Superhydrophobic sand grains structured with aligned Cu(OH)2 nano-needles for efficient oily water treatment

Highlights: • The aligned Cu(OH)₂ nano-needles are successfully constructed on the sand gain surfaces; • The as-prepared functional sands show superior superhydrophobicity; • The discrete superhydrophobic sand is a good candidate for oil-water separation • This work is expected to change our traditional understanding of sand and the reutilization of natural desert sand. Desert sand as an abundant natural resource rarely has been reconsidered and reutilized due to its superhydrophilicity. Aiming at the combination of super-wettability with sand resource, we successfully design the aligned Cu(OH)₂ nano-needles on the sand grain surfaces through a skillful strategy and conferred superhydrophobic properties on them in this study. The water contact angle and rolling angle are shown to be ~ 158° and ~ 6°, which break our traditional understanding towards desert sand, i.e., superhydrophilicity. More importantly, the selective superhydrophobic-superoleophilic wettability and the cavities between nano-needles and sand grains allow the sand to be a good candidate for efficient oily water treatment. The as-prepared superhydrophibic sand can not only absorb light oils from water surface, but separate heavy oils from oil/water mixtures. The speed of oil/water separation is up to 16,985 L m^{− 2} h^{− 1} when a 0.35 cm thickness of superhydrophobic sand layer is used. Significantly, it exhibits both high separation rate and high separation efficiency (> 99.5%). The as-prepared superhydrophobic sands are expected to become a new candidate of highly efficient oil/water separation material and to realize the reutilization of desert sand resource.