Synthesis of nanomagnetite modified g-C3N4/ferric xanthan gum for efficient static and dynamic Pb2+ adsorption: kinetic and thermodynamic investigations.

In this study, three solid adsorbents were constructed, namely nanomagnetite/graphitic carbon nitride (NgCN), ferric xanthan gum (X), and a nanomagnetite/graphitic carbon nitride/ferric xanthan gum composite (NgCNX). The fabricated adsorbents were characterized using various physicochemical tools. Using static and dynamic adsorption approaches, the influences of adsorbent dosage, initial Pb2+ ion concentration, solution pH, shaking time, flow rate, and bed height were systematically evaluated. Batch adsorption data revealed that NgCNX demonstrated a Langmuir qm of 433.6 mg/g at pH 4 and 20 °C. Kinetic studies showed that Pb2+ ion adsorption was well described by the nonlinear PFO and Avrami models. Additionally, nonlinear adsorption isotherm analyses indicated good fitting to the Langmuir (R2≥0.9334), Temkin, Redlich-Peterson, and Sips models for all samples. The thermodynamic parameters shown that, the adsorption of Pb2+ onto the synthesized materials is spontaneous, as indicated by the negative ΔG° values (-5.25-8.38 kJ/mol at all the investigated temperatures), endothermic with the positive ΔH° values (0.015-0.026 kJ/mol), and supplemented by increased randomness at the solid-liquid interface, as revealed by the positive ΔS° values (0.018-0.026 kJ/mol·K), verifying the favorable adsorption process. NgCNX achieved the highest column adsorption capacity (24.5 mg/g) at a bed height of 1 cm, a flow rate of 6 mL/min, and 100 mg/L as an initial concentration of Pb2+ ions, with an exhaustion time of 80.30 min, and a breakthrough time of 40.00 min. The Thomas, Clark, and Yoon-Nelson models adequately described the breakthrough curves of dynamic column adsorption of Pb2+ ions. The results demonstrated that NgCNX exhibits excellent capacity for adsorption, strong affinity for Pb2+ ions, and rapid kinetics, suggesting its suitability for water treatment technologies.