Citric acid-cross linked with magnetic metal-organic framework composite sponge for superior adsorption of indigo carmine blue dye from aqueous solutions: Characterization and adsorption optimization via Box–Behnken design

Abstract

A novel sponge composite (Fe3O4@Pd-MOF/CSC) capable of effectively eliminating indigo carmine blue (ICB) dye from water, was synthesized using an effective single-step hydrothermal method under acidic conditions, employing citrate crosslinking chitosan. The adsorbent was thoroughly characterized using various techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Brunauer–Emmett–Teller surface area (BET) analysis. Our research indicated that the Fe3O4@Pd-MOF/CSC composite sponge possesses an impressive surface area of 1076.8 m2/g and the highest adsorption capacity (qmax) of 778.8 mg/g. The study delved into various factors influencing the adsorption process, including pH levels, indigo carmine blue concentration, adsorbent dosage, and temperature. Both the adsorption isotherm and kinetics were aligned with the Langmuir equation and the pseudo-second-order equation, respectively, for comprehensive analysis. The adsorption energy was determined to be 18.22 kJ/mol, indicating a chemisorption adsorption mechanism. According to adsorption thermodynamics, the process was observed to be both endothermic and spontaneous. Additionally, the material absorption increased with rising temperatures. Moreover, the Fe3O4@Pd-MOF/CSC composite sponge demonstrated magnetic properties, allowing for easy extraction from the solution after the adsorption process. The adsorbent displayed satisfactory efficiency even after being reused six times, demonstrating no alteration in chemical composition. Furthermore, X-ray diffraction (XRD) pattern showed consistent results before and after the reuse process. Electrostatic contact, π-π interaction, hydrogen bonding, and pore filling were identified as the primary mechanisms through which the Fe3O4@Pd-MOF/CSC composite sponge interacted with ICB. The adsorption outcomes were optimized using Box–Behnken-design (BBD).