ZIF-8 derived Fe single atom catalysts prepared by low-temperature pyrolysis for efficient peroxymonosulfate activation

The Fe-N-C catalysts featuring abundant FeNx sites activating peroxymonosulfate (PMS) have been considered an attractive approach to water treatment and purification. It was reported that the coordination numbers of FeNx could be precisely controlled by varying the pyrolysis temperature, thereby affecting the catalytic activity. However, almost all Fe-N-C catalysts were prepared through energy-consuming high-temperature pyrolysis strategies, the activation performance and mechanism under low-temperature pyrolysis conditions are still unclear. In this work, three single-atom Fe catalysts (FeSA-NC-300/500/1000) based on ZIF-8 were synthesized at different pyrolysis temperatures. Results showed that the degradation efficiency of sulfamethoxazole (SMX) in the FeSA-NC-500/PMS and FeSA-NC-1000/PMS systems could reach 100 % within 30 min, while only 91.9 % in the FeSA-NC-300/PMS system. Combined with the turnover frequency (TOF) of the catalysts, it was found that the catalytic activity of FeSA-NC-500 prepared by low-temperature pyrolysis was close to that of FeSA-NC-1000, which was superior to many reported Fenton-like catalysts. Mechanism analysis manifested that both radical (·OH, SO4−·, and ·O2−) and nonradical (1O2, high-valent Fe-oxo species, and electron transfer) pathways coexisted in the FeSA-NC/PMS systems. Impressively, the larger production intensity of reactive species occurred in FeSA-NC-500/PMS and FeSA-NC-1000/PMS systems. The difference between these FeSA-NC catalysts in actual printing and dyeing wastewater treatment offered some guidance for wider environmental applications. This work also provided a direction on the design and understanding of green and energy-saving Fe-N-C catalysts.