Durability evaluation of superhydrophobic copper foams for long-term oil-water separation

Abstract

Superhydrophobic three-dimensional porous composites with good mechanical stability and high efficiency are promising candidates for oil-water separation application. Hence, several superhydrophobic copper foams were fabricated via the in situ growth of patterned Cu(OH)2 nanoneedles or ZnO nanocrystals (e.g. ZnO nanocones and ZnO nanorods) on the skeleton and followed by chemically modification. All the superhydrophobic copper foams showed efficient oil-water separation ability, especially the samples with ZnO nanorods arrays on the pre-nanostructured skeleton. The durability of superhydrophobic copper foams were then evaluated. Although the superhydrophobic samples kept separation efficiency higher than 95% after cycled evaluation, the pre-roughened copper foams exhibited the best performance against various damage among the samples. Microstructural evolution revealed that the coverage of the copper skeleton became from smooth swelling micro-crystals into rough nano-crystals after the pre-treatment of electrodepositing copper nanoparticles. The rough nanocrystals could not only avoid the formation of loose hierarchical structure, but also improve the binding force between patterned nanorods and the matrix. The fabricated closely-patterned ZnO nanorods could thus remain stable under the damage compared to others, presenting great mechanical robustness. Furthermore, we achieved a long-term efficient oil-water separation using the durable foams by periodic removal of residual oil in nanostructure gaps.