Fabrication of calcium alginate/gum arabic/egg shell composite microbeads for adsorptive removal of methylene blue dye from aqueous solutions

Abstract This study focuses on the design and application of calcium alginate/gum arabic/eggshell powder composite microbeads (CA/GA/ES10) for the removal of methylene blue dye from aqueous solutions through the adsorption method. The characterization of adsorbents was conducted utilizing ATR-FTIR, SEM, XRD, TGA, and pH pzc . The pH pzc value of CA/GA/ES10 composite microbeads was determined as 5.56. From optimization studies, the contact time, adsorbent dosage, and pH values were determined as 60 min, 0.1 g/50 mL, and ≅ 7, respectively. The adsorption raw data have been utilized in the non-linear Langmuir, Freundlich, Temkin, and Sips models. The maximum adsorption capacity of CA/GA/ES10 composite microbeads, as per the Sips, was determined to be 33.30 mg/g at 298 K. The high correlation coefficients ( $$r^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>r</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> = 0.9976) and low error functions ( $$\chi^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>χ</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> = 0.03) indicate that the non-linear Langmuir is the most appropriate isotherm for the adsorption process. From the Langmuir model, the maximum adsorption capacity was determined as 29.71 mg/g at 298 K. The adsorption process adheres to a non-linear pseudo-second-order ( $$r^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>r</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> = 0.9999) and Elovich ( $$r^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>r</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> = 0.9999) models. According to thermodynamic results, the adsorption process occurs exothermic ( $$\Delta H^{^\circ } = - 3.77\;{\text{kJ/mol}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mmultiscripts> <mml:mi>H</mml:mi> <mml:mrow/> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:mmultiscripts> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mn>3.77</mml:mn> <mml:mspace/> <mml:mtext>kJ/mol</mml:mtext> </mml:mrow> </mml:math> ) and spontaneous ( $$\Delta G^{^\circ } = - 25.83\;{\text{kJ/mol}}\;{\text{at}}\;298\;{\text{K}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mmultiscripts> <mml:mi>G</mml:mi> <mml:mrow/> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:mmultiscripts> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mn>25.83</mml:mn> <mml:mspace/> <mml:mtext>kJ/mol</mml:mtext> <mml:mspace/> <mml:mtext>at</mml:mtext> <mml:mspace/> <mml:mn>298</mml:mn> <mml:mspace/> <mml:mtext>K</mml:mtext> </mml:mrow> </mml:math> ) in nature. The impact of varying salt concentrations on the adsorption process was assessed. According to the salt effect, the removal percentage decreased from 81.12 to 65.15% with the addition of NaCl, and from 81.12 to 58.78% with the addition of CaCl 2 . The reusability tests show that the composite microbeads created can be used repeatedly for up to 7 cycles. After the 7th cycle, the removal of MB dye decreased from 81.11 to 53.45%. All results showed that the prepared ternary composite microbeads are effective adsorbents for the removal of cationic dye from aqueous solutions. Graphical abstract