In-situ encapsulation synthesis of hierarchically porous Fe-SAPO-34 via a dry gel conversion method for organic pollutants removal through PDS activation

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.