| Summary: | 博士 === 中原大學 === 化學研究所 === 98 === The photoluminescence (PL) of nano-scaled mesoporous silica (NMS) is about ten times the intensity of micro-sized one (MMS). Deconvolution of PL peaks shows that major PL originates from the non-bridging oxygen hole center (NBOHC) generated from the breakage of the strained siloxane bridges (Si-O-Si). The peak width of 29Si solid-sate NMR for NMS is broader that that for MMS. PL intensity and NMR peak width increase with the decrease of NMS size. This first direct evidence illustrates that NMS has more variations in Si-O-Si bond angles or Si-O lengths than MMS. More bond strain on NMS leads to the favor on the breakage of Si-O-Si, generation of more NBOHC sites and strong PL. Time-resolved photoluminescence of NMS was studied at variable temperatures to identify the relaxation process. The reasonable mechanism of photoluminescence enhancement was proposed in this study.
The photoluminescence of aluminosilicate mesoporous materials is about 60 times the intensity of silicate mesoporous material from our initial investigation. The PL properties of aluminosilicate mesoporous SBA-15 prepared by post-synthesis method with variable amounts, coordination have been carefully studied. The PL results indicated that the PL intensities of AlSBA-15 were proportional to the amount of 4-coordinated alumnium. Eventually, we will suggest a mechanism for unusual intensity enhancement according to our above observation results. In addition, we observed an interesting phenomenon in these Al-NMS materials called persistant photoluminescence (PPL). We propose that the dominant mechanism of the observed PPL effect can be attributed to the incorporation of aluminum.
We first report the formation of arrays of ZnSe nanoparticles inside the nanoscale channels of mesoporous silica SBA-15 via vapor-solid reaction. A series of different weight ratios of ZnSe to SBA-15 was synthesized and mesoporous silica with different pore diameters was also applied for preparing different nanosizes of ZnSe. Band transition energies of ZnSe/SBA-15 increase with the decrease of host pore size due to the quantum size effect. The particle sizes of confined ZnSe in SBA-15 were further evaluated by the Brus’ equation using measured band gaps of ZnSe/SBA-15 and closely related to mesopore diameters of SBA-15 scaffolds. TEM image of ZnSe/SBA-15 shows that most ZnSe is filled into SBA-15 nanoporous channels and has similar size of mesopore.
Order nanoporous carbon materials have received tremendous attention due to their high surface area up to 2000 m2/g and regular pore size which bring about potentials application in catalysis, energy storage, sensing and adsorbents. In this study we present a novel synthetic method to fabricate the mesoporous carbons. We used mesoporous silicas as a hard template, furfuryl alcohol as carbon source via catalyst-free, low-temperature vapor-solid deposition method. These carbon material contained ultra high surface area, dual mesopore structure, controllable pore diameter, and superior stability in high temperature treatment. The H2 uptake capacity as high as 2.25 Wt% at 850 mmHg and 77K, was observed.
Finally, lamellar mesostructured aluminosilicate MCM-50 with varied Si/Al molar ratios have been synthesized successfully. The lamellar Al-MCM-50 is a framework aluminosilicate derived from silica by isomorphous substitution of 4-coordinated silicon by 4-coordinated aluminum. The peak width of 29Si solid-sate NMR for Al-MCM-50 and Si-MCM-50 is much narrower than that for other mesoporous materials. This evidence illustrates that MCM-50 has less variations in Si-O-Si bond angles or Si-O lengths than other mesoporous materials. Therefore, four resonances of Q4(0Al), Q4(1Al), Q3(0Al) and Q3(0Al) can be convoluted from Al-MCM-50 spectra and first used for the quantitative determination of aluminium distribution over the interior of aluminosilicate and interface between aluminosilicate and surfactant. X-ray photoelectron spectroscopy (XPS) of Al-MCM-50 reveals that the surface Si/Al ratio of Al-MCM-50 is corresponding with the calculated result from 29Si NMR spectra. Bulk compositions of materials also measured by elemental analysis are consistent with 29Si NMR results.
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