Abstract
Recently, separation of oil from oily wastewater has caught much attention due to the increased oil pollution caused by our daily life, industrial wastes, and offshore oil spills. However, conventional techniques still have limitations to date, including low efficiency, high cost, and second contamination. Diatom is a silica-based phytoplankton that can be found abundantly in aqueous environment, and it produces almost 25% of the oxygen we breathe. After the death of diatom, the silica-based cell wall remains and forms a fossilized material known as diatomite. Owing to its water-absorbing and porous nature, diatomite becomes a potential candidate for oil/water separation. In this study, we utilized diatomite as raw material to fabricate a hierarchically porous plate via the freeze-casting technique. After purification, the nanostructure of diatom could be well-preserved, and aligned hierarchical micro-sized channels and nano-sized pores were successfully synthesized through the optimized cooling rate and water content. The hierarchically porous plate displays both superhydrophilicity and underwater superoleophobicity evaluated by various oils, such as soybean oil, hexane, dodecane and n-hexadecane. Additionally, our work demonstrates superior oil/water separation efficiency, high water permeance, and high oil intrusion pressure. Moreover, the as-synthesized plate shows low adhesion to oil underwater that the oil can be washed away easily by water flushing, and maintained good durability even after several separation cycles. Finally, the plate exhibits excellent environmental stability under harsh environments, including strong acid, base, saturated sodium chloride solution, and hot water. To recapitulate, we synthesized a cost-effective, eco-friendly, and robust diatomite-based porous plate by freeze casting method which showed superior oil/water separation performance, reliability and stability. With these advantages, it has potential to be further applied in the separation of large amount of oily waste water and is suitable for long-term applications.