Enhanced usage of visible light by BiSex for photocatalytic degradation of methylene blue in water via the tunable band gap and energy band position

The increasing demand for new materials with narrow bandgap energy, capable of harvesting the photons in the visible range, is central in the remediation of environmental pollutants by photocatalytic reactions. For the first time, we report a novel visible light driven photocatalyst of Bi2Se3/Bi1.007Se0.993 by the formation of solid solution composite. Both the individual Bi2Se3 and Bi1.007Se0.993 have very low photocatalytic efficiency under visible light irradiation; however, Bi2Se3/Bi1.007Se0.993 provides much higher efficiency in decomposing methylene blue (MB). Especially in the presence of H2O2, the reaction rate was enhanced by 15 times and 100% of MB degradation was obtained in 90 min. Characterization results confirmed that the bandgap of Bi2Se3/Bi1.007Se0.993 was greatly broadened to 1.38 eV compared with Bi2Se3 of 0.3 eV, which matched well with visible range. Moreover, the relative conduction band position vs. NHE of Bi2Se3/Bi1.007Se0.993 was −0.3 V, which was more negative than that of Bi1.007Se0.993 of +0.2 V. It was responsible to the excellent photocatalytic activity due to harvesting the photons in the visible range. Finally, N-type semiconductor based reduction O2 to O2
- - and photoreduction of H2O2 into
- OH involved reaction mechanism under the visible light irradiation was proposed based on all the experimental results.