Synthesis of bifunctional silica aerogels for robust and simultaneous removal of Hg(II) and malachite green: Performance and mechanism

Abstract

The pollution of heavy metal ions and dyes to water endanger the ecosystem and public health. Adsorption has been widely used for the removal of water pollutants because of its low cost and simple operation. Herein, a family of nitrogen- and sulfur-containing bifunctional silica aerogels with different structure and composition were prepared for robust and simultaneous removal of Hg(II) and malachite green (MG). The optimal adsorption pH for Hg(II) and MG are 6 and 10, and the maximum adsorption capacity are 215.35 and 1227.14 mg·g⁻¹. The adsorption kinetic and isotherm process can be described by pseudo-second-order and Langmuir model. The aerogels can simultaneous removal Hg(II) and MG efficiently. They also exhibit impressive affinity and adsorption selectivity for Hg(II) and MG with the existence of multiple contaminants and high saline environments. Adsorption mechanism implies the adsorption for Hg(II) mainly depends on the interaction with amino and sulfur groups, while the binding of MG mainly depends on the formation of hydrogen bonds. The aerogels display satisfactory adsorption performance in real water sample and good reusability. The regeneration rate can maintain 91.50 % and 90.23 % for Hg(II) and MG after five regeneration cycles. The work may provide efficient bifunctional silica aerogels for the simultaneous decontamination metal ions and dyes with practical application.