Template-free Synthesis of Large-Pore-Size Porous Magnesium Silicate Hierarchical Nanostructures for High-Efficiency Removal of Heavy Metal Ions

It remains a big challenge to develop high-efficiency and low-cost adsorption materials to remove toxic heavy metal ions in water. Here, we developed a template-free synthesis method to fabricate high surface area and large pore size magnesium silicate hierarchical nanostructures in a mixed solvent of ethanol and water and carefully investigated the corresponding adsorption behavior for Pb2+, Zn2+, and Cu2+ in aqueous solution. The results reveal that the ethanol volume fraction in the solvent plays an important role to optimize the pore structure, which directly determines the adsorption capacity and the adsorption rate for heavy metal ions. When the ethanol volume fraction is beyond 50%, the obtained magnesium silicate presents a flowerlike structure with a hierarchical pore distribution: 0.5–2, 2–30, and 30–200 nm. When the ethanol volume faction is 90%, for example, the sample exhibits a maximum adsorption capacity of 436.68, 78.86, and 52.30 mg/g for Pb2+, Zn2+, and Cu2+ ions, which has a BET surface area of 650.50 m2/g and an average pore diameter of 6.89 nm, respectively. Also, the sample presents excellent repeated adsorption performance after three elutions. The obtained materials show widely promising and practical applications in water treatment in a wide pH range from 2.8 to 5.8.