Efficient degradation of Congo red by persulfate activated with different particle sizes of zero-valent copper: performance and mechanism

In this study, Congo red (CR) was degraded by different particle sizes of zero-valent copper (ZVC) activated persulfate (PS) under mild temperature. The CR removal by 50 nm, 500 nm, 15 mu m of ZVC activated PS was 97%, 72%, and 16%, respectively. The co-existence of SO42- and Cl- promoted the degradation of CR, and HCO3- and H2PO4- were detrimental to the degradation. With the reduction of ZVC particle size, the effect of coexisting anions on degradation grew stronger. The high degradation efficiency of 50 nm and 500 nm ZVC was achieved at pH=7.0, while the high degradation of 15 mu m ZVC was achieved at pH=3.0. It was more favorable to leach copper ions for activating PS to generate reactive oxygen species (ROS) with the smaller particle size of ZVC. The radical quenching experiment and electron paramagnetic resonance (EPR) analysis indicated that SO4-center dot, center dot OH and center dot O-2(-) existed in the reaction. The mineralization of CR reached 80% and three possible paths were suggested for the degradation. Moreover, the degradation of 50 nm ZVC can still reach 96% in the 5th cycle, indicating promising application potential in dyeing wastewater treatment.

Automated summary

In this study, Congo red (CR) was degraded using different particle sizes of zero-valent copper (ZVC) activated persulfate (PS). The degradation efficiency varied with ZVC particle size, with 50 nm and 500 nm ZVC achieving higher removal rates of CR compared to 15 μm ZVC. The coexistence of certain anions promoted the degradation, while others were detrimental. The smaller the ZVC particle size, the stronger the influence of coexisting anions on the degradation. The degradation pathways and mineralization of CR were identified, and the potential application of 50 nm ZVC in dyeing wastewater treatment was demonstrated with high degradation efficiency even after multiple cycles.