Qibo Liu,Yi Wang,Xiaoguang Sang,Jingce Bi,Ningning Liu,Xia Zhang,Zhuopeng Wang,Yide Han
The agglomeration and leaching of metal species are critical issues for iron-based catalysts to remove tetracycline (TC) through peroxydisulfate (PDS) activation. In this work, iron-oxide species confined in cha cage of silicon aluminum phosphate zeolite (Fe-SAPO-34) was successfully synthesized by in-situ encapsulation method to address the above challenges. In Fe-SAPO-34/PDS system, approximately 92.6% TC was removed within 150 min at experimental conditions: [pH] = 3, [TC] = 20 mg/L, [Catalyst] = 0.10 g/L, [PDS] = 1 mM. Meanwhile, the biggest degradation rate constant is 0.03689 min −1 , which surpasses the counterpart systems. This result originates from the well dispersion of Fe-oxide species in Fe-SAPO-34, providing more active sites for TC degradation. As expected, the Fe-oxide species leaching concentration is ultra-low (0.018 mg/L) in Fe-SAPO-34/PDS system, which is attributed that SAPO-34 has a confinement effect of cha cage and eight-ring pore openings to limit its leaching. The radical quenching tests and electron paramagnetic resonance (EPR) technology verify singlet oxygen ( 1 O 2 ) is the primary reactive oxygen species (ROS) in Fe-SAPO-34/PDS system. Furthermore, two possible pathways for TC degradation are proposed in line with the intermediate identified by liquid chromatography-mass spectrometry (LC-MS).
Qibo Liu,Jingce Bi,Zhouxiao Zhai,Wen Tian,Ningning Liu,Xia Zhang,Zhuopeng Wang,Huanying Zhou,Yide Han
Rate-limiting mass transfer is a critical issue for using iron-based catalysts supported by zeolites to activate peroxydisulfate (PDS) in the field of advanced oxidation processes (AOPs). In this study, hierarchically porous Fe-SAPO-34-DGC was synthesized via combing in-situ encapsulation method with dry gel conversion (DGC) technology. Tetracycline (TC) was applied as a model pollutant, about 91.5% TC in Fe-SAPO-34-DGC/PDS system can be degraded within 90 min, while it can be achieved for about 150 min in Fe-SAPO-34-HT/PDS system. Meanwhile, the degradation rate constant of Fe-SAPO-34-DGC/PDS system is 0.02391 min -1 , which is approximately 1.6 times higher than that of Fe-SAPO-34-HT/PDS system. The excellent catalytic performance of Fe-SAPO-34-DGC is caused by well dispersed iron-oxide species (the size about 1.47 nm) in cha cage and nanoplate-like morphology as well as mesoporous structure, resulting in the generation of more active sites for PDS activation and faster mass transfer and easier access to active sites. Moreover, the characterized results indicate that the absence of Si(3Al) species is favorable of the formation of nanoplate-like morphology, further leading to the formation of the mesoporous structure because of stacking. Besides, iron-oxide species in Fe-SAPO-34-DGC are confined in cha cage that can effectively keep back its leaching. Furthermore, the possibility of membrane reactor established by Fe-SAPO-34-DGC for practical environmental water treatment was evaluated. Therefore, this method combing in-situ encapsulation method with dry gel conversion technology provides an alternative pathway for construction of iron-based catalysts supported by zeolites to remove organic pollutants through PDS activation.
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