| 摘要: | 在0.1 M硫酸中，使用掃描隧道顯微鏡（STM）研究Au(100)電極上的氰化離子（CN-）吸附。Au(100)電極在 -0.2 V時呈現”hex”重構結構，加入KCN後轉變為(1 × 1)相，這一轉變通過即時原位STM成像揭示。關於這個相變的細節已經被揭示出來，在正電位時，CN 氧化吸附於金電極上，生成AuCNad，然後發生陽極蝕刻，形成葉狀表面形態，在負電位下形成線狀特徵和迷宮狀結構。這些特徵在pH 7的KCN溶液中也被觀察到。在正電位下，Au(100)表面溶解，形成淺凹陷(~3 nm)。這個蝕刻過程足夠緩慢，以至於可以使用STM來跟踪這一過程。
在0.1 M 過氯酸鉀（KClO4）中，CN的吸附導致Au(100)表面向fcc(210)結構重構，為CN創造了一個更穩定的六重配位環境。在正電位下，可以區分出兩個氧化步驟，O1和O2，其反應過程分別為AuCN-ad → AuCNad + e-，以及連續反應AuCNad + CN- → Au(CN)2-和Au (exposed) + CN- → AuCNad + e-。第一個反應導致了一個從有序(2 × 2)結構到無序的轉變。在第二個過程中，觀察到Au(100)的蝕刻。
在pH 7的KClO4中，CN的吸附可以在Au(100)電極上形成凹槽，這些表面特徵可以作為模板，可用於沉積外來金屬（如銅）以製備Cu-Au表面合金。KCN的吸附和隨後的蝕刻過程高度依賴於KCN的濃度和pH值。在更鹼性的溶液中，隨著KCN濃度的增加，金電極的溶解速率會加快。
使用有序的Au(100)電極在0.1 M硫酸中進行了多巴胺的電化學檢測，在含有1 mM抗壞血酸（AA）和1 µM多巴胺的溶液中，透過循環伏安法實驗觀察到了多巴胺的氧化，在金圓盤電極和Au(111)電極上未觀察到這個特徵，反映了Au電極表面結構對多巴胺電化學分析的重要性。在含有1 mM AA的0.1 M PBS中，多巴胺的檢測極限約為50 µM，比酸性溶液中的檢測極限差。這種差異歸因於在Au(100)電極上吸附的陰離子（AA-，PO4-）的影響。此外，多巴胺的氧化還表現出更不可逆的特性，將鹵化物或偽鹵化物修改到Au(100)表面可以抑制AA的氧化，表明吸附物種的極性會抑制AA擴散到電極。
最後，在目前的研究中對五種鹵化物和偽鹵化物進行了比較，發現KCN是分析多巴胺最合適的改性劑。CN修飾的Au(100)電極可以在含有1 mM AA的溶液中檢測到5 µM的多巴胺。相比於，裸露的Au(100)電極的檢測極限為50 µM。
;The adsorption of cyanide (CN-) on Au(100) electrode was first examined by high resolution scanning tunneling microscope (STM) in 0.1 M sulfuric acid. The Au(100) electrode assumed that hex reconstruction structure at -0.2 V, which transformed into the (1 × 1) phase upon the addition of KCN, as revealed by real – time in situ STM imaging. The details of this phase transition have been revealed. As the potentials was made positive, oxidation occurred to produce AuCNad en route to anodic etching leading to a leaf-like surface morphology. Cyanide was irreversibly adsorbed to the Au(100) electrode, yielding linear features at negative potentials and a maze-like structure. These features were also found in pH 7 KCN solution. At positive potentials, the Au(100) surface dissolved, creating shallow pits on Au atom in depth. This etching process was slow enough that one could use STM to follow this event.
In 0.1 M KClO4 the adsorption of CN caused the Au(100) surface faceting into the fcc(210) structure, creating a more stable six – fold coordination environment for CN. At positive potentials, two oxidation steps, O1 and O2, can be distinguished, which are outlined as AuCN-ad → AuCNad + e-, and consecutive reactions AuCNad + CN- → Au(CN)2- and Au (exposed) + CN- → AuCNad + e-. The first reaction resulting in a order-to-disorder trasntion, The first reaction resulting in an order-to-disorder transition, causes the (2 × 2) structure to become disordered. The etching of Au(100) in the second process was also observed.
It is noteworthy that the adsorption of CN could produce depressed trenches on the Au(100) electrode in pH 7 KClO4. These surface features could serve as templates for fabricating Au surface alloys by depositing a foreigner metal, such as copper. The adsorption of KCN and the subsequent etching process are highly dependent on the concentration of KCN and the pH value. Gold electrode would dissolve faster with an increase of KCN concentration in more alkaline solutions.
The electrochemical detection of dopamine was examined by using an ordered Au(100) electrode in 0.1 M sulfuric acid. The oxidation of dopamine is evident in a cyclic voltammetric experiment with Au(100) electrode in a solution containing 1 mM ascorbic acid (AA) and 1 µM dopamine. This feature was not observed with Au disk and Au(111) electrodes, reflecting the importance of surface structure of Au electrode in conducting electrochemical analysis of dopamine. In 0.1 M PBS containing 1 mM AA, the detection limit for dopamine is approximately 50 µM, which is inferior to that found in acidic solutions. This contrast is attributed to the influence of anions (AA-, PO4-) that were adsorbed on the Au(100) electrode. Moreover, the redox features of dopamine appeared to be more irreversible. Modification of halides or pseudohalides on the Au(100) surface can inhibit the oxidation of AA, which speaks to the polarities of these entities and the suppressive effect on the diffusion of AA to electrode.
Finally, among the five halides and pseudohalides studied in the current study, KCN is the most suitable modifier to analyze dopamine. The CN-coated Au(100) electrode can detect dopamine down to 5 µM in a solution containing 1 mM AA. In comparison, the detection limit is 50 µM for a bare Au(100) electrode. |
