Synthesis of Cs₃PMo₁₂O₄₀/Bi₂O₃ composite with highly enhanced photocatalytic activity under visible-light irradiation

A novel visible-light-active Cs₃PMo₁₂O₄₀/Bi₂O₃ (CsPMo/Bi₂O₃) composite was prepared by a simple dissolution-precipitation method. The as-prepared samples were characterized by XRD, XPS, FT-IR, SEM, UV-Vis DRS, N₂ adsorption-desorption isotherms and electrochemical analysis. The results revealed that Bi₂O₃ was successfully modified by trace CsPMo. After the addition of H₃PMo₁₂O₄₀ acid (HPMo), the surface of Bi₂O₃ can be roughed. Subsequently, the presence of Cs₂CO₃ can neutralize the protons of HPMo forming CsPMo precipitate on Bi₂O₃. Comparing to naked Bi₂O₃ and CsPMo, the binary composite exhibited many beneficial characteristics in charge generation and separation, such as formation of p-n heterojunction, decreased band gap, enhanced photocurrent response and greatly reduced charge transfer resistance. The photocatalytic activities of the as-prepared samples were evaluated by the degradation of phenol under visible light. The calculated pseudo-first-order rate constants for phenol degradation were 2.7 and 14.8 times relative to that on Bi₂O₃ and CsPMo, respectively. Dramatically enhanced photocatalytic performance can be observed when the optimal CsPMo/Bi₂O₃ composite (2.5% CsPMo) was applied. The major active species involved in the degradation process are in the following order: superoxide radical (O₂^-) > hydroxyl radical (OH) ≈ hole (h⁺). Besides, the CsPMo/Bi₂O₃ composite also displayed good stability in cyclic experiments.