One-step solid state synthesis of facet-dependent contact TiO2 hollow nanocubes and reduced graphene oxide hybrids with 3D/2D heterojunctions for enhanced visible photocatalytic activity

Abstract

One-step solid state calcination strategy via a template-engaged topotactic transformation process has been developed to construct serials of 3D TiO2 hollow nanocubes (TiO2-HNCs) with 2D reduced graphene oxide (rGO) heterojunction hybrids with facet-dependent contact for the first time. The effect of calcination temperature and TiOF2/GO mass ratio on the morphology and photocatalytic activity of TiO2-HNCs/rGO hybrids was systematically discussed. The study indicated that 3D TiO2 hollow nanocubes were assembled by six regular nanosheets and GO can effectively reduce the solid-state calcination temperature and facilitate the topological transformation from cubic TiOF2 to TiO2-HNCs through 3D/2D heterojunctions hybridized to TiO2-HNCs, which also provided a transferring photo-induced electrons bridge to sensitize TiO2-HNCs for enhancing visible light response. The infrared spectra (IR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopic studies revealed that rGO principally hybridized on the surface as sp2 graphitic carbon in extended p-π conjugated environments and a small percentage of rGO created carbonate structure by substituted surface Ti atoms in the TiO2-HNCs lattice. Due to the superior sensitization and charge carrier mobility of rGO, the photodegradation activity of Rhodamine B (RhB) of as-prepared T300/5rGO hybrid improved 4.6 times compared to P25 with a degradation yield of 99% within 90 min under simulated sunlight irradiation (>420 nm) and still remained over 95% after 5 recycles. The enhanced photoreactivity of TiO2-HNCs/rGO was mainly attributed to the strong hybridized interaction through chemical bonds between TiO2-HNCs and rGO, which formed 3D/2D facet-dependent contact heterojunctions and further verified by its good dispersibility and stability. The unique facet-dependent contacting rGO with {1 0 1} instead of {0 0 1} facets of TiO2-HNCs facilitated the injection and transfers of photo-induced electrons from {1 0 1} facet of TiO2-HNCs to rGO, thus retarding the recombination of electron-hole pairs, which was not only increasing the numbers of active sites, but also facilitating the adsorption of dye molecules, and improving light-harvesting ability, thereby enhancing visible photoreactivity of TiO2-HNCs/rGO hybrids.