Two-phase hydrothermal synthesis of TiO2–graphene hybrids with improved photocatalytic activity

Highlights: •TiO2–graphene hybrids were synthesized via a two-phase hydrothermal method. •Assembly of TiO2 and graphene takes place at two-phase interface. •The phase transfer between two phases hinders the aggregation of samples. •Hybrids show improved photocatalytic properties and adsorption capacities. -- Abstract: TiO2–graphene hybrids (TGHs) were one-pot synthesized by a simple two-phase hydrothermal method, without the synthesis of TiO2 in advance. The structures, morphologies, and photocatalytic properties of samples for methyl orange were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry and differential scanning calorimetry, transmission electron microscopy, Raman spectrum, X-ray photoelectron spectroscopy, diffuse reflectance absorption spectrum, specific surface area, and photoluminescence. Experimental results show that the synthesis of TiO2, reduction of graphene oxide, and combination of them were realized simultaneously. The as-synthesized TGHs showed improved photodegradation performances compared to neat TiO2, commercial P25, and TGH synthesized by a single-phase (water) method. The improved photodegradation performances of TGHs are attributed to the suppressed recombination of electrons and holes caused by the effective transfer of photo-generated electrons from TiO2 to graphene. Moreover, the phase transfer of sample between the water and the chloroform in the two-phase system plays a crucial role in the enhancement of photocatalytic performances of TGHs, because through the phase transfer the aggregation of TGHs can be effectively hindered, leading to higher specific surface area, excellent adsorption capacity, and improved photocatalytic properties