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<p>This study highlights the potential of laboratory-synthesized citrate-functionalized graphene oxide (CGO) as an effective adsorbent for the removal of Pb (II) and Cd (II) from aqueous solutions for both single and binary systems. Scanning electron microscopy revealed that CGO possesses more wrinkled and uneven surface morphology than pristine Graphene oxide (GO), while energy-dispersive X-ray spectroscopy confirmed the elemental composition, including carbon, oxygen, and silicon. Fourier-transform infrared spectroscopy identified key surface functional groups responsible for metal ion adsorption, including carboxyl, hydroxyl, and siloxane. X-ray diffraction patterns revealed the reduced interlayer spacing in CGO compared to GO, and Raman spectroscopy indicated the reduction of structural disorder after citrate functionalization of GO. Thermogravimetric analysis demonstrated enhanced thermal stability after citrate functionalization as compared to pristine GO. X-ray Photoelectron Spectroscopy confirmed the functionalization of GO after chemical treatment and the metal ion binding mechanism after adsorption for both single and binary adsorption systems. Batch adsorption experiments showed that CGO exhibited maximum adsorption capacities of 135.39&#xa0;mg/g for Pb (II) and 58.18&#xa0;mg/g for Cd (II) at pH 4.5 and 298&#xa0;K in a single-component system. Pb (II) consistently exhibited higher selectivity than Cd (II) for adsorption onto CGO, particularly in binary metal ion systems. Adsorption behaviour followed the Langmuir isotherm model and pseudo-second-order kinetic model (R<sup>2</sup> &gt; 0.99), suggesting uniform monolayer adsorption and strong interaction between metal ions and active adsorbent sites. Thermodynamic analysis confirmed that the adsorption process was endothermic and spontaneous for both single and binary systems. The unreacted shrinking core model was successfully applied to describe mass transfer phenomena during the adsorption process. Regeneration studies revealed that CGO retained substantial equilibrium adsorption capacity even after four successive adsorption–desorption cycles. In fixed-bed column simulations using Aspen Adsorption® V12, longer breakthrough times were achieved with increased bed height and reduced flow rate. Mechanistically, the adsorption process was governed by a combination of molecular mass transport, electrostatic attraction, surface complexation through deprotonated oxygen-containing functional groups, and ion exchange.</p>

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Adsorptive Removal of Pb (II) and Cd (II) Using Citrate-Functionalized Graphene Oxide: A Comprehensive Study on Characterization and Mathematical Modelling of Single and Binary Metal Systems

  • 期刊论文

  • 发表日期：

    2025年11月8日

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  • Soumyadeep Das,
  • Pathan Jaleel Khan,
  • Sonali Sengupta

摘要

This study highlights the potential of laboratory-synthesized citrate-functionalized graphene oxide (CGO) as an effective adsorbent for the removal of Pb (II) and Cd (II) from aqueous solutions for both single and binary systems. Scanning electron microscopy revealed that CGO possesses more wrinkled and uneven surface morphology than pristine Graphene oxide (GO), while energy-dispersive X-ray spectroscopy confirmed the elemental composition, including carbon, oxygen, and silicon. Fourier-transform infrared spectroscopy identified key surface functional groups responsible for metal ion adsorption, including carboxyl, hydroxyl, and siloxane. X-ray diffraction patterns revealed the reduced interlayer spacing in CGO compared to GO, and Raman spectroscopy indicated the reduction of structural disorder after citrate functionalization of GO. Thermogravimetric analysis demonstrated enhanced thermal stability after citrate functionalization as compared to pristine GO. X-ray Photoelectron Spectroscopy confirmed the functionalization of GO after chemical treatment and the metal ion binding mechanism after adsorption for both single and binary adsorption systems. Batch adsorption experiments showed that CGO exhibited maximum adsorption capacities of 135.39 mg/g for Pb (II) and 58.18 mg/g for Cd (II) at pH 4.5 and 298 K in a single-component system. Pb (II) consistently exhibited higher selectivity than Cd (II) for adsorption onto CGO, particularly in binary metal ion systems. Adsorption behaviour followed the Langmuir isotherm model and pseudo-second-order kinetic model (R2 > 0.99), suggesting uniform monolayer adsorption and strong interaction between metal ions and active adsorbent sites. Thermodynamic analysis confirmed that the adsorption process was endothermic and spontaneous for both single and binary systems. The unreacted shrinking core model was successfully applied to describe mass transfer phenomena during the adsorption process. Regeneration studies revealed that CGO retained substantial equilibrium adsorption capacity even after four successive adsorption–desorption cycles. In fixed-bed column simulations using Aspen Adsorption® V12, longer breakthrough times were achieved with increased bed height and reduced flow rate. Mechanistically, the adsorption process was governed by a combination of molecular mass transport, electrostatic attraction, surface complexation through deprotonated oxygen-containing functional groups, and ion exchange.