矽酸鹽與矽酸鋁中孔分子篩的光學性質與做為奈米澆鑄法模板之應用

Optical properties and nano-casting applications of silicate and aluminosilicate mesoporous materials

鄭博文(Po-Wen Cheng)

指導教授 ： 林嘉和 ； 鄭吉豐

中原大學/理學院/化學研究所/博士(2010年)

https://doi.org/10.6840/cycu201000644

摘要

本論文主要分為兩部份，第一部份探討奈米尺寸之矽酸鹽、矽酸鋁中孔徑分子篩的光激螢光行為及機制。並利用時間鑑別螢光光譜、變溫光激螢光光譜等實驗技巧，研究並討論奈米尺寸中孔分子篩的發光機制。從光激螢光實驗結果，發現矽酸鹽奈米尺寸中孔分子篩之螢光強度比起一般微米級的中孔分子篩高出10倍左右，利用變溫光激螢光光譜與時間鑑別螢光光譜證明兩者發光行為一致，源自二氧化矽本身之點缺陷-非橋氧電洞中心(Non-bridge oxygen hole center)。我們從29Si固態核磁共振光譜結果得知，奈米尺寸矽酸鹽中孔分子篩其Si-O-Si鍵角較一般微米級的中孔分子篩更不規則，其鍵角較為扭曲容易斷裂進而形成光激發光中心。由實驗結果發現奈米尺寸矽酸鋁中孔分子篩其光激螢光強度伴隨著金屬含量增多而提高，且其強度較矽酸鹽MCM-41高出近六十倍。此外，我們亦發現到奈米尺寸矽酸鋁中孔徑分子篩本身具有奇特之長效螢光現象(persistent photoluminescence, PPL)，此一特性與鋁含量以及鍛燒溫度有顯著的關聯性。我們藉由透過微波表面修飾的方法，使用不同種類有機鋁化合物並改變鋁的添加量，使矽酸鹽中孔分子篩SBA-15的表面形成具有不同配位數(coordination number)的矽酸鋁位置，由實驗結果得知矽酸鋁中孔分子篩的光激螢光強度與四配位鋁的含量有明顯的線性關聯性，進一步推導矽酸鋁中孔分子之光激螢光強度增強行為，並提出相關之解釋。
中孔洞分子篩SBA-15具有規則且高單一性之中孔徑大小，故常應用其孔徑的侷限特性來作為奈米鑄造模板，本論文之第二部分即利用此原理，製備金屬或半導體奈米顆粒或奈米孔洞碳材。使用不同孔徑大小之中孔洞分子篩SBA-15做為半導體奈米模板，利用氣固相反應的方式，成功的將能隙2.7eV的硒化鋅半導體植入中孔徑孔洞材料，合成出不同尺寸的硒化鋅奈米粒子。將這些奈米粒子所量測能隙，利用Brus’ equation理論反推估其奈米顆粒尺寸，所計算得到之結果與孔洞大小相當吻合，顯示能透過孔洞侷限效應來成功的合成不同奈米尺寸硒化鋅晶體。此外，中孔洞分子篩SBA-15亦可被當作奈米鑄模用來製作高表面積奈米孔洞碳材，我們使用不具催化裂解性質之純矽SBA-15當作奈米鑄模，在200℃C氣化前驅物於SBA-15孔洞中及同時進行聚合反應，再經900℃高溫真空下碳化，再經HF溶液蝕去SBA-15後可得到一系列具不同孔洞性之奈米孔洞碳材，奈米孔洞碳材具有良好的結構完整性，僅透過控制前驅物濃度的方式，可以合成出具單一孔洞性或是有兩種孔洞性的奈米孔洞碳材。並對所合成出之奈米孔洞碳材進行氫氣吸附能力測試，發現在壓力為850 mmHg溫度77K時，其氫氣儲存能力可達2.25 wt%，可見其擁有良好的應用潛力。
本論文的最後，首度合成不同Si/Al配比的矽酸鋁層狀奈米複合材料Al-MCM-50，透過29Si固態核磁共振光譜與X光光電子光譜(XPS)對Al-MCM-50進行研究，從29Si固態核磁共振結果可計算出鋁原子均勻的分布於Q3與Q4位置，與從元素分析(ICP-AES)與X光光電子光譜的結果相吻合，顯示Al-MCM-50上的鋁原子均勻的分佈在矽酸鋁層狀結構之內部與層狀結構和介面活性劑之間的界面上。

關鍵字

奈米尺寸中孔分子篩 ； 奈米澆鑄法 ； 光激螢光 ； 硒化鋅奈米晶體 ； 奈米孔洞碳材

並列摘要

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.

並列關鍵字

nanoscaled mesoporous material ； photoluminescence ； ordered mesoporous carbon ； Zinc selenide nanocrystal ； nano-casting

參考文獻

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