Rapid synthesis of a silsesquioxane-based disulfide-linked polymer for selective removal of cationic dyes from aqueous solutions

Developing a facile and rapid method to prepare adsorbents for an efficient and selective removal of dyes is of great importance for human health and environment. In this work, a silsesquioxane-based disulfide-linked polymer (DLP) was rapidly synthesized by a simple oxidative coupling reaction of octa(3-mercaptopropyl) silsesquioxane within 2 min at room temperature. The synthesized DLP demonstrated selective and efficient adsorption of cationic dyes over anionic dyes with the maximum capacities of 12.94 mg g(-1) for methylene blue, 18.47 mg g(-1) for rhodamine B and 26.69 mg g(-1) for crystal violet. The high uptake and selectivity for cationic dyes was attributed to the electrostatic interactions between the anionic charges from sulfur and oxygen anions formed by the deprotonation of thiols and hydroxyls in the DLP and the cationic charges from the dyes, and the swelling behavior of the DLP. To investigate the adsorption process, the effect of various factors such as contact time, initial concentration, temperature, and pH on the adsorption activity of cationic dyes was studied. The adsorption equilibrium data showed a better fitting to the Langmuir isotherm model than the Freundlich model and the adsorption kinetics fitted well with the pseudo-second-order kinetic model, indicating that the adsorption process is mostly governed by the chemisorption behavior. Additionally, the absorbent was recyclable with the adsorption capacity being > 95% after five times recycle adsorption. These results indicated that the present disulfide-linked polymer could be promisingly applied as an efficient adsorbent for the selective removal of cationic dyes from industrial wastewater.