Self-assembled reduced graphene oxide-TiO ₂ nanocomposites: Synthesis, DFTB+ calculations, and enhanced photocatalytic reduction of CO ₂ to methanol

A facile combined method, namely sonothermal-hydrothermal, was adopted to assemble titanium dioxide (TiO ₂ ) nanoparticles on the surface of reduced graphene oxide (RGO) to form nanocomposites. Characterization techniques confirm that RGO-TiO ₂ composite is well constituted. Enhanced photocatalytic CO ₂ reduction to methanol by the composites under UVA and visible irradiation suggests the modification in the band gap of the composite and promotion of the separation of photogenerated carriers, yielding methanol production rate of 2.33 mmol g ⁻¹ h ⁻¹ . Theoretical investigation demonstrated that combining RGO with TiO ₂ resulted in an upward shift of TiO ₂ bands by 0.2 V due to the contribution of RGO electrons. Relatively strong adsorption of RGO over the (101) anatase surface with the binding energy of approximately 0.4 kcal mol ⁻¹ per carbon atom was observed. Consideration of orbitals of TiO ₂ , RGO and RGO-TiO ₂ composite led to a conclusion that UVA photoreaction proceeds via the traditional mechanism of photogenerated electron transfer to RGO while visible light CO ₂ reduction proceeds as a result of charge transfer photoexcitation that directly produces electrons in RGO and holes in TiO ₂ . Superior photocatalytic activity of RGO-TiO ₂ composite in the present study is attributed to the formation of tight contact between its constituents, which is required for efficient electron and charge transfer.