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/NaBiO3·2H2O/NaBiO3·xH2O or binary BiO2−x/NaBiO3·xH2O 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.Graphical abstract