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.