Modified approaches to prepare nano-magnesium silicates with hierarchical pore structure and their performance towards adsorption of Cd²⁺

A series of flower-like magnesium silicate samples with hierarchical pore were prepared by the solvothermal method under template-free conditions using sodium dodecyl sulfate as the modifier and ethanol-water as the solvent. These samples were characterized by various methods and were evaluated for the adsorption of heavy metal Cd²⁺. The results showed that the adding modifier did not change the crystal structure of the magnesium silicate samples. In the range of 2~80 nm, they still showed hierarchical pore distribution mainly composed of mesopores and macropores, which facilitates the rapid transport of adsorbent within the pore channel. Therefore, the adsorption of Cd²⁺ was greatly accelerated. Meanwhile, the larger specific surface area (as high as 553 m²/g) of these samples significantly increased the theoretical maximum adsorption amount of Cd²⁺ up to 295.3 mg/g due to more available adsorption sites. The adsorption dynamic behavior of the samples on Cd²⁺ was in accordance with the pseudo-second-order adsorption model, and their thermodynamic behavior follows the Langmuir adsorption model. The adsorption mechanism of the sample was proposed as electrostatic adsorption and exchange of metal ions and acidic groups on its surface with ions in solution. The obtained magnesium silicate materials are expected to remove heavy metals from wastewater.