi> </msup> <mo>=</mo> <mo>+</mo> <mn>9.03</mn> </mrow> </math></EquationSource> </InlineEquation> kJ mol−1). Moreover, reusability investigations indicated that the composite microbeads can be utilized multiple times. Following the tenth cycle, the adsorption efficiency fell by 32.33%, resulting in a value of 51.23%. The findings indicate that the developed unique, sustainable, and cost-effective composite microbeads serve as a prospective and highly efficient adsorbent for the elimination of cationic contaminants from wastewater. Graphical Abstract

Removal of toxic methylene blue dye from aqueous solutions by adsorption technique using magnetic loaded tea waste and its sodium alginate composite microspheres

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发表日期：

2025年5月20日

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Meltem Guven,
Birol Isik,
Fatih Cakar,
Ozlem Cankurtaran

摘要

This study presents the utilization of Fe₃O₄-doped black tea waste (TW) as an efficient, sustainable, and cost-effective adsorbent for the extraction of MB dye from wastewater, alongside the formulation of composite microbeads created by incorporating varying ratios of the black tea-magnetite mixture into sodium alginate (SA), a natural biopolymer. The characterization of composite microbeads was performed using FTIR-ATR, SEM, EDX, and pH_pzc analyses. The surface charge of the adsorbent surface was determined as 6.43 from pH_pzc. From the optimum condition studies, the contact time (60 min), adsorbent dosage (0.1 g/50 mL), and the initial pH (≅ 7) were determined. The raw data were utilized in various non-linear isotherm and kinetic models. The correlation coefficients and error functions indicated that the Langmuir model is the most suitable isotherm model for the adsorption process, with a maximum adsorption capacity of 41.28 mg g⁻¹ for the SA/TW/Fe₃O₄/30 composite microspheres at 298 K. The kinetic and error results indicated that the process adhered to a pseudo-second-order kinetic model. The thermodynamic characteristics indicated that the adsorption process was spontaneous ( ${\Delta G}^{o}=-25.09$ ${Δ G}^{o} = - 25.09$ kJ mol⁻¹) and endothermic ( ${\Delta H}^{o}=+9.03$ ${Δ H}^{o} = + 9.03$ kJ mol⁻¹). Moreover, reusability investigations indicated that the composite microbeads can be utilized multiple times. Following the tenth cycle, the adsorption efficiency fell by 32.33%, resulting in a value of 51.23%. The findings indicate that the developed unique, sustainable, and cost-effective composite microbeads serve as a prospective and highly efficient adsorbent for the elimination of cationic contaminants from wastewater.

Graphical Abstract