Synthesis of mixed-mode based functionalized mesoporous silica through RAFT polymerization and its application for dye adsorption

The surface characteristics had a huge impact on adsorption effects. In this paper, the functionalized mesoporous silica based on mixed-mode including hydrophobic (π-π stacking) and electrostatic interactions were designed and prepared through reversible-addition fragmentation chain transfer (RAFT) polymerization. Firstly, the styrene and maleic anhydride were alternately copolymerized on the mesoporous silica with high grafting density, and then the carboxyl groups and amino groups were introduced through the ring-opening of maleic anhydride groups, respectively. The adsorption results indicated that the materials showed high adsorption ability for ionic dyes, with maximum adsorption quantity of around 200 mg/g for methylene blue adsorbed by SiO2@poly(MA-ST)-COOH and around 250 mg/g for azophloxine adsorbed by SiO2@poly(MA-ST)-TETA, and the adsorption rate was fast. Besides, through the elution of absorbed methylene blue with 1 mol/L HCl and absorbed azophloxine with 0.1 mol/L NaOH, the desorption efficiency was above 90%, and the adsorbents showed superior reusability. The adsorption mechanism study further proved that the π-π stacking and electrostatic interactions were effectively integrated during the adsorption process. These findings manifested that the materials could effectively remove ionic dyes from wastewater, with advantages of simple preparation, mixed-mode interactions and high adsorption performance, and would be extended to the adsorption treatments of other dyes and heavy metal ions.