Photoionization of organic molecules in MCM-41, AlMCM-41 and metal containing AlMCM-41 mesoporous materials.

摘要

A family of mesoporous MCM-41 and AlMCM-41 materials was successfully synthesized. Transition metal ions such as Ni(II), Cu(II), Fe(III) and Cr(III) were incorporated into these mesoporous materials by ion-exchange. The samples were characterized by powder X-ray diffraction (XRD) and nitrogen adsorption. Elemental compositions of these materials were determined by electron microprobe analysis or X-ray fluorescence.; Photoionization of photosensitizer molecules N-alkylphenothiazine (PC_n), N,N,N′,N′-tetramethylbenzidine (TMB), pyrene (Py) and meso-tetraphenylporphine (H₂ TPP) was studied in MCM-41 and modified MCM-41 mesoporous materials at room temperature. Electron spin resonance (ESR) make it possible to quantify and identify the photoionization yield of PC_n+., TMB+., Py+. and H₂TPP+. radical cations in the materials. Incorporation of Al into MCM-41 frameworks enhances the electron-accepting ability of the framework. Increasing the alkyl chain length of PC_n affects the alkylphenothiazine cation radical photoyield and stability. The H₂TPP+. photoyield was found to depend on the pore size in C_n-MCM-41 but the pore size was found to have no significant effect on the photoyield in C_n -AlMCM-41 materials. The photoyield intensity depends on the amount of the metal ion incorporated into MCM-41 materials. It is clear that Cr(V) is an electron acceptor during the photoirradiation of Cr-AlMCM-41/PC ₁. PC_n+., TMB+., Py +. and H₂TPP+. cation radicals are stable in these oxides at room temperature from several hours to several days. These materials are shown to be effective heterogeneous hosts to achieve long-lived photoinduced electron transfer of photosensitizer molecules at room temperature.