Abstract
Clays are widely used as sorbents for heavy metals due to their high specific surface areas, low cost, and ubiquitous occurrence in most soil and sediment environments. However, the low loading capacity for heavy metals is one of their inherent limitations. In this work, a novel SiO2–Mg(OH)2 nanocomposite was successfully prepared via sequential acid–base modification of raw sepiolite. The structural characteristics of the resulting modified samples were characterized by a wide range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nitrogen physisorption analysis. The results show that a hierarchical nanocomposite constructed by loading the Mg(OH)2 nanosheets onto amorphous SiO2 nanotubes can be successfully prepared, and the nanocomposite has a high surface area (377.3 m2/g) and pore volume (0.96 cm3/g). Batch removal experiments indicate that the nanocomposite exhibits high removal efficiency toward Gd(III), Pb(II), and Cd(II), and their removal capacities were greatly enhanced in comparison with raw sepiolite, due to the synergistic effect of the different components in the hierarchical nanocomposite. This work can provide a novel route toward a hierarchical nanocomposite by using clay minerals as raw material. Taking into account the simplicity of the fabrication route and the high loading capacities for heavy metals, the developed nanocomposite also has great potential applications in water treatment.
Highlights
Heavy metals or potential toxic metals are significant environmental pollutants, and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional, and environmental reasons
The morphology and textures of raw sepiolite, acid-activated sepiolite, and sepiolite treated by sequential acid–base were first observed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques
The raw sepiolite had a nanofiber-like structure with a length of several micrometers and a width of ca. 30–40 nm
Summary
Heavy metals or potential toxic metals are significant environmental pollutants, and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional, and environmental reasons. The term “heavy metals” refers to any metallic element that has a relatively high density and is toxic or poisonous even at low concentration [1]. Heavy metals, such as Pb(II), Hg(II), Cd(II), Co(II), Ni(II), and Cr(VI), are known to be prominent pollutants and even carcinogenic agents, Minerals 2019, 9, 298; doi:10.3390/min9050298 www.mdpi.com/journal/minerals. Rare earth elements (REEs) were widely exploited and used in industrial and high-tech fields as a result of their irreplaceable roles in designing magnetic, luminescent, catalytic, hydrogen storage, and superconductive materials [6,7,8]. The recycling of REEs is an urgent task [7]
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