Construction of expanded graphite/xanthan gum-glutamine grafted composite for efficient batch and fixed column bed...

One viable approach to addressing the increasing concern about lead ions (Pb²⁺ ions) pollution is the development of unconventional adsorbents with enhanced adsorption capacities. The current investigation highlights the development of high-performance adsorbents, namely expanded graphite (EG), expanded graphite/xanthan gum composite (EGX), a glutamine/xanthan gum composite (Xg), and composite from expanded graphite/xanthan gum-glutamine composite (EGXg). Physicochemical characterization approaches validated that the developed EGXg adsorbent featured a pore radius measuring 1.653 nm, surface point of zero charge at pH_PCZ = 6.7, and surface area = 255.69 m²/g. The results for Pb²⁺ ions adsorption confirmed that the experimental data were best described by the pseudo-first order kinetic model and the Langmuir adsorption isotherm, indicating an exothermic and spontaneous process as evidenced by the thermodynamic analysis. A batch adsorption capability of 508.54 mg/g had been maximally achieved with EGXg at a 1.0 g/L dosage, with stirring for 30 min at 25 °C and a pH = 6. A drop in adsorption efficiency of just 4.2 %, 3.9 %, and 1.2 % was observed for EGX, Xg, and EGXg, respectively, over six rounds of reusability. The dynamic adsorption capacity has been assessed at 167.96 mg/g for a flow rate of 8 mL/min, an influent Pb²⁺ions concentration of 120 mg/L, and 2 cm bed height. The Pb²⁺ ions column adsorption measurements on EGXg closely align with the Thomas and Yoon-Nelson nonlinear models.