Stable Fe3O4 submicrospheres with SiO2 coating for heterogeneous Fenton-like reaction at alkaline condition

In the traditional Fenton process, the efficient generation of hydroxyl radical (HO center dot) strongly relies on an acidic circumstance and the iron ions would precipitate and form large amounts of hazardous iron-containing sludge at alkaline pH. To realize stable heterogeneous Fenton-like catalytic degradation at alkaline condition, Fe3O4 submicrospheres with SiO2 coating were successfully synthesized by using water glass as the silica sources via a facile ultrasound assisted method. The as-obtained Fe3O4@SiO2 spheres were further used as catalysts for the Fenton-like degradation of tetracycline hydrochloride (TC). The Fe3O4@SiO2 submicrospheres exhibited superior catalytic activity in higher pH environment (pH value = 11), and the degradation efficiency toward TC was ca. 80% after ten successive runs. The kinetics for the catalytic degradation of TC were agreed well with the second-order kinetic model. The reaction rate constant (k) over the Fe3O4@SiO2 submicrospheres at a pH value of 11 was 7.69 times greater than that at a pH value of 3. Reactive species scavenging experiments revealed that HO center dot and superoxide radical (O-2(-)center dot/ HO2-center dot) played a dominant role during the Fenton-like degradation of TC at pH 3 and pH 11, respectively. Possible Fenton-like degradation pathways of IC were proposed through the identification of intermediates using the high performance liquid chromatography coupled with mass spectrometry (HPLC-MS), which involved cleavage of methyl groups, N-dirnethyl group, and hydroxy groups, ring-opening reaction, etc. The degradation efficiency of TC was close to 91.5% and total organic carbon (TOC) in solution was eliminated by about 91.4% at the optimized conditions. In a word, with the unique acidic surface properties and abundant Si-OH bonds, the Fe3O4@SiO(2 )submicrospheres exhibited well dispersion, good catalytic activity, strong alkali resistance and excellent recydability in an ultrasonic-Fenton-like system. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study successfully achieved stable Fenton-like catalytic degradation under alkaline conditions by synthesizing Fe3O4 submicrospheres with SiO2 coating. The Fe3O4@SiO2 submicrospheres exhibited superior catalytic activity in higher pH environments, with a degradation efficiency of 80% towards tetracycline hydrochloride (TC). The kinetics followed a second-order model, and reactive species scavenging experiments revealed the dominant roles of different radicals at pH 3 and pH 11.