Novel and Reusable Graphene Oxide-Coated Reticulated Open-Cell Mullite Foams for Methylene Blue Dye Adsorption

Reticulated open-cell mullite (ROM) foams coated with graphene oxide (GO) multilayers as novel and reusable composites (ROM/GO) were first fabricated and functionalized to remove methylene blue (MB) dye from aqueous solutions. In this study, the ROM foams were produced via a replica technique utilizing rice husk as a starting raw material of silica (SiO₂) mixed with commercially available alumina (Al₂O₃) in the step of slurry preparation. GO was synthesized by a modification of Hummer's method and dispersed in a fixed weight ratio in an aqueous solution. The HCl-pretreated ROM foams were dip-coated for up to 5 cycles using a fixed weight ratio of GO in an aqueous solution. The experimental results revealed that the ROM/GO foams provided 100% adsorption efficiency for MB within 30 min. The adsorption kinetics of the ROM/GO foams followed the first-order model. Based on the microstructural investigations on the surfaces of the ROM foams compared with the ROM/GO foams, the adsorption performance was related to the unique porous structure of the ROM foams, incorporating the physicochemical properties of the GO-multilayered coating. Finally, the ROM/GO foams are considered as sustainable and cost-effective adsorbents due to their reusable functionality for at least 5 cycles of MB removal.