Fabrication of superhydrophobic and superoleophilic copper oxide nanostructures without organic modifiers for oil–water separation

Superhydrophobic and superoleophilic hierarchical urchin-like copper oxide powders were synthesized by a facile one-step method without the use of low-surface-energy modifiers. The selective wettability of the powders toward water and oil makes them suitable for oil adsorption from oil-in-water emulsions. In addition, the hierarchical CuO structures were grown in situ on a stainless-steel mesh, which was used for the separation of heavy oil–water mixtures. The synergistic combination of micro-/nanoscale roughness and a reduction in the polar component of surface free energy through hydroxylation of the copper oxide surface likely leads to a significant decrease in wettability and the development of superhydrophobic and superoleophilic properties, as evidenced by a static water contact angle of 161.1° ± 2° and an oil contact angle of 0°, measured on the CuO-coated mesh surface. The superhydrophobic copper oxide particles demonstrated a high oil adsorption selectivity greater than 19. The immiscible chloroform/water mixture was separated via a simple filtration method using a superhydrophobic/superoleophilic copper oxide–coated mesh filter, achieving a separation efficiency of approximately 98% and a chloroform permeation flux of about 7300 L m⁻² h⁻¹. In addition, copper oxide powder showed promising potential as a selective oil adsorbent for the treatment of oil-in-water emulsions and the cleanup of oil spills when used in the form of sorbent booms or pillows.