Abstract
In this study, we report the synthesis and application of mesoporous CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles (MNPs) for the simultaneous removal of inorganic arsenic (iAs). The hybrid adsorbent had a core-shell and mesoporous structure with an average diameter of 260 nm. The nanoscale size and mesoporous character impart a fast adsorption rate and high adsorption capacity for iAs. In total, 0.1 mg L−1 As(V) and As(III) could be adsorbed within 2 min, and the maximum adsorption capacities were 114.8 mg g−1 for As(V) and 143.6 mg g−1 for As(III), higher than most previously reported adsorbents. The anti-interference capacity for iAs adsorption was improved by the electrostatic repulsion and size exclusion effects of the MIL-100(Fe) shell, which also decreased the zero-charge point of the hybrid absorbent for a broad pH adsorption range. The adsorption mechanisms of iAs on the MNPs are proposed. An Fe-O-As structure was formed on CoFe2O4@MIL-100(Fe) through hydroxyl substitution with the deprotonated iAs species. Monolayer adsorption of As(V) was observed, while hydrogen bonding led to the multi-layer adsorption of neutral As(III) for its high adsorption capacity. The high efficiency and the excellent pH- and interference-tolerance capacities of CoFe2O4@MIL-100(Fe) allowed effective iAs removal from natural water samples, as validated with batch magnetic separation mode and a portable filtration strategy.
Highlights
All reagents used in the experiment were of analytical grade. 1, 3, 5-Benzenetricarboxylic acid (H3BTC), FeCl3·6H2O and CoCl2·6H2O were purchased from Bodi Chemical Reagent Co., Ltd., Tianjin, China
Mercaptoacetic acid (MAA), ethylene glycol (HOCH2CH2OH), polyethylene glycol (PEG-6000), nitric acid (HNO3), hydrofluoric acid (HF) and humic acid (HA) were purchased from Fuchen Chemical Reagent Co., Ltd., Tianjin, China. 1000 mgL−1 of As(V) and As(III) stock solutions were obtained from Sigma-Aldrich Co., Ltd., Shanghai, China
Transmission electron microscopy (TEM) images were obtained from JEM-2010HR microscope
Summary
Preparation and characterization of the hybrid adsorbents. Mesoporous CoFe2O4 magnetic nanoparticles (MNPs) were synthesized by a facile one-pot hydrothermal treatment of CoCl2, FeCl3, CH3COONa, and PEG-6000. 1 mM of SO42−, CO32−, SiO32−, Congo red, 0.1 mM PO43−, and 50 mg L−1 humic acid (HA) were selected to evaluate the effects on the removal efficiency of iAs on CoFe2O4@MIL100(Fe) with CoFe2O4 as a comparison (the concentrations of these species are much higher than those found in natural water systems). The anti-interference capacity of the hybrid adsorbent for iAs adsorption was obviously improved after coating with MIL-100(Fe) because of the electrostatic repulsion interactions between those anions and the negatively charged MIL-100(Fe) shell (Fig. 3E and F). Macromolecules, such as Congo red and HA, did not affect the adsorption of iAs because of the size exclusion effect of the crystalline MIL-100(Fe) with the 1-nm pores[50]. As(V) is present mainly as negatively charged H2AsO4− and HAsO42− species at pH 7,
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