Fe3O4-decorated MXene for the effective removal of 133Ba and 137Cs: synthesis, characterization, and optimization via response surface methodology (RSM)

Abstract

In this study, a composite material consisting of MXenes (Ti₃C₂T_x) and Fe₃O₄ in the ratio of 70 : 30 w/w% (MXF-30) was synthesized via solvothermal method. The material was characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller measurements (BET) to understand the relationship between the structure and properties for radionuclide removal (¹³³Ba and ¹³⁷Cs). Batch experiments employing Box–Behnken design (BBD) were conducted to investigate the impacts of operating parameters such as initial pH, contact time, and initial concentration of Ba²⁺ and Cs⁺ ions (containing radiotracers ¹³³Ba and ¹³⁷Cs). The optimized conditions suggested by BBD were found to be pH 5.5, 240 min contact time, and 0.1 mol L⁻¹ radionuclides. Under these conditions, the experimental values and values predicted from the models for maximum adsorption capacity were in agreement, i.e., 4.18 and 4.07 mmol g⁻¹ for Ba²⁺ and 6.34 and 6.12 mmol g⁻¹ for Cs⁺ ions, respectively. The results of studies in a solution containing a mixture of ions (Na⁺, K⁺, Ca²⁺, Co²⁺, and Mg²⁺) confirmed that pH 5.5 and 8.0 are suitable for Cs⁺ and Ba²⁺ adsorption, respectively. In addition, MXF-30 showed higher affinity for Cs⁺ due to increased interlayer spacings via the encapsulation mechanism. The typical mechanism of the adsorption of Ba²⁺ and Cs⁺ ions was proposed to be a combination of encapsulation (physisorption) and surface complexation (chemisorption).