Reduced graphene oxide/graphitic carbon nitride composite for piezocatalysis and piezocatalytic activation of persulfate to degrade sulfamethoxazole

Piezocatalysis, relying on piezopotential and piezoelectric properties of catalysts, is intriguing deep research enthusiasm in water and wastewater treatment for its potential application on organic degradation. In this study, a novel piezocatalytic oxidation system, reduced graphene oxide/graphitic carbon nitride-persulfate-ultrasound (rGO/CN-PDS-US), in which g-C3N4 was proved to be piezoelectric, was constructed to degrade the antibiotics (sulfamethoxazole, SMX) in water. In rGO/CN-US system, 80.0 % of SMX was degraded in 30 min. The degradation efficiency of SMX was further improved to 95.7 % in presence of PDS. Density function theory (DFT) calculation results illustrated that deformation of g-C3N4 caused by ultrasonic vibration would generate dipole moment along the plane, which was the source of piezopotential. The piezoelectrically generated electron-hole pairs could efficiently separate with the assistance of in-built piezoelectric field. In this process, the electrons would effectively transfer from g-C3N4 to rGO. Compared with rGO/CN-US system, the degradation efficiencies of SMX by US alone and rGO/CN without US were only 1.1 % and 48.8 % respectively. After dosing PDS, the degradation efficiency further improved due to the facilitated electron transfer between PDS and piezocatalyst. Analyzed by DFT, CO had the highest reaction activity compared with COC, COOH, CHO and OH groups in rGO/CN-PDS-US system. Finally, the radicals and degradation products were analyzed, and possible degradation pathways of SMX under rGO/CN-PDS-US oxidation was proposed. This work provided a green and efficient piezocatalytic technology to remove antibiotic from water, and the mechanism was expected to be mutually beneficial for facilitating electron transfer among g-C3N4, rGO and PDS.