Efficient catalytic degradation of p-nitrophenol using a novel 2D nanoflake array MWCNTs/PPy/PDA-nZVI catalyst

Heterogeneous Fenton-like catalyst, nano zero-valent iron (nZVI) is being increasingly investigated as an environmental-friendly and low-cost reagent for water purification. However, low utilization ratio of active sites and poor stability make its application in realistic scenario challenging. Herein, a unique two-dimensional (2D) nanoflower-like catalyst via anchoring nZVI on multiwalled carbon nanotubes/polypyrrole/polydopamine (MWCNTs/PPy/PDA) was successfully constructed on the surface of stainless steel (SS) mesh for p-nitrophenol (PNP) degradation. The 2D nanoflake array structure with ultrathin thickness (about 50 nm) inhibited nZVI agglomeration and promoted the exposure of active sites. PNP can be degraded with the modified kinetic rate constant (K-value) up to 76.02 μmol g−1 s−1, surpassing other Fenton-like systems by factors of 1580.4–1267. And the removal rate maintained 90.6 % in the 6th cycle. Notably, a continuous flow reactor was established and exhibited an unprecedented reaction rate constant of 1457.8 min−1, outperforming batch reactor with 2––3 orders of magnitude. The highly efficient catalysis was attributed to unique 2D nanoflake morphology, enhanced utilization ratio of reactive sites, special nanoconfinement effect and the convection-accelerated mass transfer. Density functional theory (DFT) calculations further substantiated the accelerated Fe (III)/Fe (II) redox cycling and electron transfer between substrate and nZVI. This study provides necessary inspiration and guidance in rational designing of efficient nZVI catalytic reactor toward environmental applications and more.