Efficient adsorption of Congo red by micro/nano MIL-88A (Fe, Al, Fe-Al)/chitosan composite sponge: Preparation, characterization, and adsorption mechanism

MIL-88A crystals with three different metal ligands (Fe, Al, Fe-Al) were prepared by hydrothermal method for the first time. The three materials' crystal structure and surface morphology are different, leading to different adsorption properties of Congo red (CR). The maximum adsorption capacities of MIL-88A (Fe), MIL-88A (Fe-Al), and MIL-88A (Al) are 607.7 mg center dot g(-1), 536.4 mg center dot g(-1), and 512.1 mg center dot g(-1) respectively. In addition, MIL-88A was combined with chitosan (CS) respectively, and MIL-88A/CS composite sponge was prepared by the freeze-drying method, which not only solved the defect that MIL-88A powder was difficult to recover but also further improved the removal ability of CR by the adsorbent. The maximum adsorption capacities of MIL-88A (Fe-Al)/CS, MIL-88A (Fe)/CS, MIL-88A (Al)/CS, and CS are 1312 mg center dot g(-1), 1056 mg center dot g(-1), 996.7 mg center dot g(-1), and 769.6 mg center dot g(-1), respectively. The structure and physicochemical properties of the materials were analyzed by SEM, FTIR, XRD, TGA, BET, and Zeta. The adsorption process of CR follows pseudo-second-order kinetics and Langmuir, Sips isotherm model. Combined with thermodynamic parameters, the adsorption behavior was described as endothermic monomolecular chemical adsorption. The removal of CR is attributed to electrostatic interactions, hydrogen bonding, metal coordination effects, and size-matching effects.

Automated summary

For the first time, MIL-88A crystals with different metal ligands (Fe, Al, Fe-Al) were prepared using the hydrothermal method. These materials showed different crystal structures and surface morphologies, leading to varying adsorption properties towards Congo red (CR). The maximum adsorption capacities for MIL-88A (Fe), MIL-88A (Fe-Al), and MIL-88A (Al) were found to be 607.7 mg·g(-1), 536.4 mg·g(-1), and 512.1 mg·g(-1), respectively. Furthermore, the combination of MIL-88A with chitosan (CS) and the freeze-drying method produced a MIL-88A/CS composite sponge, which not only addressed the difficulty in recovering MIL-88A powder but also enhanced the CR removal capability of the adsorbent. The maximum adsorption capacities for MIL-88A (Fe-Al)/CS, MIL-88A (Fe)/CS, MIL-88A (Al)/CS, and CS were 1312 mg·g(-1), 1056 mg·g(-1), 996.7 mg·g(-1), and 769.6 mg·g(-1), respectively. The structure and physicochemical properties of the materials were assessed using SEM, FTIR, XRD, TGA, BET, and Zeta. The adsorption of CR followed pseudo-second-order kinetics and the Langmuir, Sips isotherm model, indicating endothermic monomolecular chemical adsorption. The removal of CR was attributed to electrostatic interactions, hydrogen bonding, metal coordination effects, and size-matching effects.