Synthesis and characterization of nickel-, vanadium- and titanium-containing mesoporous oxide materials, and photoionization of organic molecules in microporous and mesoporous oxide materials

A novel family of mesoporous materials MCM-41 and MCM-48 are successfully synthesized. Some catalytically important metal ions such as Al, Ni, Ti and V are also incorporated into the structures of mesoporous materials by direct synthesis or ion-exchange. Different mesophases are characterized by powder X-ray diffraction (XRD) and nitrogen adsorption. The locations and adsorbate interactions of metal ions such as Ni and Ti in MCM-41 and MCM-48 are critical for acidic and redox catalytic properties. Electron spin resonance (ESR) and electron spin echo modulation (ESEM) and UV-Vis spectroscopies make it possible to characterize the incorporated paramagnetic transition metal ions in these materials. The ESR and ESEM results indicate that the local environment of Ni(I) or Ti(III) in synthesized NiAlMCM-41 or TiMCM-48 is different from that in ion-exchanged Ni-AlMCM-41 or Ti-AlMCM-48. Since nickel or titanium in Ni-AIMCM-41 or Ti-AlMCM-48 is clearly in a nonframework site, these results supports that nickel and titanium in synthesized NiAlMCM-48 and TiMCM-48 are in the framework sites, respectively. Diffuse reflectance (DR) UV-Vis results confirm that vanadium and titanium are incorporated into the tetrahedral framework sites.; ESR and DR UV-Vis spectroscopies have been used to detect the photoionization yield of alkylphenothiazine (PC_n) and tetraphenylporphyrin (H ₂TPP) in V- and Ti containing microporous AlPO-5,11 and mesoporous MCM-48 and SBA-15 materials. Incorporation of Ti, V and Al into MCM-48 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 AlPO pore size affects the of methylphenothiazine cation radical photoyield in MAPO-5,11 (M = Ti, V). It is clear that V(V) is an electron acceptor during the photoirradiation of PC₁-VAPSO-5 and PC_n-VMCM-48. Ti(IV) sites in TAPO-5,11, TiMCM-48 and TiSBA-15 greatly enhance electron-accepting ability of the frameworks probably by reduction of Ti(IV) to Ti(III). PC_n 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 PC_n and H₂TPP at room temperature.