Encapsulation of direct blue dye into mesoporous silica-based materials

Mesoporous hexagonal silica CMI-1, MCM-41, SBA-15 and Al-incorporated silica AlCMI-1 with pore sizes of 2, 2.7, 3.8 and 3.6 nm, respectively, have been synthesized and used as host materials for the fabrication of optical materials by the encapsulation of direct blue 71 dye. The surface silanol groups of these mesoporous silicas were functionalized by silylation with 3-(aminopropyl)-triethoxysilane or methyltrimethoxylsilicate, which allow a successful doping of organic dye molecules. X-ray diffraction, N2 adsorption, thermogravimetric analysis, infrared, UV–vis diffuse reflectance and solid-state NMR spectroscopy were used to structurally characterize these composite products. It is found that the dye molecules of direct blue 71 have been encapsulated in the pores of MCM-41, SBA-15 and AlCMI-1, whereas attached on the external surface of CMI-1. The steric effect from the pore size of the host materials is significant. Moreover, Al-species in the AlCMI-1 were believed to take an important role in the dye encapsulation, resulting in a larger blue-shift of 21 nm than other mesoporous dye/silica composites.