Cobalt-iron Oxide, Alloy and Nitride: Synthesis, Characterization and Application in Catalytic Peroxymonosulfate Activation for Orange II Degradation

Kaixin Zhu,Zoltán Klencsár,Changzi Jin,Junhu Wang,Ayyakannu Ganeshraja

doi:10.3390/catal7050138

Abstract

In meeting the need for environmental remediation in wastewater treatment and the development of popular sulfate-radical-based advanced oxidation processes (SR-AOPs), a series of Co/Fe-based catalysts with confirmed phase structure were prepared through extended soft chemical solution processes followed by atmosphere-dependent calcination. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and 57Fe Mössbauer spectroscopy were employed to characterize the composition, morphology, crystal structure and chemical state of the prepared catalysts. It was shown that calcination in air, nitrogen and ammonia atmospheres generated Co-Fe catalysts with cobalt ferrite (CoFe2O4), Co-Fe alloy and Co-Fe nitride as dominant phases, respectively. The prepared Co/Fe-based catalysts were demonstrated to be highly efficient in activating peroxymonosulfate (PMS) for organic Orange II degradation. The activation efficiency of the different catalysts was found to increase in the order CoFe2O4 < Co-Fe nitride < Co-Fe alloy. Sulfate radical was found to be the primary active intermediate species contributing to the dye degradation for all the participating catalysts. Furthermore, a possible reaction mechanism was proposed for each of the studied catalysts. This study achieves progress in efficient cobalt-iron catalysts using in the field of SR-AOPs, with potential applications in environment remediation.

Highlights

Industries such as textiles, printing, plastics, pharmaceuticals, rubber, etc., may bring great threats to the water environment, owing to the production of lots of organic pollutants, most of which are carcinogenic, teratogenic, mutagenic and resistant to biodegradation [1]
Based on the X-ray diffraction (XRD) patterns (Figure 1), all the diffraction peaks of CFA-500 and CFA-600 can be attributed to CoFe2 O4 spinel ferrite (JCPDS 00-022-1086)
CFNH-500 calcined at lower temperature still contained alloy beside the main nitride phase

Summary

Introduction

Industries such as textiles, printing, plastics, pharmaceuticals, rubber, etc., may bring great threats to the water environment, owing to the production of lots of organic pollutants, most of which are carcinogenic, teratogenic, mutagenic and resistant to biodegradation [1]. On account of their superior oxidation ability, good safety, wide range of pH conditions, sulfate-radical-based advanced oxidation processes (SR-AOPs) have emerged as a promising technique and a favorable alternative to H2 O2 based organics degradation processes [3]. With respect to other transition-metal-based catalysts, cobalt ions and their composites were reported to be more efficient as peroxymonosulfate (PMS) activators in most organic pollutant degradations [4]. Since the first report about Co2+ catalytic decomposition of PMS, homogeneous processes on different Co2+ counteranions [5], such as nitrate, sulfate, chloride and acetate, and heterogeneous processes on cobalt oxides and supported composites [6,7,8], have been explored in succession. Even though other transition metals (Mn, Cu, Zn, Ni etc.) [14] were effective in PMS activation, the cobalt system with no need for activity-enhancing assistance (such as microwave, UV, visible light, thermal activation, etc.)

Methods

Results

Conclusion