Valorization of plastics and goethite into iron-carbon composite as persulfate activator for amaranth oxidation

Abstract

In this work, iron-carbon composites were prepared by co-pyrolysis of polyethylene (PE) and goethite (alpha-FeO (OH)) and used as a persulfate (S2O82-) activator for catalytic oxidation of an azo dye chemical, amaranth. The instrumental characterization of the composites indicated the composites were composed of graphitic carbon layers embedded with iron minerals. The graphitic property of the carbon and the types of iron mineral phase in the composites were highly dependent on the pyrolytic temperature employed during their production. The increase of pyrolytic temperature led to more graphitization of carbon as well as sequential phase transformation of goethite into hematite (alpha-Fe2O3) at 250 degrees C, magnetite (Fe3O4) at 600 degrees C, and wustite (FeO)/zero-valent iron (Fe-0) at 900 degrees C. Amaranth degradation experiments with the composite produced from PE:goethite mixture at 2:1 mass ratio at 900 degrees C resulted in complete removal of 10 mg L-1 amaranth within 5 mM in the presence of 0.1 g L-1 composite and 4 mM persulfate. Oxidation of amaranth occurred through reactions with hydroxyl- (OH center dot) and sulfate radicals (SO4 center dot-) generated from S2O82- activation by the composite, and experiments with quenching agents suggested SO4 center dot- was more dominant radical in the oxidation process. The catalytic ability of the composite for S2O82- activation was well maintained during 10 repeated cycles of amaranth degradation. As a result, it was demonstrated that iron-loaded S2O82- activator can be prepared through a strategic combination of iron oxide and plastic by using co-pyrolysis.