Superhydrophobic PODS-modified nickel foam with reversible wettability for oil-water separation

Abstract

In this work, superhydrophobic and superoleophilic nickel foam was fabricated to effectively purify oil-water mixtures. Octadecyltrichlorosilane (OTS) was utilized to form polymerized octadecylsiloxane (PODS) coatings on the nickel foam through hydrolysis and subsequent polycondensation reactions. The surface composition and morphology of the nickel foam were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The initially smooth surface of the nickel foam became rough upon being coated with the PODS. The incorporation of long alkyl chains from the PODS coating, along with the introduced roughness, synergistically provided the nickel foam with superhydrophobic and superoleophilic properties. The PODS-modified nickel foam demonstrated a water contact angle (WCA) of 151.3° and oil contact angle (OCA) of 0°, exhibiting excellent wettability selectivity towards water and oil. Additionally, it showcased a remarkable permeation flux of 7468.4 ± 236.3 L·m−2·h−1 when tested with a water-n-hexane emulsion. This superior performance enabled efficient separation of oil and water. Notably, even after 20 cycles, the PODS-modified nickel foam maintained a separation efficiency of over 98.4 %. Furthermore, the wettability of the PODS-modified nickel foam could be easily switched from superhydrophobicity to superhydrophilicity through a straightforward prewetting treatment using ethanol. In this process, ethanol served as a mediator between the hydrophobic surface and water. Once the prewetted foam was thoroughly dried, the hydrophilic channels were eliminated, thus restoring the superhydrophobicity of the nickel foam. This reversible transition of wettability holds great potential for the development of smart filters capable of effectively addressing diverse challenges in oily wastewater treatment.