Design and simple synthesis of composite Bi₁₂TiO₂₀/Bi₄Ti₃O₁₂ with a good photocatalytic quantum efficiency and high production of photo-generated hydroxyl radicals

Abstract

Hybrid Bi₁₂TiO₂₀/Bi₄Ti₃O₁₂ composites with different Bi : Ti molar ratios were successfully fabricated using a one-step solid-state calcination. These samples were characterized using X-ray diffraction, specific surface area analysis, scanning electron microscopy, high-resolution microscopy, selected-area electron diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence analyses, and photocurrent and electrochemical impedance spectroscopy. Some specified techniques were also used to investigate the photocatalytic properties and the formation of radical species under UV-vis irradiation. The composites provide an efficient pathway for photo-produced electrons and holes to diffuse and transfer to the exterior of the particles for photodegradation, because of the good contact between hybrid Bi₁₂TiO₂₀ and Bi₄Ti₃O₁₂. Therefore, the hybrid Bi₁₂TiO₂₀/Bi₄Ti₃O₁₂ can prolong the carrier lifetime as compared to any individual material (Bi₁₂TiO₂₀ or Bi₄Ti₃O₁₂). In particular, the hybrid Bi₁₂TiO₂₀/Bi₄Ti₃O₁₂ composite with a Bi : Ti ratio of 12 : 6 had the longest photo-generated carrier lifetime and produced the maximum amount of hydroxyl radicals during UV-vis irradiation; therefore, it demonstrated the best photo-catalytic properties. A Z-scheme mechanism was proposed to explain the hydroxyl radical yield and photodegradation.