Activation of amorphous Bi2WO6 with synchronous Bi metal and Bi2O3 coupling: Photocatalysis mechanism and reaction pathway

Amorphous semiconductors usually suffer from low photocatalysis efficiency due to the fast charge recombination rate. In this work, to activate the amorphous Bi2WO6, Bi2O3 and Bi particles were in sequence deposited over its surface via a facile in situ chemical reduction of amorphous Bi2WO6 by NaBH4 at room temperature. In the resultant ternary Bi/Bi2O3/Bi2WO6, the well-formed heterojunctions (i.e. Bi-Bi2O3 and Bi2O3-Bi2WO6) and the surface plasmon resonance effect of Bi both contribute to an increase in charge carrier concentration, an efficient e(-)/h(+) separation and then an enhanced visible light photocatalytic performance. The molar ratio of Bi, Bi2O3 and Bi2WO6 in composite can be modulated by the dosage of NaBH4, and consequently the amount of each heterojunction (i.e. Bi/Bi2O3 or Bi2O3/Bi2WO6) as well as the intensity of SPR effect could be tuned. The photocatalytic NO removal test under visible light irradiation shows that BWO-0.8 (0.8 denotes the molar ratio of NaBH4 to Bi2WO6) presents a maximum NO removal efficiency of 55.4%, much higher than that of the pristine amorphous Bi2WO6 (10%). The enhanced activity can be attributed to the balanced SPR effect of Bi metal and the heterojunction effect, making their overall contribution maximized. The pathway study of photocatalytic NO oxidation by in situ FT-IR suggests that NO is converted to nitrates adsorbed over the catalyst surface. The present work could provide a new approach to activate the amorphous semiconductors for efficient visible light photocatalysis.