表面電漿共振效應在奈米金銀修飾二氧化矽球之光催化還原二氧化碳研究

由於大氣中的二氧化碳濃度持續升高，進而造成全球暖化和氣候變遷等問題，近年來科學家嘗試使用光催化或電催化等還原方法將二氧化碳轉變成可再利用的能源以解決大氣中二氧化碳過量的問題。本研究選用具有強表面電漿共振效應(LSPR)之金屬元素作為光催化的活性位點，例如金、銀等，進一步探討其對於二氧化碳的光催化還原反應效果。此外，金、銀等過渡金屬元素含有多電子的d軌域，可以幫助穩定CO雙鍵的中間態，提高多電子轉移的機會，進而產生各種多碳產物如乙醛、乙醇等。為了研究表面電漿共振效應對於光催化反應的影響同時增加有效的催化面積，本研究使用二氧化矽球做為基材，主要是利用Stöber溶膠凝膠法合成，並於其表面生長金銀奈米島狀結構。最後透過還原金屬離子的方式將金屬島狀結構生長於矽球上，改變生長液中所添加的金屬前驅物的量，可以調整島狀結構的間隙大小，並更進一步探討其與光催化還原二氧化碳的關係。最後將乘載好金銀奈米島的粉末樣品照射類太陽光源並連接氣相層析儀可以了解到產物生成速率以及光催化效率和二氧化碳還原產物種類。從結果可知，在長上適量銀的二氧化矽球對乙醇選擇性為54%，乙醛選擇性為34%，且光催化效率是最好為0.0485﹪，但隨著銀的負載量提升，光子效率降低導致還原效率降至0.0295﹪，而觀察到銀奈米島可幫助光催化二氧化碳產物乙醇與乙醛之選擇性提升，之後或許可以使用較大尺寸的矽球使銀島長得更加均勻，增加產物的產率。

關鍵字

局部表面電漿共振；二氧化矽球；金銀奈米粒子；二氧化碳還原； '光催化還原

並列摘要

As the continuous increased concentration of carbon dioxide (CO2) in the atmosphere may cause the problems of global warming and climate change, recently, the reduction methods such as photocatalysis and electrocatalysis have been proposed to capture CO2 in the atmosphere by directly converting CO2 into renewable energy. Because the electrons in the d orbitals can help stabilize the intermediate state of the CO double bond, the usage of transition metal elements (such as Au and Ag) may increase the chance of multi-electron transfer to enhance the production of multi-carbon products (such as acetaldehyde and ethanol). In addition, metal elements with strong surface plasmon resonance (LSPR) effect can also improve the photocatalytic efficacy. In order to study the effect of surface plasmon resonance on the photocatalytic CO2 reduction, in this work, silica spheres were used as the substrate. In addition, the gold and silver nano-island structures grown on the surface of the silica spheres were used as the active sites. The silica spheres were synthesized by the Stöber sol-gel method, and the nano-island structures were grown on the silica spheres by a seed-mediated method. The gap distance of the nano-island structures can be controlled by adjusting the amount of the added metal precursor. For the photocatalytic CO2 reduction, the as-prepared samples were irradiated with a solar-like light source, and the products were collected by a gas chromatograph system to analyze the types of products, generation rate, and photocatalytic efficiency. According to the results, the samples with appropriate amount of silver showed the highest photocatalytic efficiency 0.0485 and selectivity for ethanol of 54﹪and acetaldehyde of 34﹪. Besides, the silver nano-islands can promote the selectivity of ethanol and acetaldehyde in photocatalytic reduction. However, the photon efficiency decreased with increasing silver loading. Our results demonstrated the plasmon enhanced CO2 reduction with the usage of nano-islands structures. In addition, it maybe can use large size of silica spheres to make silver nano-island grow more uniformly and increase the yield of products.