| 摘要: | 近年來，在分子檢測領域上表面增強拉曼散射(Surface-enhanced Raman scattering, SERS)為一項重要的技術。本篇論文使用聚4乙烯吡啶(poly(4-vinylpyridine), P4VP)分別以旋鍍法(spin coating)及靜電紡絲法(electrospun)製備奈米薄膜及奈米纖維兩種形貌，再以低溫裂解方法鍛燒出高品質的富含氮碳奈米片(nitrogen-enriched carbon nanosheets, NECNS)以及富含氮碳奈米帶(nitrogen-enriched carbon nanoribbons, NECNR)，作為表面增強拉曼散射基材，並利用鍛燒溫度及有機-無機的混摻來調控材料性質以及改變材料表面形貌，來探討其對表面增強拉曼散射-化學機制(chemical mechanism, CM)的影響。
首先，與石墨烯及高分子碳奈米片(CNS)比較，以500 oC鍛燒形成的NECNS，具有優秀的表面增強拉曼散射(SERS)性質。具有高結晶性的石墨烯雖然更有利於使R6G分子以J-聚集體方式吸附於基材上，而J-聚集體扮演重要增強拉曼訊號的活性區域。不過NECNS具有更佳的電荷傳遞能力以及偶極-偶極交互作用力，因此影響了表面增強拉曼散射性質。第二部分，在合成過程中，將醋酸亞鐵溶液中的鐵原子摻雜於碳奈米結構當中，使P4VP鏈段中吡啶環與金屬前驅物離子交互作用產生鍵結，形成富含Fe-N組成的碳奈米結構，金屬鹽的摻雜可以減少吡啶團的熱穩定性。其豐富的Fe-N結構於碳奈米片中經由化學機制使吸附染料分子的基材之拉曼訊號有顯著性的提升。第三部分，以不同種類的鐵前驅物與P4VP之間分別以配位錯合物及氫鍵的模式形成鍵結，經過鍛燒後可調控材料的碳結晶度及電荷傳遞能力，進而影響了基材對R6G的吸附能力及SERS增強的效應，其中以摻雜醋酸亞鐵(FeAc)及二茂鐵乙酸(FAA)具有最廣的溫度調控範圍，而摻雜二茂鐵甲醇(FM)在500 oC鍛燒可產生具有最佳的表面增強拉曼散射之碳材。第四部分，以靜電紡絲製備富含Fe-N鍵結的碳奈米帶，在SERS的表現與碳奈米片性質相同，因此更容易製備。在形貌調控，高比表面積的珠狀結構的表面增強拉曼散射較佳。;In recent years, surface-enhanced Raman scattering (SERS) is a powerful technology for molecular sensing. In this thesis, we fabricated low-temperature pyrolysis, high-quality, nitrogen-enriched carbon nanosheets (NECNS) and nitrogen-enriched carbon nanoribbons (NECNR) from spin-coated polymer thin films and electrospun poly(4-vinylpyridine) (P4VP) polymer nanofibers. The carbon nanomaterials were used as substrates for molecular sensing through SERS spectroscopy. To investigate the effect of chemical mechanism on SERS performance, the surface properties of the carbon nanomaterials were modififed by carbonization at different temperatures and by hybriding iron-based precursors. In addition to CM, morphological effects on SERS performance were also studied.
First, NECNS materials that were prepared by carbonization at 500 oC have superior SERS performance, as compared with graphene and carbon nanosheets (CNS). J-aggregates were favorred when R6G molecules adsorbed on the top of graphene. J-aggregates could enhance Raman signals. In comparison, NECNS materials have better charge transfer ability and stronger dipole-dipole interactions than graphene. Thus, the NECNS materials exhibit better SERS performance than graphene.
In the second part, as P4VP chains have functional pyridine rings available to bind with metal precursor ions through favorable interactions, iron (Fe) atoms could be incorporated into the carbon nanostructures with the aid of Fe(II) acetate. The incorporation of metal salt can decrease the thermal stability of pyridinic groups to produce carbon nanostructures having a surface enriched with Fe-N bound species, which form because the N atoms in the aromatic rings bind directly to Fe atoms. The abundant Fe-N species in these carbon nanostructures enabled a superior enhancement of Raman signals of adsorbed dye molecules through a chemical mechanism.
In the third part, different kinds of iron precursors were incorporated into P4VP chains. Iron precursors are bound with P4VP through coordinate bonding or hydrogen bonding. After carbonization, the material′s degree of graphitization and charge transfer ability can be modified by carbonized P4VP films doped with various iron precursors. These properties, in turn, affect the adsorption ability of the substrate and the effect of SERS enhancement. P4VP-FeAc and P4VP-FAA have a wide range of carbonization temperatures, while the P4VP-FM has the best surface-enhanced scattering when carbonized at 500 oC.
Finally, nitrogen-enriched carbon nanoribbons (NECNR) were prepared by electrospun P4VP polymer. Iron acetate (FeAc) was incorporated into the NECNR to enrich the Fe-N bond. Sample preparation is easy because the performance in SERS is the same as that of nitrogen-enriched carbon nanosheets (NECNS). A bead-like structure with a high specific surface area has better SERS performance in terms of morphology control. |
