The effect of increasing the hydrophobicity of poly(propylene) (PP) fibers, the most frequently used synthetic filter materials, on depth filtration performance was investigated. Reduced graphene oxide (RGO) was employed to fabricate highly hydrophobic surfaces by a dip-coating method. The anchoring of RGO on the surface of the PP fibers was confirmed by the appearance of signals corresponding to RGO in Raman and X-ray photoelectron spectra. In addition, scanning electron microscopy images revealed the presence of wrinkled and folded RGO sheets on the PP fibers. The water contact angle increased from 108 to 125 after the first RGO coating, and it was saturated at about 135. Using kaolin as model hydrophilic particles, the depth filters with RGO-coated PP fibers showed a superior performance in terms of water flux and trans-filter pressure in comparison with those with the pristine and hydrophilic PP fibers prepared by coating functionalized GO. More importantly, particle detachment was enhanced by the hydrophobic coating during backwashing. This can be ascribed to the weakened attractive force between the RGO-coated fiber surfaces and kaolin particles due to the increase of hydrophobicity. This approach provides an effective means of enhancing the performance of synthetic fiber-based depth filters.
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