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.