High nickel- and titania-containing mesoporous silicas: synthesis and characterisation
thesisposted on 19.01.2011, 11:20 authored by Wei Wang
In order to heighten the nickel content in mesoporous silica frameworks, a new direct synthesis method, called modified DS method, has been developed instead of the commonly used direct synthesis method. In addition, with the aim of incorporating a high amount of titania into SBA-15 mesoporous silica without blocking its mesopores, a multistep impregnation method, called the MSI method, has also been developed. By using the two developed methods, high nickel- and high titania-containing mesoporous silicas obtained werc synthesized. The nickel- and titania-containing mesoporous silicas were characterised by various techniques, i.e. XRD, TEM, EDX, SENI, N2-sorption, XPS, FTIR, UV-Vis-DRS, UV-VIS, TPR, and Raman spectroscopy. For nickel-containing mesoporous silicas synthesized by the modified DS method, satisfactory mesostructures were obtained and the nickel content was increased up to 14.7 wt.%. So far, no reports have been published on synthesis of mesoporous MCM-41-type silica with higher nickel content than 3.6 wt.% using DS method. Via our modified IDS method, high BET surface area (>840 rný/g) and pore volume (>-0.73 cm3/g were also achieved. Nickel was found to be incorporated into the silica frameworks. Formation of nickel phyllosilicates was also confirmed. After activation, mesostructurcs were still intact. Small nickel clusters embedded in the silica walls were found. A high amount of titania (up to 24.4 wt.%) was incorporated into the mesoporous SBA-15 silica via the multistep impregnation method. No damage to the SBA-15 silica mesostructures was caused. The existence of small titania nano-domins was confirmed to be present by Raman and UV-vis-DRS measurements. High dispersion of them was realized via this method according to the results of low-anglc XRD, TEM and N2-sorption measurements. Importantly, no blockage of mesopores was observed. Photo-activity tests showed the superiority of the materials synthesized by the MSI method to those by one-step impregnation method.
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