ZnCuAl-LDH/Bi2MoO6 Nanocomposites with Improved Visible Light-Driven Photocatalytic Degradation

In this study, pure Bi2MoO6 was synthesized via a solvothermal method. A ZnCuAl-layered double hydroxide (LDH)/Bi2MoO6 (denoted as LDH/Bi2MoO6) nanocomposite was synthesized via a steady-state coprecipitation route using Bi2MoO6 as the matric material. LDH was deposited on the surface of Bi2MoO6 with a close contact interface. The specific surface area of the resulting LDH/Bi2MoO6 composite increased up to 19.1 m(2).g(-1) owing to the stacking arrangement between LDH and the Bi2MoO6 nanosheets, resulting in the generation of a large number of reactive sites. In addition, the light absorption region of the LDH/Bi2MoO6 composite was larger than those of pure LDH and Bi2MoO6 because of the formation of a heterojunction structure and the possible quantum size effect. The photocatalytic performance of the as-prepared samples was evaluated by carrying out the degradation of rhodamine B (RhB) using them under visible light irradiation. Compared to pure LDH and Bi2MoO6, the LDH/Bi2MoO6 nanocomposite exhibited enhanced photocatalytic activity for the degradation of RhB. With an increase in the LDH content, the photocatalytic activity of the LDH/Bi2MoO6 composite first increased and then decreased. Although the addition of an optimum amount of LDH was beneficial for the generation of electron-hole pairs, excessive LDH on the surface of Bi2MoO6 decreased the visible light absorption ability of both the components, thus reducing photocatalytic activity of the composite. This indicates that an appropriate LDH:Bi2MoO6 molar ratio is necessary for obtaining LDH/Bi2MoO6 composites with excellent photocatalytic activity. Furthermore, the LDH/Bi2MoO6 composite showed high photocatalytic stability and reusability. The structure of the LDH/Bi2MoO6 composite remained almost unchanged even after four photodegradation cycles. The enhanced photocatalytic performance of the composite can be attributed to the combined effect of its heterojunction structure and high specific surface area, which are beneficial for effective separation of photogenerated charge carriers and the availability of a large number of active sites for photocatalysis. It was found that center dot OH and O-2(center dot-) were the main reactive species, while e(-) and h(+) contributed little to the photodegradation process. The generation, transfer, and separation of photoinduced electrons and holes in the composites were investigated by transient photocurrent responses, electrochemical impedance spectroscopy Nyquist plots, and photoluminescence measurements. The results showed that the heterojunction structure of the composites played a key role in enhancing their photocatalytic activity. A possible photodegradation mechanism was proposed for the composite. This study will provide a facile approach for the preparation of LDH- and/or Bi2MoO6-based nanocomposites. The LDH/Bi2MoO6 nanocomposite prepared in this study showed huge potential to be used as a visible-light photocatalyst for degrading environmental pollutants.