Researchers from Qatar University (QU), Maimoona Mohamed and Nada Yahya Deyab, along with their supervisor Dr. Shabi Abbas Zaidi, have made progress in addressing the challenge of oil-water separation.
Their research focuses on developing a novel material for efficient oil recovery from oil-water mixtures. By modifying polyurethane (PU) sponges and cotton with reduced graphene oxide (rGO), they have achieved promising results in terms of hydrophobicity, oil-absorption efficacy, reusability, and cost-effectiveness, offering a promising solution to address the issue of water and soil pollution caused by oil spills.
The 3D porous structure of polyurethane sponges has shown promise in oil-water separation applications; however, its poor hydrophobicity limits its oil-absorption efficiency. To overcome this limitation, the team focused on enhancing the hydrophobicity of the sponge by modifying it with graphene oxide (GO) and subsequently reducing it to reduced graphene oxide (rGO) using a readily available green reducing agent, L-ascorbic acid (L-AA).
The process of synthesizing GO involved mixing 1g of graphite flakes with 23 ml of 98% H2SO4, followed by stirring for 24 hours at room temperature. Subsequently, 100mg of NaNO3 was added, and the mixture was stirred for 30 minutes. Afterward, 3g of KMnO4 was gradually introduced, and the resulting mixture was heated and stirred for about 30 minutes.
Further additions of water, followed by the introduction of 10 ml of 30% H2O2, completed the synthesis process. The obtained GO was then centrifuged to remove any un-oxidized graphite and dried to obtain a powder-like substance. Individual sheets of synthesized GO were dispersed in distilled water for reduction and modification studies.
To fabricate rGO-PU sponges, the team employed a green method that utilized L-ascorbic acid as a reducing agent. The PU sponges were initially cut into small pieces and thoroughly rinsed with distilled water and acetone before being dried. An aqueous dispersion of GO was prepared through sonication, and L-AA was dissolved in it. The dry PU sponges were immersed in this mixture and left for 48 hours with mild stirring.
Then, the sponges were washed and dried to obtain rGO-PU sponges. The same protocol was applied to obtain rGO-cotton. The modified surfaces of both rGO-PU and rGO-cotton exhibited superior absorption behavior and water contact angles compared to their bare counterparts.
The capabilities of the rGO-PU sponge were put to the test by absorbing and collecting oil from an oil-water mixture, reportedly achieving a remarkable recovery rate of approximately 97%. Moreover, the rGO-PU sponge demonstrated excellent reusability and compressibility without any signs of cracking or leaking. In a comparative study, the team found that the highly compressible and porous nature of the rGO-PU sponge outperformed the rGO-cotton surfaces in various samples.