Efficiently harvesting the ultrasonic vibration energy of two-dimensional graphitic carbon nitride for piezocatalytic degradation of dichlorophenols

Mechanical energy harvesting by piezoelectric materials to drive catalysis reactions has recently received extensive attention for fuel production and environmental remediation. It has been well known that some two-dimensional (2D) ultrathin structures which are not piezoelectric in bulk become intrinsically piezoelectric because of the loss of centrosymmetry. In this work, we synthesized a nanosheet-like 2D g-C 3 N 4 catalyst with a thickness of 3-5 nm that showed a significant piezoelectric response. The ultrasound-vibration-induced interior piezoelectric field drove electrons and holes to migrate in opposite directions towards the surface of nanosheets, leading to the formation of active species. This 2D g-C 3 N 4 presented excellent piezocatalytic performance for the degradation of dichlorophenols, and the decomposition efficiency for 2,4-dichlorophenol (2,4-DCP), 2,5-dichlorophenol (2,5-DCP) and 2,6-dichlorophenol (2,6-DCP) reached 98.5%, 85.5%, and 72.1%, respectively, after a 150 min ultrasonic treatment. Furthermore, the good stability and reusability of the 2D g-C 3 N 4 were demonstrated, and a possible degradation pathway was proposed based on the determined intermediates. The findings in this work clearly reveal that the metal-free 2D g-C 3 N 4 should be a promising catalyst to efficiently remove organic pollutants from the environment. The ultrasound-induced piezoelectric field drives electrons and holes to migrate in opposite directions towards the surface of 2D g-C 3 N 4 , leading to the formation of active species, which further degrade dichlorophenols into small molecules.