Efficient oil-water separation by a robust superhydrophobic coating prepared directly from commercial lacquer using silanized multi-walled carbon nanotubes as filler

The mechanical robustness of superhydrophobic surface is essential for practical applications. In this work, multi-walled carbon nanotubes with copious hydroxyl groups (MWCNTs-OH) were firstly silanized, with the presence of a small amount of HCl aquesous solution as catalyst, by trimethoxymethylsiane (MTMS) in petroleum ether. Upon hydrolyzation and condensation, silica derived from MTMS could wrap the MWCNTs spirally like the vines wrapping the trees via forming SiOC bondings between the MWCNTs and silica. The resultant MWCNTs@MTMS composite exhibits superhydrophobic and superoleophilic properties. When added into one of commercial lacquers (LK-1014) as a filler, the mixture could be easily sprayed on various substrates with arbitrary dimensional size and shape. The optimized mass ratio of MWCNTs@MTMS to LK-1014 is about 1:20 for fabricating coating with both superior mechanical robustness and superhydrophobic and superoleophilic properties. The adhesions to some substrates and wear resistances were verified via the adhesive tape adhesion tests and sandpaper wear experiments. A copper mesh with sprayed coating was measured to have a water-resistance height of 14.6 cm, corresponding to an invasion pressure of 1430.8 Pa. Folding the sprayed copper meshes into boxes allows continuous separation of oil–water mixture with high separation efficiency (higher than 96 %), fairly large fluxes (higher than 120 kL·m−2·h−1) and application durability. Using filter paper with such coating for the separation of water-in-oil emulsions, an efficiency up to 99.9 % could be reached.