S-scheme CuO/ZnO p-n heterojunctions for endorsed photocatalytic reduction of mercuric ions under visible light

Abstract

Heterojunction photocatalysts signify a green approach for the treatment of toxins below light radiation through reduction or oxidation. However, realizing these photocatalysts under visible light is still a key role issue. In this work, mesoporous ZnO nanoparticles with a surface area of 250 m2 g−1 were synthesized polymer-assisted sol–gel process. The obtained ZnO formed an S-scheme p-n heterojunction by adding CuO through thermal decomposition of nitrate solution at 3.0–12.0 et.%. The constructed CuO/ZnO heterojunction revealed a similar mesoporous surface texture but with wider light absorption and a narrower bandgap of 2.60–2.73 eV compared with 3.18 and 1.85 eV for parent ZnO and CuO. The CuO/ZnO was utilized for photocatalytic reduction of mercuric ions (Hg2+) as well-known heavy metal ions existed in wastewater systems. The 9.0 wt% CuO-added ZnO achieved a comprehensive Hg2+ photoreduction with an oxidation rate of 38.8 µm min−1 in 40 min exposure at an optimized dose of 1.6 g L−1. The obtained 9 %CuO/ZnO also unveiled robust recyclability for five runs. The superior activity of this obtained photocatalyst is regarded to the powerful S-scheme heterojunction formation between ZnO and CuO besides the relatively broader light absorption and high surface area.