Making silica nanoparticle-covered graphene oxide nanohybrids as general building blocks for large-area superhydrophilic coatings.

We report a facile strategy to synthesize silica nanoparticles-coated graphene oxide (GO-SiO2) nanohybrids in a water-alcohol mixture at room temperature. AFM observations revealed that silica nanoparticles with ca. 50 nm in size were densely and evenly covered on graphene oxide sheets. Due to the space layer of silica nanoparticles, micro-scale GO-SiO2 hybrid plates could be individually dispersed in water and polar organic solvents, promising good solution-based processibility. The growth process of GO-supported silica is traced by TGA and XRD measurements, showing that 24 hours is enough to achieve a fine cover effect for the disappearance of (002) diffraction peak of GO. Based on the high dense overlaying of silica nanoparticles, up to micro-scale silica sheets with thickness of ca. 8 nm were readily fabricated by burning GO-SiO2 at 650 °C in air. Likewise, a centimeter-scale semitransparent film of silica nanosheets was prepared by calcining a GO-SiO2 film. Interestingly, the GO-SiO2 nanohybrids exhibit excellent hydrophilic nature and can be directly applied as a general kind of building blocks to construct large-area superhydrophilic surfaces on arbitrary substrates (e.g., lotus leaf, ceramic tile and polypropylene) through the simple drop-coating method. Such a coating methodology paves the way for making large-area superhydrophilic surface without extra process treatments and damaging the intrinsic structure of substrates.