Fabrication of Z-scheme ZnO/Bi2O4 heterojunction photocatalyst with superior photocatalytic nitrogen fixation under visible light irradiation

Abstract ZnO/Bi2O4 heterojunctions with different ratios were successfully synthesized by one-step hydrothermal method. The photocatalytic activity for nitrogen fixation was investigated by Nessler's reagent spectrophotometry and ion chromatography method for comparison. As a result, the NH4+ concentration over 10%ZnO/Bi2O4 catalyst measured by ion chromatography is 0.22 mmol L−1 h−1·gcat−1 after 150 min visible light irradiation, which is about 1/135 of that obtained by Nessler's reagent method. Furthermore, the photocatalytic activity for degradation of methyl orange and ciprofloxacin was also evaluated. 10%ZnO/Bi2O4 shows optimal photocatalytic degradation efficiency (97.5 % and 95.6 % for methyl orange and ciprofloxacin), which are 40.7 and 28.3 times that of pure ZnO. Various characterization techniques and photoelectrochemical tests have proved that such enhanced photocatalytic activity was due to the heterojunction formation between ZnO and Bi2O4, which possesses a lower charge transfer resistance and efficient electron-hole pairs separation.