Fabrication of full-spectrum response Bi2O4/BiO2-x heterojunction as high-performance photocatalyst for organic pollutants removal by a two-step hydrothermal method

Though Bi2O4 photocatalyst has attracted enormous concern because of its strong absorption in visible light region recently, the high recombination possibility of photoinduced electron-hole pairs and lack of the near-infrared light (NIR) harvesting capability for Bi2O4 alone restrict its photocatalytic performance. Herein, Bi2O4/BiO2-x junction was developed by a two-step hydrothermal method. A ternary BiO2-x/NaBiO3 center dot 2H(2)O/NaBiO3 center dot xH(2)O or binary BiO2-x/NaBiO3 center dot xH(2)O intermediate product was formed firstly during the first hydrothermal reaction depending on the concentration of NaOH solution. Then, Bi2O4/BiO2-x heterostructure was produced when the ternary and binary intermediate product underwent the second hydrothermal process in deionized water. The content of BiO2-x in the Bi2O4/BiO2-x heterojunction could be easily tuned by changing the NaOH concentration in the first-step hydrothermal reaction. Bi2O4/BiO2-x heterojunction could not only raise the charge carriers' separation efficiency but also broaden the optical absorption range to NIR area. As a result, the optimal Bi2O4/BiO2-x sample exhibits improved visible light photocatalytic degradation activity toward methyl orange (MO) and phenol, which is 2.67-fold and 2.84-fold higher than pristine Bi2O4 and BiO2-x, respectively. Under NIR irradiation, the optimal Bi2O4/BiO2-x sample also reveals superior catalytic activity for the degradation of MO, which is 11.99 times as high as that of single Bi2O4. The role of NaOH in the first-step hydrothermal reaction is discussed. The probable photocatalytic mechanism of Bi2O4/BiO2-x junction is put forward as well. This work supplies a novel strategy for designing full-spectrum response bismuth-based oxide heterojunction with high photocatalytic performance for organic pollutant removal.