Abstract
The pollution caused by microplastics around the world is an increasingly significant issue that has to be tackled with different methods and technologies. Here, we report a straightforward and rapid process combining electrodeposition and electrophoresis to produce a durable superhydrophobic coating on an aluminum substrate (UNS A91070) that has a static contact angle (153°), sliding angle (1°), and contact angle hysteresis (1°). Field emission scanning electron microscopy and high-resolution transmission electron microscopy showed the presence of a hierarchical structure with nanolayers that were 70 nm thick. The chemical composition was also analyzed using attenuated total reflectance-Fourier transform infrared spectroscopy and high-resolution X-ray photoelectron spectroscopy, which revealed that the hierarchical structure was composed of zinc laurate (Zn(C11H20COO)2) that decreased the surface free energy of the system. Moreover, the coating showed high durability against abrasion caused by the P1200 SiC paper due to the presence of TiO2 particles in the upper layers as well as the homogeneous chemical composition of the hierarchical structure. Finally, taking advantage of the superoleophilic properties of superhydrophobic surfaces, the ability of the coating to remove high-density polyethylene microplastics from water was studied.
Highlights
The presence of solid pollutants such as microplastics (MPs) is a concerning issue around the globe that will affect the economy, the quality of food and soils, and the health of animals and the human population
The chemical composition was analyzed using attenuated total reflectance-Fourier transform infrared spectroscopy and high-resolution X-ray photoelectron spectroscopy, which revealed that the hierarchical structure was composed of zinc laurate (Zn(C11H20COO)2) that decreased the surface free energy of the system
It is well known that these materials present superoleophilic properties and underwater superoleophilicity, with oil contact angles (OCA) and underwater oil contact angles (UWOCA) lower than 10◦ [9,10,11]
Summary
The presence of solid pollutants such as microplastics (MPs) is a concerning issue around the globe that will affect the economy, the quality of food and soils, and the health of animals and the human population. MPs are smaller than 5 mm in size and present a wide variety of morphologies such as rounded and irregular shapes or fibers. It is necessary to study different materials that can remove MPs without affecting their size and causing surface contamination. In this scenario, and apart from the previously cited methods, the wettability of MPs should be considered. The surface free energy of different materials plays a key role in the removal of MPs. Superhydrophobic materials are surfaces with extremely high water contact angles (WCA > 150◦), low sliding angles (SA < 10◦), and low contact angle hysteresis (CAH < 10◦), thereby showing water repellency [8]. The use of ceramic particles such as SiO2, Al2O3, or TiO2 increases the roughness of the surface, which is a key point for superhydrophobic surfaces, leading to the heterogeneous Cassie-Baxter wetting state as well as increasing the durability of the coating itself [29,30,31]
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