Recyclable Mg-MOF-74@cellulose aerogel composites for efficient removal of heavy metals from wastewater

In this study, Mg-MOF-74, an environmentally friendly metal-organic framework material with non-toxic Mg elements as the framework centers, was loaded onto low-cost and green cellulose aerogels via an in-situ growth approach to construct the Mg-MOF-74@CA composite with a three-dimensional porous structure, overcoming the problems that Mg-MOF-74 nanoparticles tend to agglomerate and cannot be easily recovered. The removal performance of the synthesized Mg-MOF-74@CA composite towards Pb(II), Cd(II), and Cu(II) was evaluated by combining batch experiments, model fittings, and characterization analyses (SEM, XRD, FTIR, MIP, TG, and XPS). The results show that the porosity of Mg-MOF-74@CA is 84.447%. The removal of Pb(II), Cd(II), and Cu(II) by Mg-MOF-74@CA reach the equilibriums at about 5 h. And the removal of Pb(II), Cd(II), and Cu(II) by Mg-MOF-74@CA are strongly influenced by solution pH, while almost independent of ionic strength and humic acid (HA). The strong complexation of Pb(II), Cd(II), and Cu(II) with the surface sites of Mg-MOF-74@CA is the main removal mechanism. The maximum adsorption capacities of Mg-MOF-74@CA towards Pb(II), Cd(II), and Cu(II) at 298 K are 223.555, 160.033, and 74.349 mg/g, respectively. Interestingly, the selective binding order of Mg-MOF-74@CA for Pb(II), Cd(II), and Cu(II) is Cu(II)>Pb(II)>Cd(II). In summary, the Mg-MOF-74@CA composite has good application prospects in practical wastewater treatment.