Laser-structured superhydrophobic/superoleophilic aluminum surfaces for efficient oil/water separation

The current demand for oil/water separation with an efficient, cost-effective, and environmentally friendly method is increasing. A laser-structured superhydrophobic/superoleophilic aluminum was prepared by using a nanosecond laser. The aluminum plate was used for oil/water separation without external force, which can replace the traditional porous materials. The effect of hole diameter and spacing on the effectiveness of oil/water separation is discussed. The results show that the aluminum plate with a hole size of 0.5 mm can be considered a more appropriate choice for the oil/water mixtures with large water content. In addition, complete separation of oil and water can be achieved in the hole spacing range of 1.0-3.0 mm. The oil separation speed can be increased without changing the water permeability by reducing the hole spacing, which is positively related to the hole spacing. Separation efficiencies were tested with various oil/water mixtures. The aluminum plate with a hole size of 0.5 mm can quickly separate the different oil mixtures with less than 50% oil content while achieving an oil separation efficiency of up to 99%. Due to the difference in dynamic viscosity of various oil phases, the separation efficiencies of the petrol, kerosene, and diesel are slightly different but can still be maintained above 99%. The laser-processed aluminum plate has several advantages of high porosity, high surface of superhydrophobic properties, and easy tunable structures. In practical applications, the hole size and the spacing should be appropriately adjusted according to specific conditions, such as different oils, the mixing ratios, etc., to obtain the best separation efficiency and speed.