Weiwei Li,Wenlan Ji,Murat Yılmaz,Tian C. Zhang,Shaojun Yuan
Arsenic is a toxic carcinogen, and arsenic pollution in groundwater is one of the most serious environmental problems in the world. Thus, it is an urgent problem to efficient removal of arsenic from groundwater. In this work, a novel MWCNTs/MIL-53(Fe) nanocomposite was successfully synthesized to improve the water stability of MIL-53(Fe) by incorporation of carboxylated multi-walled carbon nanotubes (MWCNTs) using a one-pot hydrothermal method, and was then used to efficiently adsorb As(V) ions from groundwater. Adsorption experimental results demonstrated an ultrafast adsorption rate of As(V) on the MWCNTs/MIL-53(Fe) nanocomposites in solution pH values of 3 to 10, and the adsorption equilibrium could be reached in circa 20 min with an adsorption capacity of 27.24 mg·g −1 in a low As(V) concentration of 10 mg·L −1 . The adsorption kinetics of As(V) on the MWCNTs/MIL-53(Fe) was found in line with the pseudo-second-order (PSO) kinetic model, and was simultaneously controlled by both internal diffusion and liquid film diffusion. The adsorption isotherm data conformed to the Redlich-Peterson isotherm model, indicating both physical and chemical adsorption occurred at heterogeneous interfaces. Moreover, the postulated adsorption mechanism of As(V) on MWCNTs/MIL-53(Fe) nanocomposites was ascribed to hydrogen-bond interaction, electrostatic attraction and chemical complexation. Therefore, the as-prepared MWCNTs/MIL-53(Fe) nanocomposites not only exhibit superior water stability and outstanding adsorption performance in removing arsenic-contaminated groundwater, but also offer a novel insight for rational preparation of water-stable MOF-based composites.
Yili Xie,Chen Tian,Weiyi Chen,Can Wu,Zhangbin Liu,Ping Ning,Hong Deng,Zhang Lin
Manganese ferrite (MnxFe3−xO4) microspheres with a spinel structure are very effective adsorbents for arsenic (As) removal. In this study, highly ordered mesoporous MnxFe3−xO4 has been synthesized by a facile and convenient solvothermal method. By comparing the different doping amounts of manganese (Mn), the results show that Mn1.8Fe1.2O4 has a relatively higher efficiency for arsenate (As(V)) removal due to the modified surface complexes caused by the optimum Mn substitution. Rietveld XRD refinement reveals that Mn1.8Fe1.2O4 microspheres possess the highest distribution ratio of Mn/Fe situated between the octahedral (Oh) and the tetrahedral (Td) sites of the unit cell. The as-prepared Mn1.8Fe1.2O4 microspheres with MnO6Oh sites in Fdm symmetry exhibit a promising ability for toxic As(V) adsorption, which is mainly attributed to the increase of coordinated complexes. Extended X-ray absorption fine structure (EXAFS) analysis indicates that the coordination structures of As(V) on Mn1.8Fe1.2O4 are present as bidentate binuclear complexes with a regular distance of As–Fe = 3.41 Å. Apart from this, As(V) can also bind with Mn-doped sites through the monodentate coordination mode at a distance of As–Mn = 3.51 Å with a preferred coordination number (CN) of 4.4. This work discloses the correlation between the superior As(V) adsorption ability and MnO6Oh sites in Mn1.8Fe1.2O4 and provides an emerging and promising method to enhance the adsorption capacity of As via modifying Mn doping sites based on the pollutant structure to achieve synergistic adsorption effects.
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