Modulating charge transport in semiconductor photocatalysts by spatial deposition of reduced graphene oxide and platinum

Abstract

Spatially controlled deposits of reduced graphene oxide (rGO) and Pt on TiO2 were fabricated and assessed for the photocatalytic degradation of a range of organic compounds including carboxylic acid (oxalic acid), alcohols (tert-butanol, isopropanol), and halogenated aromatics (2,4-dichlorophenoxy acetic acid, 2,4-D). By selectively depositing Pt onto rGO that is attached to TiO2 (Pt–rGO/TiO2) or rGO onto Pt/TiO2 (rGO/Pt–TiO2), and by comparing with Pt/TiO2 and rGO/TiO2, we established the actual roles of Pt and rGO in photocatalysis. The deposition of Pt on TiO2, which formed the Schottky barrier at the interface, was found to be much more efficient in enhancing photocharge separation than rGO attachment, which merely extracts the photoelectrons interfacially. Both Pt and rGO show catalytic effects in the surface electron transfer. For the same Pt and rGO loading, the most efficient configuration was achieved by rGO/Pt–TiO2 since the rGO interfacially extracts the photoelectrons from the Pt sink, while providing additional sites for the reduction of molecular oxygen. The complex relationships between the physicochemical properties of the composites and the photocatalytic efficiencies of direct hole oxidation (oxalic acid), indirect oxidation by hydroxyl radicals (isopropanol and tert-butanol), and dearomatization and dechlorination (2,4-D) were established. Based on this, further enhancement of the photocatalytic activity of the composite photocatalysts was achieved by adding and optimizing the loading of Pt onto the rGO component of the rGO/Pt–TiO2 to enhance electron transfer on rGO. As a result, photocatalytic efficiency 3.5-fold that of the optimized Pt/TiO2 was achieved. For the same amount of Pt loading in Pt/TiO2, a detrimental effect was measured.