Polyoxometalate intercalated La-doped NiFe-LDH for efficient removal of tetracycline via peroxymonosulfate activation

In this work, a series of La-doped NiFe-layered double hydroxides containing a novel Keggin type poly-oxometalate interlayer (NiFeLa{HPW}-LDH) were synthesized and initially applied as heterogeneous catalyst for peroxymonosulfate (PMS) activation. Characterizations indicated that polyoxometalate anions were successfully intercalated in the layers of NiFeLa-LDH. Experiment results showed that NiFeLa{HPW}-LDH exhibited better catalytic performance than the counterpart precursor. The influences of various experimental parameters, such as pH value, initial TC concentration, HPW intercalation content, catalyst loading and peroxymonosulfate concentration were investigated in detail. Quenching experiments and the results of electron paramagnetic resonance (EPR) demonstrated the SO4-center dot and HO center dot were the dominant reactive radicals engaging in the degradation process. Furthermore, the formation of a complex of Ni(II)/Fe(II)/La(III)-(HO)OSO3- and the succeeding redox cycle of Ni(II)/Ni(III)/Ni(II), Fe(II)/Fe(III)/Fe(II), La(III)/La(IV)/La(III) were responsible for the generation of active radicals via activating PMS. Meanwhile, it's worth noting that the intercalated HPW also played a vital role in electron transfer.

Automated summary

A novel NiFeLa{HPW}-LDH catalyst was synthesized and exhibited superior catalytic performance for PMS activation compared with the precursor. The degradation process was mainly driven by SO4· and HO· as reactive radicals, with the formation of Ni(II)/Fe(II)/La(III) complexes and subsequent redox cycles of Ni/Fe/La playing vital roles in generating active radicals. The intercalated HPW also played a significant role in electron transfer during the process.