In situ graphitization of small organic molecules on the surface of nano titanium dioxide to construct highly efficient photosynthetic hydrogen peroxide composite catalyst

Abstract

Hydrogen peroxide (H2O2) is a good strategic choice for developing sustainable energy. In recent years, although many researchers have focused on photocatalytic preparation of H2O2, the progress is still limited for the problems of low efficiency of H2O2 production, complex catalyst preparation, and high cost of catalyst. Here, a novel method to construct a hybrid photocatalyst was developed with one-step graphitization of specific organic small molecules, in which C, N, and O could be introduced simultaneously along with the formation of graphite-like structures within the inner pores of the nano-TiO2 surface. It not only changed the surface defects of TiO2 to successfully reduce its promotion on the photodecomposition of H2O2 but also adjusted the band gap of the catalyst and broadened its visible light absorption range. Besides, it also provided another two-electron oxygen reduction reaction pathway to enhance the catalytic activity of the photosynthesis of H2O2; thus, 11.78 mM/h H2O2, which exceeds all previously reported productivities, was produced under simulated sunlight. The modified catalyst not only has excellent ultraviolet light activity with an apparent quantum efficiency of 34.9% at 365 ± 5 nm but also has very good visible light activity with apparent quantum efficiency of 17.8% at 420 ± 5 nm and more than 1.66% solar-to-chemical conversion (>420 nm), which is very rare for nano-TiO2 and much promising for application. Our present research has proved that the organic molecule tetraethyl 4,4'-(1,4-phenylene)bis(2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate) successfully changed the surface defect modes of TiO2, making the oxygen defect that promotes the decomposition of H2O2 change to the C defect that is conducive to the photocatalytic generation of H2O2, and thus, the photocatalytic performance has been greatly improved. Thus, it is an important instruction for developing highly efficient and low-cost photocatalysts for synthesizing H2O2.