Ultrasonic-assisted fabrication of a direct Z-scheme BiOI/Bi2O4 heterojunction with superior visible light-responsive photocatalytic performance

Abstract

Z-scheme heterojunctions photocatalysts for the transfer and separation efficiency of carriers are increasingly popular. Here, a direct Z-scheme BiOI/Bi2O4 heterojunction was successfully constructed via an ultrasonic-assisted hydrothermal method. X-ray diffraction, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy results confirmed the successful construction of the BiOI/Bi2O4 heterojunction. The optimized BiOI/Bi2O4 photocatalyst offered enhanced degradation rates under visible light: these values were approximately 2.8- and 30-fold higher than Bi2O4 and BiOI, respectively. Interestingly, the ultrathin, in-situ prepared Bi2O2CO3 nanosheets grew on the surface of a BiOI/Bi2O4 heterojunction under visible light irradiation, and the presence of the resulting Bi2O2CO3 further increased the degradation efficiency. This was confirmed using photoluminescence and electrochemical impedance spectroscopy studies. The Z-scheme electron transfer paths contribute to faster separation and transfer of photo-generated carriers. The radical trapping experiments certified that holes and superoxide radicals were the main active species. Furthermore, the positions of the conduction band of BiOI and Bi2O4 samples were investigated via Mott-Schottky measurements. Finally, a Z-scheme photocatalytic mechanism was proposed for the BiOI/Bi2O4 heterojunction. This work provides an effective strategy to construct Z-scheme heterojunctions for removal of organic pollutants.