MOFs-derived hollow FeCo@C as peroxymonosulfate activator for degradation of organic pollutants: Insight into the catalytic sites by experimental and theoretical study

•FeCo@C exhibited excellent catalytic performance for PMS activation.•SO4−, OH and 1O2 were the dominant ROS responsible for OG removal.•The stability of FeCo@C was superior to that of precursor FeCo-MOF-74.•The (110) facet of FeCo served as preferred sites based on theoretical calculation.•The toxicological simulation verified the reduced toxicity of products. A hollow sphere (FeCo@C) is developed and serves as a highly efficient catalyst of peroxymonosulfate (PMS) for degradation of orange G (OG) with a pseudo first-order constant of 0.119 min−1 that was 5.15 and 1.43 times of Fe@C and Co@C, respectively. X-ray photoelectron spectroscopy and Density Functional Theory (DFT) calculations demonstrated that the (110) crystal plane of FeCo alloy was the most active site for activation of PMS to generate SO4− and OH. The quenching experiments and EPR test indicated that SO4−, OH, and 1O2 were generated in FeCo@C/PMS system and acted as the predominant reactive species. The synergistic effects between Fe and Co species were responsible for the high catalytic performance of FeCo@C. The carbon in FeCo@C act as a carrier to improve the stability with good reusability over five cycles at pH 7.0 and 9.0, as well as an electron mediator and activator to enhance the catalytic performance. Effects of PMS dosage, catalyst concentration, solution pH, and humic acids on OG removal were also investigated. Furthermore, the reduced toxicity of intermediate products was verified by quantitative structure–activity relationship (QSAR). This work demonstrates a feasible strategy for designing of high-performance and stable catalysts for the organic pollutant degradation based on PMS oxidation processes.