Insight into heterogeneous photo-Fenton degradation of naphthol by natural magnetite: Redundancy analysis and toxicity assessment

Abstract

Magnetite is a ubiquitous iron mineral in nature and its iron ions are usually isomorphically substituted by Ti and V cations, which shows a high ability for degradation of organic contaminants via the photo-Fenton process. However, numerous reports pay more attention to the activity of synthetic magnetite rather than natural magnetite. Here, three types of natural magnetite (HG01, HG02, and GCL01) with different Ti and V contents were investigated from the perspective of the difference in structural property, catalytic activity, H2O2 decomposition, and reactive oxygen species generation. Structural characterization exhibited that the purity of natural magnetite obeyed the order: GCL01 > HG02 > HG01. HG01 contained the highest Ti content in the form of ilmenite, followed by HG02 and GCL01. Moreover, HG01 yielded the highest photo-Fenton catalytic activity with 99.5 % of naphthol degradation and 96.0 % of H2O2 decomposition after 60 min reaction. The superior activity of HG01 was attributed to the relatively high Ti and V content as demonstrated by redundancy analysis. Mechanistic investigation implied that the Ti and V in the octahedral sites of the magnetite surface can accelerate the electron transfer from Fe(III) to Fe(II), resulting in higher Fenton activity. Besides, ilmenite in HG01 enhanced naphthol degradation because H2O2 accelerated the separation of photoelectron-holes pairs to promote O2− production. Furthermore, as revealed by gas chromatography-mass spectrometry and the toxicity of identified products predicted by the ECOSAR model, the toxicity of naphthol can effectively reduce accompanied by the harmless products generated. The high reusability, low iron ions residual in water, harmless end products, and easily recycled with magnetic separation suggest that natural magnetite has a promising application prospect for wastewater purification.