Improving the reduction and sensing capability of Fe3O4 towards 4-nitrophenol by coupling with ZnO/Fe0/Fe3C/graphitic carbon using ZnFe-LDH@carbon as a template

Abstract

FeOx-carbon composites are highly active for biomolecule electroanalysis; but not for environmental pollutants such as 4-nitrophenol (4-NP). This is due to the weak electroreduction capability of FeOx towards 4-NP. Herein, we demonstrate that by hybridizing Fe3O4 with ZnO/Fe0/Fe3C/graphitic carbon (g-C) this limitation is mitigated leading to exceptional 4-NP reduction and detection. The Fe3O4/ZnO/Fe0/Fe3C/g-C heterostructure is synthesized via carbothermal reduction of ZnFe-LDH@carbon under N2. The effect of temperature, LDH composition, and g-C on the microstructure and chemical composition of the heterostructure are thoroughly investigated. The presence of ZnO and g-C induce structural pores within Fe3O4/ZnO/Fe0/Fe3C/g-C by preventing the aggregation of Fe3O4 particles which leads to high ECSA and mass transfer. Meanwhile, a temperature > 800 °C is crucial to avoid the inactive ZnFe2O4 phase and transform ZnFe-LDH@carbon fully into Fe3O4/ZnO/Fe0/Fe3C/g-C.The Fe0 site facilitates 4-NP adsorption, while Fe3C acts as a conductive channel for fast electron transfer at Fe2+/Fe3+ redox couple sites in Fe3O4 where 4-NP electroreduction occurs. These properties work in synergy leading to high sensitivity, ultra-low 4-NP detection limit, and selectivity in PBS as well as tap and river water. The results of this study show that the electroanalytical performance of Fe3O4 for environmental pollutants can be tuned by coupling it with the appropriate interface(s).