Facile construction of CoO/Bi2WO6 p-n heterojunction with following Z-Scheme pathways for simultaneous elimination of tetracycline and Cr(VI) under visible light irradiation

Developing low-cost, efficient and sustainable utilization of visible light catalysts to eliminate antibiotic and heavy metals contaminants simultaneously remains a huge challenge. Herein, a unique CoO/Bi2WO6 p-n heterojunction was successfully synthesized by a facile and simple solvothermal method for simultaneous elimination of tetracycline and Cr(VI) under visible light irradiation. Benefiting from p-n heterojunction following Z-Scheme pathways, 30 wt% CoO/Bi2WO6 heterojunction displayed the best photocatalytic activity for tetracycline degradation (90.7%) and Cr(VI) reduction (57.5%) singly after 90 min reaction. The reaction rate constant for CoO/Bi2WO6 heterojunction towards tetracycline degradation and Cr(VI) reduction were 0.02607 min−1 and 0.00909 min−1, which are 4.23, 4.92 times of pure CoO and 3.46, 4.61 times of pure Bi2WO6, respectively. It is related to the formation of p-n heterojunction, which avoids the agglomeration induced inactivation, extends the spectral response and facilitates the separation and utilization of charge carriers. More interestingly, the higher photocatalytic efficiencies are achieved to simultaneously eliminate the mixed tetracycline and Cr(VI), which are 1.03 and 1.76 times that of single tetracycline and Cr(VI), respectively. Moreover, the 30 wt% CoO/Bi2WO6 heterojunction photocatalyst can be reused for ten cycles and exhibits satisfactory properties of stableness and reusability. Furthermore, the possible reaction pathway and photocatalytic mechanism for TC degradation and Cr(VI) reduction were revealed based on capturing experiments of active species, electron spin resonance and liquid chromatography mass spectrometry. These findings provide a great promise of CoO/Bi2WO6 p-n heterojunction photocatalyst in mixed contaminants remediation.