Graphene hybridized high energy faceted titanium dioxide for transparent self-cleaning coatings

A transparent superhydrophilic self-cleaning nanocoating is fabricated and developed by hybridizing anatase TiO2 with graphene sheets. In the hybrid preparation, ellipsoidal TiO2 nanocrystals are grown exclusively over the graphene sheets, exposing high energy {001} and {010}/{100} facets. The hybrid is synthesized by a hydrothermally modified sol-gel method using CTAB (Cetyltrimethylammonium bromide) as the capping agent under an acidic pH 3 and using very low weight percentage of graphene with respect to as grown TiO2. The synthesized samples are studied for its phase, crystallinity, exposed facets, and optical properties using Raman, TEM and DRS UV–vis analyses. During the hydrothermal treatment, the graphene oxide sheets are reduced to graphene layers simultaneously on which in-situ growth of TiO2 nanocrystals takes place. A close chemical contact between both TiO2 and graphene established is confirmed from XRD, XPS and FTIR analyses. The photocatalytic activity studied from degradation of Methylene blue dye is increased by graphene hybridization, with a change in kinetic rate constant k = 9.23 × 10−3 min-1 for pristine TiO2 to 24.7 × 10−3 min-1 for the hybrid. The fabricated nanocoating of the hybrid over a glass substrate showed about 94% transparency throughout the visible region and a superhydrophilic behavior with the water contact ˜0° within 15 min of UV irradiation. The charge transfer mechanism by the reduced recombination rate in the hybrid is clearly investigated by PL spectra and TCSPC techniques.