Encapsulation of Congo red dye into mesoporous silica-based materials: A study on adsorption and sensing properties

The functionalized mesoporous materials provide suitable adsorption sites for the reaction between surface of the solid and dye molecules. The surface silanol groups of the calcined MCM-41 were take part in a functionalization process via silylation with 3-(aminopropyl)-triethoxysilane (APTES). X-ray diffraction, FTIR, UV-vis diffuse reflectance spectroscopy and BET methods were used to structurally characterize the products. A comparative study has been carried out on the adsorption of congo red from aqueous solution by surfactant-containing MCM-41, AlMCM-41 and modified MCM-41. The leaching of dye was tested for these hybrid systems with water and ethanol solvents. Equilibrium adsorption data follows both Langmuir and Freundlich isotherms. Our prepared organic-inorganic hybrid materials are permeable to HCl and NH3 gases and ionic species. These hybrid systems can act as a pH indicator and as a selective chelating agent.