Ultrahydrophobic melamine sponge via interfacial modification with reduced graphene oxide/titanium dioxide nanocomposite and polydimethylsiloxane for oily wastewater treatment

Three-dimensional (3D) porous absorbents have attracted significant attention in the oily wastewater treatment technology due to their high porosity and elasticity. Given their amphiphilic surface, they have a propensity to simultaneously absorb water and oil, which restricts their range of applications. In this study, a reduced graphene oxide and titanium dioxide nanocomposite (rGO/TiO 2 ) was used to fabricate an ultrahydrophobic melamine sponge (MS) through interfacial modification using a solution immersion technique. To further modify it, polydimethylsiloxane (PDMS) was grafted onto its surface to establish stronger covalent bonds with the composite. The water contact angle of the sponge (rGO/TiO 2 /PDMS/MS) was 164.2 degrees , which satisfies the condition for ultrahydrophobicity. The evidence of its water repellency was demonstrated by the Cassie - Baxter theory and the lotus leaf effect. As a result of the increased density of rGO/TiO 2 /PDMS/MS, it recorded an initial capacity that was 2 g/g lower than the raw MS for crude oil absorption. The raw MS retained 53% of its initial absorption capacity after 20 cycles of absorption, while rGO/TiO2/PDMS/MS retained 97%, suggesting good recyclability. Excellent oil and organic solvent recovery (90% - 96%) was demonstrated by rGO/TiO 2 /PDMS/MS in oil - water combinations. In a continuous separation system, it achieved a remarkable separation efficiency of 2.4 x 10 6 L/(m 3 . h), and in turbulent emulsion separation, it achieved a demulsification efficiency of 90% - 91%. This study provides a practical substitute for massive oil spill cleaning. (c) 2023 Hohai University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY -NC -ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).