Synthesis and characterization of TiO2–graphene nanocomposites modified with noble metals as a photocatalyst for degradation of pollutants

Abstract

TiO2–graphene (TiO2–GR) nanocomposites were synthesized using photocatalytic reduction method. TiO2–GR nanocomposites were thereafter doped with noble metals (Pt and Pd) by chemical reduction of the corresponding cations. The samples were characterized by different techniques. The addition of GR to TiO2 decreases the crystalline size of TiO2 due to the homogeneous dispersion of the TiO2 nanoparticles on GR sheets and prevention of coagulation of TiO2 nanoparticles during synthesis process. In addition, the surface area of TiO2 was increased by addition of GR and deposition of noble metals which helps to prevent agglomeration of graphene sheets and TiO2 nanoparticles. Red shifts to the higher wavelength have been detected for both TiO2–GR and M-TiO2–GR nanocomposites. X-ray photoelectron spectroscopy demonstrated that graphene oxide is reduced to GR by the UV irradiated TiO2 nanoparticles, TiC bonds are formed, and Ti3+ sites are also present on the surface of photocatalyst. The photocatalytic activity of all samples was evaluated for the photodegradation of two pollutants (2,4-dichlorophenoxyacetic acid and Reactive Red 195) in aqueous medium under UV and visible irradiations. The M-TiO2–graphene nanocomposites exhibited excellent photocatalytic activity within both UV and visible regions. The results confirm that the addition of GR as well as noble metal to TiO2 nanoparticles increases electron transport, thus impeding the charge recombination of the excited TiO2. The highest photocatalytic activity was observed for Pt–TiO2–GR nanocomposites due to its high photonic efficiency.