Piezocatalytic degradation of 2,4-dichlorophenol in a water environment by a g-C3N4/CdS heterojunction catalyst: interfacial electric field boosting mechanism

Graphitic carbon nitride (GCN) has been explored as a potential piezocatalyst to degrade environmental contaminants through harvesting mechanical energy. However, the low crystalline level and its uniplanar hydrogen bond induce poor charge transport ability, and therefore drastically suppress the piezocatalytic performance. Herein, a GCN/CdS composited catalyst was constructed by the in situ growth of CdS nanoparticles on the GCN surface. Due to the difference in Fermi levels, an S-scheme heterojunction was formed, and the interfacial electric field (IEF) could efficiently promote the charge transfer ability, which was demonstrated by its enhanced piezo-current response and reduced electrochemical resistance. The ultrasound-induced opposite polarization potentials on the GCN and CdS surfaces triggered redox reactions, and the produced electron and hole were driven by the IEF at the interface to quench with each other to maintain the piezoelectric potentials. Using 2,4-dichlorophenol (2,4-DCP) as a model pollutant, the S-scheme heterojunction showed much higher piezocatalytic activity than the individual GCN and CdS. The apparent rate constant of GCN/CdS with the optimized mass ratio (50 : 50) was 3.6 and 2.9 times higher than those of GCN and CdS, respectively. Furthermore, the effect of pH value, 2,4-DCP concentration and cycling number on the piezocatalytic behavior of GCN/CdS was systematically investigated. The degradation pathway of the pollutants during piezocatalysis was revealed by LC-MS study. Finally, by determining the band structure and detecting the produced ROSs, a possible mechanism is proposed to clarify the piezocatalytic process.