Fabrication of redox-mediator-free Z-scheme CdS/NiCo2O4 photocatalysts with enhanced visible-light driven photocatalytic activity in Cr(VI) reduction and antibiotics degradation

Tremendous efforts have been made to design novel type semiconductor photocatalysts as promising candidates to solve the problem of aquatic pollution. However, the exploration of photocatalysts with high activity and stability for removing heavy metal ions and antibiotics from water through visible light photocatalysis is still a challenge. In this work, a series of Z-scheme photocatalysts X% CdS/NiCo2O4 (X = 30, 40, 50, 60, 70) have been successfully constructed by a hydrothermal method. By anchoring the CdS nanoparticles on the surface of NiCo2O4 nanosheets, the obtained CdS/NiCo2O4 exhibits the narrower bandgap energy compare to CdS nanoparticles, which can enhance the visible light harvesting efficiency and suppress the electron-hole recombination, improving the photocatalytic activity. Moreover, the introduction of NiCo2O4 nanosheets cannot only inhibit the aggregation of CdS nanoparticles and increase the stability of the composite, but also improve the adsorption of pollutants on the surface of the composite. By virtue of these advantages, the best-performing CdS/NiCo2O4 (60 % CdS/NiCo2O4) revealed outstanding visible-light driven photocatalytic activity toward the degradation of Cr (VI) and Tetracycline Hydrochloride (TC-HCl) under the irradiation of a low energy consuming light (LED lamp, 5 W). Compared with pure CdS nanopaticles, the catalytic performance of 60 % CdS/NiCo2O4 for Cr (VI) and TC-HCl increased approximately 3.9 times and 32.7 times, respectively. Furthermore, the 60 % CdS/NiCo2O4 exhibits fantastic recyclability, its catalytic activity is nearly unchanged even after six cycles. Meaningfully, as an efficient visible-light photocatalyst, 60 % CdS/NiCo2O4 can be applied to reduction of Cr (VI) and degradation of TC-HCl in natural water samples (Yellow River water, which collected in Lanzhou section), which greatly expanded its application in practice.

Automated summary

A series of CdS/NiCo2O4 photocatalysts with Z-scheme structure were successfully constructed, showing enhanced visible light harvesting efficiency and suppressed electron-hole recombination, leading to significantly improved photocatalytic activity for pollutant degradation in water.