Facile preparation of novel hydrophobic sponges coated by Cu₂O with different crystal facet structure for selective oil absorption and oil/water separation

In this work, a series of novel Cu₂O@sponge composite materials including cubic Cu₂O@sponges, octahedral Cu₂O@sponges and cubo-octahedral Cu₂O@sponges were prepared through a facile dip coating method to coat Cu₂O particles on melamine sponge, all of which possess very highly hydrophobic and oleophilic properties. The crystal phase, microstructure and surface functional group of the as-prepared materials were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectra. The effect of different crystal facet of Cu₂O on contact angle, wettability and oil absorption was systematically investigated. Meanwhile, the DFT calculation results show that the surface energy has significant influence on the hydrophobic property of Cu₂O, and the calculated surface energies of Cu₂O (111) and Cu₂O (100) crystal surface are 0.73 and 1.29 J/m², respectively. On basis of the DFT calculations and experimental results, the octahedral Cu₂O with eight (111) crystal facet-coated sponges has the highest hydrophobic properties with the contact angle of 149°, which therefore shows very high separation efficiency in oil/water separation and quickly absorbs floating oils on the water surface. Additionally, all the Cu₂O@sponges composite materials indicate excellent oil absorption performances and reusability in terms of hydrophobicity and oil absorbency, which would provide new materials for the potential application of oil/water separation.