Design and synthesis of Z-scheme heterojunction-based ZnO-MnWO4@g-C3N4 ternary nanocomposite for efficient methylene blue degradation

The paper presents a novel highly photo-efficient Z-scheme heterojunction-based ZnO-MnWO4@g-C3N4 ternary nanocomposite synthesized using coprecipitation and ultrasonication methods. The results showed that 94.5 % methylene blue (MB 10 ppm) could be photodegraded under visible light irradiation within 50 min with 10 mg of catalyst. The ZnO-MnWO4@g-C3N4 (1CN:1ZM) with 1:1 displayed excellent results with 94.50 % degradation efficiency towards MB as compared to two other ratios (1CN:2ZM, 2CN:1ZM). The kinetic data revealed that the developed nanocomposite's degradation rate is 2.57 times faster than the pure g-C3N4. A possible double Z-scheme pathway is proposed based on all the components' potential positions. The photoactivated electrons accumulated at the conduction band (CB) of the g-C3N4, while holes accumulated at the valence band (VB) of MnWO4 of the ZnO-MnWO4@g-C3N4 nanocomposite. The catalyst's efficiency remained stable after three cycles, showing the nanocomposite's sustainable stability. The enhanced photocatalytic activity was attributed to the synergistic effect of the ternary nanocomposite, which promoted the separation of photoinduced charge carriers and increased the surface area of the photocatalyst. The study provides a new way to design and develop efficient photocatalysts for environmental remediation applications.