Synthesis of heterostructure δ-MnO₂/h-MoO₃ nanocomposite and the enhanced photodegradation activity of methyl orange in aqueous solutions

The growing extent of dye pollution by human activities has engendered an urgent need for removing of them through adjustable approaches. The adsorption–photocatalytic technique is attractive and widely employed to address the above issue, since it could achieve pollutant mineralization by the reactive species generated under the light irradiation without other chemicals. In this paper, a series of δ-MnO₂/h-MoO₃ nanocomposites was successfully synthesized by a simple two-step method. The structure and morphology of the as-prepared nanocomposite have been assessed by XRD, FESEM, TEM, XPS and BET surface area measurements, and the optical properties were detected by the UV–Vis diffuse reflectance, photoluminescence (PL) and photocurrent measurements. Photocatalytic performances of the prepared δ-MnO₂/h-MoO₃ nanocomposite were evaluated through photodegradation of dyes in solution under simulated sunlight irradiation. After a simple two-step preparation process, the specific surface area (S_BET) of the δ-MnO₂/h-MoO₃ composite was increased by about 4.5 times compared to the pure δ-MnO₂ and h-MoO₃, and this may result in a great adsorption property for the nanocomposite. With a broader absorption edge, high electron transfer efficiency and lower recombination efficiency of the photogenerated electrons and holes, the photocatalytic activity of the heterostructure δ-MnO₂/h-MoO₃ composites was improved heavily compared to the single-phase samples. Especially, when 20 mg of δ-MnO₂ (0.6 g)/h-MoO₃ composite was used to degrade methyl orange (MO) aqueous solution (100 mL, 15 mg L⁻¹), the degradation efficiency could reach 80.55% within 115 min under simulated sunlight irradiation. Additionally, the photodegradation cyclic tests showed that the nanocomposite exhibited excellent stability, as the degradation efficiency reaches 71.02% within 95 min after four cycles, which makes it to have a bright prospect of industrial application. Finally, the reasonable mechanism for the enhanced photocatalytic activity of the heterostructure δ-MnO₂/h-MoO₃ composites was investigated by active species trapping experiments, and the results showed that the synergistic effect between δ-MnO₂ and h-MoO₃ as well as the unique flower ball-stick morphology of composites lead to an excellent photocatalytic performance.