Monodispersed inorganic/organic hybrid spherical colloids: Versatile synthesis and their gas-triggered reversibly switchable wettability

Here we report a versatile one-step method for producing five types of highly monodisperse transition metal oxide/organic hybrid colloids of IVb (Ti, Zr, Hf) and Vb (Nb, Ta) groups with reversibly switchable hydrophobicity and hydrophilicity. Such materials have been synthesized by simply mixing long chain carboxylic acids, amines with metal alkoxides in an alcohol solution followed by addition of a small amount of water, due to the co-effect of metal–organic coordination and the hydrophobic long chain. Moreover, the wetting behavior of the carboxyl and amine groups are dramatically changed from hydrophobic to hydrophilic based on their ionization degree. Therefore, because of the presence of long chain carboxylic acids or amines within the spheres, the metal oxide–organic complexes respond on exposure to basic or acidic gases by reversibly switching between hydrophobic and hydrophilic states, without damaging the metal oxide spheres.