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

Abstract

• La-doped NiFe-LDH containing Keggin type polyoxometalate interlayer were synthesized. • The NiFeLa{HPW}-LDH exhibited better catalytic performance than NiFeLa-LDH. • The intercalated HPW played a vital role in electron transfer. • SO 4 − and OH were the main radicals in catalytic degradation of tetracycline. • The formation of the complex and redox cycle were responsible for the catalysis. In this work, a series of La-doped NiFe-layered double hydroxides containing a novel Keggin type polyoxometalate 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 SO 4 − and HO were the dominant reactive radicals engaging in the degradation process. Furthermore, the formation of a complex of Ni(II)/Fe(II)/La(III)−(HO)OSO 3 − 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.