Synthesis of iron-based metal–organic framework@bacterial cellulose aerogels by an <i>in situ</i> growth method for multifunctional dye removal and oil–water separation applications

Dyes and oily wastewater are among the most prevalent types of industrial wastewater pollutants, posing long-term threats to the environment and water resources due to their complex compositions and treatment difficulties. To achieve the separation and removal of these two categories of pollutants, this study developed two types of lightweight composite aerogels based on bacterial cellulose (BC). In this study, MIL-53-Fe (MIL-53) was loaded onto pure BC and polydopamine (PDA)-decorated BC (PBC) by <i>in situ</i> growth and then freeze-dried to prepare an MIL-53@BC aerogel (MIL-53@BCA) and MIL-53@PBC aerogel (MIL-53@PBCA), respectively. Results confirmed that both composite aerogels exhibited low densities (∼25 ± 5 mg cm^-3) and robust structural stability. In terms of performance, both materials demonstrated promising potential for water treatment applications. Static adsorption experiments revealed that the equilibrium adsorption capacities of MIL-53@BCA and MIL-53@PBCA for Congo Red (CR) were 119.80 mg g^-1 and 122.17 mg g^-1, respectively. Adsorption kinetics conformed to the pseudo-first-order and pseudo-second-order models, while isotherm behavior was well-described by the Langmuir and Freundlich models. Thermodynamic analysis indicated that the adsorption process was spontaneous, exothermic, and entropy-increasing. Photocatalytic degradation experiments under visible light irradiation showed that both materials were effective in degrading methylene blue (MB) and rhodamine B (RhB). Gravity-driven oil-water separation testing confirmed the materials' ability to efficiently separate oil-water mixtures of varying densities and exhibited the simultaneous adsorption of residual dyes in the lower phase during the separation process. Therefore, the MOF-loaded cellulose aerogels developed in this study demonstrated integrated functionalities of adsorption, photocatalysis, and oil-water separation, proving their potential for the integrated remediation of wastewater treatment.