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

Huidong Cai; Xiang Li; Dachao Ma; Qingge Feng; Dongbo Wang; Zheng Liu; Xu Wei; Kao Chen; Haiying Lin; Siying Qin; Feiyan Lu

doi:10.1016/j.scitotenv.2020.144200

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

Sci Total Environ. 2021 Apr 10:764:144200. doi: 10.1016/j.scitotenv.2020.144200. Epub 2020 Dec 25.

Authors

Huidong Cai¹, Xiang Li², Dachao Ma³, Qingge Feng⁴, Dongbo Wang³, Zheng Liu³, Xu Wei³, Kao Chen¹, Haiying Lin³, Siying Qin³, Feiyan Lu¹

Affiliations

¹ School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China.
² School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China; College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, PR China.
³ School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China; Guangxi Universities Key Laboratory of Environmental Protection, Guangxi University, Nanning 530004, PR China.
⁴ School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China; College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, PR China; Guangxi Universities Key Laboratory of Environmental Protection, Guangxi University, Nanning 530004, PR China. Electronic address: fengqg@gxu.edu.cn.

PMID: 33418355
DOI: 10.1016/j.scitotenv.2020.144200

Abstract

In the traditional Fenton process, the efficient generation of hydroxyl radical (HO) 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 and superoxide radical (O₂^- / HO₂^-) played a dominant role during the Fenton-like degradation of TC at pH 3 and pH 11, respectively. Possible Fenton-like degradation pathways of TC 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-dimethyl 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 41.4% at the optimized conditions. In a word, with the unique acidic surface properties and abundant Si-OH bonds, the Fe₃O₄@SiO₂ submicrospheres exhibited well dispersion, good catalytic activity, strong alkali resistance and excellent recyclability in an ultrasonic-Fenton-like system.

Keywords: Alkaline conditions; Degradation pathways; Fe(3)O(4)@SiO(2) submicrospheres; Fenton-like catalyst; SiO(2) coating.