Efficient photocatalytic production of H2O2 and photodegradation of tetracycline by CdS/square tubular g-C3N4 S-scheme heterojunction photocatalyst

Photocatalytic technology is an effective method for clean energy production and wastewater treatment. In this work, a square tubular g-C3N4 (MCN) is first synthesized by the aid of thermal polymerization of melamine in mixed KCl/LiCl molten salt and then loaded with CdS nanoparticles via a solvothermal method to obtain the final composite (MCN@CdS). This complex exhibits dual catalytic characteristics: photocatalytic oxygen reduction to produce hydrogen peroxide and photocatalytic degradation ability of antibiotics. The specific surface area (SSA) of MCN was enhanced by calcination with the help of molten salt, and the introduction of CdS expanded the absorption edge of MCN@CdS. In addition, electrochemical impedance and photocurrent spectroscopy confirmed that separation and migratory efficiency of photoproduced charge carriers could be promoted by the combination of MCN and CdS. As a result, the yield of hydrogen peroxide photocatalyzed by MCN@CdS is up to 0.95 mmol· L−1 in 80 min under visible light, which is 1.2 and 1.9 times larger than that of pure MCN and CdS. More importantly, the removal rate of tetracycline photocatalyzed by MCN@CdS, within 30 min with the participation of O2, achieved up to 99.5 %, 4 times faster than that in O2-free environment.