Microwave-enhanced catalytic degradation of p-nitrophenol in soil using MgFe2O4

The application of MgFe2O4 as microwave (MW) absorber and catalyst to removal p-nitrophenol (PNP) in soil has been investigated, including the catalytic performance, removal route, and reaction mechanisms. Five types of MgFe2O4 nanoparticles were synthesized with chemical co-precipitation (M-1, M1-1, and M1-2), gel combustion (M-2), and reverse micelle (M-3) methods, respectively, and characterized by FTIR, XRD, and SEM technologies. The results showed that the chemical co-precipitation of MgFe2O4 (M-1, calcined at 600 degrees C for 2 h) with higher O-H and H-O-H contents and higher Mg2+/Fe3+ occupying tetrahedral sites had the highest catalytic performance for PNP degradation. The enhancement of MW catalytic performance was attributed to the significant increased and hypodispersion of "hot spots" on MgFe2O4 surface (>1000 degrees C) and the generation of various active species ((OH)-O-center dot and center dot O-2(-)). Water and oxygen molecular as active species donors played an important role in the catalytic process. The main degradation products were phenol, hydroquinone, 1,2,4-trihydroxybenzene, and dihydroxynitrobenzene. Three stages were occurred in the MW catalytic process. A part of PNP was firstly thermal desorbed from soil with soil temperature increasing, and PNP was further catalytically oxidized by (OH)-O-center dot and center dot O-2(-) species from the disassociation of water and oxygen. Parts of PNP and its decomposed products were directly encapsulated in soil by thermal stabilization. (C) 2015 Elsevier B.V. All rights reserved.