Simultaneous adsorption of cationic and anionic dyes using a novel multifunctional mesoporous silica

In the present work a multifunctional nanoadsorbent was synthesized via a well-designed stepwise route, led to the grafting of an amine group on the interior and acidic sites on the exterior of bimodal mesoporous silica nanoparticles (UVM-7). First, amine and thiol groups were grafted on the interior and exterior pores of silica through co-condensation and post synthesis treatment, respectively. Then, the oxidation of thiol on UVM-7 caused to create sulfonic acid and the subsequent template extraction was carried out to obtain the NH2/UVM-7/SO3H. The results of XRD, the nitrogen sorption, SEM, TEM, FT-IR and elemental analysis revealed the presence of both types of functional groups on UVM-7. Then, simultaneous adsorption of anionic and cationic dyes (Methylene Blue [MB] and Direct Red 23 [Dr]) using NH2/UVM-7/SO3H was investigated. UVVis spectrophotometry was utilized for the determination of dyes in single and binary solutions. Langmuir and Freundlich models were used for the fitting of obtained experimental adsorption data and the constants of both isotherms were calculated for MB and Dr. Morover, the calculation of thermodynamic parameters revealed that the adsorption of MB and Dr on NH2/UVM-7/SO3H was endothermic and spontaneous. Furthermore, the simultaneous adsorption of both dyes regardless of their different electrostatic charge is the main characteristics of NH2/UVM-7/SO3H which was specially used for treatment of industrial wastewater.