Selective adsorptive removal of anionic dyes from aqueous solutions using MIL-101@GO: Effect of GO

Metal−organic framework (MOF)@graphene oxide (GO) composite materials possess the advantages of both GO and MOFs, and thus, they can be employed as effective dye adsorbents. This paper proposes a simple strategy for the preparation of MIL-101 @GO composite materials to effectively adsorb anionic dyes (Congo red, o-cresolsulfonphthalein, methyl orange, and acid chrome blue K) by adding GO to MIL-101 to form a nano-packed structure. The maximum adsorption uptakes of MIL-101 @GO were 2734.9, 484.5, and 1762.8 mg g–1 for Congo red, o-cresolsulfonphthalein, and methyl orange, respectively. These values significantly exceed the corresponding values of the original MIL-101 because of additional factors that promoted adsorption, namely hydrogen bonding and the presence of agglomerate pores. Only the maximum adsorption uptake for acid chrome blue K was lower than that of MIL-101, because of steric hindrance. Our analysis showed that the adsorption behavior of MIL-101 @GO toward Congo red, o-cresolsulfonphthalein, and methyl orange is governed by a synergistic interplay of hydrogen bonding, electrostatic interactions, π–π interactions, the adsorption space, and agglomerate pores in the composite, whereas the adsorption behavior toward acid chrome blue K is mainly limited by steric hindrance. Understanding these interactions may contribute to the development of improved sustainable composite adsorbents.