負載金之中孔洞二氧化矽奈米材料的合成與催化應用

Abstract

負載金之中孔洞二氧化矽奈米粒子(mesoporous silica nanoparticles, MSNs)被認為是一種潛在的功能性材料，其可在催化反應、傳感、等離子體光催化、及表面增強拉曼光譜(surface-enhanced Raman spectroscopy, SERS)來檢測內分泌干擾物質等領域具有諸多應用。由於MSN具有均勻的孔徑、有序的孔洞結構和高比表面積，經常用來做為模板以達到限制高度分散且大小均一的金奈米粒子的生長的目的。因此，我們以MSN作為模板，利用後修飾的方法將氨基官能機團修飾於表面，使得金前驅物附著於材料，藉此金奈米顆粒將被限制在孔道中，並且在液相溶液中具有良好的懸浮性，如此一來，即可均勻的塗布在矽晶片上。在這篇論文中，將展示負載金之中孔洞二氧化矽奈米粒子的應用。 在本研究的第一部分，我們設計了負載奈米金之磷鎢酸(Phosphotungstic acid, PTA) 修飾的中孔洞二氧化矽奈米粒子，應用於甘油的選擇性氧化催化反應。我們分別使用了兩種中孔洞二氧化矽材料來做為金奈米粒子的載體，如：具有垂直奈米孔道的中孔洞薄膜材料SBA-15(⊥)及擴孔的中孔洞二氧化矽奈米粒子ex-MSN，並透過後修飾的方法將固體酸(PTA)引入於孔道中，可有效的催化甘油。整體而言，Au/PTA-ex-MSN催化劑在選擇性甘油氧化催化反應中具有優異的甲酸選擇性42.9%，TON高達1576，及雙氧水的消耗率達87.7%。 在第二部分的研究中，我們將Au/ex-MSN塗布在矽晶片上作為SERS的基板，應用於原位光催化反應進行產物變化的檢測，並且也透過SERS檢測低劑量的環境激素。在此，我們透過SERS進行4-氨基苯硫酚(4-aminothiophenol, 4-ATP)的原位氧化追蹤反應，以了解中間產物4,4'-二巰基偶氮苯（4,4’-dimercaptoazobenzene, DMAB）和最終產物4-硝基苯硫酚(4-nitrothiophenol, 4-NTP)的變化，其中，Au/ex-MSN於空氣中透過633奈米雷射光激發顯現高的可見光活性，且具有明顯的拉曼信號，因此，證明4-ATP透過光催化可被激發產生4-NTP。此外，我們也應用Au/ex-MSN作為SERS的基板來檢測水中最常見的環境激素-卡馬西平(carbazepene, CBZ)，透過檢測不同濃度的CBZ (10-2 mol/L to 10-7 mol/L)獲得了線性的濃度校正曲線。根據上述結果，Au/ex-MSN可作為高效的SERS基板，並應用於原位光催化反應檢測及低劑量汙染物的偵測。

Gold nanoparticles supported on mesoporous silica nanoparticles (MSNs) have been consider as a potential function material for catalytic reaction, sensing, plasmonic photocatalysis, detecting analytes by surface-enhancement Raman spectroscopy (SERS) and so on. The mesoporous MSNs with uniform pore size, ordered pore structure, and high surface area are promising, supports and/or nano-reaction vessel for synthesis and for confining highly dispersed Au nanoparticles (NPs) with uniform size. Herein, we applied MSNs as a support and then modified amine group on the surface of MSNs to adhere gold precursor. Hence, the Au nanoparticles were confined into the channels of MSNs and it can be well suspended in liquid phase, as well as can uniformly distribute on a silicon wafer. Two parts of relevant applications are demonstrated here for the Au nanoparticles supported on/in MSNs. The first part is about selective glycerol oxidation, the second part is about in situ studies of plasmonic photocatalysis process and detection environmental hormone-carbazepene at low concentration. In the first part, we designed a mesoporous silica confined Au NPs/phosphotungstic acid (PTA) material for selective catalytic conversion of glycerol oxidation. Two kinds of silica materials were employed as supports for Au NPs, eg, mesoporous thin film with perpendicular nanochannels (SBA-15(⊥)) and pore-expanded mesoporous silica nanoparticles (ex-MSN), respectively. Meanwhile, solid acid PTA was introduced into the silica nanochannels via post-modification, which can efficiently catalyze glycerol. Overall, our Au/PTA-exMSN catalyst shows excellent selective catalysis ability in convert glycerol to formic acid with outstanding selectivity of 42.9%, and TON up to 1576, and a high H2O2 consumption efficiency of 87.7%. In the second part, spin coating Au/ex-MSN on Si wafer was used as substrate for in situ detecting products variation during photocatalytsis reaction and detecting low dose of environmental hormone under SERS. The in situ oxidation tracking reaction of 4-aminothiophenol (4-ATP) was carried out by SERS to understand the variation of intermediate product 4,4’-dimercaptoazobenzene (DMAB) and final product 4-nitrothiophenol (4-NTP). Particularly, the Au/ex-MSN exhibits high visible light activity for photocatalysis 4-ATP into final oxidation product 4-NTP in air atmosphere under 633 nm laser irradiation with showing an obvious Raman signal of final oxidation product. The result indicates that our substrate can be used to study in situ catalytic oxidation reaction mechanism with SERS. In addition, we also conducted experiment to detect the most common pollutant of environmental hormone in water – CBZ. A concentration range from 10-2 mol/L to 10-7 mol/L of CBZ can be detected by applying Au/ex-MSN as SERS substrate. A linear calibration curve was obtained for detecting the concentration of CBZ in nature environment. Based on the above experimental results, the Au/ex-MSN as a highly efficient SERS substrate can be apply in in situ detecting reactions and low dose pollutant.